- Tandem RCM-Pauson-Khand reaction for access to tricycles in one step
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Starting from conveniently designed dienynes complexed to cobalt, a tandem RCM-intramolecular Pauson-Khand reaction yields tricyclic compounds. The methodology allows the synthesis of 6,5,5 and 7,5,5 systems.
- Rosillo, Marta,Casarrubios, Luis,Dominguez, Gema,Perez-Castells, Javier
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Read Online
- Scope of the chromium(II)-mediated synthesis of E-alkenylstannanes from aldehydes and Bu3SnCHBr2
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The synthesis of E-alkenylstannanes from aldehydes and a mixture of Bu3SnCHBr2, LiI and CrCl2 is described. A mechanism is proposed to account for the alkene geometry in chromium(II)-mediated alkene synthesis which involves stereoselective addition by a gem-dichromium reagent to an aldehyde followed by a stereospecific elimination step.
- Hodgson, David M.,Boulton, Lee T.,Maw, Graham N.
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Read Online
- Chemoselectivity in the Chromium(II)-Mediated Synthesis of E-Alkenylstannanes from Aldehydes and Bu3SnCHBr2
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The synthesis of functionalised E-alkenylstannanes from aldehydes and a mixture of Bu3SnCHBr2, LiI and CrCl2 is described.
- Hodgson, David M.,Boulton, Lee T.,Maw, Graham N.
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Read Online
- A Bifunctional Copper Catalyst Enables Ester Reduction with H2: Expanding the Reactivity Space of Nucleophilic Copper Hydrides
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Employing a bifunctional catalyst based on a copper(I)/NHC complex and a guanidine organocatalyst, catalytic ester reductions to alcohols with H2 as terminal reducing agent are facilitated. The approach taken here enables the simultaneous activation of esters through hydrogen bonding and formation of nucleophilic copper(I) hydrides from H2, resulting in a catalytic hydride transfer to esters. The reduction step is further facilitated by a proton shuttle mediated by the guanidinium subunit. This bifunctional approach to ester reductions for the first time shifts the reactivity of generally considered "soft"copper(I) hydrides to previously unreactive "hard"ester electrophiles and paves the way for a replacement of stoichiometric reducing agents by a catalyst and H2.
- Kaicharla, Trinadh,Ngoc, Trung Tran,Teichert, Johannes F.,Tzaras, Dimitrios-Ioannis,Zimmermann, Birte M.
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supporting information
p. 16865 - 16873
(2021/10/20)
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- Carbohydrate/DBU Cocatalyzed Alkene Diboration: Mechanistic Insight Provides Enhanced Catalytic Efficiency and Substrate Scope
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A mechanistic investigation of the carbohydrate/DBU cocatalyzed enantioselective diboration of alkenes is presented. These studies provide an understanding of the origin of stereoselectivity and also reveal a strategy for enhancing reactivity and broadening the substrate scope.
- Yan, Lu,Meng, Yan,Haeffner, Fredrik,Leon, Robert M.,Crockett, Michael P.,Morken, James P.
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supporting information
p. 3663 - 3673
(2018/03/21)
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- One and Two-Carbon Homologation of Primary and Secondary Alcohols to Corresponding Carboxylic Esters Using β-Carbonyl BT Sulfones as a Common Intermediate
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Herein we report the efficient one- and two-carbon homologation of 1° and 2° alcohols to their corresponding homologated esters via the Mitsunobu reaction using β-carbonyl benzothiazole (BT) sulfone intermediates. The one-carbon homologation approach uses standard Mitsunobu C-S bond formation, oxidation and subsequent alkylation, while the two-carbon homologation uses a less common C-C bond forming Mitsunobu reaction. In this latter case, the use of β-BT sulfone bearing esters lowers the pKa sufficiently enough for the substrate to be used as a carbon-based nucleophile and deliver the homologated β-BT sulfone ester, and this superfluous sulfone group can then be cleaved. In this paper we describe several methods for the effective desulfonylation of BT sulfones and have developed methodology for one-pot alkylation-desulfonylation sequences. As such, overall, a one-carbon homologation sequence can be achieved in a two-pot (four step) procedure and the two-carbon homologation in a two-pot (three step) procedure (three-pot; four step when C-acid synthesis is included). This methodology has been applied to a wide variety of functionality (esters, silyl ethers, benzyls, heteroaryls, ketones, olefins and alkynes) and are all tolerated well providing good to very good overall yields. The power of our method was demonstrated in site-selective ingenol C20 allylic alcohol two-carbon homologation.
