The effect of lithium ion on the stereoselectivity of the intramolecular michael addition of an n-arylsulfoximine anion

The stereochemical outcome of the intramolecular Michael addition of a sulfoximine carbanion to a Z-configured alpha,beta-unsaturated ester is dependent on lithium ion coordination between the oxygen on the sulfoximine and the carbonyl oxygen of the ester, based on both experimental and computational studies. Formally, this leads to a more sterically congested structure than might otherwise be preferred. Indeed, addition of HMPA, a substance capable of effective solvation of lithium cations, changes the stereochemical course of the reaction dramatically.