GENERATION OF CONFIGURATIONALLY STABLE, ENANTIOENRICHED ALPHA-OXY-ALPHA-METHYLBENZYLLITHIUM - STEREODIVERGENCE OF ITS ELECTROPHILIC SUBSTITUTION

The deprotonation of (R)- or (S)-1-phenylethyl N,N-diisopropylcarbamate with s-butyllithium/TMEDA in unpolar solvents (e.g. ether or hexane) at -78 degrees C produces configurationally stable ion pairs which are substituted stereospecifically by different electrophiles. In several examples, complete stereoretention or inversion, respectively, was achieved. Electrophiles, which have an energetically low LUMO, such as acid chlorides, heterocumulenes and trialkyltin chlorides prefer antarafacial attack. If the leaving group has a high tendency to interact with the lithium cation, such as in esters, suprafacial substitution with retention takes place.