Implementationof new, highfyenantioenrichedheterocyclesfor use in auxiliary-supported asymmetricalkylations is detailed. These new auxiliaries proved effective in enforcing pi-facial selectivityin cnolatemethylatkmswithincreasingdiastercoselectivity resultingfmmbrdkk aryl-stecrirrg groups. The sources for rmanticipatcdkinetic effects and alkylation prucfuctdecompositionsare discussed.O 1997Elsevier ScienceLtd.
Auxiliary-mediated asymmetric alkylation of carboxylic acids is now widely applied in the research production of optically enriched carboxylic acid derivatives. Numerous auxiliaries have been introduced that provide high levels of asymmetric induction (see for example 1-5, Scheme 1).l Following this prescript, the chiral appendage is covalently attached to the carboxylic acid allowing for the differentiation between pi-faces generated upon enolate formation. Subsequent diastereoselective alkylation and removal of the auxiliary delivers optically pure carboxylic acids. Despite the general successes of this method, enolate methylations of existing auxiliary analogues occurs less selectively. For example, the methylations of butyryl enolates 1 (R = i-Pr) and 5 (R= H) resulted in de. of 86V0.*c,g Furthermore, enolate methylations of more complex substrates