Novel π2s+π2a Electrocyclization of Triethylenic-Malonic Acids Exemplified for a One-Pot Synthesis of New γ-Dilactones cis-Fused with a Cyclopentene

Abstract : A new, easy and rapid synthesis of γ-dilactones is cis-fused with a cyclopentenic ring via cyclization of 7-chlorotriethylenic-malonic acids. The key step implicates an intramolecular cyclization to a cyclopentenyl cation, according to an electrocyclic π2s + π2a conrotatory process. This cyclopentenyl cation led to unstable γ-lactones intermediates that are rearrange to more stable isomers. δ-lactones (6Z and 6E-(3-chlorobut-2-en-2-yl)-5-methyl-3,6-dihydro-2H-pyran-2-one) were obtained as secondary products. Mechanistic pathways were considered. The structures of the newly synthesized compounds were established by elemental and spectral data.