Reaction of ketenes with N,N ‐disubstituted α‐aminomethyleneketones VIII. Synthesis of N,N ‐disubstituted 4‐amino‐3‐chloro‐6‐phenyl‐2 H ‐pyran‐2‐ones

The dipolar 1,4‐cycloaddition of dichloroketene to N,N ‐disubstituted 3‐amino‐1‐phenyl‐2‐propene‐1‐onesled directly to N,N ‐disubstituted 4‐amino‐3‐chloro‐6‐phenyl‐2 H ‐pyran‐2‐ones only in the case of an usual aliphatic N,N ‐disubstitution. In the case of partial or full aromatic N ‐substitution, N,N ‐disubstituted 4‐amino‐3,3‐dichloro‐3,4‐dihydro‐6‐phenyl‐2 H ‐pyran‐2‐ones were instead obtained, which were dehydrochlorinated with DBN to the corresponding 4‐amino‐3‐chloro‐6‐phenyl‐2 H ‐pyran‐2‐ones.