Synthesis and funcionalization of indole skeleton compunds via nitrosoarene-alkyne cycloadditions.

Indoles are one of the most important and abundant classes of N-heterocycles, being present in the form of innumerable natural products and bioactive compounds. A class of indole derivatives which have received considerable attention in recent years are N-hydroxyindoles. The biological role of N-hydroxyindoles is still an area of active investigation since they have been shown to possess biological activity in certain cases. 3-Aroylindoles are another class of indole derivatives, known as bioactive compounds with interesting properties. Not many indolization procedures are known to afford directly 3-acylindoles starting from commercially available reactants. Our general interest in this topic lead us to disclose a novel and regioselective indole synthesis by annulation reaction between nitro- and nitrosoarenes with alkynes. Indoles, N-hydroxy- and N-alkoxyindoles were afforded in moderate to excellent yields and good regioselectivity. Using conjugated alkynones as starting materials the reaction proceeded with the regioselective formation of 3-acylindoles and/or N-hydroxy-3-acylindoles. Highly functionalizable indole derivatives were synthesized and different derivatization reactions were developed.