Pteridine studies. Part XLIII. Reactions of pteridine with some Michael reagents

Abstract

Pteridine reacted with various Michael reagents to give three kinds of products. (i) Dimedone, barbituric acid, thiobarbituric acid, diethyl malonate, and ethyl benzoylacetate added across the 3,4-double bond to yield 4-substituted 3,4-dihydropteridines (1). (ii) Benzyl (and ethyl) acetoacetate, and acetylacetone produced 8-substituted 5,5a,8a,9-tetrahydro-7-methylfuro[2,3-g]pteridines (2); all were formed by simple addition of one molecule of the Michael reagent across the 5,6- and 7,8-bonds of pteridine. (iii) Malononitrile and cyanoacetamide gave pyrido[2,3-b]pyrazines (4) by addition across the 3,4-bond followed by scission of that bond and a nitrogen-eliminating recyclisation. Explanations of this diverse behaviour are suggested. U.v. and ¹H n.m.r. spectra are reported and discussed.