- trans-2-Phenylcyclohexanol. A Powerful and Readily Available Chiral Auxiliary
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The title alcohol has been shown to be a powerful and readily available chiral auxiliary for use in ene reactions of the derived glyoxylate ester.
- Whitesell, James K.,Chen, Hwang-Hsing,Lawrence, Robert M.
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Read Online
- Chiral ligand controlled enantioselective opening of oxirane and oxetane
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Enantioselective opening of oxide ring was achieved by the combination of a chiral ether and phenyllithium in the presence of boron trifluoride to give the corresponding alcohol in 47% ee.
- Mizuno, Masashi,Kanai, Motomu,Iida, Akira,Tomioka, Kiyoshi
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Read Online
- BiCl3-Facilitated removal of methoxymethyl-ether/ester derivatives and DFT study of -O-C-O- bond cleavage
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A simple method for the cleavage of methoxymethyl (MOM)-ether and ester derivatives using bismuth trichloride (BiCl3) is described. The alkyl, alkenyl, alkynyl, benzyl and anthracene MOM ether derivatives, as well as MOM esters of both aliphatic and aromatic carboxylic acids, were deprotected in good yields. To better understand the molecular roles of BiCl3and water for MOM cleavage, two possible binding pathways were investigated using the density functional theory (DFT) method. The theoretical results indicate the differential initial binding site preferences of phenolic and alcoholic MOM substrates to the Bi atom and suggest that water plays a key role in facilitating the cleavage of the MOM group.
- Pacherille, Angela,Tuga, Beza,Hallooman, Dhanashree,Dos Reis, Isaac,Vermette, Mélodie,Issack, Bilkiss B.,Rhyman, Lydia,Ramasami, Ponnadurai,Sunasee, Rajesh
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supporting information
p. 7109 - 7116
(2021/05/03)
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- Palladium-catalyzed asymmetric hydrogenation of 2-aryl cyclic ketones for the synthesis oftranscycloalkanols through dynamic kinetic resolution under acidic conditions
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The first efficient palladium-catalyzed asymmetric hydrogenation of 2-aryl cyclic ketones has been described through dynamic kinetic resolution under acidic conditions, providing a facile access to chiraltranscycloalkanol derivatives with excellent enantioselectivities.
- Li, Xiang,Zhao, Zi-Biao,Chen, Mu-Wang,Wu, Bo,Wang, Han,Yu, Chang-Bin,Zhou, Yong-Gui
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supporting information
p. 5815 - 5818
(2020/06/03)
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- Chemoselective Oxidation of Equatorial Alcohols with N-Ligated λ3-Iodanes
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The site-selective and chemoselective functionalization of alcohols in complex polyols remains a formidable synthetic challenge. Whereas significant advancements have been made in selective derivatization at the oxygen center, chemoselective oxidation to the corresponding carbonyls is less developed. In cyclic systems, whereas the selective oxidation of axial alcohols is well known, a complementary equatorial selective process has not yet been reported. Herein we report the utility of nitrogen-ligated (bis)cationic λ3-iodanes (N-HVIs) for alcohol oxidation and their unprecedented levels of selectivity for the oxidation of equatorial over axial alcohols. The conditions are mild, and the simple pyridine-ligated reagent (Py-HVI) is readily synthesized from commercial PhI(OAc)2 and can be either isolated or generated in situ. Conformational selectivity is demonstrated in both flexible 1,2-substituted cyclohexanols and rigid polyol scaffolds, providing chemists with a novel tool for chemoselective oxidation.
- Mikhael, Myriam,Adler, Sophia A.,Wengryniuk, Sarah E.
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p. 5889 - 5893
(2019/08/26)
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- Diversity-Oriented Synthesis of Bioactive Azaspirocycles
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A collection of novel azaspirocyclic β-arylethylamines was prepared in good yield and excellent diastereoselectivity by an expedient strategy that features condensation of a cyclic ketone with an amino allylsilane and a tandem aza-Sakurai cyclization to generate several different spirocyclic N-heterocycles. Subsequent elaboration of the spirocyclic scaffold was achieved via Pictet-Spengler cyclizations, Suzuki cross-coupling reactions, N-functionalizations, and olefin refunctionalization reactions to create a diverse library of compounds, several of which have nanomolar affinity for the sigma 1 receptor and transmembrane protein 97 (TMEM97).
