Synthesis of bis(trifluoromethylated) pyrazine-containing nitrogen heterocycles from hexafluorobiacetyl and ortho-diamines. Stabilization of the covalent dihydrates of pteridines and pyrido[3,4-b]pyrazines by trifluoromethyl groups

Abstract

An investigation of the structures of the reaction products derived from perfluorobutane-2,3-dione (PFBD) and a variety of ortho-diamines has been undertaken with the aim of determining the extent to which trifluoromethyl groups stabilize covalently bound hydrates. The substituted quinoxalines as well as the pyrido[2,3-b]pyrazine (25) and the lumazines (27), (29), and (31) were all found to exist as completely dehydrated aromatic species. Depending on the reaction conditions, both the aromatic form (33) and the stable, neutral covalent dihydrate form (34) could be obtained from the reaction of PFBD with 4,5-diamino-6-hydroxypyrimidinium sulphate (32). The pyrido[3,4-b]pyrazine system (36) as well as the pteridine (38) were also found to exist as stable, neutral covalent dihydrates in which the pyrazine ring is selectively hydrated.