摘要:
Base-induced cyclization of fully substituted alpha-chloro beta,gamma-unsaturated ketones results in substituted cyclopentenones. Potassium tert-butoxide, 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(N)2' 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-disubstituted, 2,3,5-trisubstituted, and 2,3,5-tetrasubstituted 2-cyclopenten-1-ones.