Reduction of Imines with Trichlorosilane Catalyzed by Chiral Lewis Bases

Reduction of Imines with Trichlorosilane Catalyzed by Chiral Lewis Bases 

Chiral Amine Synthesis Methods, Developments and Applications. Edited by Thomas C. Nugent Copyright 2010 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 978-3-527-32509-2 

By contrast, metal free organocatalysts [6] can be viewed as an attractive altemative to those processes in which the metal is not vital for the key bond forming event. The advantages are obvious no metal leaching to the product, reduced toxicity, and lower cost of the catalysts and their regeneration. Therefore, the prime goal here is to develop new, robust processes that could compete with their established, metal catalyzed counterparts. 

Silanes are widely recognized as efficient reagents for reduction of carbonyl and heterocarbonyl functionality. In the case of alkyl and arylsilanes, the reaction requires catalysis by Lewis acids or transition metal complexes 1, 3] however, with more Lewis acidic trichloro or trialkoxysilanes, an altemative metal free activation can be accomplished. Thus, it has been demonstrated that extracoordinate silicon hydrides, formed by the coordination of silanes to Lewis bases, such as tertiary amines 7a], DMF [7b] or MeCN, and so on [7], can serve as mild reagents for the reduction of imines to amines [8]. In the case of trichlorosilane, an inexpensive and relatively easy to handle reducing reagent, and DMF as a Lewis basic promoter, the intermediacy of hexacoordinate species has been confirmed by Si NMR spectro scopy [7b]. 

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P. and Stoncius, S. (2010) Reduction of imines with trichlorosilane catalyzed by chiral Lewis bases, in Chiral Amine Synthesis (Methods, Developments and Applications) (ed. T. Nugent), John Wiley Sons, Ltd, Chichester, p. 131 ... 

Table 15.8 Asymmetric reduction of imines 106 derived from aromatic amines with trichlorosilanes catalyzed by chiral Lewis bases 110,112-115,118, and 120-124 (Scheme 15.25 and Figures 15.5 and 15.6).

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