(NHC)copper(I) hydride catalyzed ketone hydrosilylation is an efficient method for the enantioselective synthesis of secondary alcohols. Herein, we represent a computational study of this reaction using density functional theory (DFT) on realistic model systems. This study is supported by kinetic investigations, using in situ FTIR measurements. The calculations validate the previously proposed reaction mechanism and explain the high activity of (OR1) x R2 3–x Si–H types of silanes. Experimental evidence in favor of the monomeric (NHC)CuH form of the catalyst is also given. Combining experimental and theoretical results furthermore highlights a Lewis base activation of the hydrosilane, leading to a modified suggestion for the mechanistic scheme of the catalytic cycle.

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A series of enlarged quinidine-derived organocatalysts are synthesized based on the concept of polyalkylation. The larger size of the catalysts allows their recycling with organic solvent nanofiltration membranes. It is shown that the compounds are robust and suitable for multiple reuses. In addition, a marked improvement in catalytic performance is observed.-(SIEW, W. E.; ATES, C.; MERSCHAERT, A.; LIVINGSTON*, A. G.; Green Chem. 15 (2013) 3, 663-674,

Abstract-A new asymmetric synthesis of 2-substituted chiral chromanes has been achieved. The key step is the intramolecular conjugate addition of a phenolic nucleophile on a a,b-unsaturated ester catalyzed by Cinchona alkaloids. The high ee's obtained with cinchonine and its derivatives have been rationalized by ab initio quantum chemistry calculations of transition state structures. Ó 2004 Elsevier Ltd. All rights reserved.Functionalized chromanes possess potentially useful biological properties.1 In the scope of a research program, we developed earlier the synthesis of 2,6-disubstituted-chromanes from 6-substituted chromanones 2 ( Fig. 1).Although high overall yields of racemic material were obtained, this approach suffered from the need to perform an optical resolution in the last step of the synthesis.In order to improve the productivity of the process without having to develop a new route, we sought to utilize a chiral base in the Wittig-oxa-Michael step (Fig. 2). The results of those efforts are reported herein. Initially very low enantioselectivities (ca. 28% ee with cinchonine) were obtained in a tandem process by heating a mixture of lactol 1, phosphorane, and cinchonine to 80-100°C. In this temperature range, we observed that the phosphorane alone was able to catalyze the cyclization thus competing with the chiral catalyst. Therefore, we modified the procedure and performed the reaction sequentially: (i) the Wittig step was carried out at ambient temperature (ii) the remaining phosphorane and the triphenylphosphine oxide by-product were removed by silica gel treatment, and (iii) the chiral