Nitrogen bridgehead compounds. Part 5. Cyclization of 2-(2-pyridylaminomethylene)-succinates and -glutarates

Abstract

A study has been made of the cyclization reactions of some 2-(2-pyridylaminomethylene)-succinates (7) and -glutarates (8) in phosphoryl chloride–polyphosphoric acid. In the cyclization of the succinates (7) we have found that of the possible cyclic products pyrido[1,2-a]pyrimidines (9) and pyridylpyrrolinones (13) are formed, and the latter, subsequently, may form pyridylpyrroles (15) although the reaction conditions favour the formation of pyridopyrimidines (9). The ratio of pyridopyrimidines (9) and pyridylpyrroles [(13) : (15)] was independent of the geometry of the starting succinates (7), but was dependent upon the substituent of the pyridine ring, and on its position. Substituents in position 6 hindered the formation of pyridopyrimidines (9) while those in position 3 inhibited the formation of pyridylpyrrolinones (13). From the homologous glutarates (8) only pyrido[1,2-a]pyrimidines (10) are formed.