Synthesis of Saturated Imidazolidin[1,5-a]- and Thiazolidin[3,4-a]perhydroquinoxalin-4-one and Imidazolidin[1,5-a]piperazin-4-one Derivatives. Ring Contraction of Perhydroquinoxalin-4-one to Perhydrobenzimidazolin-2-one - Zaleska, Barbara; Socha, Robert; Karelus, Marcin; Grochowski, Jacek; Serda, Paweł (Synthesis, 2004)