Transition-Metal-Free Synthesis of Pyrrolo[1,2-a]pyrazines via Intramolecular Cyclization of N-Propargyl(pyrrolyl)enaminones

A concise transition-metal-free strategy for the synthesis of pyrrolo[1,2-a] pyrazines with enone substituents has been developed. It includes the following key steps: (a) cross-coupling of pyrroles with acyl(bromo) acetylenes in solid alumina at room temperature to give 2(acylethynyl)pyrroles; (b) addition of propargylamine to the above acetylenes to form the corresponding N-propargylenaminones; and (c) chemo- and stereoselective base-catalyzed (Cs2CO3/DMSO) intramolecular cyclization of the synthesized propargylic derivatives to form (acylmethylidene)pyrrolo[1,2-a]pyrazines of Z-configuration.