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.