Chemical switching in reaction behavior of azine: synthesis of a novel thienodiazepine derivative

Abstract We previously have reported that an acid-promoted condensation of a hydrazonoester derived from phenylalanine afforded an azine which was converted to a pyrrole through 3 steps: isomerization to dienamine, [3,3]-sigmatropic rearrangement, and cyclization. In this study, reaction behavior of the intermediate proved to be switched depending on the type of the aromatic ring. Hydrazonoesters derived from thienylalanines afforded various thienodiazepine derivatives under thermal acidic conditions. A more reactive thiophene ring is likely to undergo Friedel-Crafts reaction prior to isomerization to dienamine.