Intramolecular polar [4(⊕)+2] cycloadditions of aryl-1-aza-2-azoniaallene salts: unprecedented reactivity leading to polycyclic protonated azomethine imines.

The first example of aryl-1-aza-2-azoniaallene salts undergoing a [4 + 2]-cycloaddition reaction in which the azo bond and one aromatic π-bond make up the 4π component is described. This intramolecular reaction appears to be concerted and provides high yields of protonated azomethine imine products that contain a 1,2,3,4-tetrahydrocinnoline core. Substituted alkenes provided products that contain all carbon or nitrogen bearing quaternary centers in high yield.