- Lepovitz, Lance T.,Martin, Stephen F.
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- (Poly)cationic λ3-Iodane-Mediated Oxidative Ring Expansion of Secondary Alcohols
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Herein, a simplified approach to the synthesis of medium-ring ethers through the electrophilic activation of secondary alcohols with (poly)cationic λ3-iodanes (N-HVIs) is reported. Excellent levels of selectivity are achieved for C–O bond migration over established α-elimination pathways, enabled by the unique reactivity of a novel 2-OMe-pyridine-ligated N-HVI. The resulting hexafluoroisopropanol (HFIP) acetals are readily derivatized with a range of nucleophiles, providing a versatile functional handle for subsequent manipulations. The utility of this methodology for late-stage natural product derivatization was also demonstrated, providing a new tool for diversity-oriented synthesis and complexity-to-diversity (CTD) efforts. Preliminary mechanistic investigations reveal a strong effect of alcohol conformation on the reactive pathway, thus providing a predictive power in the application of this approach to complex molecule synthesis.
- Walters, Jennifer C.,Tierno, Anthony F.,Dubin, Aimee H.,Wengryniuk, Sarah E.
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supporting information
p. 1460 - 1464
(2018/04/06)
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- Visible-Light-Mediated Aerobic Oxidation of Organoboron Compounds Using in Situ Generated Hydrogen Peroxide
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A simple and general visible-light-mediated oxidation of organoboron compounds has been developed with rose bengal as the photocatalyst, substoichiometric Et3N as the electron donor, as well as air as the oxidant. This mild and metal-free protocol shows a broad substrate scope and provides a wide range of aliphatic alcohols and phenols in moderate to excellent yields. Notably, the robustness of this method is demonstrated on the stereospecific aerobic oxidation of organoboron compounds.
- Weng, Wei-Zhi,Liang, Hao,Zhang, Bo
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supporting information
p. 4979 - 4983
(2018/08/24)
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- Diastereoselective and enantioselective alkaline-hydrolysis of 2-aryl-1-cyclohexyl acetate: a CAL-B catalyzed deacylation/acylation tandem process
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Candida antarctica lipase proved to be a particularly efficient lipase for the resolution of racemic 2-arylcyclohexyl acetate in hydrolysis reaction with Na2CO3 in an organic medium. The (1R,2S)-trans-2-arylcyclohexanols 2a–2d were obtained with high ee values (up to >99%) and the selectivity reached E > 200. The influence of the enol ester and the solvent on (±)-trans-2-arylcyclohexanol in the CAL-B catalyzed acylation was also studied and compared with the deacylation. The CAL-B exhibits a better affinity for the alkaline hydrolysis reaction compared with acylation with the enol esters in the same organic solvents. The best conditions were applied to resolve a stereoisomeric mixture cis/trans-2-phenyl-1-cyclohexanol and its corresponding acetate by acylation and deacylation. The obtained results show a highly enantio- and diastereoselectivity of the CAL-B during the acylation and the deacylation in favor of the trans-(R)-enantiomer product. The resolution of a mixture of cis/trans-2-arylcyclohexanols was an easy, convenient approach to provide only one stereoisomer of a mixture of four with high enantiomeric excess.
- Belkacemi, Fatma Zahra,Merabet-Khelassi, Mounia,Aribi-Zouioueche, Louisa,Riant, Olivier
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supporting information
p. 1644 - 1650
(2017/10/12)
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- Directed β C-H Amination of Alcohols via Radical Relay Chaperones
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A radical-mediated strategy for β C-H amination of alcohols has been developed. This approach employs a radical relay chaperone, which serves as a traceless director that facilitates selective C-H functionalization via 1,5-hydrogen atom transfer (HAT) and enables net incorporation of ammonia at the β carbon of alcohols. The chaperones presented herein enable direct access to imidate radicals, allowing their first use for H atom abstraction. A streamlined protocol enables rapid conversion of alcohols to their β-amino analogs (via in situ conversion of alcohols to imidates, directed C-H amination, and hydrolysis to NH2). Mechanistic experiments indicate HAT is rate-limiting, whereas intramolecular amination is product- and stereo-determining.
- Wappes, Ethan A.,Nakafuku, Kohki M.,Nagib, David A.
