The Dimroth rearrangement. Part X. The exceptionally slow rearrangement of 1,2-dihydro-2-imino-1,4-dimethylpyrimidines

Abstract

2-Amino-4-methylpyrimidine reacts with methyl iodide to give only 1,2-dihydro-2-imino-1,4-dimethylpyrimidine. The structure of this imine is confirmed by alkaline hydrolysis to give mainly 1,2-dihydro-1,4-dimethyl-2-oxo-pyrimidine, which differed from the known 1,6-dimethyl isomer; the minor products are 4-methyl-2-methyl-aminopyrimidine, formed from the imine by very slow Dimroth rearrangement, and 2-hydroxy-4-methylpyrimidine. 2-Amino-5-bromo(or carbamoyl or cyano)-4-methylpyrimidine also methylates at the 1-position, as shown by ¹H n.m.r. spectra, and the imines undergo Dimroth rearrangement much more slowly than their homologues which lack the 4-methyl group or have both a 4-and a 6-methyl group. 2-Amino-4-t-butylpyrimidine behaves similarly.