Pyrimidine reactions. Part XX. Thermal rearrangement of 5-(p-substituted phenyl)-2(and 4)-methoxypyrimidines

Abstract

2(and 4)-Methoxy-5-phenylpyrimidine and some p-substituted derivatives are rearranged by heating in triethylamine to give the corresponding N-methyl-2(or 4)-oxopyrimidines. The log k₁ values for rearrangement of the 2-methoxypyrimidines show a rectilinear relationship to the known σ values for p-substituted phenyl groups, save when such values are highly negative. 4-Methoxy-5-phenylpyrimidine and its p-nitro-derivative rearrange more rapidly than their respective 2-methoxy-isomers; in addition, each gives a mixture of N-1 and N-3 methylated products in which the latter predominates. These facts are consistent with the recently proposed intermolecular and ionic nature of such rearrangements. Some of the intermediate 2-hydroxy-5-phenylpyrimidines and their N-methyl derivatives are made by a novel modification of the principal pyrimidine synthesis, namely condensation of urea or N-methylurea with 3-imino-2-phenylpropionaldehyde or a derivative. ¹H N.m.r. and u.v. spectra are used to follow rearrangements and to confirm structures.