Solvent-controlled bifurcated cascade process for the selective preparation of dihydrocarbazoles or dihydropyridoindoles.

A solvent-controlled cascade process has been identified for the dual purpose of the preparation of either dihydrocarbazoles or dihydropyridoindoles from identical N-aryl-α,β-unsaturated nitrones and electron-deficient allene starting materials. These reactions proceed smoothly under mild metal-free conditions affording a range of two types of skeletally distinct indole-based heterocycles in high yield and diastereoselectivity. These transformations demonstrate the use of a bifurcated cascade process that hinges on the ring-opening event of a benzazepine intermediate for the synthesis of skeletally diverse heterocyclic products and rapid access to biologically-significant, indole-based structures.