Organostannanes Derived from (−)-Menthol: Controlling Stereochemistry during the Preparation of (1R,2S,5R)-Menthyldiphenyltin Hydride and Bis((1R,2S,5R)-menthyl)phenyltin Hydride

Abstract

Reaction of (1R,2S,5R)-menthylmagnesium chloride (MenMgCl) with triphenyltin chloride in THF proceeds with epimerization of the C-1 carbon of the menthyl group and results in a mixture of (1R,2S,5R)-menthyltriphenyltin (1) and (1S,2S,5R)-menthyltriphenyltin (2). Addition of Lewis bases such as triphenylphosphine to the THF solution of triphenyltin chloride prior to addition of the Grignard reagent suppresses epimerization and enables isolation of pure 1. An epimerization mechanism involving one-electron-transfer reactions is postulated. Compound 1 is the precursor for reactions that lead to the formation of a series of compounds, namely, (1S,2S,5R)-menthyldiphenyltin iodide (4), (1S,2S,5R)-menthyldiphenyltin fluoride (5), (1S,2S,5R)-menthyldiphenyltin hydride (6), (1S,2S,5R)-menthylphenyltin dibromide (7), and (1S,2S,5R)-menthylphenyltin dichloride (8). The synthesis of the dimenthyl derivatives bis((1S,2S,5R)-menthyl)diphenyltin (9), bis((1S,2S,5R)-menthyl)phenyltin iodide (10), bis((1S,2S,5R)-menthyl)phenyltin hydride (11), and bis((1S,2S,5R)-menthyl)tin di(chloroacetate) (12) is described. Crystal structure determinations of 7, 8, and 12 confirm the absolute configuration of the menthyl groups.