The use of hydrazone-type 1-azatriene derivatives for the synthesis of 3-methyl isoquinolines through a one pot microwave-assisted cyclization was developed and evaluated. The 1-azatrienes were generated by reaction of 2-propenylbenzaldehydes with hydrazines. Their subsequent electrocyclization gave rise to 3-methylisoquinolines, as well as to 3-methyl-3,4-dihydroisoquinolines as reaction by-products. The reaction conditions were optimized, and its scope and limitations were explored.