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-tetrahydropyrimidines 1 , by cyclization of N-acyl-N′-aryltrimethylenediamines 2 with trimethylsilyl polyphosphate. Precursors 2 were obtained by aminolysis of the corresponding N-(3-bromopropyl)amides 3. The ¹H nmr spectra of tetrahydropyrimidines 1 are analyzed, discussing the influence of substituents in positions 1 and 2 of the heterocyclic ring. Alkaline hydrolysis of compounds 1 , which originates exclusively N-acyl-N′-aryltrimethylenediamines 2 , through an intermediate carbinolamine, was also studied. Cleavage of such an intermediate is discussed in the light of the stereoelectronic control theory. Reduction of compounds 1 with borane, leads regiospecifically to N-alkyl-N′-aryltrimethylenediamines 6.