Two-step Synthesis of New γ-Lactones via Cyclization of 7-Chloro-2-(methoxycarbonyl)-4-6-dimethylocta-(2E,4E,6E)-trienoic acid

International audienceA new rapid synthesis of γ-lactones, cis fused with a cyclopentenic ring by thermal cyclization of 7-chloro-2-(methoxycarbonyl)-4-6-dimethylocta-7-phenyl (or methyl) (2E,4E,6E)-trienoic acids was reported. The key step implicates an intramolecular cyclization to a cyclopentenyl cation, according to an electrocyclic π2s + π2a conrotatory process, published in a recent paper (from the corresponding diacids). We have investigated the thermal behavior of the corresponding half-esters since; if the cyclization obeys to the proposed mechanism, the diacids, half-esters must also cyclize in a similar manner. Saponification of these led to γ-dilactones via intermediary cyclopropanes. Mechanistic pathways were investigated