Bisiminopropadienes R-N=C=C=C=N-R from Pyridopyrimidines

Abstract

Chlorination of the N,N′-di(2-pyridyl)malonamide 13a affords 2-chloro-8-methyl-4-(2-(4-picolinyl)imino-4H-pyrido[1,2-a]pyrimidine 17a. Flash vacuum thermolysis of 17a causes efficient ring opening to the valence-tautomeric ketenimine 18a/19a, elimination of HCl, and formation of the bis(4-methyl-2-pyridyl)iminopropadiene, R-N=C=C=C=N-R 20a.