In the last few decades,t he transition metal-catalyzed activation of inert C À Hb onds has led to af undamental changei nt he field of synthetic chemistry.M osto ft hese C À Ha ctivation reactions deal with simplef unctionalizations or additions. However, recent years have witnessed an increase of the transition metal-catalyzed activation of C À H bond and annulation reactions.T hese annulation reactions are appealing to the organic chemista st hey affordh ighly valuable cyclic compounds in ar apid and sustainable manner from readilya vailable compounds.T his review article attemptst oh ighlight the Scheme 44. Ruthenium(II)-catalyzed synthesis of benzo[ij]imidazo[2,1,5-de]quinolizinium salts.Scheme 45. Ruthenium(II)-catalyzed decarboxylative annulation of keto acids.Scheme46. Possible mechanism for formation of isocoumarin.Scheme47. Ruthenium(II)-catalyzeda nnulation of 2-arylquinolinone and 2-arylbenzoxazinone with internal alkynes. Scheme 71. Possible mechanism for formationofq uinazoline.Scheme 72. Ruthenium(II)-catalyzed synthesis of spiro-cyclopentane-naphthalenones.

The first decarbonylative insertion of an alkyne through C-H/C-C activation of six-membered compounds is reported. The Ru-catalyzed reaction of 3-hydroxy-2-phenyl-chromones with alkynes works most efficiently in the presence of the ligand PPh to provide spiro-indenebenzofuranones. Unlike previously reported metal-catalyzed decarbonylative annulation reactions, in the present decarbonylative annulation reaction, the annulation occurs before extrusion of carbon monoxide.

An inexpensive Ru(ii) complex catalyzes the oxidative annulation reaction of disubstituted alkynes with benzamidines to provide highly valuable 1-aminoisoquinolines in high yields. The reaction also features excellent regioselectivity with some unsymmetrical alkynes.