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.

We have developed a heterogenized catalyst of Cu(ii) complex immobilized onto nanosilica obtained from rice husk (RH), through Schiff-base condensation between 3-aminopropyltriethoxysilane (APTES) functionalized nanosilica and acetamide.

A bis-N-heterocyclic carbene (NHC) functionalized with chloropropyltriethoxysilane over silica was used to synthesize a well-defined immobilized palladium complex. This complex is a suitable and easily retrievable catalyst for Suzuki-Miyaura cross-coupling reactions under mild aqueous conditions. Excellent yields and conversions were obtained with low palladium loadings (down to 0.03 mol% Pd). The catalyst can be reused up to six cycles without the loss of its activity. The catalytic role of the NHC complex of palladium during coupling between bromobenzene and phenylboronic acid was investigated theoretically. The oxidative addition step is predicted to be endothermic in agreement with the experimental conditions.

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