1,1'-BINAPHTHALENE-2,2'-DIOL AS A CHIRAL AUXILIARY - DIASTEREOSELECTIVE ALKYLATION OF BINAPHTHYL ESTERS, COMPLEX-INDUCED PROXIMITY EFFECTS IN ENOLATE FORMATION, AND ONE-STEP SYNTHESIS OF AN OPTICALLY-ACTIVE BETA-SUBSTITUTED KETONE

Diastereoselective alkylation of enolates derived from (S)-naphthyl phenylacetate 1 with LDA in THF gave the S,S-isomer as a major product. The diastereoselectivity increased as the bulkiness of the alkylating agent was increased. The low diastereomeric excess (similar to 70%) of methylation was markedly raised to 92% by the use of n-BuLi as a base due to the complex-induced proximity effect (CIPE) in enolate formation. This highly diastereoselective methylation was used to synthesize the clinically important anti-inflammatory drugs (S)-naproxen (60) and (S)-suprofen (68). The stereochemistry of ketene trimethylsilyl acetals generated from several phenylacetates was investigated to understand the origin of the diastereoselectivity in this alkylation. Methyl phenylacetate (46) predominantly gave a (Z)-enolate by kinetic deprotonation, while the (E)-enolate was predominantly obtained from phenyl phenylacetate (47). An optically active ketone (88) was synthesized from binaphthyl ester 84 by a one-pot procedure involving the 1,4-addition, followed by the 1,2-addition, of organometallics. The CIPE again played a crucial role in the high enantiomeric excess in this case.