Study on selectivity in the reaction of 2-substituted pyridinium-N-imines with dimethyl acetylenedicarboxylate

Abstract Reactions of 2-X-pyridinium- N -imines (X = F, Cl, Br, CN, OPh, NH 2 , N -morpholine) with dimethyl acetylenedicarboxylate (DMAD) have been studied. In the case of X = Cl, Br, CN, OPh both 7-substituted- and 7- H -pyrazolo[1,5- a ]pyridines are formed. The 7-H/7-X ratio usually increases with the growing solvent polarity. The reaction of N -amino-2-iminopyridine with DMAD gives substituted pyrido[1,2- b ][1,2,4]triazine.