- A comparison between conventional and ultrasound-mediated heterogeneous catalysis: Hydrogenation of 3-buten-1-ol aqueous solutions
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A power flow scheme applicable to probe-type ultrasound reactors is presented, that has been deduced from both theoretical estimates and experimental measurements employing a thermal insulated vessel. Under typical conditions for water at 1 atm pressure, 77% of the electrical power is converted into mechanical motion of the probe, that in turn is dissipated to both acoustic power (～12%) and cavitational heating (～88%). Approximately 92% of the mechanical power of the probe was converted into heat, with the remaining power presumably converted into audible acoustic and/or mechanical motion. In a second type of experiment performed here, heterogeneous catalysis experiments have been performed at 298 K in an isothermal (i.e., jacketed) reaction vessel comparing chemistry in conventional (e.g., thermal) versus ultrasound-assisted systems. Both product state distribution and reaction rate measurements have been performed for the hydrogenation (using hydrogen gas) of aqueous 3-buten-1-ol solutions employing Pd-black powder. Products from the heterogeneous catalysis include isomerization to cis- and trans-2-buten-1-ol, as well as hydrogenation to 1-butanol. A reaction scheme involving surface-bound alkyl-radical species, consistent with previous published work, is proposed to explain product formation. Based on the observed differences in cis- to trans-2-buten-1-ol ratios in conventional versus ultrasound experiments, employing untreated and prereduced catalysts, it has been determined that ultrasound creates catalyst site(s) enhancing the cis-to-trans 2-buten-1-ol ratio from 0.25 to 0.55. In addition, comparing the total isomerization to hydrogenation ratio (cis- plus trans-2-buten-1-ol to 1-butanol ratio), for ultrasound-assisted and conventional catalysis, reveal a ～5-fold enhancement in isomerization relative to the more energetically favored hydrogenation due to the application of ultrasound. Finally, the product formation rates for 1-butanol, as well as isomerization plus hydrogenation, revealed that conventional and ultrasound experiments showed both a nonlinear dependence with applied ultrasound power and no differences between untreated and prereduced catalysts. The observed reaction rate enhancements were 1:36:183 for the conventional, 90 W ultrasound, and 190 W ultrasound experiments, respectively.
- Disselkamp,Judd,Hart,Peden,Posakony,Bond
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Read Online
- Deconvoluting the memory effect in Pd-catalyzed allylic alkylation: Effect of leaving group and added chloride
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An analysis of product distributions in the Tsuji-Trost reaction indicates that several instances of reported "memory effects" can be attributed to slow interconversion of the initially formed syn- and anti- [Pd(η3-allyl)] complexes. Addition of chloride triggers a true memory effect, in which the allylic terminus originally bearing the leaving group has a higher reactivity. The latter effect, termed regioretention, can be rationalized by ionization from a palladium complex bearing a chloride ion, forming an unsymmetrically substituted [Pd(η3-allyl)] complex. DFT calculations verify that the position trans to the phosphine ligand is more reactive both in the initial ionization and in the subsequent nucleophilic attack.
- Fristrup, Peter,Jensen, Thomas,Hoppe, Jakob,Norrby, Per-Ola
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Read Online
- Non-Cryogenic, Ammonia-Free Reduction of Aryl Compounds
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A method of reducing an aromatic ring or a cyclic, allylic ether in a compound includes preparing a reaction mixture including a compound including an aromatic moiety or a cyclic, allylic ether moiety, an alkali metal, and either ethylenediamine, diethylenetriamine, triethylenetetramine, or a combination thereof, in an ether solvent; and reacting the reaction mixture at from ?20° C. to 30° C. for a time sufficient to reduce a double bond in the aromatic moiety to a single bond or to reduce the cyclic, allylic ether moiety.
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- Total Synthesis of Mycinolide IV and Path-Scouting for Aldgamycin N
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Proof-of-concept is provided that a large estate of 16-membered macrolide antibiotics can be reached by a “unified” approach. The key building block was formed on scale by an asymmetric vinylogous Mukaiyama aldol reaction; its alkene terminus was then converted either into the corresponding methyl ketone by Wacker oxidation or into a chain-extended aldehyde by catalyst-controlled branch-selective asymmetric hydroformylation. These transformations ultimately opened access to two structurally distinct series of macrolide targets. Notable late-stage maneuvers comprise a rare example of a ruthenium-catalyzed redox isomerization of an 1,3-enyne-5-ol into a 1,3-diene-5-one derivative, as well as the elaboration of a tertiary propargylic alcohol into an acyloin by trans-hydrostannation/Chan-Lam-type coupling. Moreover, this case study illustrates the underutilized possibility of forging complex macrolactone rings by transesterification under essentially neutral conditions.
- Herlé, Bart,Sp?th, Georg,Schreyer, Lucas,Fürstner, Alois
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supporting information
p. 7893 - 7899
(2021/03/03)
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- Molecular Recognition and Cocrystallization of Methylated and Halogenated Fragments of Danicalipin A by Enantiopure Alleno-Acetylenic Cage Receptors
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Enantiopure (P)4- and (M)4-configured alleno-acetylenic cage (AAC) receptors offer a highly defined interior for the complexation and structure elucidation of small molecule fragments of the stereochemically complex chlorosulfolipid danicalipin A. Solution (NMR), solid state (X-ray), and theoretical investigations of the formed host-guest complexes provide insight into the conformational preferences of 14 achiral and chiral derivatives of the danicalipin A chlorohydrin core in a confined, mostly hydrophobic environment, extending previously reported studies in polar solvents. The conserved binding mode of the guests permits deciphering the effect of functional group replacements on Gibbs binding energies ΔG. A strong contribution of conformational energies toward the binding affinities is revealed, which explains why the denser packing of larger apolar domains of the guests does not necessarily lead to higher association. Enantioselective binding of chiral guests, with energetic differences ΔΔG293 K up to 0.7 kcal mol-1 between diastereoisomeric complexes, is explained by hydrogen- and halogen-bonding, as well as dispersion interactions. Calorimetric studies (ITC) show that the stronger binding of one enantiomer is accompanied by an increased gain in enthalpy ΔH but at the cost of a larger entropic penalty TΔS stemming from tighter binding.
