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.