- Bon, David J.-Y. D.,Ková?, Ond?ej,Ferugová, Vendula,Zále?ák, Franti?ek,Pospí?il, Ji?í
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p. 4990 - 5001
(2018/05/17)
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- Enantioselective allylic hydroxylation of w-alkenoic acids and esters by P450 BM3 monooxygenase
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Chiral allylic alcohols of w-alkenoic acids and derivatives thereof are highly important building blocks for the synthesis of biologically active compounds. The direct enantioselective C-H oxidation of linear terminal olefins offers the shortest route toward these compounds, but known synthetic methods are limited and suffer from low selectivities. Described herein is an enzymatic approach using the P450 BM3 monooxygenase mutant A74G/L188Q, which catalyzes allylic hydroxylation with high to excellent chemo- and enantioselectivities providing the desirable secondary alcohols.
- Neufeld, Katharina,Henssen, Birgit,Pietruszka, J?rg
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supporting information
p. 13253 - 13257
(2015/02/19)
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- Scope and mechanism of the Pt-catalyzed enantioselective diboration of monosubstituted alkenes
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The Pt-catalyzed enantioselective diboration of terminal alkenes can be accomplished in an enantioselective fashion in the presence of chiral phosphonite ligands. Optimal procedures and the substrate scope of this transformation are fully investigated. Reaction progress kinetic analysis and kinetic isotope effects suggest that the stereodefining step in the catalytic cycle is olefin migratory insertion into a Pt-B bond. Density functional theory analysis, combined with other experimental data, suggests that the insertion reaction positions platinum at the internal carbon of the substrate. A stereochemical model for this reaction is advanced that is in line both with these features and with the crystal structure of a Pt-ligand complex.
- Coombs, John R.,Haeffner, Fredrik,Kliman, Laura T.,Morken, James P.
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supporting information
p. 11222 - 11231
(2013/08/23)
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- Combination of RCM and the Pauson-Khand reaction: One-step synthesis of tricyclic structures
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The combination of ring-closing metathesis (RCM) followed by an intramolecular Pauson-Khand reaction gives direct entry to tricyclic compounds. The RCM was carried out on a hexacarbonylcobalt-complexed alkyne, this complex acting as a protecting group against enyne metathesis. The procedure was studied for dienynes containing heteroatoms and allows the building of [6,5,5] and [7,5,5] tricyclic systems. The feasibility of the process depends strongly on the nature of the substrate. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.
- Rosillo, Marta,Arnaiz, Eduardo,Abdi, Delbrin,Blanco-Urgoiti, Jaime,Dominguez, Gema,Perez-Castells, Javier
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experimental part
p. 3917 - 3927
(2009/04/07)
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- Synthesis of unsaturated dibasic acid esters from five-, six-, and seven-membered cycloalkanones
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A new route to diesters of symmetrical octene-, decene-, and dodecenedioic acids was proposed. The ratio of the cis/trans-isomers was 1:4. The synthesis involved oxidative splitting of five-, six-, and seven-membered cycloalkanones with hydrogen peroxide into the corresponding ω-alkenoic acids followed by esterification and metathesis over Re2O7/B 2O3-Al2O3-SnMe4.
- Starostin,Furman,Ignatenko,Barkova,Nikishin
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p. 2016 - 2019
(2007/10/03)
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- Vitamin D analogues
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The invention concerns novel bi-aromatic compounds having the formula: which are analogs of vitamin D, the process of preparing them, as well as their use in pharmaceutical compositions in human or veterinary medicine, particularly in dermatology, cancer treatment, treatment of auto-immune diseases, and in organ or tissue transplants. Cosmetic compositions and methods of use are also included.
