Chiral pyridine N-oxides derived from monoterpenes as organocatalysts for stereoselective reactions with allyltrichlorosilane and tetrachlorosilane

The synthesis of enantiomerically pure C-2-symmetric dipyridylmethane ligands and related N,N'-dioxides is reported. A procedure for the synthesis of a few new enantiomerically pure C-2-symmetric pyridine N-oxides and the preparation of four pyridine N-oxides with oxygen and nitrogen atoms as further coordinating elements in the heterocycle framework is described. All compounds were prepared from naturally occurring monoterpenes. These new compounds were assessed as organocatalysts in two different reactions, namely the allylation of aldehydes with allyltrichlorosilane that afforded homoallylic alcohols in good yields and up to 85% ee and the stilbene oxide opening by the addition of tetrachlorosilane that gave chlorohydrin in quantitative yield and up to 70% ee. (C) 2008 Elsevier Ltd. All rights reserved.