Construction of 1,2-dihydro-1,3,5-triazines via reactions involving amidines.

1,2-Dihydro-1,3,5-triazine compounds were synthesized through three sets of reactions of amidines with, respectively, paraformaldehyde, aldehydes and N-arylnitrones under different conditions. The catalysts used in these three reactions were Cu(OAc)2, ZnI2 and CuCl2·2H2O, respectively. Most of the substrates tested for these reactions provided the target products in moderate to good yields. In the reactions involving paraformaldehyde, Cu(OAc)2 also accelerated the release of formaldehyde from paraformaldehyde during the catalytic reaction process. In the case of the reactions involving nitrones, CuCl2·2H2O not only catalyzed the normal progress of the main reaction, but also promoted the reaction of nitrones to produce nitroso compounds and aldehydes.