The present invention relates to a new synthesis for the preparation of 5-(substituted benzyl)-2,4-diamino-pyrimidines, including new pyrimidine derivatives. More particularly, a new synthesis of ormetoprin, diaveridine and related compounds, including novel derivatives, is disclosed. The synthesis involves the condensation of a substituted benzene and an acrylonitrile derivative to directly give enol ether intermediates, which upon subsequent reaction by known techniques with guanidine, provides the desired 5-(substituted benzyl)-2,4-diamino-pyrimidines, including novel compounds. The pyrimidine end products are useful as potentiators of sulfonamides and as antibacterial agents.