- Carreira, Erick M.,Diederich, Fran?ois,Fischer, Stefan,Gropp, Cornelius,Husch, Tamara,Trapp, Nils
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supporting information
(2020/03/13)
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- Vapor-phase catalytic dehydration of butanediols to unsaturated alcohols over yttria-stabilized zirconia catalysts
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Vapor-phase catalytic dehydration of butanediols (BDOs) such as 1,3-, 1,4-, and 2,3-butanediol was investigated over yttria-stabilized tetragonal zirconia (YSZ) catalysts as well as monoclinic zirconia (MZ). BDOs were converted to unsaturated alcohols with some by-products over YSZ and MZ. YSZ is superior to MZ for these reactions in a view point of selective formation of unsaturated alcohols. Calcination temperature of YSZ significantly affected the products selectivity as well as the conversion of BDOs: high selectivity to unsaturated alcohols was obtained over the YSZ calcined at high temperatures over 800 °C. In the conversion of 1,4-butanediol at 325 °C, the highest 3-buten-1-ol selectivity of 75.3% was obtained over the YSZ calcined at 1050 °C, whereas 2,3-butanediol was less reactive than the other BDOs. In the dehydration of 1,3-butanediol at 325 °C, in particular, it was found that a YSZ catalyst with a Y2O3 content of 3.2 wt.% exhibited an excellent stable catalytic activity: the highest selectivity to unsaturated alcohols such as 2-buten-1-ol and 3-buten-2-ol over 98% was obtained at a conversion of 66%. Structures of active sites for the dehydration of 1,3-butanediol were discussed using a crystal model of tetragonal ZrO2 and a probable model structure of active site was proposed. The well-crystalized YSZ inevitably has oxygen defect sites on the most stable surface of tetragonal ZrO2 (101). The defect site, which exposes three cations such as Zr4+ and Y3+, is surrounded by six O2? anions. The selective dehydration of 1,3-butanediol to produce 3-buten-2-ol over the YSZ could be explained by tridentate interactions followed by sequential dehydration: the position-2 hydrogen is firstly abstracted by a basic O2? anion and then the position-1 hydroxyl group is subsequently or simultaneously abstracted by an acidic Y3+ cation. Another OH group at position 3 plays an important role of anchoring 1,3-butanediol to the catalyst surface. Thus, the selective dehydration of 1,3-butanediol could proceed via the speculative base-acid-concerted mechanism.
- Ohtsuka, Shota,Nemoto, Takuma,Yotsumoto, Rikako,Yamada, Yasuhiro,Sato, Fumiya,Takahashi, Ryoji,Sato, Satoshi
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- SYNTHESIS OF (2S,3R,4R)-4,5-DIHYDROXYISOLEUCINE AND DERIVATIVES
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The invention relates to a method for the preparation of a 4,5-dihydroxyisoleucine derivative comprising the steps of asymmetric Claisen rearrangement of a Z-aminocrotyl-glycin ester and subsequent kinetic resolution of the product diastereomer mix by acylase, and subsequent Sharpless dihydroxylation of the resulting 2-amino-3-methylpent-4-enoicacid derivative.
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Page/Page column 23
(2019/10/19)
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- Rhenium-catalyzed deoxydehydration of renewable triols derived from sugars
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An efficient method for the catalytic deoxydehydration of renewable triols, including those obtained from 5-HMF, is described. The corresponding unsaturated alcohols were obtained in good yields using simple rhenium(vii)oxide under neat conditions and ambient atmosphere at 165 °C.
- Wozniak, Bartosz,Li, Yuehui,Tin, Sergey,De Vries, Johannes G.
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supporting information
p. 4433 - 4437
(2018/10/17)
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- Encapsulation of Crabtree's Catalyst in Sulfonated MIL-101(Cr): Enhancement of Stability and Selectivity between Competing Reaction Pathways by the MOF Chemical Microenvironment
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Crabtree's catalyst was encapsulated inside the pores of the sulfonated MIL-101(Cr) metal–organic framework (MOF) by cation exchange. This hybrid catalyst is active for the heterogeneous hydrogenation of non-functionalized alkenes either in solution or in the gas phase. Moreover, encapsulation inside a well-defined hydrophilic microenvironment enhances catalyst stability and selectivity to hydrogenation over isomerization for substrates bearing ligating functionalities. Accordingly, the encapsulated catalyst significantly outperforms its homogeneous counterpart in the hydrogenation of olefinic alcohols in terms of overall conversion and selectivity, with the chemical microenvironment of the MOF host favouring one out of two competing reaction pathways.
- Grigoropoulos, Alexios,McKay, Alasdair I.,Katsoulidis, Alexandros P.,Davies, Robert P.,Haynes, Anthony,Brammer, Lee,Xiao, Jianliang,Weller, Andrew S.,Rosseinsky, Matthew J.
