Stereochemistry of the Monoalkylation of (1R)-3-endo-(p-Methoxybenzyl)isobornyl Propionate

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

References

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Current address: Department of Chemistry, University of Wisconsin - Eau Claire, Eau Claire, WI 54702-4004, USA, e-mail: [e-mail].