Nitrogen bridgehead compounds. Part 42. Cyclization of diethyl 2-(2-pyridyl-aminomethylene)-succinates and -glutarates in ethanolic sodium ethoxide

Abstract

2-(Pyridylaminomethylene) -succinates (1 ) and -glutarates (2) were treated with ethanolic sodium ethoxide solution. The succinates (1 ) gave, in reversible reactions, pyridopyrimidines (3) and pyridylpyrrolinones (5), and also underwent Z-E geometric isomeritation. The cyclizations (Z) - (1 ) to (3) and ( 0 -( 1 ) to ( 5) were more rapid than the isomerization of (1). Thus, short (I-min) reactions starting from (Z) -(I ) produced the pyridopyrimidine (3) and those from (€)-(1) the pyridylpyrrolinone (5) in good yield. Longer (1 5-min) reactions yielded equilibrium mixtures, consisting mainly of pyridylpyrrolinones (5). Substituents at position 6 of the pyridine ring inhibited the formation of the pyridopyrimidines, whereas those at position 3 hindered or inhibited the formation of the pyridyl pyrrol i nones.The unsubstituted glutarate (2a) formed the pyridopyrimidine (4a) whereas the 6-substituted ones did not yield any cyclic product.Results of the sodium ethoxide ring closure were compared with those of the previously studied POCI,-PPA and thermal cyclizations.