Novel π_2s+π_2a 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 π 2s + π 2a 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.

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

“…Characteristics of compounds 1 and 7 are in accordance with those described in the literature for related products [1]. Dimethyl propylidenemalonate and β-chloro α-ethylenic aldehydes were synthesized according to well-known procedures [1].…”

“…Dimethyl propylidenemalonate and β-chloro α-ethylenic aldehydes were synthesized according to well-known procedures [1]. Malonic acid, half-esters 1.…”

“…In a recent paper, published in this journal [1], we report that thermal cyclization of 2-((2E,4E)-5-chloro-2,4-dimethylhexa-2,4-dienylidene)malonic acids led to new γ-dilactones (Scheme 1).…”

Recent Advances in the Interrupted Nazarov Reaction

“…Apart from 2,4‐dienocarbonyl compounds, 2,4,6‐trienes containing a dicarboxyl group at the terminal carbon atom are involved in the interrupted iso ‐Nazarov reaction (Scheme ) . The reaction proceeds under catalyst‐free conditions because it is promoted by a carboxyl group.…”