1,6-electrocyclization of 1-azatriene derivatives

1-Cyanomethylene-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinolinium mesylate (10) readily reacted with alpha,beta-unsaturated aldehydes to afford 1-azatrienes 12a-h, which could be cyclized to give 6,7-dihydro-4H-benzo[a]quinolizines 14a-h. The reaction mechanisms were investigated by computational methods.