Synthesis and autoxidation of new tetracyclic 9H,10H-indolizino[1,2-b]indole-1-ones

The new tetracyclic 9H,10H-indolizino[1,2-blindole-1-one derivatives (7a-d, 7ea, 7eb) have been synthesized by modified Fischer indole synthesis from the enol ether of 2,5-dihydroxy-7-methyl6-cyano-indolizine (3) and arylhydr azines (4a-g). Attempted N-methylation of 7a-d produced a series of autoxid ized products including 10-hydroperoxy-1 -methoxyindolizino[ 1,2-b]indole ( 9a-d) as the major product accompanied with methylperoxides (10a-d and 11a- d) and 2-formyl-3(pyridine-2-yl)indole (12a, 12c) derivatives as the minor products. A plausible mechanism of the autoxidation is postulated based on the isolation of some intermediates. The reaction is thought to proceed thr ough azaenolate/enamine intermediates following a novel type of autoxidatio n.