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supporting information
p. 4532 - 4537
(2018/03/26)
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- Total Synthesis of the Marine Macrolide Amphidinolide F
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A new and efficient convergent approach toward the synthesis of amphidinolide F is described through the assembly of three fragments. The two trans-tetrahydrofurans were built by a diastereoselective C-glycosylation with titanium enolate of bulky N-acetyloxazolidinethiones. The side chain was inserted by a Liebeskind-Srogl cross-coupling reaction. A sulfone condensation/desulfonylation sequence, a Stille cross-coupling, and a macrolactonization were applied to connect the fragments.
- Ferrié, Laurent,Fenneteau, Johan,Figadère, Bruno
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supporting information
p. 3192 - 3196
(2018/06/11)
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- Total Synthesis of Putative Chagosensine
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The marine macrolide chagosensine is the only natural product known to date that embodies a Z,Z-configured chloro-1,3-diene unit. This distinguishing substructure was prepared by a sequence of palladium-catalyzed 1,2-distannation of an alkyne precursor, regioselective Stille cross-coupling at the terminus of the resulting bisstannyl alkene with an elaborated alkenyl iodide, followed by chloro-destannation of the remaining internal site. The preparation of the required substrates centered on cobalt-catalyzed oxidative cyclization reactions of hydroxylated olefin precursors, which allowed the 2,5-trans-disubstituted tetrahydrofuran rings, embedded into each building block, to be formed with excellent selectivity. The highly strained macrolactone could ultimately be closed under forcing Yamaguchi conditions. Comparison of the spectral data of the synthetic sample with those of authentic chagosensine methyl ester confirmed that the structure of this intriguing compound has been mis-assigned by the isolation team.
- Heinrich, Marc,Murphy, John J.,Ilg, Marina K.,Letort, Aurélien,Flasz, Jakub,Philipps, Petra,Fürstner, Alois
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supporting information
p. 13575 - 13581
(2018/09/25)
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- Asymmetric Reductive Carbocyclization Using Engineered Ene Reductases
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Ene reductases from the Old Yellow Enzyme (OYE) family reduce the C=C double bond in α,β-unsaturated compounds bearing an electron-withdrawing group, for example, a carbonyl group. This asymmetric reduction has been exploited for biocatalysis. Going beyond its canonical function, we show that members of this enzyme family can also catalyze the formation of C?C bonds. α,β-Unsaturated aldehydes and ketones containing an additional electrophilic group undergo reductive cyclization. Mechanistically, the two-electron-reduced enzyme cofactor FMN delivers a hydride to generate an enolate intermediate, which reacts with the internal electrophile. Single-site replacement of a crucial Tyr residue with a non-protic Phe or Trp favored the cyclization over the natural reduction reaction. The new transformation enabled the enantioselective synthesis of chiral cyclopropanes in up to >99 % ee.
- Heckenbichler, Kathrin,Schweiger, Anna,Brandner, Lea Alexandra,Binter, Alexandra,Toplak, Marina,Macheroux, Peter,Gruber, Karl,Breinbauer, Rolf
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supporting information
p. 7240 - 7244
(2018/06/15)
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- METHOD FOR PRODUCING UNSATURATED ALCOHOL AND CATALYST
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PROBLEM TO BE SOLVED: To provide a method for the selective production of allyl type unsaturated alcohol from 1,3-diol. SOLUTION: As shown in the following reaction formula, a catalyst comprising zirconium oxide (ZrO2) and calcium oxide (CaO) acts on diol, to produce allyl type unsaturated alcohol (where R1-R4 independently represent H, a C1-5 alkyl group or the like). SELECTED DRAWING: None COPYRIGHT: (C)2017,JPOandINPIT
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Paragraph 0038; 0043
(2017/07/31)
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- Vapor-phase dehydration of C4 unsaturated alcohols to 1,3-butadiene
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Vapor-phase dehydration of C4 unsaturated alcohols such as 3-buten-1-ol, 2-buten-1-ol and 3-buten-2-ol were performed to produce 1,3-butadiene over various solid catalysts including ordinary solid acid catalysts such as Al2O3, SiO2-Al2O3, and TiO2 and basic rare earth metal oxides such as Yb2O3 and CeO2. In the reaction of 3-buten-1-ol, 1,3-butadiene could not be selectively produced because the acid catalysts decomposed 3-buten-1-ol into propylene. In contrast to the acid catalysts, CeO2 inhibited the decomposition of 3-buten-1-ol and showed a relatively high performance for the formation of 1,3-butadiene. In the dehydration of 2-buten-1-ol and 3-buten-2-ol, however, acid catalysts were effective for the formation of 1,3-butadiene. Among the tested catalysts, commercial SiO2-Al2O3 showed a relatively high catalytic performance, although it deactivated rapidly. We prepared a series of SiO2/Al2O3 catalysts by depositing SiO2 species onto Al2O3 support, and the SiO2/Al2O3 with a SiO2 content of 10?wt.% showed more stable catalytic activity than the commercial SiO2-Al2O3. Furthermore, modification of SiO2/Al2O3 with Ag at a loading of 3–5?wt.% was found to be efficient for inhibiting the coke formation and improving the catalytic stability of SiO2/Al2O3 in the dehydration of both 2-buten-1-ol and 3-buten-2-ol under hydrogen flow conditions.