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supporting information
p. 10204 - 10207
(2017/08/10)
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- Enantioselective Hydroazidation of Trisubstituted Non-Activated Alkenes
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A one-pot procedure for the enantioselective hydroazidation of non-activated trisubstituted alkenes is described. Hydroboration with monoisopinocampheylborane (IpcBH2) provides dialkylboranes that are in situ selectively converted into monoalkyl-substituted catecholboranes; these undergo radical azidation upon treatment with benzenesulfonyl azide and a radical initiator. Enantiomerically enriched azides were thus obtained in yields of 59–81 % and enantioselectivities of up to 94:6 e.r. (98:2 e.r. if the intermediate dialkylborane is purified by crystallization). A rapid access to enantiomerically pure (+)-rodocaine is also described. The use of other arenesulfonyl radical traps enables enantioselective hydroallylation, hydrosulfanylation, and hydrobromination reactions with yields of 71–86 %.
- Meyer, Daniel,Renaud, Philippe
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supporting information
p. 10858 - 10861
(2017/08/30)
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- Diastereoselective and Enantioselective Silylation of 2-Arylcyclohexanols
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The silylation-based kinetic resolution of trans 2-arylcyclohexanols was accomplished by employing a triaryl silyl chloride as the derivatizing reagent with a commercially available isothiourea catalyst. The methodology is selective for the trans diastereomer over the cis, which provides an opportunity to selectively derivatize one stereoisomer out of a mixture of four. By employing this technology, a facile, convenient method to form a highly enantiomerically enriched silylated alcohol was accomplished through a one-pot reduction-silylation sequence that started with a 2-aryl-substituted ketone.
- Wang, Li,Akhani, Ravish K.,Wiskur, Sheryl L.
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supporting information
p. 2408 - 2411
(2015/05/27)
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- Enantioselective cross-coupling of meso -epoxides with aryl halides
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The first enantioselective cross-electrophile coupling of aryl bromides with meso-epoxides to form trans-β-arylcycloalkanols is presented. The reaction is catalyzed by a combination of (bpy)NiCl2 and a chiral titanocene under reducing conditions. Yields range from 57 to 99% with 78-95% enantiomeric excess. The 30 examples include a variety of functional groups (ether, ester, ketone, nitrile, ketal, trifluoromethyl, sulfonamide, sulfonate ester), both aryl and vinyl halides, and five- to seven-membered rings. The intermediacy of a carbon radical is strongly suggested by the conversion of cyclooctene monoxide to an aryl [3.3.0]bicyclooctanol.
- Zhao, Yang,Weix, Daniel J.
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supporting information
p. 3327 - 3340
(2015/03/30)
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- Nickel-catalyzed regiodivergent opening of epoxides with aryl halides: Co-catalysis controls regioselectivity
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Epoxides are versatile intermediates in organic synthesis, but have rarely been employed in cross-coupling reactions. We report that bipyridine-ligated nickel can mediate the addition of functionalized aryl halides, a vinyl halide, and a vinyl triflate to epoxides under reducing conditions. For terminal epoxides, the regioselectivity of the reaction depends upon the cocatalyst employed. Iodide cocatalysis results in opening at the less hindered position via an iodohydrin intermediate. Titanocene cocatalysis results in opening at the more hindered position, presumably via TiIII-mediated radical generation. 1,2-Disubstituted epoxides are opened under both conditions to form predominantly the trans product.
- Zhao, Yang,Weix, Daniel J.
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supporting information
p. 48 - 51
(2014/01/23)
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- Synthesis of PDE IV inhibitors. First asymmetric synthesis of two of GlaxoSmithKline's highly potent Rolipram analogues
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Asymmetric syntheses of two of GlaxoSmithKline's highly potent phosphodiesterase IV inhibitors CMPI 1 and CMPO 2 have been accomplished from nitroethane and simple precursors in 8 and 7 steps, respectively. The suggested synthetic strategy involves as a key stage the silylation of enantiopure six-membered cyclic nitronates. In vitro studies of PDE IVB1 inhibition revealed a significant difference in the activity of CMPI 1 and CMPO 2 enantiomers.
- Zhmurov, Petr A.,Sukhorukov, Alexey Yu.,Chupakhin, Vladimir I.,Khomutova, Yulia V.,Ioffe, Sema L.,Tartakovsky, Vladimir A.
