CHIRAL CARBANIONS .1. CONFIGURATIONAL STABILITY AND REACTIONS OF ALPHA-ACYLOXY-SUBSTITUTED ALPHA-METHYLBENZYLLITHIUM COMPOUNDS

Racemic and optically active 1-phenylethyl esters of pivalic, (-)-camphanic and 2,4,6-triisopropylbenzoic acid were prepared. The esters 7a of pivalic acid were deprotonated with lithium 2,2,6,6-tetramethylpiperidide (Li-TMP) to form alpha-oxy-alpha-methylbenzyllithium compounds which are partly configurationally stable prior to acylation with starting material. Camphanic ester (-)-7b cannot be deprotonated by Li-TMP and tBuLi is added to the ester function to afford ketone (-)-1-Phenylethyl 2,4,6-triisopropylbenzoates 16 were transformed within minutes to carbanions 19 by using sBuLi/TMEDA in THF, hexane, toluene and sBuLi without TMEDA in toluene/20% diethyl ether at -78 degrees C. The carbanions are configurationally stable only in toluene/20% diethyl ether and racemise partly in the other solvents. They read with a variety of electrophiles with either retention [MeOD, AcOD, (MeO)(2)CO, ClCO(2)Me] or inversion (Me(3)SnCl) of configuration. Carbanions 19 rearrange on warning to -20 degrees C to hydroxy ketone 24 with racemisation.