New Triene Synthesis from Sorbic Acid: Two-Step Synthesis of cis- and trans-Galbanolenes

Article abstract of DOI:10.1016/S0040-4039(00)92216-0

The lithium dianion of sorbic acid reacts with hexanal at the C(2)-position to afford separable anti- and syn-hydroxy carboxylic acids 3 and 4 (87percent; 3/4=59:41 or 79percent; 3/4=16:84), whose stereospecific anti-decarboxylative elimination respectively affords (3E,5Z)- and (3E,5E)-1,3,5-undecatriene (1) and (2) (cis- and trans-galbanolenes (1) and (2) (69percent).An alternative route to 1 involves conversion of 3,4 to cis-lactone 7 (45percent after chromatography) followed by thermal syn-decarboxylation (81percent).The described procedure is both new and of general applicability, as illustrated by the synthesis of trienes with different substitution pattern.Key Words: Sorbic acid; aldol reaction; triene synthesis; olefination; decarboxylative elimination.