Stereochemistry of the monoalkylation of (1R)-3-endo-(p-methoxybenzyl)isobornyl propionate

Article abstract of DOI:10.1055/s-2002-33115

The alkylation of the lithium enolate of (IR)-3-endo-(p-methoxybenzyl)isobornyl propionate in THF gives predominantly the (R)-2-methylalkanoic esters in de's of 25-42%. The structure of the alkyl halide does not affect the outcome, although the most reactive halides give the greatest de levels. The formation of the enolate in THF-HMPA reverses the stereochemistry of the alkylation with ethyl bromide from 42% R to 23% S. The stereochemistry of the reaction is interpreted in terms of a conformational shift on deprotonation of the ester.