The Configuration Stability of Chiral Lithio α-Amino Carbanions. The Effect of Li-O vs. Li-N Complexation.

Article abstract of DOI:10.1016/S0040-4020(01)90460-0

α-Lithio pyrrolidine, as its N-t-BOC or formamidine derivative, has been generated in high enantiomeric purity via Sn-Li exchange of the enantiomerically enriched (88-95percent) α-tributylstannane derivative, 4.The alkylation of these lithio carbanions gave 2-methyl pyrrolidines as well as providing a measure of their configurational stability.It was found that the α-lithio formamidines were configurationally more stable than the t-BOC derivatives and this is attributed to, the stronger O-Li bond which weakens the adjacent C-Li bond, thus allowing configurational decay to occur more readily.This is the first report wherein a difference is observed between O-Li-C and N-Li-C configurational stability.