- Sun, Daolai,Arai, Shigenori,Duan, Hailing,Yamada, Yasuhiro,Sato, Satoshi
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- Synthesis of highly selective nano-structured functionalized SBA-15 metformin palladium composite catalyst in partial hydrogenation of alkynes
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In this research, a heterogeneous Nano-Structured functionalized SBA-15 metformin palladium composite catalyst is reported for the selective hydrogenation of alkynes. In the first place, A series of the heterogeneous mesoporous SBA-15 metformin palladium catalyst were prepared and afterwards the condition and the ratio of used materials were optimized to give rise a suitable high performance catalyst. The final nano-structured catalyst was characterized by X-ray powder diffraction, BET surface area, FT-IR spectrophotometer, Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) and served in partial hydrogenation of different alkynes, with high selectivity and high yield. The liquid phase hydrogenation was conducted under mild condition of room temperature and atmospheric pressure. The reactions were monitored every half an hour by gas chromatography and all of them were completed during 4-6 hours. The products were characterized by 1H-NMR, 13C-NMR, FT-IR, and Mass Spectrometry (MS) that strongly confirmed the (Z)-double bond configuration of produced alkenes. This prepared catalyst is competitive with the best palladium catalysts known for the selective liquid phase hydrogenation of alkynes and can be easily recovered and regenerated with keeping high activity and selectivity over multiple cycles with a simple regeneration procedure.
- Kojoori, Reza Kia
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p. 3144 - 3149
(2016/11/18)
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- Partial hydrogenation of alkynes on highly selective nano-structured mesoporous silica MCM-41 composite catalyst
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In this research, we have developed a silica MCM-41/Metformin/Pd (II) nano composite catalyst for the selective hydrogenation of alkynes to the corresponding (Z)-alkenes under a mild condition of atmospheric pressure and room temperature. Firstly, functionalized Si-MCM-41 metformin catalyst with the optimum performance was prepared. Then, the synthesized catalyst was elucidated by X-ray powder diffraction, BET surface area, FT-IR spectrophotometer, Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) and applied in partial hydrogenation of different alkynes, with high selectivity and high yield. The products were characterized by 1H-NMR, 13C-NMR, FT-IR, and Mass Spectrometry (MS) that strongly approved the (Z)-double bond configuration of produced alkenes. This prepared catalyst is competitive with the best palladium catalysts known for the selective liquid phase hydrogenation of alkynes and can be easily recovered and regenerated with keeping high activity and selectivity over at least three cycles with a simple regeneration procedure.
- Kojoori, Reza Kia
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p. 1121 - 1128
(2017/01/25)
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- Tandem Allylboration-Prins Reaction for the Rapid Construction of Substituted Tetrahydropyrans: Application to the Total Synthesis of (-)-Clavosolide A
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Tetrahydropyrans are common motifs in natural products and have now been constructed with high stereocontrol through a three-component allylboration-Prins reaction sequence. This methodology has been applied to a concise (13 steps) and efficient (14 % ove
- Millán, Alba,Smith, James R.,Chen, Jack L.-Y.,Aggarwal, Varinder K.
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supporting information
p. 2498 - 2502
(2016/02/18)
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- Asymmetric Enzymatic Synthesis of Allylic Amines: A Sigmatropic Rearrangement Strategy
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Sigmatropic rearrangements, while rare in biology, offer opportunities for the efficient and selective synthesis of complex chemical motifs. A "P411" serine-ligated variant of cytochrome P450BM3 has been engineered to initiate a sulfimidation/[2,3]-sigmatropic rearrangement sequence in whole E. coli cells, a non-natural function for any enzyme, providing access to enantioenriched, protected allylic amines. Five mutations in the enzyme substantially enhance its activity toward this new function, demonstrating the evolvability of the catalyst toward challenging nitrene transfer reactions. The evolved catalyst additionally performs the highly enantioselective imidation of non-allylic sulfides.
- Prier, Christopher K.,Hyster, Todd K.,Farwell, Christopher C.,Huang, Audrey,Arnold, Frances H.
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supporting information
p. 4711 - 4715
(2016/04/19)
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- A computational study of vicinal fluorination in 2,3- Difluorobutane: Implications for conformational control in alkane chains
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A comprehensive conformational analysis of both 2,3-difluorobutane diastereomers is presented based on density functional theory calculations in vacuum and in solution, as well as NMR experiments in solution. While for 1,2-difluoroethane the fluorine gauc
- Fox, Stephen J.,Gourdain, Stephanie,Coulthurst, Anton,Fox, Clare,Kuprov, Ilya,Essex, Jonathan W.,Skylaris, Chris-Kriton,Linclau, Bruno
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supporting information
p. 1682 - 1691
(2015/01/30)
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- HIV PROTEASE INHIBITORS
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The present invention is directed to 2,5,6-substituted morpholine derivatives and their use in the inhibition of HIV protease, the inhibition of HIV replication, the prophylaxis of infection by HIV, the treatment of infection by HIV, and the prophylaxis,
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Page/Page column 26; 27
(2015/07/07)
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- Copper-catalyzed enantioselective allylic alkylation of terminal alkyne pronucleophiles
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The copper-catalyzed enantioselective allylic alkylation of terminal alkynes with primary allylic phosphates was developed by the use of a new chiral N-heterocyclic carbene ligand bearing a phenolic hydroxy group at the ortho position of one of the two N-aryl groups. This reaction occurred with excellent γ-branch regioselectivity and high enantioselectivity, forming a controlled stereogenic center at the allylic/propargylic position. Various terminal alkynes, including silyl, aliphatic, and aromatic alkynes, could be used directly without premetalation of the C(sp)-H bond. On the basis of the results of experiments using an isomeric secondary allylic phosphate, which gave a branched product through an α-selective substitution reaction with retention of configuration, a reaction pathway involving 1,3-allylic migration of Cu in a ([σ + π]-allyl)copper(III) species is proposed.
