Allyltrimethoxysilane addition to N-acylhydrazones:: Two catalytic methods employing CuCl and fluoride

Two alternative reaction conditions developed for allyltrimethoxysilane addition to N-benzoylhydrazones enable efficient and versatile access to homoallylic alpha-branched amines. Aldehyde hydrazones, both aromatic and aliphatic, and ketone hydrazones all give good yields. One set of conditions employs catalytic amounts of CuCl and tetrabutylammonium triphenyldifluorosilicate (TBAT); improved yields and reaction times are obtained at 80 degreesC in the presence of bis(diphenylphosphino)ethane (dppe) and t-BuOH as additives. The second set of conditions employs 20 mol% TBAT as a fluoride source in a metal-free catalytic system; here t-BuOH offers only modest improvement, and ambient temperatures are optimal. For example, under this second set of conditions, the N-benzoylhydrazone from ethyl pyruvate affords the homoallylic tert-alkyl amine adduct in 78% yield.