Synthesis of 1,2‐disubstituted‐1,4,5,6‐tetrahydropyrimidines

Cyclization of benzoyl derivatives of N‐substituted trimethylenediamines with polyphosphoric acid or the corresponding ethyl ester, afforded 1, 2‐disubstituted‐1, 4, 5, 6‐tetrahydropyrimidines. PPE was the more advantageous reagent. The excessive protonation of the starting material and the cleavage of the ether function produced by PPA explains the failure of this reagent to cause ring closure in some cases. Synthesis of the starting materials is described. Analytical and spectroscopic data of the new compounds are presented.