Simple route to multisubstituted tetrahydropyrimidines

As part of our ongoing investigation into the synthetic application of nitroenamines several new densely substituted pyrimidine and pyrrolo-pyrimidine derivatives were prepared. Thus, 2-nitromethylenepyrrolidine and some open chain nitroenamines of phenyl-(2-nitro-1-phenyl-vinyl)-amine type were reacted with ethyl glyoxylate and a substituted aniline usually in a one-pot procedure to furnish the key intermediates for a subsequent cyclization. These compounds including a molecular fragment of 1,3-diamine type were subjected to a simple ring closure with formaldehyde to give the title compounds in good yields. The protocol reported has the advantages of mild reaction conditions, easy workup and inexpensive reagents.In an attempted removal of the 4-methoxy-phenyl protecting group from the 4-methoxy-phenyl substituted hexahydropyrrolo[1,2-c]pyrimidine derivative, an unexpected periodic acid mediated ring cleavage and phenyl group migration was discovered. The structures of the synthesized new compounds were confirmed by spectral data, and, particularly, the hindered rotation and the unusual 1H NMR characteristics of 4-(4-nitro-phenyl)-but-3-enoic acid ethyl ester derivative were discussed.