Synthesis of Enantiomerically Enriched Allenes via Chiral, Configurationally Stable 1-Lithio-2-alkynyl Carbamates

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Abstract
Enantiomerically enriched, configurationally stable propargylic anions 5 are produced by deprotonation of optically active secondary 2-alkynyl N,N-diisopropylcarbamates 4. The lithium intermediates 5 add aldehydes with a high degree of chirality transfer in the formation of the allenyl carbinols 7 and 8 [(4-hydroxy-1,2-alkadienyl) N,N-diisopropylcarbamates]. A method for trapping short-lived chiral carbanions is introduced, which is based on the deprotonation of the optically active precursor 4 with sec-butyllithium in the presence of pivalaldehyde.

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