Reduction of 3,4-dimethoxybenzaldehyde (I) with NaBH4 provided benzyl alcohol (II). After conversion of (II) to the benzyl chloride (III) using SOCl2, its reaction with PPh3 (IV) in refluxing xylene afforded phosphonium salt (V). Subsequent Wittig reaction of the corresponding ylide with 4,4-(ethylenedioxy)cyclohexanone (VI) produced the benzylidene derivative (VII), which was reduced to benzyl compound (VIII) by catalytic hydrogenation over Pd/C. The ketal protecting group of (VIII) was then removed by acid hydrolysis to yield cyclohexanone (IX). Finally, the target tetrahydroquinazoline was obtained by condensation of (IX) with cyanoguanidine (X) at 180 C.

Reduction of 3,4,5-trimethoxybenzaldehyde (I) with NaBH4 provided benzyl alcohol (II). After conversion of (II) to the benzyl chloride (III) using SOCl2, its reaction with PPh3 (IV) in refluxing xylene afforded phosphonium salt (V). Subsequent Wittig reaction of the corresponding ylide with 4,4-(ethylenedioxy)cyclohexanone (VI) produced the benzylidene derivative (VII), which was reduced to benzyl compound (VIII) by catalytic hydrogenation over Pd/C. The ketal protecting group of (VIII) was then removed by acid hydrolysis to yield cyclohexanone (IX). Finally, the target tetrahydroquinazoline was obtained by condensation of (IX) with cyanoguanidine (X) at 180 C.