ABSTRACT
Polymethylhydrosiloxane (PMHS), a safe and inexpensive polymer co-product of the silicon industry, is an efficient alternative reducing agent for C=O and C=N bonds when associated with catalysts (1). Mimoun et al. recently reported a new system based on zinc hydride catalysts which enables the chemoselective reduction of unfunctionalized and a,/?-unsaturated-aldehydes, ketones and esters (2). Because gummy silicon residues, which are usually associated with silane reductions, do not form, this PMHS system is attractive for synthetic / industrial purposes. Nevertheless, in contrast to tin-catalyzed reductions of ketones with PMHS (li), this system cannot be operated in protic solvents due to a dehydrogenative silylation of the solvent by PMHS; therefore, the recovered product is a silyl ether which must be subjected to a separate hydrolysis step (2). We report a diaminemodified zinc catalyst system that overcomes these limitations and broadens the scope of this process. The present system proceeds in alcoholic solvent and allows fast, chemoselective reduction of a large range of functionalized ketones and imines to the corresponding alcohols and amines in a one-step procedure.
