Reactions of ethyl cyanoformate with cycloimmonium salts: a direct pathway to fused or substituted azaheterocycles

Abstract

Aromatic cycloimmonium salts underwent different reaction pathways when treated with ethyl cyanoformate in triethyl amine medium, including selective γ-cyano substitutions (in case of phenanthrolinium and quinolinium salts) and 3+2 dipolar cycloadditions (for phthalazinium and isoquinolinium salts). When using phthalazinium salts, besides the 3+2 cycloaddition products (imidazo[2,1-a]phthalazines), we obtained 8,8a,16,16a-tetrahydropyrazino-[2,1-a;4,5-a′]-diphthalazines as secondary products via a 3+3 cycloaddition dimerization. The structures of the synthesized compounds have been proved by spectral data, and X-ray diffraction for three of the new derivatives.