Abstract
A novel route to fused indoles via two consecutive palladium catalyzed reactions, an intramolecular Heck reaction followed by a reductive N-heteroannulation, has been developed. For example, reaction of 2-bromo-3-nitro-1-(3-butenyloxy)benzene with palladium diacetate, and tri(o-tolyl)phosphine in the presence of triethylamine gave a readily separable mixture (18:4:1) of dihydro-4-methylene-5-nitro-2 H-1-benzopyran, 4-methyl-5-nitro-2 H-1-benzopyran, and 4-methyl-5-nitro-4 H-1-benzopyran. Reaction of pure dihydro-4-methylene-5-nitro-2 H-1-benzopyran with palladium diacetate, 1,3-bis(diphenylphosphino)propane, and carbon monoxide in DMF (120 °C, 70 h, 60 psi CO) gave 3,5-dihydro-2 H-pyrano[4,3,2- cd]indole in 63% yield.
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