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

Treatment of iminophosphorane 3, derived from ethyl a-azido-2-(allyloxy)cinnamate, with aromatic isocyanates in toluene at 150 °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 a-azido-2-(allyloxy)-3-methoxycinnamate, reacts with aromatic isocyanates to give the corresponding carbodiimides, which by thermal treatment at 150 °C undergo a consecutive electrocyclic ring closure/Claisen rearrangement/intramolecular amination process to give 1,9-diazaphenalene derivatives 18 in moderate yields. © 1990, American Chemical Society. All rights reserved.