Ring Expansion Strategy toward Seven/Eight-Membered 1,4-Diazaheterocycle Ketones from Imidazolidines with Cyclobutenones/Diarylcyclopropenones

A ring expansion strategy for the synthesis of diverse homopiperazin-5-ones and 1,4-diazocine-5-ones is described. Imidazolidines undergo Zn(OTf)₂-catalyzed ring expansion with cyclobutenones to produce homopiperazin-5-one derivatives. Alternatively, Cu(MeCN)₄BF₄-catalyzed (5 + 3) cycloaddition between imidazolidines and diarylcyclopropenones provides access to eight-membered 1,4-diazocine-5-ones under mild conditions.