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p. 8082 - 8091
(2013/12/04)
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- Influence of chiral thiols on the diastereoselective synthesis of γ-lactams from cyclic anhydrides
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The synthesis of γ-lactams from both four-component and imine-anhydride reactions is reported. The synthesis of 2-phenylcyclohexanethiol is described and this compound was evaluated along with an additional seven chiral thiols. A range of selectivity and yields was observed and comparisons to established reactions are made in order to account for the observed reactivity.
- Younai, Ashkaan,Fettinger, James C.,Shaw, Jared T.
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scheme or table
p. 4320 - 4327
(2012/07/28)
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- Tunable cross coupling of silanols: Selective synthesis of heavily substituted allenes and butadienes
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1,3-Dienyl-2-silanols with a wide range of substitution patterns are readily obtained by palladium-catalyzed silaboration of 1,3-enynes followed by Suzuki-Miyaura cross coupling with aryl bromides. Subsequent Hiyama-Denmark cross coupling with aryl iodides provides either 1,3- or 1,2-dienes in high yields. The site selectivity can be fully controlled by the choice of activator used in the coupling reaction. In the presence of strong bases such as NaOt-Bu, KOt-Bu, and NaH, clean formation of 1,2-dienes takes place via allylic rearrangement. In contrast, stereo- and site-selective formation of tetra- and trisubstituted 1,3-dienes results from use of Ag2O and Bu 4NF·3H2O, respectively, as activators. Under microwave heating at 100 °C the base-mediated cross couplings are largely accelerated and are completed within one hour or less. The ratio of diastereomeric allenes varies depending on the substitution pattern of the silanol and ranges from >99:1 to 52:48.
- Zhou, Hui,Moberg, Christina
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supporting information
p. 15992 - 15999
(2012/11/07)
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- Catalytic hydrogen atom transfer (HAT) for sustainable and diastereoselective radical reduction
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Going cyclic! A catalytic cycle and cyclic transition states enable a novel sustainable and catalytic hydrogen atom transfer (HAT) for highly diastereoselective radical reductions. Readily available nontoxic silanes are the terminal reductants for epoxides that are opened by bifunctional titanocene(III) hydride catalysts. Copyright
- Gansaeuer, Andreas,Klatte, Max,Braendle, Gerhard M.,Friedrich, Joachim
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p. 8891 - 8894
(2012/10/08)
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- Enantioselective acylation of rac-2-phenylcycloalkanamines catalyzed by lipases
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The kinetic resolution of some 2-phenylcycloalkanamines was performed by means of aminolysis reactions catalyzed by lipases, with Kazlauskas' rule being obeyed in all cases. The size of the ring and the stereochemistry of the stereogenic centers of the amines had a strong influence on both the enantiomeric ratio and the reaction rate of these aminolysis processes. Lipase B from Candida antarctica (CAL-B) showed excellent enantioselectivities toward trans-2-phenylcyclohexanamine in a variety of reaction conditions (E >150), whereas lipase A from C. antarctica (CAL-A) was the best catalyst for the acylation of cis-2-phenylcyclohexanamine (E = 34) and trans-2- phenylcyclopropanamine (E = 9).
- Gonzalez-Sabin, Javier,Gotor, Vicente,Rebolledo, Francisca
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p. 3070 - 3076
(2007/10/03)
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- Reduction of carbonyl compounds by lanthanide metal/2-propanol: In-situ generation of samarium isopropyloxide for stereoselective Meerwein-Ponndorf- Verley reduction
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The reduction of ketones and aldehydes with lanthanide metals (La, Ce, Sm, Yb) and a catalytic amount of iodine (5 mol %) in iPrOH proceeded smoothly to produce the corresponding alcohols as the major products in good yield, while in THF, methanol, and ethanol the pinacols were mainly produced. The yields of alcohols were improved most effectively by the use of Sm metal, the amount of pinacol produced thus being minimized. The actual reducing agent may be samarium isopropyloxide, which mediates the Meerwein-Ponndorf-Verley-type hydride-transfer reaction, since the reaction can be carried out catalytically with respect to samarium. The stereoselectivities of the reductions of the 2- and 4-substituted cyclohexanones with Sm/iPrOH were higher than those achieved with SmI2/iPrOH or Sm/ H20. The asymmetric reduction of acetophenone could be achieved to give the 1-phenylethanol in up to 95% ee in the presence of the chiral ligand 7. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.
