Synthesis and Diels-Alder Reactions of 1,3-Dimethyl-4-(phenylsulfonyl)-4H-furoindole. A new Annulation Strategy for the Construction of Ellipticine and Isoellipticine

Article abstract of DOI:10.1021/jo00197a039

The novel fused heterocycle 1,3-dimethyl-4-(phenylsulfonyl)-4H-furo<3,4-b>indole (4) is synthesized from 3-ethylindole (6) in six steps (46percent yield) or from indole-3-carboxaldehyde (12) in four steps (21percent yield).Furoindole 4 undergoes Diels-Alder reactions with dimethyl acetylenedicarboxylate, N-phenylmaleimide, benzyne, and 3,4-pyridyne (5) to give the expected adducts 17, 18a,b, 19, and 23a,b, respectively.Deoxygenation and desulfonylation of 19 and 23a,b, respectively, give benzocarbazole 22 and a readily separable mixture of the pyridocarbazole alkaloids ellipticine (1a) and isoellipticine (2a).