Tartrate-Derived Aryl Aldehyde Acetals in the Asymmetric Directed Metalation of Chromium Tricarbonyl Arene Complexes

Article abstract of DOI:10.1021/jo00075a008

A series of three chromium tricarbonyl benzaldehyde acetal complexes were prepared from benzaldehyde diethyl acetal and (+)-diethyl tartrate.These compounds were ortho-lithiated by a number of bases, and the diastereoselectivity of lithiation was determined by quenching of the resulting anions with Me3SiCl.Complexes 1 and 2 were found to give moderate levels of diastereoselection, while the combination of complex 3 and 2.4 equiv of n-BuLi under equilibrating conditions gave an 86percent de of silylated products.Other electrophiles gave slightly higher de's (88percent to >/= 94percent), and all products derived from 3 were separable by column chromatography.Hydrolysis of the ortho-methylated product to the corresponding benzaldehyde complex (-)-21 as well as X-ray structural analysis of the trimethylsilylated complex demonstrated that preferential pro-R deprotonation had occurred.