Synthesis of Polysubstituted 3‐Methylisoquinolines through the 6π‐Electron Cyclization/Elimination of 1‐Azatrienes derived from 1,1‐Dimethylhydrazine

A convenient one pot microwave‐assisted 6π‐electron cyclization/aromatization approach toward 3‐methylisoquinolines is reported. The starting 1‐azatriene derivatives were prepared in situ by reaction of 2‐propenylbenzaldehydes with 1,1‐dimethylhydrazine, which exhibited superior performance when compared with other hydrazine derivatives. Minor amounts of the related 3,4‐dihydro isoquinolines were formed concomitantly with the isoquinolines, and a mechanism for their generation was proposed. The reaction conditions were optimized, and its scope and limitations were explored. In general, the transformation proceeded in moderate to good yields. The scope and limitations of the use of 1,1‐dimethylhydrazine for accessing 3‐methyl isoquinolines from 2‐propenylbenzaldehydes through a one‐pot hydrazonation, 6π‐electron cyclization of 1‐azatrienes and final elimination were examined.