Skeleton Diversity by Cyclopropanation of Tricyclic Acylenamines

Abstract

Aiming at the structural diversification of phakellin-and isophakellin-type pyrrole-imidazole alkaloids on the skeleton level, the reaction of dipyrrolopyrazinones and pyrroloindolizines with dichlorocarbene was investigated. Conversions resulted in ring expansion affording novel chlorinated and brominated dipyrroloazepinones, pyridopyrroloazepinones, and dipyrrolopyrazinones. Structures of the tetracyclic products with hitherto unknown architectures have been secured by X-ray analyses.

Synthesis and Unexpected Oxidization of the Tricyclic Core of Ugibohlin, Isophakellin, and Styloguanidine

“…To further clarify the role of the 4-amino-substituents in the autoxidation, the 4-unsubstituted tetrahydropyrrolo[2,3- f ]indolizin-9-one 29 was prepared by adopting Lindel’s approach to form the corresponding aldehyde 5d .…”

“…From a literature survey, Al-Mourabit and Lindel both demonstrated that the acid-promoted electrophilic aromatic substitution of N -[(pyrrol-2-yl)carbonyl]pyrrolidine-2-carbaldehydes effectively afforded the tricyclic pyrrolo[2,3- f ]indolizine skeleton (Scheme ). But their further elaboration at the C4- and C4a-positions of the pyrroloindolizine achieved only limited success.…”