2-Acylthioacetamides in the Biginelli Reaction

We have demonstrated for the first time a Biginelli reaction of 2-acylthioacetamides with aromatic aldehydes and ureas or thioureas, leading to N-Ar1-4-Ar2-6-R1-1-R2-2-oxo(thioxo)-1,2,3,4-tetrahydro-pyrimidine-5-carbothioamides. The regioselectivity of this process matched the concept of hard/soft Lewis acids and bases. It was established that nitrous acid or other oxidants converted the synthesized compounds into N-Ar1-4-Ar2-6-R1-1-R2-2-oxo(thioxo)-1,2,3,4-tetrahydropyrimidine-5-carboxamides, and not the expected 4-Ar2-6-R1-1-R2-5-(1,3-benzothiazol-2-yl)-1,2,3,4-tetrahydropyrimidin-2-ones(thiones).