Thermolysis of 2-(3-phenylsulfonylprop-1-ynyl)benzonitrile: an aza-Myers type cyclization to isoquinolines

Thermolysis of 2-(3-phenylsulfonylprop-1-ynyl)benzonitrile (3) in refluxing benzene containing cyclohexa-1,4-diene and triethylamine gave isoquinolone 4 in 7% yield and compound 5 in 10% yield and 14% of the starting material was recovered. When this cyclization reaction was carried out under oxygen atmosphere, compound 4 was isolated in 14% yield and 20% of the starting benzonitrile 3 was recovered. Under refluxing carbon tetrachloride, cyclization of 3 gave the chloroisoquinoline 6 in 18% yield and 5 in 22% yield. The isolation of compounds 4 and 6 strongly suggests the formation of biradical 8 through a (Z)-hexa-2,4,5-trienenitrile intermediate 7.