- Harada, Ayumi,Makida, Yusuke,Sato, Tatsunori,Ohmiya, Hirohisa,Sawamura, Masaya
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supporting information
p. 13932 - 13939
(2015/02/05)
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- Efficient and exceptionally selective semireduction of alkynes using a supported gold catalyst under a CO atmosphere
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A new efficient method for chemo- and regio-selective semireduction of alkynes using CO/H2O as the hydrogen source catalyzed by gold supported on high surface area TiO2 was developed. A facile and practical synthesis of 1,2-dideuterioalkenes was also realized by using CO/D2O as the reducing agent. the Partner Organisations 2014.
- Li, Shu-Shuang,Liu, Xiang,Liu, Yong-Mei,He, He-Yong,Fan, Kang-Nian,Cao, Yong
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supporting information
p. 5626 - 5628
(2014/05/20)
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- Asymmetric syntheses of enantiopure C(5)-substituted transpentacins via diastereoselective Ireland-Claisen rearrangements
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Asymmetric syntheses of (S,S,S)-2-amino-5-methylcyclopentanecarboxylic acid and (S,S,S)-2-amino-5-phenylcyclopentanecarboxylic acid were achieved in 9 steps from commercially available starting materials via the Ireland-Claisen rearrangement of two enanti
- Davies, Stephen G.,Fletcher, Ai M.,Roberts, Paul M.,Thomson, James E.,Zammit, Charlotte M.
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supporting information
p. 7037 - 7039
(2013/09/02)
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- Synthesis of allylic and homoallylic alcohols from unsaturated cyclic ethers using a mild and selective C-O reduction approach
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Unsaturated cyclic ethers can be mildly and selectively reduced with catalytic amounts of B(C6F5)3 in the presence of an alkylsilane. The allylic position is preferentially reduced with minimal or no scrambling of olefin geometry. For electronically equivalent substrates, steric factors guide the reducing agent to the least substituted site.
- MacK, Daniel J.,Guo, Boying,Njardarson, Jon T.
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supporting information; experimental part
p. 7844 - 7846
(2012/09/05)
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- Benign catalysis with iron: Unique selectivity in catalytic isomerization reactions of olefins
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The use of noble metal catalysts in homogeneous catalysis has been well established. Due to their price and limited availability, there is growing interest in the substitution of such precious metal complexes with readily available and bio-relevant catalysts. In particular, iron is a "rising star" in catalysis. Herein, we present a general and selective iron-catalyzed monoisomerization of olefins, which allows for the selective generation of 2-olefins. Typically, common metal complexes give mixtures of various internal olefins. Both bulk-scale terminal olefins and functionalized terminal olefins give the corresponding products under mild conditions in good to excellent yields. The proposed reaction mechanism was elucidated by in situ NMR studies and supported by DFT calculations and extended X-ray absorption fine structure (EXAFS) measurements.
- Jennerjahn, Reiko,Jackstell, Ralf,Piras, Irene,Franke, Robert,Jiao, Haijun,Bauer, Matthias,Beller, Matthias
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experimental part
p. 734 - 739
(2012/06/04)
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- Development of an intramolecular aryne ene reaction and application to the formal synthesis of (±)-crinine
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A general and high yielding annulation strategy for the synthesis of various carbo- and heterocycles, based on an intramolecular aryne ene reaction is described. It was found that the geometry of the olefin is crucial to the success of the reaction, with exclusive migration of the trans-allylic-H taking place. Furthermore, the electronic nature of the aryne was found to be important to the success of the reaction. Deuterium labeling studies and DFT calculations provided insight into the reaction mechanism. The data suggests a concerted asynchronous transition state, resembling a nucleophilic attack on the aryne. This strategy was successfully applied to the formal synthesis of the ethanophenanthridine alkaloid (±)-crinine.
- Candito, David A.,Dobrovolsky, Dennis,Lautens, Mark
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supporting information
p. 15572 - 15580
(2012/11/07)
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- Intramolecular aryne-ene reaction: Synthetic and mechanistic studies
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Although the chemistry of arynes is well developed, some challenges still remain. The ene reaction of arynes has not gained widespread use in synthesis as a result of poor yields and selectivity. A general, high yielding and selective intramolecular aryne-ene reaction is described providing various benzofused carbo- and heterocycles. Mechanistic data is presented, and a rationale for the resulting stereochemistry is discussed.
- Candito, David A.,Panteleev, Jane,Lautens, Mark
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supporting information; experimental part
p. 14200 - 14203
(2011/10/31)
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- The asymmetric aza-claisen rearrangement: development of widely applicable pentaphenylferrocenyl palladacycle catalysts
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Systematic studies have been performed to develop highly efficient catalysts for the asymmetric aza-Claisen rearrangement of trihaloacetimidates. Herein, we describe the stepwise development of these catalyst systems involving four different catalyst generations finally resulting in the development of a planar chiral pentaphenylferrocenyl oxazoline palladacycle. This complex is more reactive and has a broader substrate tolerance than all previously known catalyst systems for asymmetric aza-Claisen rearrange-ments. Our investigations also reveal that subtle changes can have a big impact on the activity. With the enhanced catalyst activity, the asymmetric aza-Claisen rearrangement has a very broad scope: the methodology not only allows the formation of highly enantioenriched primary allylic amines, but also secondary and tertiary amines; al-lylic amines with N-substituted quaternary stereocenters are conveniently accessible as well. The reaction conditions tolerate many important functional groups, thus providing stereoselective access to valuable functionalized building blocks, for example, for the synthesis of unnatural amino acids. Our results suggest that face-selective olefin coordination is the enantioselectivitydetermining step, which is almost exclusively controlled by the element of planar chirality.
