Base-Induced Cyclization of α-Chloro- β,γ-Unsatured Ketones. Facile Synthesis of Tri- and Tetrasubstituted 2-Cyclopenten-1-ones

Article abstract of DOI:10.1021/jo00002a042

Base-induced cyclization of fully substituted α-chloro β,γ-unsatured ketones results in substituted cyclopentenones.Potassium tert-butoxyde, lithium diisopropylamide, sodium hydroxide, and ammonium hydroxide can be used as the base for this process.In the case of ammonium hydroxide , it is proposed that initial formation of an enamine is followed by an intramolecular S_N2'reaction of the enamine carbon.For all other bases, the reaction most likely proceeds through a ketone enolate.Application of this novel cyclization has been extended to the synthesis of several 2,3-substituted, 2,3,5-trisubstituted, and 2,3,5,5-tetrasubstituted 2-cyclopenten-1-ones.