Tandem Reduction−Chloroallylboration of Esters: Asymmetric Synthesis of Lamoxirene, the Spermatozoid Releasing and Attracting Pheromone of the Laminariales (Phaeophyceae)

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Abstract
The asymmetric synthesis of all four stereoisomers of lamoxirene (cis-2-cyclohepta-2,5-dienyl-3-vinyloxirane), the spermatozoid-releasing and -attracting pheromone of the Laminariales (Phaeophyceae), is reported. Chiral ethyl cyclohepta-2,5-diene carboxylates, prepared by a divinylcyclopropane Cope rearrangement, were effectively alkylated by means of a novel tandem DIBAL-H reduction/asymmetric α-chloroallylboration using (Z)-γ-chloroallyldiisopinocampheylboranes. The ensuing syn-α-chlorohydrins were transformed into the corresponding vinyloxiranes with DBU, providing all four isomers of the pheromone in good chemical and excellent optical yield (90−97% ee). Spermatozoid-release assays were conducted with the sympatrically growing species L. digitata, L. hyperborea, and L. saccharina and established (1‘S,2R,3S)-1c as the most active isomer in all cases.

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