Abstract
Reaction of 1, 2, 4-thiadiazolium salts with dialkyl acylphosphonates (II) afforded ring expanded products, 1, 2, 4-thiadiazine derivatives. In the reaction of 4-(4-amino-2-methyl-5-pyrimidinyl) methyl-3-methyl-1, 2, 4-thiadiazolium bromide hydrobromide (VII) with dialkyl benzoylphosphonates (IIb, c), however, 10a (1-dialkylphosphoroyl) benzyl-4, 5, 10, 10a-tetrahydro-3, 8-dimethyl-1, 2, 4-thiadiazolo [4', 5'-1, 2] pyrimido [4, 5-d] pyrimidine (VIIIb, c) were obtained as major products and the 1, 2, 4-thiadiazine derivative (IX) as a minor product. Acid treatment of VIIIb, c gave XIb, c, which were intermediates of the reaction of the thiadiazolium salt (VII) with phosphonate (IIb, c), and these were converted to VIIIb, c and IX by alkaline hydrolysis.
