Synthesis of Isoquinoline Derivatives by a Tandem Aza-Wittig/Electrocyclization Strategy and Preparation of the Unknown 1,9-Diazaphenalene Ring by a Consecutive Electrocyclic Ring Closure/Claisen Rearrangement/Intramolecular Amination Process

Article abstract of DOI:10.1021/jo00312a020

Treatment of iminophosphorane 3, derived from ethyl α-azido-2-(allyloxy)cinnamate, with aromatic isocyanates in toluene at 150 deg C leads to the corresponding isoquinoline derivatives 5 by a tandem electrocyclic ring closure/Claisen rearrangement of the intermediate carbodiimide.Fremy's salt promoted oxidation of compounds 5 yields the 5,8-isoquinolinequinone allides 6, which by heating undergo cyclization to 2H-pyrano<2,3-f>isoquinolines 7.Iminophosphorane 14, derived from ethyl α-azido-2-(allyloxy)-3-methoxycinnamate, reacts with aromatic isocyanates to give thecorresponding carbodiimides, which by thermal treatment at 150 deg C undergo a consecutive electrocyclic ring closure/Claisen rearrangement/intramolecular amination process to give 1,9-diazaphenalene derivatives 18 in moderate yields.