Synthesis of decahydropyrrolo[1,2-a]tetrazolo[1,5-d]pyrazines via Strecker reaction and intramolecular [3+2] cycloaddition

This paper reports an efficient two-step method for synthesizing a series of new (5aS, 10R)-10-aryl-5,5a, 6,7,8,10-hexahydropyrrolo[1,2-a]tetrazolo[1,5-d]pyrazines by a catalyst-free three-component Strecker reaction followed by an intramolecular [3+2] cycloaddition. The first step involved three-component coupling of aldehydes, (S)-2-(azidomethyl)pyrrolidine and potassium cyanide in presence of water to form (R)-2-((S)-2-(azidomethyl)pyrrolidin-1-yl)-2-phenylacetonitriles (3a-3v). In the next step products (3a-3v) underwent intramolecular [3+2] cycloaddition on heating to form (5aS, 10R)-10-aryl-5,5a, 6,7,8,10-hexahydropyrrolo[1,2-a] tetrazolo[1,5-d] pyrazines (4a-4v). The present methodology is cost-effective, operationally simple, and applicable for various aromatic, aliphatic and heterocyclic aldehydes, and gives desired products in satisfactory yields and diastereoselectivities. A proposed mechanism for synthesis of 3a and 4a is reported.