Azimines as 1,3-dipoles

Abstract

Benzocinnoline N-ethoxycarbonylimides [e.g.(4)] react with acetylenic esters and dicyanoacetylene to give the stable azomethine imines [e.g.(6)] by initial 1,3-dipolar cycloaddition and spontaneous electrocyclic ring opening of the triazolines so formed. The regiospecificity observed with 3-methoxybenzocinnoline 6-ethoxycarbonylimide (14) confirms this reaction sequence. The N-imide (4) reacts with olefins to give benzocinnoline presumably by decomposition of the unstabilised adducts which were not isolated. The azomethine imines (6) are readily oxidised to stable radical cations (7).

Benzocinnoline N-benzoylimide (4; COPh for CO₂Et) undergoes the same 1,3-dipolar cycloaddition reactions.