Cycloadditions of 1,2,3-Triazines Bearing C5-Electron Donating Substituents: Robust Pyrimidine Synthesis.

The examination of the cycloaddition reactions of 1,2,3-triazines 17–19, bearing electron-donating substituents at C5, are described. Despite the noncomplementary 1,2,3-triazine C5 substituents, amidines were found to undergo a powerful cycloaddition to provide 2,5-disubstituted pyrimidines in excellent yields (42–99%; EDG = SMe > OMe > NHAc). Even select ynamines and enamines were capable of cycloadditions with 17, but not 18 or 19, to provide trisubstituted pyridines in modest yields (37–40% and 33% respectively).