New synthetic route to tetracyclic quinazolin-4(3H)-one ring system

摘要

Reactions of dithiazoles (1a-e) and (9a-b) with 3,4-dimethoxy-phenethylamine (2) in CH_2Cl_2 at room temperature produce 3,4-dihydro-3-(3,4-dimethoxyphenethyl)-4-oxoquinazoline-2-carbonitriles (3a-d) and 4-hydroxy-4-phenyl-3,4-dihydroquinazoline-2-carbonitriles (10a-b), respectively. Compounds (3a-d) on treatment with TFAA/HCl at 120-130 deg C gave 3-(3,4-dimethoxy- phenethyl)quinazoline-2,4(1H,3H)-diones (5a-d) in excellent yields. Quinazolin-4(3H)-ones (3a-d), quinazoline-2,4(1H,3H)-diones (5a-d) and their thieno analogs (3e and 5e) as well as 4-hydroxy-3-(3,4-dimethoxy- phenethyl)-4-phenyl-3,4-dihydroquinazoline-2-carbonitiles (10a-b) are cyclized in the presence of P_2O_5/POCl_3 in xylene at 130 deg C to tetracyclic benzazepino[2,3-b]quinazolinones (8a-d), isoquino[1,2-b]quinazolines (6a-d), thienopyrimidinones (6e and 8e) as well as isoquino[1,2-c]quinazoline-6-carbonitriles (11a-b), respectively, in good yields.