Reaction of ketenes with N,N‐disubstituted α‐aminomethyleneketones. XX. Synthesis of 2H‐pyrano[2,3‐f]quinazoline derivatives

The polar 1,4‐cycloaddition of dichloroketene to N,N‐disubstituted (E)‐6‐aminomethylene‐7,8‐dihydro‐(2‐methyl)(2‐phenyl)quinazolin‐5(6H)‐ones III , prepared in good yields from 7,8‐dihydro‐(2‐methyl)‐(2‐phenyl)quinazolin‐5(6H)‐ones via their 6‐hydroxymethylene derivatives I and II , gave in satisfactory to excellent yields N‐N‐disubstituted 4‐amino‐3,3‐dichloro‐3,4,5,6‐tetrahydro‐(8‐methyl)(8‐phenyl)‐2H‐pyrano‐ [2,3,‐f]quinazolin‐2‐ones IV , which are derivatives of the new heterocyclic system pyrano[2,3‐f]quinazoline. This cycloaddition occurred both in the case of aliphatic and aromatic N‐substitution only with 2‐phenyl‐enaminones III , whereas with 2‐methyl derivatives III the reaction took place only in the case of aromatic N‐monosubstitution. Dehydrochlorination of IV with DBN afforded, generally in excellent yields, N,N‐disubstituted 4‐amino‐3‐chloro‐5,6‐dihydro‐(8‐methyl)(8‐phenyl)‐2H‐pyrano[2,3‐y]quinazolin‐2‐ones, which were dehydrogenated with DDQ to give N,N‐disubstituted 4‐amino‐3‐chloro‐(8‐methyl)(8‐phenyl)‐2H‐pyrano[2,3‐f]quinazolin‐2‐ones in excellent yields.