Carbonylation of 1-Lithiobutadiene with Carbon Monoxide Followed by Intramolecular Acyllithiation of CC Double Bond and Intermolecular Acylation with Acid Chloride: Scope, Applications, and Mechanistic Aspects

The carbonylation of a 1-lithio-1,3-butadiene derivative with CO gave rise to a butadienyl acyllithio intermediate, which underwent an immediate intramolecular acyllithiation of the CC double bond, affording a lithio cyclopentadienyl enolate. The X-ray structural analysis of the enolate revealed a dimer connected with a “Li₂O₂” four-membered ring. Subsequent intermolecular acylation of this enolate with acid chlorides afforded β-keto-3-cyclopentenones, γ-keto-2-cyclopentenones, or cyclopentadienyl ester derivatives. The stereo- and regioselectivity of the in situ generated lithio cyclopentadienyl enolate with various acid chlorides was investigated and analyzed, showing that the formation of the above products was significantly dependent on both the substituents on the butadienyl skeleton and the bulkiness of acid chlorides.