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

✍ Scribed by Bartolo Gabriele; Lucia Veltri; Vito Maltese; Rosella Spina; Raffaella Mancuso; Giuseppe Salerno

• Publisher: John Wiley and Sons
• Year: 2011
• Tongue: English
• Weight: 245 KB
• Volume: 2011
• Category: Article
• ISSN: 1434-193X
• DOI: 10.1002/ejoc.201100739

✦ Synopsis

Abstract

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.