The starting compound is 3,6-dichloropyridazine (I), which is reacted with morpholine (II) in a suitable solvent to give 3-morpholino-6-chloropyridazine (III). This, upon reaction with hydrazine hydrate as solvent, gives the hydrazine derivative (IV), which by reaction with acetonylacetone (V) in acetic acid yields directly the title compound. [14C]-Labeled compound is synthesized by a microscale procedure with 45% chemical yield and 98% radiochemical purity.
The cyclization of methyl acetoacetate (I), 2-methoxybenzaldehyde (II) and thiourea (III) by means of HCl in refluxing ethanol gives the tetrahydropyrimidine (IV), which is finally cyclized with chloroacetic acid (V) and benzaldehyde (VI) by means of sodium acetate in a refluxing mixture of acetic acid and acetic anhydride.