Vinyl azides in heterocyclic synthesis. Part 6. Synthesis of isoquinolines by intramolecular aza-Wittig reaction

Abstract

Azidocinnamates containing ortho-carbonyl substituents are versatile intermediates for heterocyclic synthesis. Isoquinolines (8) and (9) are formed under mild neutral conditions by intramolecular aza-Wittig reactions of iminophosphoranes, readily derived from azides (1) and (2), respectively, with triethyl phosphite. The azafluoranthene (10) can also be prepared from the azide (3)via the isolable iminophosphoranes (11) and (12). Thermolysis of the azides (1) in toluene or xylene gives the 4-substituted indoles (13) in varying yield (Table 2). Similarly the indoles (14) and (19) are formed from the azides (3) and (6a and b) respectively.