Chiral Dilithiomethane Derivatives: Structure Determination and Application in Stereoselective Reactions

The synthesis and X-ray analysis of chiral dilithiomethane analogues derived from sulfoximines are presented. The structures of the sulfoximine-stabilised mono- and dilithio salts have been compared and allow a rationalization of the second lithiation. Organophosphorus-based dilithiomethane derivatives are also structurally described. The gas-phase structures of N,S,S-trimethylsulfoximine 19 and of its mono- and dilithiated isomers 20–21 were calculated by ab initio methods employing different levels of theory. For an application in asymmetric synthesis, the dilithiation of (N-methyl)-S-ethyl-S-phenylsulfoximine (11) afforded a chiral dinucleophile that undergoes highly regio- and stereoselective alkylation reactions with electrophiles. The transmetallation of a chiral dilithiomethane reagent such as 14 with ClTi(OiPr)3 followed by addition of an aldehyde, constitutes a simple one-pot process for the formation of (E)-alkenylsulfoximines with excellent diastereoselectivity.