Purines, pyrimidines, and imidazoles. Part 60. Some oxazolo[3,2-a]pyrimidines and a novel conversion of a cyanouracil into a barbituric acid derivative

Abstract

The synthesis of several 6-acetyl(or 6-cyano)-2,3-dihydro-7-oxo-7H-oxazolo[3,2-a]pyrimidines (1) from 5-acetyl(or 5-cyano)-1-[2-hydroxy(or 1-ethyl or 2-phenyl)ethyl] uracils and 5-acetyl(or 5-cyano, or 5-cinnamoyl, or 5-N-ethoxycarbonylcarbamoyl)-1-(1-ethyl-2-hydroxyethyl)uracils (2) by cyclisation of their toluene-4-sulphonates or methanesulphonates with triethylamine is described. The reaction of 6-cyano-1-(1-ethyl-2-hydroxyethyl)-2,3-dihydro-7-oxo-7H-oxazolo[3,2-a]pyrimidine (1e) with cyclohexylamine produced 5-amino-6-cyclohexyliminomethyl-1-ethyl-2,3-dihydro-7-oxo-7H-oxa-zolo[3,2-a]pyrimidine (6a) which with hot water gave ammonia and 5-cyclohexylaminomethylene-1-(1-ethyl-2-hydroxyethyl)barbituric acid (7a).

Similar reactions occurred with butylamine and benzylamine and with related oxazolopyrimidines, but in contrast compound (1e) and morpholine gave the isocytosine (11). The structures assigned were confirmed by the synthesis of the acid (7a) and of the related 5-cyclohexylaminomethylene-1-methylbarbituric acid and by ¹H n.m.r., i.r., u.v., and mass spectroscopy.