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

Abstract

S y n t h e s i s o f S a t u r a t e d I m i d a z o l i d i n [ 1 , 5 -a ] F u s e d S y s t e m sAbstract: Saturated fused systems such as imidazolidin[1,5-a]-and thiazolidin[3,4-a]perhydroquinoxalin-4-one as well as imidazolidin[1,5-a]piperazin-4-one derivatives were prepared by cyclocondensation reactions of appropriate perhydroquinoxalin-3-one and piperazin-3-one derivatives with diiodomethane and thiophosgene. An unusual ring contraction of perhydroquinoxalin-3-one derivatives to perhydrobenzimidazolidin-2-one derivatives by reaction with 1,2-dibromoethane was proved using crystal structure analysis with synchrotron and laboratory radiation sources.

The Synthesis of a New Fused Heterocyclic System: Hexahydro[1,5]Oxathiocino[2,3-b]Pyrazine

“…In mechanistic terms, this route shows similarities with the one described in the previous paper, 7 in which the structure of the rearranged product was confirmed by X-ray analysis. The electrophilic attack takes place exclusively at the sulfur and the nitrogen atoms of the thioamide fragment of 1.…”

“…In contrast to the above, ring closure by bielectrophilic attack of 1,3-dibromopropane on the perhydroquinoxaline 1 leads to the precedented 7 ring contraction to a perhydrobenzimidazole and formation of the thiazine ring in 6 (Scheme 3).…”

“…We have recently reported that some saturated 1,4-diazines such as the derivatives of quinoxaline (1) and piperazine (2) are very useful building blocks in heterocyclisations with diiodomethane, leading to the fused imidazo[1,5-a]quinoxaline and imidazo [1,5-a]pyrazine systems 3 and 4 respectively (Scheme 1). 7 As a sequel to this study we investigated the reaction of the 1,4-diazines 1, 2a and 2b with 1,3-dibromopropane. We surmised that cyclisations analogous to those in Scheme 1 would furnish larger-sized ring systems.…”