Synthesis of 1-Aryl-1,4,5,6-tetrahydro-pyrimidines and 1-Aryl-3-substituted 1,4,5,6-Tetrahydropyrimidinium Salts

Abstract

A synthetic approach to 1-aryl-1,4,5,6-tetrahydropyrimidines (1) is described, by ring closure of N-aryl-N'-formyl-1,3-propanediamines (5) with trimethylsilyl polyphosphate (PPSE). Quaternization of compounds (1) with methyl (or ethyl) iodide led to the corresponding cyclic amidinium salts (2), while treatment of compound (1a) with 2,4-dinitrochlorobenzene yielded an open chain product resulting from hydrolysis of the salt. An alternative method was employed for the synthesis of 1-aryl-1,4,5,6-tetrahydropyrimidinium salts bearing a branched alkyl or an aryl substituent on N3, not accessible through alkylation. Such compounds were obtained in high yields by dehydrogenation of the corresponding hexahydropyrimidines (3). The scope and limitations of both procedures are discussed.