Crystal Structures of (+)-Sparteine Surrogate Adducts of Methyllithium and Phenyllithium

Abstract

The crystal structures of aggregates between MeLi and PhLi and a (+)-sparteine surrogate ((+)-2) have been determined. The MeLi adduct 4 reveals a 2:2 dimer, while the PhLi adduct 6 forms a rare example of a 4:2 ladder structure, each capped by two of the diamine ligands. The observation that (+)-2 is equally effective as (−)-sparteine in s-BuLi-mediated asymmetric deprotonations, but leading to the opposite sense of stereoselectivity, is explained on the basis of the crystal structures and a computational study. Moreover, the crystal structure of the 2;2 dimer between MeLi and (−)-sparteine has been redetermined with advanced accuracy.