Indole Synthesis via Cyclative Formation of 2,3-Dizincioindoles and Regioselective Electrophilic Trapping.

Upon zincation of two acidic protons attached to the nitrogen and the sp-carbon atoms, a N-protected 2-ethynylaniline cyclizes to a 2,3-dizincioindole at 120 °C. Driven by the energy gain due to formation of two C-Zn bonds, this reaction occurs smoothly without side reactions, although this transformation is intrinsically endothermic in its bare anionic form. The resulting dizinc intermediate can be functionalized with one or two different electrophiles either inter- or intramolecularly on either C or C selectively, depending on the choice of catalyst and the electrophiles.