Synthesis of 2-(2-Imino-2,3-dihydropyrido[3,2-e]-1,3-thiazin-(Z)-4-ylidene)acetamide Derivatives

A facile two-step preparation of the title pyridothiazine derivatives starting from commercially available 2-chloro-6-methylpyridine-3-carbonitrile is described. The reaction of this nitrile with magnesium enolates of tertiary acetamides affords ( Z)-3-amino-3-(2-chloro-6-methylpyridin-3-yl)propenamide derivatives, which in turn are allowed to react with isothiocyanates in the presence of sodium hydride to give the desired products in satisfactory yields.