Study on 1,4-hydride shift triggered spirocyclization of arylidene imidazolones: substituent control on formation of indane or tetrahydrobenzazepine systems

A rare process of 1,4-hydride or formal 1,6-hydride shift occurs in the (o-dialkylaminomethyl)arylidene imidazolones under the action of aluminum chloride. Only sterically hindered amino derivatives are able to enter the spirocyclization reaction, and the substituent would control this direction. Either five-membered indane in case of diisopropylamino derivatives, or seven-membered tetrahydrobenzazepines in case of dibenzylamino derivatives are formed in 46–84% yield.