Synthesis of nitrogen‐containing heterocycles 10. Reaction of 2‐amino‐1h‐imidazole derivatives with ethoxymethylene compounds

Abstract

AbstractThe direct annelation reaction of 4‐substituted 2‐amino‐l‐benzylideneamino‐1H‐imidazoles (1) or 2‐amino‐1‐isopropylideneamino‐1H‐imidazole (8) with ethoxymethylenemalononitrile (I) gave successfully bicyclic imidazo[1,2‐a]pyrimidine compounds 2 and 9 in high yields. The reactions of other ethoxymethylene compounds of lower reactivity, i.e., ethyl ethoxymethylenecyanoacetate (II) and diethyl ethoxymethylenemalonate (III), with 2‐amino‐1H‐imidazoles under similar conditions afforded the corresponding enamines 3, 4 and 10, which, upon heating in the presence of an acid or a base, could readily be cyclized to form imidazopyrimidines except for 1‐isopropylideneamino compound 10. In general, the 3‐phenyl compounds (3b and 4b) did not cyclize to the type 2 compound resulting in a full recovery of the starting enamines.