A H-1 AND C-13 NMR-STUDY OF THE STRUCTURE OF SULFUR-STABILIZED LITHIATED ALLYLIC CARBANIONS

NMR studies of the solution structures of lithiated (E)-1-(t-butylthio )but-2-ene (4) and lithiated (E)-1-(phenylthio)but-2-ene (6) are repor ted. The structure of lithiated (E)-1-(t-butylthio)but-2-ene (4) is be st described as a transoid carbanion with the allylic carbons C1, C2, and C3 having intermediate sp(2)-sp(3) hybridization. In (4) the heter oatom and non-allylic substituent do not play any significant role in carbanion stabilization. Lithiated (E)-1-(phenylthio)but-2-ene (6) dif fers from (4) in that it exhibits cis geometry about the C1-C2 bond an d the phenylthio group participates in helping to stabilize allylic ch arge. There is a discrepancy between the geometry about the C1-C2 bond in the solution and solid structures of (4) in the presence of TMEDA.