[Copper(I)(Pyridine-Containing Ligand)] Catalyzed Regio- and Steroselective Synthesis of 2‑Vinylcyclopropa[b]indolines from 2-Vinylindoles

The functionalization of indole core is an interesting research field because the indole moiety is present in a huge number of bioactive natural products and pharmaceutical compounds. For this reason, the proposal of new methodologies for indole synthesis and functionalization is still of great interest in synthetic organic chemistry. In the context of our studies on metal-catalyzed cycloaddition reactions of vinylindoles and on functionalization of indole core, we decided to investigate the reactivity of 2-vinylindoles with diazo compounds. We envisioned in this way to functionalize these indole derivatives by means of a new reaction pattern. Thus, the reaction between 2-vinylindole and ethyl diazoacetate was conducted in the presence of copper(I) complexes having a pyridine-containing macrocycle as ligand and led to a series of cyclopropyl vinylindolines with satisfactory yields and with complete regio- and diasteroselectivity. Optimization of conditions, scope and proposed mechanism of the reaction will be illustrated, with preliminary results on an enantioselective version.