Synthesis of Exocyclic Allenes by Double Reduction with Lithium Aluminum Hydride

Abstract

Exocyclic allenes are well represented among allenecontaining natural products, such as the grasshopper ketone. Allenes have been demonstrated in certain circumstances to embody similar properties to alkynes, and consequently have shown potential as alternative functional groups to be utilized as molecular scaffolds for pharmaceutical development. Commonly syntheses of exocyclic allenes rely on extended conjugate additions, or SN2-like alkylations and reductions of alkynyl epoxides.1 We report rapid synthesis of exocyclic allenes with 2 molar equivalents of lithium aluminum hydride in reduction of a vinylogously propargylic intermediate alcoholate with an attached trimethylsilyl group,2,3 thus providing a new, potentially general, method for their preparation.