Abstract

CARBOXYLATE-ASSISTED RUTHENIUM-CATALYZED ALKYNE ANNULATIONS BY C_H/HET_H BOND FUNCTIONALIZATIONS

Dr.*S.Murali Krishna, Dr.L.K.Ravindranath, Dr.Y.Padmalatha

ABSTRACT

This Account summarizes the evolution of versatile ruthenium (II) complexes for annulations of alkynes via C_H/N_H, C_H/O_H, or C_H/N_O bond cleavages. To achieve selective C_H bond functionalizations, we needed to understand the detailed mechanism of the crucial C_H bond metalation with ruthenium (II) complexes and particularly the importance of carboxylate assistance in this process. As a consequence, our recent efforts have resulted in widely applicable methods for the versatile preparation of differently decorated arenes and heteroarenes, providing access to among others isoquinolones, 2-pyridones, isoquinolines, indoles, pyrroles, or r-pyrones. Most of these reactions used Cu (OAc)2 H2O, which not only acted as the oxidant but also served as the essential source of acetate for the carboxylate-assisted ruthenation manifold. Notably, the ruthenium (II)-catalyzed oxidative annulations also occurred under an ambient atmosphere of air with cocatalytic amounts of Cu(OAc)2 3H2O. Moreover, substrates displaying N_O bonds served as “internal oxidants” for the syntheses of isoquinolones and isoquinolines. Detailed experimental mechanistic studies have provided strong support for a catalytic cycle that relies oninitial carboxylate-assisted C_H bond ruthenation, followed by coordinative insertion of the alkyne, reductive elimination, and reoxidation of the thus formed ruthenium(0) complex.

Keywords: Isoquinolones and isoquinolines, ruthenium, alkynes.