- Fukuzawa, Shin-Ichi,Nakano, Narihito,Saitoh, Takahide
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p. 2863 - 2867
(2007/10/03)
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- Recyclable Polyurea-Microencapsulated Pd(0) Nanoparticles: An Efficient Catalyst for Hydrogenolysis of Epoxides
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(Matrix presented) Pd nanoparticles (~2 nm in size) microencapsulated in polyurea is an efficient and recyclable catalyst for reductive ring-opening hydrogenolysis of epoxides, using either HCOOH/Et3N or H2 as a hydrogen donor.
- Ley, Steven V.,Mitchell, Claire,Pears, David,Ramarao, Chandrashekar,Yu, Jin-Quan,Zhou, Wuzong
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p. 4665 - 4668
(2007/10/03)
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- The design of novel N-4′-pyridinyl-α-methyl proline derivatives as potent catalysts for the kinetic resolution of alcohols
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A novel family of chiral acylation catalysts based on a N-4′-pyridinyl-α-methyl proline structure has been studied. A set of 31 compounds has been easily prepared and screened in the kinetic resolution of racemic alcohol 33 resulting in high enantioselectivities in most cases. From results obtained, H-bonding interactions between the catalyst and the substrate would appear essential to afford high enantioselectivity during the catalytic acylation. Additional solvent dependence and anhydride studies have been made to better identify the mechanism. This work has been further extended to the study of a number of structurally different alcohols. Ethanolamine derivatives in particular were found to be highly effective substrates (up to S = 18.8) in the kinetic resolution.
- Priem, Ghislaine,Pelotier, Béatrice,Macdonald, Simon J. F.,Anson, Mike S.,Campbell, Ian B.
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p. 3844 - 3848
(2007/10/03)
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- Diastereoselective reduction of alkenylboronic esters as a new method for controlling the stereochemistry of up to three adjacent centers in cyclic and acyclic molecules
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(figure presented) cis-Boronates are readily available via a diastereoselective Pd-catalyzed reduction of tetrasubstituted alkenylboronic esters using H2. Applying the reaction conditions presented to unsaturated open-chain boronic esters allows the stereochemistry of up to three adjacent centers to be controlled.
- Hupe, Eike,Marek, Ilan,Knochel, Paul
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p. 2861 - 2863
(2007/10/03)
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- Free-radical hydroxylation reactions of alkylboronates
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The radical hydroxylation of B-alkylcatecholboranes, easily prepared by hydroboration of olefins, has been investigated. When molecular oxygen was used as oxidizing agent, the corresponding alcohols were obtained directly without alkaline treatment. The presence of Lewis base additives such as Et3N or DABCO has a benefic effect on the selectivity and yield. Alternatively, 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) reacts cleanly with B-alkylcatecholboranes to afford alkyl radicals that can be trapped by a second equivalent of TEMPO to give alkoxyamines. Reduction of the alkoxyamines with zinc in acetic acid affords the desired alcohols. The whole procedure is particularly mild and does not require any basic condition. The two approaches presented in this paper are valuable and represent mild alternatives to the classical alkaline oxidation of organoboranes to alcohols.
- Cadot, Christine,Dalko, Peter I.,Cossy, Janine,Ollivier, Cyril,Chuard, Rachel,Renaud, Philippe
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p. 7193 - 7202
(2007/10/03)
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- The photochemistry of the 4-cyanobenzoic acid esters of trans- and cis-2-phenylcyclohexanol
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Irradiation of trans-2-phenylcyclohexyl 4-cyanobenzoate (4) in methanol results in formation of the 1-phenylcyclohexene and 4-cyanobenzoic acid as the major products. The mechanism proposed for this example of the Norrish Type II-like reaction, normally inefficient for the π,π*state of esters, begins with intramolecular electron transfer in the excited singlet state. The next step, intramolecular proton transfer, is highly exergonic as a result of the increased acidity of the benzylic hydrogen of the radical cation and the increased basicity of the carbonyl oxygen of the radical anion. The final step is cleavage of the 1,4-biradical. This mechanism is proposed on the basis of product studies, absorption spectra, fluorescence spectra, oxidation and reduction potentials, and nanosecond laser flash photolysis spectra. The stereochemical requirements for the process have also been examined using solution NMR, the X-ray structure, and MM3 calculations. The stereoisomer, cis-2-phenylcyclohexyl 4-cyanobenzoate (5), undergoes cis to trans isomerization before photofragmentation. Photolysis of the cis isomer in methanol-OD demonstrated that the cis to trans isomerization occurred by inversion at C1.
