A facile synthesis of 3‐substituted 2‐cyanoquinazolin‐4(3 H )‐ones and 3‐alkyl‐2‐cyanothieno[3,2‐ d ]pyrimidin‐4(3 H )‐ones via 1,2,3‐dithiazoles

The reaction of methyl anthranilate with 4,5‐dichloro‐1,2,3‐dithiazolium chloride (Appel's salt) in the presence of pyridine (2 equivalents) in dichloromethane at room temperature gave methyl N ‐(4‐chloro‐5 H ‐1,2,3‐dithiazol‐5‐ylidene)anthranilate ( 3a ) (50% yield), which reacted with sterically less hindered primary alkylamines to give directly 3‐alkyl‐2‐cyanoquinazolin‐4(3 H )‐ones 5 in moderate to good yields. With tert‐ butylamine, N ‐(2‐methoxycarbonylphenyl)iminocyanomethyl N ‐( tert ‐butyl) disulfide 7 and methyl 2‐( N ‐cyanothioformamido)anthranilate ( 8 ) were isolated in 33% and 59% yields, respectively. The cyano group of quinazoline 5a (R = CH 3 ) is readily displaced by various nucleophiles to give 2‐substituted quinazolinones 11–19 , which indicates that compounds 5 can be utilized as starting materials for the synthesis of new 2‐substituted quinazolines. Similarly 3‐alkyl‐2‐cyanomieno[3,2,‐ d ]pyrimidin‐4(3 H )‐ones 22 were prepared from methyl 3‐[ N ‐(4‐chloro‐5 H ‐1,2,3‐dimiazol‐5‐ylidene)]‐2‐thiophencarboxylate ( 21 ) in moderate to good yields.