Synthetic Approaches to Indolo[2,3-a]carbazole alkaloids. Syntheses of arcyriaflavin A and AT2433-B aglycone

Ozonolysis of tetrahydrophthalimides 17 and 18 or cyclohexene diester 25 and treatment of the intermediate dialdehydes (19,20,26) with an arylhydrazine affords the corresponding bis-arylhydrazones (21–24,27,28). Exposure of 21 and 23 to PSSE in CH3NO2 gives the indolo[2,3-a]carbazole alkaloids arcyriaflavin A (8) and AT2433-B aglycone (29) in low yield. bis-Phenylhydrazones (osazones) (33,34,42,44) of cyclohexandiones were synthesized by m-CPBA oxidation of 4,5-bis(trimethylsilyloxy)tetrahydrophthalimides followed by treatment of the presumed intermediate 1,2-cyclohexanediones with an arylhydrazine. These osazones were cyclized to the corresponding indolo[2,3-a]carbazoles with PPSE.