Abstract
Exocyclic allenes are relatively well-represented among allene-containing natural products. A subunit of the common carotenoid fucoxanthin, this structural motif has been exploited in syntheses of allene-containing carotenoids, terpenoids, and in preparation of analogues of prostacyclins and cephalosporins. Syntheses of this allene class typically rely on either extended conjugate additions to e.g. alk-2-en-4-ynones or syn S(N)2'-like alkylations and reductions of alkynyl oxiranes. We report reaction of trimethylsilylethynyl cycloalkenones with 2 equiv of lithium aluminum hydride results in reduction of a vinylogously propargylic intermediate alcoholate to provide 3-(2-trimethylsilyl-ethenylidenyl)cycloalkanols in good yields. This provides a new method for exocyclic allene preparation.