- Pincock,Rifai,Stefanova
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- Hydroxylation of olefins using molecular oxygen via alkylboronic esters
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Alkylboronic esters derived from olefins undergo a hydroxylation in the presence of triethylamine and molecular oxygen. Alcohols were obtained in good to excellent yields without alkaline treatment of the boronate ester intermediates. Radical-clock experiments allowed the comparison between radical and polar reaction paths.
- Cadot, Christine,Dalko, Peter I.,Cossy, Janine
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p. 1661 - 1663
(2007/10/03)
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- Diastereoselective reduction of cyclohexanones with diisobutylaluminium phenoxides in terms of the isoinversion principle
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The diastereoselectivity of the reduction of 2-substituted cyclohexanones 1-6 with 4-substituted diisobutylaluminium phenoxides a-d has been investigated as a function of temperature. The high-temperature region is found to be dominated by hydride transfer, which is controlled by steric as well as electronic effects. However, at low temperatures the Meerwein-Ponndorf-Verley reaction gains in Importance. This phenomenon is quantified by an isoinversion relationship.
- Meyer-Stork, Markus A.,Haag, Dieter,Scharf, Hans-Dieter
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p. 593 - 595
(2007/10/03)
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- Asymmetric synthesis of CDP840 by Jacobsen epoxidation. An unusual syn selective reduction of an epoxide
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An asymmetric synthesis of the PDE IV inhibitor, CDP840 (3) is reported. The absolute stereochemistry was controlled by a Jacobsen epoxidation of the Z triaryl olefin 8 (89% ee) or the E triaryl olefin 9 (48% ee). The disparate results in stereocontrol were interpreted in terms of the 'skewed side-on approach model' proposed by Jacobsen. LiBH4 · BH3 reduction of the epoxides was found to proceed with retention of configuration.
- Lynch,Choi,Churchill,Volante,Reamer,Ball
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p. 9223 - 9228
(2007/10/03)
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- Experimental and theoretical studies on the diastereoselective Diels-Alder reactions of chiral 1-alkoxy-1,3-butadienes. I: Parent system and 4-substituted derivatives
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Chiral 1-alkoxy-1,3-dienes (parent and 4-substituted) have been prepared from the corresponding chiral alkoxyacetylenes in a stereoselective manner following a 2C + 2C approach. The Diels-Alder reactions of the dienes with maleic anhydride and 4-phenyl-3H-1,2,4-triazoline-3,5-dione take place with significant diastereoselectivity. Theoretical calculations on these cycloadditions, performed with the SCF-MO procedure AM1, have been used in the stereochemical assignment of the adducts.
- Virgili, Marina,Pericas, Miquel A.,Moyano, Albert,Riera, Antoni
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p. 13427 - 13448
(2007/10/03)
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- Selektive Metallierung von Halogenarenen mit Cupraten
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Keywords: Asymmetrische Synthesen; Cuprate; Kupferverbindungen; Metallierungen
- Kondo, Yoshinori,Matsudaira, Tetsuji,Sato, Junko,Murata, Naoko,Sakamoto, Takao
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p. 818 - 820
(2007/10/03)
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- Intramolecular Meta Photocycloaddition of Conformationally Restrained 5-Phenylpent-1-enes. Part I: Bichromophoric Cyclohexane Derivatives
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The cis isomers of 1-allyl-2-phenycyclohexane and 1-benzyl-2-vinylcyclohexane yield predominantly 1,3 addition, while the trans isomers show a high selectivity for 2,6 addition, which is explained by steric interactions.Introduction of a third substituent, OH or OCH3, on the alkenyl substituted carbon of the cyclohexane ring gives almost exclusively 1,3 addition.This can mostly be explained in terms of more steric hindrance in the conformations leading to 2,6 addition.From the results described it can be concluded that for 2,6 additon two conformations are available, while the energy difference between the 1,3 conformations is much larger and therefore a completely stereoselective 1,3 addition is found (except for 6).
