Versatile Synthesis of Isoquinolines and Isochromenes by Pd‐Catalyzed Oxidative Carbonylation of (2‐Alkynyl)benzylideneamine Derivatives

Isoquinoline‐4‐carboxylic esters 3 and isochromene‐4‐carboxylic esters 4 have been conveniently prepared by direct PdI 2 ‐catalyzed oxidative heterocyclization/alkoxycarbonylation of readily available (2‐alkynylbenzylidene)amine derivatives. In particular, (2‐alkynylbenzylidene)( tert ‐butyl)amines 2 selectively afforded isoquinoline derivatives 3 by N ‐cyclization, whereas N ‐(2‐alkynylbenzylidene)‐ N′ ‐phenylhydrazines 5 led to the formation of isochromenes 4 through O ‐cyclization ensuing from water attack on the imino group of the substrate. Reactions were carried out in alcoholic solvents at 80–100 °C and under 20–80 atm (at 25 °C) of a 4:1 mixture of CO/air, in the presence of PdI 2 (2–10 mol‐%) in conjunction with KI (KI/PdI 2 molar ratio = 10). In the case of imines 2 , the use of a dehydration agent, such as trialkyl orthoformate, was necessary to obtain satisfactory yields of isoquinolines 3 .