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Page column 37-38
(2010/02/05)
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- Catalytic enantioselective synthesis of (-)-prostaglandin E1 methyl ester based on a tandem 1,4-addition-aldol reaction
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Catalytic enantioselective 1,4-additions and tandem 1,4-addition-aldol reactions of dialkylzinc reagents to cyclopentene-3,5-dione monoacetals in the presence of an in situ generated Cu(OTf)2/chiral phosphoramidite catalyst result in highly functionalized cyclopentane building blocks with ee's up to 97%. A new synthesis of cyclopentene-3,5-dione monoacetals is presented as well as its use in a tandem 1,4-addition-aldol protocol for the catalytic asymmetric total synthesis of (-)-PGE1 methyl ester. This synthesis represents a new approach to this class of natural products. By using only 3 mol % of an enantiomerically pure catalyst in the key step, the absolute configurations at three stereocenters of the basic structure of the PGE1 are established at once.
- Arnold, Leggy A.,Naasz, Robert,Minnaard, Adriaan J.,Feringa, Ben L.
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p. 7244 - 7254
(2007/10/03)
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- Polymers and surfactants on the basis of renewable resources
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A new strategy for the preparation of different polymers and special surfactants was developed. First, unsaturated fatty acid methyl esters obtained from plant oils were converted to terminally unsaturated esters and α-olefins by metathesis with ethylene using heterogeneous rhenium or homogeneous ruthenium catalysts. These esters were directly copolymerized with ethylene by an insertion-type palladium-catalyzed polymerization to functionalized polyolefins. Polyesters were synthesized by metathetical dimerization of ω-unsaturated esters and subsequent polycondensation of the produced internally unsaturated dicarboxylic esters or by acidic transesterification with petrochemical diols and additional acyclic diene metathesis polymerization, ω-epoxy fatty acid methyl esters, achieved by a new method of chemo-enzymatic epoxidation, were converted into polyethers with comb-structure catalyzed by aluminoxanes on the one hand and into sugar surfactants by nucleophilic ring-opening with amino carbohydrates on the other hand.
- Warwel, Siegfried,Bruese, Falk,Demes, Christoph,Kunz, Michael,Klaas, Mark Ruesch gen
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- Synthesis of C3-C9-alkenyl 2,3-unsaturated glucosides from glucose and some alkenols
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C3-C9-Alkenyl 2,3-unsaturated glucosides have been synthesized from glucose and C3-C9-alkenols by using Ferrier reaction with boron trifluoride etherate (BF3·Et2O) as Lewis acid catalyst in key step.
- Konstantinovic,Predojevic,Gojkovic,Ratkovic,Dimitrijevic,Mojsilovic
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p. 802 - 805
(2007/10/03)
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- A one-pot bicycloannulation method for the synthesis of tetrahydroisoquinoline systems
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A highly effective method for the synthesis of the core indolo[2,3- α]quinolizidine skeleton found in yohimbine is described. The reaction of N- monosubstituted thioamides with bromoalkenoyl chlorides furnishes thioisomunchnones as transient 1,3-dipoles that undergo ready intramolecular cycloaddition across the tethered π-bond to give thio-bicycloannulated products in a one-pot operation. The stereochemical outcome of the intramolecular reaction is the consequence of an endo cycloaddition of the neighboring π-bond across the transient thioisomunchnone dipole. A major limitation of the method is that when a hydrogen is present in the α- position of the thioamide the initially formed thio-N-acyliminium ion undergoes proton loss to produce a S,N-ketene acetal at a faster rate than dipole formation. Treatment of tetrahydro-β-carboline-1-thione with 2- bromooct-7-enoyl chloride followed by reductive removal of sulfur from the cycloadduct resulted in the formation of (±)-alloyohimbanone. Attempts to cycloadd the thioisomunchnone dipole across several nucleophilic π-bonds failed, and instead, products derived from cyclization of the π-bond onto the initially formed thio-N-acyliminium ion were formed. The resulting N,S- ketals were further converted into several tetrahydroisoquinoline alkaloids in good yield.