- Barentsen, Helma M.,Talman, Edger G.,Piet, Dennis P.,Cornelisse, Jan
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p. 7469 - 7494
(2007/10/02)
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- Silica Gel Supported Zinc Borohydride. A Novel Reagent for Hydration of Unactivated Alkenes and Alkynes
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A simple and general procedure for hydration of unactivated alkenes and alkynes producing less substituted alcohols selectively has been achieved by the reaction of the corresponding alkenes or alkynes on silica gel support with zinc borohydride in 1,2-dimethoxyethane.
- Ranu, Brindaban C.,Sarkar, Arunkanti,Saha, Manika,Chakraborty, Rupak
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p. 6579 - 6584
(2007/10/02)
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- Enzymatic resolution of trans-2-arylcyclohexan-1-ols using crude chicken liver esterase (CCLE) as biocatalyst
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Homochiral trans-2-arylcyclohexan-1-ols were synthesized via crude chicken liver esterase (CCLE) mediated enantioselective hydrolysis of the corresponding racemic acetates.
- Basavaiah,Rao
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p. 223 - 234
(2007/10/02)
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- An Unusual Anti-Markovnikov Hydration of Alkenes with Titanium(III) Tetrahydroborates
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Titanium(III) tetrahydroborate formed by the reaction of titanium tetrachloride and benzyltriethylammonium borohydride (1:4) reacts with alkenes in dichloromethane (-20 deg C) very readily to yield directly the corresponding alcohols in excellent yields after a simple aqueous work up.
- Kumar, K. S. Ravi,Baskaran, S.,Chandrasekaran, S.
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p. 171 - 174
(2007/10/02)
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- An unusual regioselctive anti-Markovnikov hydration of alkenes with zinc borohydride on silica gel support
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An efficient and general procedure of regioselective anti-Markovnikov hydration of alkenes producing less-substituted alcohols has been achieved by a simple reaction of alkene on silica gel support with zinc borohydride in 1,2-dimethoxyethane.
- Ranu,Chakraborty,Saha
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p. 4659 - 4662
(2007/10/02)
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- An Internally Activated Tin Hydride with Enhanced Reducing Ability
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Tin hydride 1 is activated for nucleophilic hydride transfer and also for radical chain reduction, depending on solvent.The nucleophilic hydride pathway is favored in methanol, and 1 can be used as a selective reducing agent for ketones.Simple ketones are not reduced in aprotic solvents, but β-hydroxy ketones are activated internally by the hydroxyl group and can be reduced in THF with good control of stereochemistry, as in the conversion from 7 to 9 (30:1 9:8).A catalytic version of the nucleophilic hydride reductions in methanol has been developed using PhSiH3 as the stoichiometric hydride source.Radical chain dehalogenations can also be achieved with 1 at room temperature and without added radical initiators.Simple xanthates are not reduced efficiently in the absence of an initiator, but the reaction proceeds in the presence of AIBN.
- Vedejs, E.,Duncan, S. M.,Haight, A. R.
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p. 3046 - 3050
(2007/10/02)
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- Samarium(III)-Catalyzed Hydroboration of Olefins with Catecholborane. AGeneral Approach to the Synthesis of Boronate Esters
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A broad selection of olefins undergo hydroboration with catecholborane in a reaction that is catalyzed by a range of samarium(III) as well as other lanthanide complexes.
- Evans, David A.,Muci, Alexander R.,Stuermer, Rainer
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p. 5307 - 5309
(2007/10/02)
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- A Facile Conversion of Alkenes to Alcohols with Benzyltriethylammonium Borohydride-Chlorotrimethylsilane
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A combination of benzyltrimethylammonium borohydride and chlorotrimethylsilane (1:1) in dichloromethane at 0 deg C has been found to be a convenient reagent system for the conversion of alkenes to alcohols, the hydroxy group of which is introduced in an anti-Markovnikov manner.
