Reaction of 3H-Pyrano[3,4-b]indol-3-ones and 3H-2-Benzopyran-3-ones with Heterodienophiles: A Two Step Synthesis for Some 9H-Pyrido[3,4-b]indoles and Isoquinolines

Abstract

A short synthetic method for 3-substituted 9H-pyrido[3,4-b] indoles 3 and isoquinolines 7 is proposed using cycloaddition-elimination reactions between 3H-pyrano[3,4-b]indol-3-ones 1 or 3H-2-benzopyran-3-ones 6 and electron-poor nitriles as ethyl cyanoformate and p-toluenesulfonyl cyanide. Extension of the method is possible neither with benzoyl cyanide nor with imines. The diene system undergoes cycloaddition with the carbonyl function of the former compound; subsequent elimination of carbon dioxide followed by an electrocyclic reaction involving the C-O bond gives ring opened ketonic compounds. Imines attack the lactone function of the pyranone system yielding ultimately a ß-lactam in some cases.