- Fischer, Daniel F.,Barakat, Assem,Xin, Zhuo-Qun,Weiss, Matthias E.,Peters, Rene
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supporting information; experimental part
p. 8722 - 8741
(2010/03/31)
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- Gosteli-claisen rearrangement: Substrate synthesis, simple diastereoselectivity, and kinetic studies
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The results of kinetic studies on the uncatalyzed [3,3]-sigmatropic rearrangement of 2-alkoxycarbonyl- substituted allyl vinyl ethers are reported. Apparently first reported by Gosteli in 1972, this variation of a Claisen rearrangement enjoyed a shadowy existence for three decades until its potential for the development of a catalytic asymmetric Claisen rearrangement was discovered. Inspired by this development, we have studied substituent and solvent rate effects, and we provide evidence that a chairlike transition state is highly favorable for the uncatalyzed Gosteli-Claisen rearrangement.
- Rehbein, Julia,Leick, Sabine,Hiersemann, Martin
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supporting information; experimental part
p. 1531 - 1540
(2009/09/05)
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- PREPARATION OF OPTICALLY PURE BETA-AMINO ACIDS HAVING AFFINITY FOR THE ALPHA-2-DELTA PROTEIN
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Disclosed are materials and methods for preparing optically active β-amino acids, which bind to the alpha-2-delta subunit of a calcium channel and are useful for treating pain, fibromyalgia, and a variety of psychiatric and sleep disorders. The method includes reacting a chiral allyl amine with a 2-alkynoate in the presence of a Lewis acid and a base to give a chiral tertiary enamine, which after reaction with ammonia, is hydrogenated to give optically active β-amino acids.
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Page/Page column 52-53
(2008/06/13)
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- Synthesis and self-photooxygenation of alkenyl-linked [60]fullerene derivatives. A regioselective ene reaction
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(equation presented) Alkenyl-linked C60 derivatives undergo self-photooxygenation regioselectively, by the preferential abstraction of allylic hydrogens on the fullerene side of the double bond.
- Chronakis, Nikos,Vougioukalakis, Georgios C.,Orfanopoulos, Michael
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p. 945 - 948
(2007/10/03)
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- Selective liquid-phase semihydrogenation of functionalized acetylenes and propargylic alcohols with silica-supported bimetallic palladium-copper catalysts
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Silica-supported, bimetallic palladium-copper catalysts were prepared in solution under mild conditions by reacting lithium di(4-tolyl)cuprate with palladium acetate in the presence of silica particles. Small bimetallic palladium-copper particles were deposited on the silica surface as confirmed with TEM-EDAX and EXAFS. The new material has been applied as catalyst in the liquid-phase semihydrogenation of mono- and disubstituted alkynes and showed high selectivity toward the cis-alkenes. The influence of addition of quinoline or potassium hydroxide to the semihydrogenation reaction mixture and the effects of exposure of the catalyst to air before use have been investigated. Silica-supported, bimetallic palladium-copper catalysts were prepared in solution under mild conditions by reacting lithium di(4-tolyl)cuprate with palladium acetate in the presence of silica particles. Small bimetallic palladium-copper particles were deposited on the silica surface as confirmed with TEM-EDAX and EXAFS. The new material has been applied as catalyst in the liquid-phase semihydrogenation of mono- and disubstituted alkynes and showed high selectivity toward the cis-alkenes. The influence of addition of quinoline or potassium hydroxide to the semihydrogenation reaction mixture and the effects of exposure of the catalyst to air before use have been investigated.
- Spee,Boersma,Meijer,Slagt,Van Koten,Geus
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p. 1647 - 1656
(2007/10/03)
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- Practical synthesis of four stereoisomers of 6-(t-butyldiphenylsiloxy)- 3,5-dimethyl-1-(triphenylmethoxy)hexane-2,4-diol via dithiane coupling with oxirane
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The anion derived from 2-substituted 1,3-dithiane derivative (S)-2-[2- (t-butyldiphenylsiloxy)-1-methylethyl]-1-3-dithiane, with n-BuLi at room temperature (r.t.) in THF was subjected to coupling with 2,3-disubstituted oxirane, (2S,3S), or (2S,3R)-2,3-epoxy-1-(triphenylmethoxy)butane, at r.t., giving the coupling products in satisfactory yield. These coupling products were subjected to de-dithioacetalization, and the resulting carbonyl compounds were stereoselectively reduced to afford four stereoisomers of 6- (t-butyldiphenylsiloxy)-3,5-dimethyl-1-(triphenylmethoxy)hexane-2,4-diol.
- Ide, Mitsuaki,Tsunashima, Keiji,Nakata, Masaya
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p. 2501 - 2507
(2007/10/03)
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- Absolute configuration and total synthesis of (+)-curacin A, an antiproliferative agent from the cyanobacterium Lyngbya majuscula
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The absolute configuration of curacin A was determined as (2R,13R,19R,21S)-1 by comparison of degradation products 2 and 3 with the same materials prepared by asymmetric synthesis. The total synthesis of 1 was completed from (1R,2S)-2-methylcyclopropaneca
- White, James D.,Kim, Tae-Seong,Nambu, Mitch
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p. 103 - 111
(2007/10/03)
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- Total synthesis of (+)-curacin A, a marine cytotoxic agent
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The total synthesis of curacin A, a cytotoxic agent that interacts with the colchicine binding site on tubulin, is described. The convergent synthesis utilizes natural product and chiral pool starting materials (geraniol, serine) and asymmetric synthesis
- Hoemann, Michael Z.,Agrios, Konstantinos A.,Aube, Jeffrey
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p. 11087 - 11098
(2007/10/03)
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- Effect of the Structure of Unsaturated Aliphatic Alcohols on the Hydrogenation Rate over Pd-Ru Membrane Catalyst
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It is shown that the rate of hydrogenation of substituted propargyl and allyl alcohols, as measured in the liquid phase on a membrane Pd-Ru alloy catalyst is described by the two-parameter Taft equation, which accounts for the induction and steric substituent effects.A positive induction effect of the substituent group promotes the reaction, whereas a negative one slows it down; an enhancement in the steric factor decreases the rate of conversion.Both induction and steric effects are stronger in reactions with ethylenic rather than acetylenic alcohols and for trans rather than cis isomers.
