Synthesis of Vicinal Dimethyl Chirons by Asymmetric Hydrogenation of

Chiral acyclic molecules with 1,2-dimethyl substitution patterns A are observed in some natural products.1-4 Synthetic methodolo-gies to obtain these fragments are far from refined; older methods feature conjugate additions to R,!-unsaturated carbonyl systems equipped with chiral auxiliaries,5 and newer ones are based on asymmetric catalysts to deliver methyl Grignards to systems with γ-chiral centers.6 The latter approach will probably emerge as the most general and practical for many applications, though it is relatively untested now. Other routes are based on asymmetric desymmetrization of meso-1,2-dimethyl substrates,7,8 conjugate additions and enolate quenching,9 or modification of readily accessible chiral building blocks, but these lack generality with respect to either the substitution patterns that can be accessed or the stereoisomers that can be made. Here we demonstrate that useful chirons B can be obtained via asymmetric hydrogenation using th