Synthesis and properties of 1-aryl-2-alkyl-1,4,5,6-tetrahydropyrimidines

A general method is described for the synthesis of 1-aryl-2-alkyl-1,4,5,6-t etrahydropyrimidines 1, by cyclization of N-acyl-N'-aryltrimethylenediamine s 2 with trimethylsilyl polyphosphate. Precursors 2 were obtained by aminol ysis of the corresponding N-(3-bromopropyl)amides 3. The H-1 nmr spectra of tetrahydropyrimidines 1 are analyzed, discussing the influence of substitu ents in positions 1 and 2 of the heterocyclic ring. Alkaline hydrolysis of compounds 1, which originates exclusively N-acyl-N'-aryltrimethylenediamine s 2, through an intermediate carbinolamine, was also studied. Cleavage of s uch an intermediate is discussed in the light of the stereoelectronic contr ol theory. Reduction of compounds 1 with borane, leads regiospecifically to N-alkyl-N'-aryltrimethylenediamines 6.