Stereochemistry of displacement reactions at the neopentyl carbon. Further observations on the triphenylphosphine-polyhalomethane-alcohol reaction

Abstract

RMe3CCHDOH was prepared by asymmetric reduction of pivaldehyde-1-d1 with isobornyloxymagnesium bromide. Displacement of the tosyl group in (R)-Me3CCHDOTs by acetate ion occurs with 85 ± 17% inversion. Reaction of (R)-Me3CCHDOH with Ph3P and CCl4 affords (+)-Me3CCHDCl, assigned the S configuration, of greater optical purity than that resulting from chloride displacement on the tosylate. The analogous reaction using CBr4 affords bromide which seems to be significantly racemized. The characteristics of the title reaction are summarized to point out major differences between it and an SN2 process.