Studies directed towards total syntheses of the tropoloisoquinoline alkaloids grandirubrine and imerubrine. Part 2. Thermolysis of 8,9-dihydro-2-hydroxy-3,10,11,12-tetra methoxyisoquino[2,1-c][1,2,3]benzotriazin-7-ium chloride: competitive modes of cyclisation leading to the indeno[1,2,3-ij]isoquinoline (azafluoranthene) skeleton

Abstract

Thermolysis of the title compound 8 produced not only the expected azafluoranthene 7 but also the regioisomeric compound 23 and its dihydro counterpart 22. A mechanism for the formation of compounds 7, 22 and 23 from precursor 8 has been advanced. Reaction of salt 8 with copper bronze in aqueous sulfuric acid produced good yields of dihydroazafluoranthene 29 together with small amounts of the reduction product 30. The tubulin binding properties of the azafluoranthenes 7, 22, 23, 24 and 29 have been determined.