- Baskaran, Sundarababu,Gupta, Varsha,Chidambaram, Nallaperumal,Chandrasekaran, Srinivasan
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p. 903 - 904
(2007/10/02)
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- ORGANOCOPPER REAGENTS IN DIMETHYL SULFIDE
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Organocopper(I) reagents, RCu, are both more stable and more reactive when prepared in dimethyl sulfide instead of ether or tetrahydrofuran.A wide range of Li reagents has been investigated with good results, as has a selection of Grignard reagents.Excellent yields of products are observed with typical substrates as α,β-unsaturated ketones and acid chlorides.
- Bertz, Steven H.,Dabbagh, Gary
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p. 425 - 434
(2007/10/02)
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- Auxiliary Structure and Asymmetric Induction in the Ene Reactions of Chiral Glyoxylates
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A variety of chiral auxiliares (1a-13a) were prepared and tested for levels of asymmetric induction control in the ene reaction of chiral glyoxylates.Structural features required for high levels of control were defined by systematic modification of the auxiliary, providing systems with induction levels that ranged from 1.2 to 1 to better than 99.9 to 0.1.
- Whitesell, James K.,Lawrence, Robert M.,Chen, Huang-Hsing
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p. 4779 - 4784
(2007/10/02)
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- BORON FLUORIDE PROMOTED OPENING OF EPOXIDES BY ORGANOCOPPER AND CUPRATE REAGENTS
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In the presence of BF3 the reaction rate of organocopper and cuprate reagents with poorly reactive epoxides is dramatically enhanced.Lithium organocuprates are the best choice among the various organocopper and cuprate reagents tested.Even the dimesityl cyanocuprate is able to react with cyclohexene oxide in excellent yield.No products of cationic rearrangements are observed.The reaction with various epoxides shows a complete stereochemical (pure anti opening) and regiochemical control (attack on the less hindered side of the epoxide).
- Alexakis, A.,Jachiet, D.,Normant, J. F.
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p. 5607 - 5620
(2007/10/02)
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- Solvolysis of cis- and trans-2-Phenylcyclohexyl-p-bromobenzene Sulphonate
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Die Solvolyse von cis- and trans-2-Phenyl-cyclohexyl-p-brombenzensulfonaten wurde in Essigsaeure, waessrigem Dioxan und waessrigem Ethanol untersucht und mit der des Cyclohexylsulfonatesters verglichen.In Essigsaeure liegt die Geschwindigkeit des cis-Isomeren gegenueber dem trans-Isomeren um den Faktor 5 hoeher, in waessrigem Dioxan und waessrigem Alkohol dagegen um den Faktor 10 bzw. 12.Produkte der Acetolyse sind hauptsaechlich Eliminierungsprodukte (1- und 3-Phenylcyclohexen 75 percent) und cis- und trans-Acetate (25 percent).In waessrigen Loesungsmitteln entstehen vorwiegend Eliminierungsprodukte (98 percent).Die Erhoehung der Geschwindigkeit des cis-Isomeren gegenueber der trans-Verbindung ist auf eine sterische Beschleunigung zurueckzufuehren.Ein solvatisiertes Ionenpaar wurde als Zwischenprodukt postuliert; fuer eine Phenylnachbargruppenwirkung ergab sich kein Hinweis.
- Youssef, Abdel-Hamid A.,Sharaf, Saber M.,Hegazy, Fatma M. El
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p. 725 - 734
(2007/10/02)
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- Properties of Bis(trifluoroacetoxy)borane as a Reducing Agent of Organic Compounds
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Reactions of bis(trifluoroacetoxy)borane-THF (1) with compounds containing representative organic functional groups were studied to determine the usefulness of 1 as a selective reducing agent.Reducible functionalities were indoles, ketones, aldehydes, imines, and compounds that readily generate carbocations in trifluoroacetic acid.Many functionalities were inert to 1.Epoxides and ortho esters suffered decomposition under the reaction conditions.Olefins and acetylenes were not hydroborated, and carboxylic acids were not reduced by 1.
- Maryanoff, Bruce E.,McComsey, David F.,Nortey, Samuel O.
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p. 355 - 360
(2007/10/02)
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- Formation of Alcohols from Alkenes with TiCl4-NaBH4
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The reaction of alkenes with TiCl4-NaBH4 in 1,2-dimethoxyethane afforded alcohols, the hydroxy group of which was introduced in an anti-Markovnikov direction.
- Kano, Shinzo,Tanaka, Yasuyuki,Hibino, Satoshi
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p. 414 - 415
(2007/10/02)
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