Synthesis of [a]Annulated Carbazoles from Indol-2(3H)-one

Abstract
Reaction of ethyl chloroformate with 3-(2-aryl-1-hydroxyethylidene)indol-2(3H)-ones 3 affords the corresponding ethyl 3-[(2-aryl-1-ethoxycarbonyloxy)ethenyl]-2-(ethoxycarbonyloxy)indole-1-carboxylates 4 from which ethyl 6-(ethoxycarbonyloxy)-11H-benzo[a]carbazole-11-carboxylates 5a,b, the corresponding 3H,10H-pyrrolo[3,2-a]- 5c, 10H-thieno[3,2-a]- 5d and 10H-thieno [2,3-a]carbazole-10-carboxylate 5e are obtained via 6π-electrocyclization.

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