SOLUTION STUDIES OF SULFUR-STABILIZED LITHIATED ALLYLIC CARBANIONS - HOESY (LI-6-H-1)NMR SPECTROSCOPY OF LITHIATED (E)-1-(T-BUTYLTHIO)BUT-2-ENE AND (E)-1-(PHENYLTHIO)BUT-2-ENE

The nature of the lithium counter cations association with sulfur-stab ilized allylic carbanions is investigated by 2-D HOESY (Li-6-H-1) spec troscopy. The association is best described as either an unsymmetrical dihapto(eta(2))-bonded lithium to the C1 and C2 carbons or a monohapt o(eta(1))-bonded lithium to C1 in a position close to C2. The lithium is spatially closer to C1 than C2 and there is no indication of intera ction with the C3 carbon. These structural traits for lithiated (E)-1- (t-butylthio)but-2-ene in THF and in the presence of TMEDA at 220 K di ffer markedly to those obtained from the low temperature X-ray crystal structure of this anionic system.