- Karavanov, A. N.,Gryaznov, V. M.,Batyrev, I. G.,Olenina, E. G.
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p. 739 - 743
(2007/10/02)
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- Regio- and Stereoselective Substitution of Hydroxy Group in Allyl Alcohols by Halogen
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A preparative method for regio- and stereoselective substitution of the hydroxy group by halogen in allyl alcohols under the action of triphenylphosphine complexes with ethyl trichloroacetate or trichloroacetonitrile has been developed.The regio- and stereoselectivity of substitution of hydroxy group by halogen with triphenylphosphine complexes and compounds containing trichloromethyl group is compared.
- Matveeva, E. D.,Erin, A. S.,Mitroshin, D. B.,Kurts, A. L.
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p. 1019 - 1022
(2007/10/03)
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- Absolute Configuration of Curacin A, a Novel Antimitotic Agent from the Tropical Marine Cyanobacterium Lyngbya majuscula
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Curacin A is a structurally novel antimitotic agent isolated from the Caribbean cyanobacterium Lyngbya majuscula.Its planar structure has been previously determined from a spectroscopic investigation, Here, we define the complete relative and absolute configuration of curacin A by comparison of products obtained from chemical degradation of the natural product with the same substances prepared by synthesis.Curacin A is shown to have 2R, 13R, 19R, 21S absolute configuration.
- Nagle, Dale G.,Geralds, Robin S.,Yoo, Hye-Dong,Gerwick, William H.,Kim, Tae-Seong,et al.
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p. 1189 - 1192
(2007/10/02)
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- The Geometry of the Carbanionic Moiety Influences the Non-Induced Diastereoselectivity of the -Wittig Rearrangement of Lithiated Diallyl Ethers
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Lithiated diallyl ethers with cis- or trans-configuration of the anionic moiety were generated from the diallyl ethers 10, from the vinylogous O,S-acetals 13, and from the O,S-acetals 14 by treatment with nBuLi (in the case of 10) or with lithium naphthal
- Goeppel, Dirk,Muenster, Ingo,Brueckner, Reinhard
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p. 3687 - 3708
(2007/10/02)
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- Reaction of (α-halogenoalkyl)thiiranes with nucleophilic reagents I. Reaction with morpholine
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By means of deuterated compounds it was established that (chloromethyl)thiirane reacts with morpholine by a mechanism involving initial opening of the thiirane ring followed by recyclization.In the case of (bromomethyl)thiirane direct substitution of the bromine begins to compete with this mechanism. 2-Methyl-2-(chloromethyl)thiirane, 2,2-dimethyl-3-(chloromethyl)thiirane, and the diastereomeric (1-chloroethyl)thiiranes were synthesized, and their reactivity toward morpholine was studied.
- Tomashevskii, A. A.,Sokolov, V. V.,Potekhin, A. A.
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p. 1610 - 1618
(2007/10/03)
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- Highly General Synthesis of - and -3-Alkylsubstituted Allyboronates via One-Carbon Homologation of Stereospecific 1-Alken-1-ylboronates
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Stereospecific 1-alkan-1-ylboronates readily react with in situ generated chloromethyllithium, producing the corresponding allylboronate in good yields and in excellent stereochemical purities.These are very important synthetic intermediates and conversion of a representative derivative, -2-(2-heptenyl)-1,3,2-dioxaborinane, 2 (R1=C4H9, R2=R3=H), into several compounds of synthetic interest is described.
- Brown, Herbert C.,Phadke, Avinash S.,Bhat, Narayan G.
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p. 7845 - 7848
(2007/10/02)
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- Chemo-enzymatic synthesis of five-membered azasugars as inhibitors of fucosidase and fucosyltransferase: An issue regarding the stereochemistry discrimination at transition states
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Three new 5-membered aza sugars which inhibit bovine α-fucosidase with K(i) values in the μM range have been prepared based on aldolase reactions.
- Wang,Dumas,Wong
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p. 403 - 406
(2007/10/02)
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- STEREOHOMOGENEUS SYNTHESIS OF (E)- AND (Z)-CROTYLTRIFLUOROSILANES AND HIGHLY STEREOSELECTIVE ALLYLATION OF ALDEHYDES
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Stereohomogeneus (E)- and (Z)-crotyltrifluorosilanes were prepared and used for the highly diastereoselective synthesis of threo- and erythro-β-methylhomoallyl alcohols, respectively, from aldehydes in the presence of fluoride ions.The mechanism of the reaction was discussed.
- Kira, Mitsuo,Hino, Takakazu,Sakurai, Hideki
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p. 1099 - 1102
(2007/10/02)
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- OXIDATIVE Si-C BOND CLEAVAGE OF ORGANOTRIFLUOROSILANES INVOLVING ORGANIC-GROUP MIGRATION FROM HYPERCOORDINATE SILICON TO OXYGEN
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Various organotrifluorosilanes react with trimethylamine-N-oxide without catalyst to give the corresponding alcohols in high yields under mild conditions.Stereospecific nature of the reaction is suggestive of the involvment of intramolecular 1,2-organic-group migration from hypercoordinate silicon to oxygen.
