Proof of Inversion of Configuration on Stannylation of a Configurationally Stable, Tertiary Benzyllithium Compound from a Single‐Crystal X‐Ray Structure Analysis

Configurationally stable, dipole‐stabilised benzyllithium compounds (R)‐and (S)‐1 b, prepared by deprotonation of the corresponding esters with sBuLi in toluene/di‐ethyl ether (5:1), reacted with (–)‐menthyldimethyltin bromide to afford the stannanes (–)‐3 and ( + )‐4, respectively. A single‐crystal X‐ray structure analysis of compound (–)‐3 proved that stannylation occurred with inversion of the configuration at the benzylic centre, assuming retention for the deprotonation step. Lithio‐destannylation and deuteration with MeOD follow a retentive course.