Abstract
The alkylation of the lithium enolate of (1R )-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.
Key words
benzylisobornyl esters - alkylations - stereoselectivity - lithium enolates - steric hindrance
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