A one-pot esterification of chiral O-trimethylsilyl-cyanohydrins with retention of stereochemistry
摘要:
Enantionicrically enriched O-TMS cyanohydrins have been transformed directly into O-acyl-cyanohydrins using various anhydrides or acid chlorides in the presence of catalytic amounts of scandium(III) triflate. The reaction occurs with full retention of stereochemistry and allows the convenient measurement of enantiomeric excesses by chiral HPLC. (C) 2002 Elsevier Science Ltd. All rights reserved.
Additions of structurally diverse α-ketonitriles to aromatic and aliphatic prochiral aldehydes yielding highly enantioenriched acylated cyanohydrins were achieved using a combination of a titanium salen dimer and an achiral or chiral Lewis base. In most cases high yields and high enantioselectivities were observed. The ee was moderate in the initial part of the reaction but increased over time. This
Inversion of the configuration of cyanohydrins by a mitsunobu esterification reaction
作者:Erwin G.J.C. Warmerdam、Johannes Brussee、Chris G. Kruse、Arne van der Gen
DOI:10.1016/s0040-4020(01)86287-6
日期:1993.1
Optically active (R)-cyanohydrins have been transformed into cyanohydrin esters of opposite configuration under Mitsunobu conditions and subsequently solvolyzed to (S)-cyanohydrins in high chemical and optical yield. The method works well for allylic and benzylic cyanohydrins. Cyanohydrins containing strongly electron donating substituents gave extensive racemization. Saturated aliphatic cyanohydrins
Asymmetric synthesis of O-benzoyl cyanohydrins by reaction of aldehydes with benzoyl cyanide catalysed by BINOLAM–Ti(IV) complexes
作者:Alejandro Baeza、Carmen Nájera、José M. Sansano、José M. Saá
DOI:10.1016/j.tetasy.2005.05.031
日期:2005.7
The asymmetric cyanobenzoylation of aldehydes has been carried out for the first time, by reaction with benzoyl cyanide in a process catalysed by either (R)- or (S)-3,3′-bis(diethylaminomethyl)-1,1′-binaphthol BINOLAM–Ti(IV) complexes at room temperature and without additives. The reaction can be described as an overall cyano-O-benzoylation of aldehydes where a Lewis acid–Brönsted base (LABB) dual
Method of preparing optically active cyanohydrin derivatives
申请人:DUPHAR INTERNATIONAL RESEARCH B.V
公开号:EP0601632A1
公开(公告)日:1994-06-15
The invention relates to a method of preparing an optically active cyanohydrin carboxylic acid ester from an optically active cyanohydrin of opposite configuration, wherein said starting cyanohydrin is converted with a carboxylic acid in the presence of a dialkyl azodicarboxylate and a triarylphosphine.
The invention also relates to a method of preparing an optically active cyanohydrin of opposite configuration by a subsequent solvolysis of the ester obtained under conservation of the configuration.
Mechanistic studies on the enantioselective BINOLAM/titanium(IV)-catalyzed cyanobenzoylation of aldehydes: Part 1
作者:Alejandro Baeza、Carmen Nájera、José M. Sansano、José M. Saá
DOI:10.1016/j.tetasy.2011.07.006
日期:2011.6
The enantioselective titanium(IV)-catalyzed cyanobenzoylation of aldehydes using 1:1 BINOLAM/Ti(OiPr)(4) mixtures as a precatalyst gave O-aroyl cyanohydrins 4 with good enantiomeric excesses. The standard optimization set carried out on the assumption of Curtin-Hammett behavior, led to no amelioration.Extensive experimental and computational studies were carried out with the purpose of identifying the key mechanistic aspects governing enantioselectivity. HCN and isopropyl benzoate were detected in the reacting mixtures. This as well as the reaction response to the presence of an exogenous base, and the failure to react in the presence of Binol/Ti(OiPr)(4) mixtures, led us to propose, not a direct but an indirect process involving an enantioselective hydrocyanation step by O-benzoylation. Computational work carried out with mononuclear monomeric M-M and dinuclear mixed dimer D-IMD as catalysts support this mechanistic proposal.On the other hand, cyanobenzoylations carried out with 1:2 or higher 1:n (up to 1:5) BINOLAM/Ti(OiPr)(4) mixtures appear to involve a reversal of the enantioselection. This, together with the fact that the benzoylation of the ligated iPrOH is a slow reaction, has led us to conclude that these cyanobenzoylations do not fit within the standard Curtin-Hammett kinetic scheme. Instead, such BINOLAM/Ti(O/Pr)(4)-catalyzed cyanobenzoylations of aldehydes rather behave as non-Curtin-Hammett kinetic schemes. Further computational analysis is needed in order to make a clear distinction between Curtin-Hammett and non-Curtin-Hammett kinetic frameworks. (C) 2011 Elsevier Ltd. All rights reserved.