- Padwa, Albert,Beall, L. Scott,Heidelbaugh, Todd M.,Liu, Bing,Sheehan, Scott M.
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p. 2684 - 2695
(2007/10/03)
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- A short synthesis of (±)-alloyohimbane via a thioisomunchnone based intramolecular dipolar-cycloaddition reaction
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Thioisomunchnone dipoles were generated by the reaction of bromoalkenoyl chlorides with thioamides. The intramolecular dipolar-cycloaddition reaction was used for a short synthesis of the yohimbanoid alkaloid (±)- alloyohimbane.
- Heidelbaugh, Todd M.,Liu, Bing,Padwa, Albert
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p. 4757 - 4760
(2007/10/03)
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- A Model Study of Intramolecular Asymmetric Radical Cyclizations of a-Ester and α-Amide Radicals
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Starting from malonate, a practical route was developed for the synthesis of α-phenylthio acid 3. Several chiral compounds including (-)-menthol, (-)-8-phenylmenthol and a camphor based oxazolidinone 8 reacted with 3 to give α-phenylthio esters or amide. These sulfides cyclized efficiently when reacted with tributyltin hydride. Among the chiral auxiliaries used, 8-phenylmenthyl group displayed moderate asymmetric induction (64% ee for cis-product and 40% ee for trans-product). Based on this results, a transition state model was proposed to explain the observed stereoselectivity. In this model, due to π,π-orbital overlap of the phenyl ring and the carbonyl, the si-face of the most stable conformer of the radical was shielded. This controlled the carbon-carbon bond formation to occur from the re-face.
- Yeh, Ru-Long,Jiaang, Weir-Torn,Tsai, Yeun-Min
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p. 253 - 260
(2007/10/03)
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- OZONOLYSIS OF ALKENES AND REACTIONS OF POLYFUNCTIONAL COMPOUNDS. XXXV. SYNTHESIS OF 8Z-DODECENYL- AND 11Z-TETRADECENYL ACETATES FROM THE CYCLIC DIMER OF BUTADIENE
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The stereoselective synthesis of 8Z-dodecenyl- and 11Z-tetradecenyl acetates which are components of the sex pheromones of many species of insect of the order Lepidoptera, was realized on the basis of the partial ozonolysis of (Z,Z)-1,5-cyclooctadiene and its isomerization product (Z,Z)-1,3-cyclooctadiene.
- Odinokov, V. N.,Ishmuratov, G. Yu.,Galeeva, R. I.,Kharisov, R. Ya.,Sokol'skaya, O. V.,at al.
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p. 646 - 651
(2007/10/02)
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- The Synthesis of Specifically and Selectively Deuteriated 4,4'-Bisalkoxyazoxybenzene Derivatives
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In connection with deuterium n.m.r. studies of molecular motion in liquid crystals we have developed a number of methods for the synthesis of selectively deuteriated 4,4'-bisalkoxyazoxybenzenes.This paper is concerned with (i) the labelling of specific methylene segments of the alkoxy-chains, (ii) the labelling of the aromatic nucleus, and (iii) the selective enrichment of the deuterium content of one alkoxy-chain relative to the other.Our studies of the n.m.r. spectra of these liquid crystals have shown that there is not (as has sometimes been supposed) a monotonic decrease in C-D quadrupole splitting in passing from the oxygen to the CD3 end of the alkoxy-chain.In -PAA (p-azoxyanisole) we have also shown that the smaller splitting is associated with the CD3O group nearest to the NO end of azoxy-group.Whereas the photorearrangement of azoxy-compounds is normally regiospecific, the photorearrangement of PAA selectively deuteriated in one methoxy-group is unusual in that it leads to isotopically scrambled products.
- Boden, Neville,Bushby, Richard J.,Clark, Leslie D.
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p. 543 - 551
(2007/10/02)
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