Reaction of bromomethylazoles and tosylmethyl isocyanide. A novel heterocyclization method for the synthesis of the core of marine alkaloids variolins and related azolopyrimidines

Article abstract of DOI:10.1021/jo0358168

A novel and efficient synthesis of the pyrido[3′,2′:4,5] pyrrolo[1,2-c]pyrimidine system, the heterocyclic core of the variolin family of marine alkaloids, is described. The route involves the reaction of 3-bromo-2-(bromomethyl)pyrrolo[2,3-b]pyridine and tosylmethyl isocyanide (TosMIC) under phase-transfer conditions. This unprecedented reaction was also used to synthesize a series of new methoxycarbonyl azolopyrimidines by reaction of TosMIC with bromomethylindoles, bromomethylbenzimidazole, and bromomethylpyrazole. Hydrolysis and decarboxylation of 5-bromo-7- methoxycarbonylpyrido[3′,2′:4,5]pyrrolo[1,2-c]pyrimidine obtained by this heterocyclization process and installation of the pyrimidine moiety in the C5 position open an alternative approach to complete a total synthesis of variolin B.