- Sato, Kazuhiko,Kira, Mitsuo,Sakurai, Hideki
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p. 4375 - 4378
(2007/10/02)
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- Stereospecific Synthesis of 2,3,6-Trisubstituted Piperidines: An Efficient Total Synthesis of (+/-)-Pumiliotoxin C
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The intramolecular cycloaddition of N-(1-alkyl-4-pentenyl)nitrones provides a highly regio- and stereoselective route to all-cis-2,6-disubstituted-3-(hydroxymethyl)piperidines 3 by way of the bicyclic isoxazolidines 2.In demonstration studies, the 2,6-dimethyl analogue was transformed into 2r,3c,6c-trimethylpiperidine (9) and into N-tert-butoxy-2c,6c-dimethylpiperidine-3r-carboxaldehyde (10).Facile and complete epimerization of the latter into the all-equatorial, 2t,3r,6t aldehyde 11 was achieved, thus giving entry into the diastereomeric 2,3,6-trisubstitutedpiperidines.These protocols can give rise to short and efficient syntheses not only of the piperidines but of bicyclic nitrogen heterocycles depending on the nature of the substituents.An additional stereogenic center was introduced into the 3-(1-hydroxyalkyl) side chain by employing trans and cis isomers of N-(1,5-disubstituted-4-pentenyl)nitrones.The methodology was used to rapidly assemble a piperidine containing four stereogenic centers starting from 2-pentanone and methyl phenyl ketone.This intermediate 20 was then easily converted into (+/-)-pumiliotoxin C (12) by way of an intramolecular alkylation with inversion of configuration.The highly convergent total synthesis was accomplished in 14 steps and 14percent overall yield with no attempt at optimization.
- LeBel, Norman A.,Balasubramanian, N.
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p. 3363 - 3368
(2007/10/02)
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- Stereoselective Preparation of Bicyclooctanones from the Products of Aprotic Conjugate Addition of Lithiated Allylic Sulfoxides to Cyclopent-2-enone and Enolate Trapping with Methyl Cyanoformate
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The lithium enolates arising by aprotic conjugate addition of lithiated but-2-enyl sulfoxides and a phosphine oxide to cyclopent-2-enone react efficiently with methyl cyanoformate to give the corresponding methyl 5-oxocyclopentanecarboxylates in good yields.The sulfoxides are smoothly deoxygenated with tributylphosphine diiodide in ether at 0 deg, and the resulting sulfides undergo intramolecular cyclization in the presence of tin(IV) chloride to give methyl oxobicyclooctanecarboxylates, again in good to excellent yields.The cyclizations are highly stereoselective in that the syn- and anti-stereochemistries of the enolate trapped products obtained from (E)- and (Z)-sulfoxides are quantitatively reflected in the products obtained from the cyclization reactions.
- Haynes, Richard K.,Katsifis, Andrew, G.
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p. 1455 - 1472
(2007/10/02)
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- Allylstannation X. Stereochemical course of the Addition Reactions of (E/Z)-Bu3SnCH2CH=CHCH3 with Aldehydes in the Presence of Lewis Acids (Bu2SnCl2, BF3.Et2O, and TiCl4)
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Reactions between (E/Z)-Bu3SnCH2CH=CHCH3 and RCHO (R= CH3, C2H5, n-C3H7, n-C4H9, n-C5H11, (CH3)2CH, (CH3)3C, C6H5, CH2=CH, CH2=C(CH3), (E)-CH3CH=CH, (E)-C3H7CH=CH, (E)-C6H5CH=CH) have been carried out in the presence of Lewis acids such as Bu2SnCl2, BF3.Et2O, and TiCl4.The stereochemical course of the reactions to give homoallylic alcohols does not necessarily depend on the formation of intermediate Lewis acid-aldehyde complexes, but rather upon the formation of allylmetal compounds (e.g.Bu2ClSnCH2CH=CHCH3, Bu2ClSnCH(CH3)CH=CHCH2, Cl3TiCH2CH=CHCH3, etc.) which are the actual species which react with the carbonyl compounds.Bu3SnCH2CH=CHCH3 does not undergo the reaction.
- Boaretto, Andrea,Marton, Daniele,Tagliavini, Giuseppe,Ganis, Paolo
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p. 199 - 208
(2007/10/02)
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- Studies on the Addition of Allyl Oxides to Sulfonylallenes. Preparation of Highly Substituted Allyl Vinyl Ethers for Carbanionic Claisen Rearrangements
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Thirty-five allyl vinyl ethers bearing an arylsulfonyl anion-stabilizing group have been prepared by addition of allylic alkoxides to (arylsulfonyl)allenes.The allyl vinyl ethers are produced as either β,γ-unsaturated or α,β-unsaturated sulfones depending upon the substitution pattern of the allene and the reaction conditions.A wide variety of substitution patterns are available by using this method.Factors that control the position and stereochemistry of the vinyl ether double bond are discussed.
- Denmark, Scott E.,Harmata, Michael A.,White, Kathleen S.
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p. 4031 - 4042
(2007/10/02)
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- AN APPROACH TO STEREOSELECTIVE FORMATION OF GLYCINOECLEPIN A SIDE CHAIN
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Claisen rearrangement was found to be an efficient method for the stereoselective construction of the glycinoeclepin A side chain.
- Okawara, Hideki,Nii, Yasushi,Miwa, Atsushi,Sakakibara, Masayuki
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p. 2597 - 2598
(2007/10/02)
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