Geminal dicarboxylates as carbonyl surrogates for asymmetric synthesis. Part II. Scope and applications

An enantioselective synthesis of allylic esters has been achieved by a nove l asymmetric alkylation of allylic gem-dicarboxylates. The catalyst derived from palladium(0) and R,R-1,2-di(2 ' -diphenylphosphinobenzamido)cyclohexe ne efficiently induced the alkylation process with a variety of nucleophile s to provide allylic eaters as products in good yield. High regio- and enan tioselectivities were observed in the alkylation with most nucleophiles der ived from malonate, whereas a modest level of ee's was obtained in the reac tions with less reactive nucleophiles such as bis(phenylsulfonyl)ethane. In the latter case, a slow addition procedure proved effective, leading to si gnificantly improved ee's. The utility of the alkylation products was demon strated by several synthetically useful transformations including allylic i somerizations, allylic alkylations, and Claisen rearrangements. Using these reactions, the chirality of the initial allylic carbon-oxygen bond could b e transferred to new carbon-oxygen, carbon-carbon, or carbon-nitrogen bonds in a predictable fashion with high stereochemical fidelity. The conversion of gem-diesters to chiral esters by the substitution reaction is the equiv alent of an asymmetric carbonyl addition by stabilized nucleophiles. In con junction with the subsequent reactions that occur with high stereospecifici ty, allylic gem-dicarboxylates serve as synthons for a double allylic trans formation.