Domino Reactions. One-Pot Preparation of Fluorenoisoquinoline Derivatives from Conjugated Ketene Imines

Article abstract of DOI:10.1021/jo00012a039

Iminophosphoranes 4, derived from ethyl α-azido-2-(allyloxy)-3-methoxycinnamates, react with ketenes to give the corresponding ketene imines, which by thermal treatment at 150-160 deg C undergo a consecutive electrocyclic ring closure/Claisen rearrangement/second ring closure/double aromatization process to give isoquinoline derivatives 7 and/or the previously unknown fluoreno<2,3,4-ij>isoquinolines 9 in moderate yields.Similarly, iminophosphoranes 14 derived from ethyl α-azido-2,3-disubstituted-4-(allyloxy)cinnamates reacted with diphenyl ketene to give the intermediate ketene imines, which at 150-160 deg C undergo a cascade of pericyclic reactions to give the isoquinolines 15 and the pentacyclic compounds 16 in moderate yields.