DOMINO REACTIONS - ONE-POT PREPARATION OF FLUORENO[2,3,4-IJ]ISOQUINOLINE DERIVATIVES FROM CONJUGATED KETENE IMINES

Iminophosphoranes 4, derived from ethyl alpha-azido-2-(allyloxy)-3-methoxycinnamates, react with ketenes to give the corresponding ketene imines, which by thermal treatment at 150-160-degrees-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 alpha-azido-2,3-disubstituted-4-(allyloxy)cinnamates reacted with diphenyl ketene to give the intermediate ketene imines, which at 150-160-degrees-C undergo a cascade of pericyclic reactions to give the isoquinolines 15 and the pentacyclic compounds 16 in moderate yields.