Shansheng Xu

Ruthenium-Catalyzed Oxidative C–H Bond Olefination of N-Methoxybenzamides Using an Oxidizing Directing Group

Ruthenium-catalyzed oxidative C-H bond olefination of N-methoxybenzamides using an oxidizing directing group with a broad substrate scope is reported. The reactions of N-methoxybenzamides with acrylates in MeOH and styrene (or norbornadiene) in CF(3)CH(2)OH afforded two types of products.

Rhodium-Catalyzed Cascade Oxidative Annulation Leading to Substituted Naphtho[1,8-bc]pyrans by Sequential Cleavage of C(sp2)–H/C(sp3)–H and C(sp2)–H/O–H Bonds

The cascade oxidative annulation reactions of benzoylacetonitrile with internal alkynes proceed efficiently in the presence of a rhodium catalyst and a copper oxidant to give substituted naphtho[1,8-bc]pyrans by sequential cleavage of C(sp(2))-H/C(sp(3))-H and C(sp(2))-H/O-H bonds. These cascade reactions are highly regioselective with unsymmetrical alkynes. Experiments reveal that the first-step reaction proceeds by sequential cleavage of C(sp(2))-H/C(sp(3))-H bonds and annulation with alkynes, leading to 1-naphthols as the intermediate products. Subsequently, 1-naphthols react with alkynes by cleavage of C(sp(2))-H/O-H bonds, affording the 1:2 coupling products. Moreover, some of the naphtho[1,8-bc]pyran products exhibit intense fluorescence in the solid state.

Ruthenium-Catalyzed Pyrrole Synthesis via Oxidative Annulation of Enamides and Alkynes

An efficient and regioselective ruthenium-catalyzed oxidative annulation of enamides with alkynes via the cleavage of C(sp(2))-H/N-H bonds is reported. The reactions can afford N-acetyl substituted or N-unsubstituted pyrroles by altering the reaction conditions slightly.

Rhodium(III)‐Catalyzed Alkenylation Reactions of 8‐Methylquinolines with Alkynes by C(sp3)H Activation

The alkenylation reactions of 8-methylquinolines with alkynes, catalyzed by [{Cp*RhCl2}2], proceeds efficiently to give 8-allylquinolines in good yields by C(sp(3))-H bond activation. These reactions are highly regio- and stereoselective. A catalytically competent five-membered rhodacycle has been structurally characterized, thus revealing a key intermediate in the catalytic cycle.

Regioselective C2 Oxidative Olefination of Indoles and Pyrroles through Cationic Rhodium(III)‐Catalyzed CH Bond Activation

Be economic with your atoms! An efficient Rh-catalyzed oxidative olefination of indoles and pyrroles with broad substrate scope and tolerance is reported. The catalytic reaction proceeds with excellent regio- and stereoselectivity. The directing group N,N-dimethylcarbamoyl was crucial for the reaction and could be removed easily.

Ruthenium-Catalyzed Oxidative Coupling/Cyclization of Isoquinolones with Alkynes through CH/NH Activation: Mechanism Study and Synthesis of Dibenzo[a,g]quinolizin-8-one Derivatives

The mechanism of [{RuCl(2)(p-cymene)}(2)]-catalyzed oxidative annulations of isoquinolones with alkynes was investigated in detail. The first step is an acetate-assisted C-H bond activation process to form cyclometalated compounds. Subsequent mono-alkyne insertion of the Ru-C bonds of the cyclometalated compounds then takes place. Finally, oxidative coupling of the C-N bond of the insertion compounds occurs to afford Ru(0) sandwich complexes that undergo oxidation to regenerate the catalytically active Ru(II) complex with the copper oxidant and release the desired dibenzo[a,g]quinolizin-8-one derivatives. All of the relevant intermediates were fully characterized and determined by single crystal X-ray diffraction analysis. The [{RuCl(2)(p-cymene)}(2)]-catalyzed C-H bond functionalization of isoquinolones with alkynes to synthesize dibenzo[a,g]quinolizin-8-one derivatives through C-H/N-H activation was also demonstrated.

Rhodium(III)-Catalyzed Intermolecular Amidation with Azides via C(sp3)–H Functionalization

The amidation reactions of 8-methylquinolines with azides catalyzed by a cationic rhodium(III) complex proceed efficiently to give quinolin-8-ylmethanamine derivatives in good yields via C(sp(3))-H bond activation under external oxidant-free conditions. A catalytically competent five-membered rhodacycle has been isolated and characterized, revealing a key intermediate in the catalytic cycle.

Ruthenium-Catalyzed Regioselective C2 Alkenylation of Indoles and Pyrroles via C–H Bond Functionalization

An efficient ruthenium-catalyzed oxidative coupling of indoles and pyrroles with various alkenes at the C2-position assisted by employing the N,N-dimethylcarbamoyl moiety as a directing group is reported. The catalytic reaction proceeds in an excellent regio- and stereoselective manner.

Investigation and Comparison of the Mechanistic Steps in the [(Cp*MCl2)2] (Cp*=C5Me5; M=Rh, Ir)-Catalyzed Oxidative Annulation of Isoquinolones with Alkynes

The mechanism of the [(Cp*MCl(2))(2)] (M = Rh, Ir)-catalyzed oxidative annulation reaction of isoquinolones with alkynes was investigated in detail. In the first acetate-assisted C-H-activation process (cyclometalated step) and the subsequent mono-alkyne insertion into the M-C bonds of the cyclometalated compounds, both Rh and Ir complexes participated well. However, the desired final products, dibenzo[a,g]quinolizin-8-one derivatives, were only formed in high yield when the Rh species participated in the final oxidative coupling of the C-N bond. Moreover, a Rh(I) sandwich intermediate was isolated during this transformation. The iridium complexes were found to be inactive in the oxidative coupling processes. All of the relevant intermediates were fully characterized and determined by single-crystal X-ray diffraction analysis. Based on this mechanistic study, a Rh(III)→Rh(I)→Rh(III) catalytic cycle was proposed for this reaction.

Synthesis, structures and catalytic properties of Group 4 metallocenes based upon [Me2E(C5H4)(C5Me4)]2 (E=Si, Ge) supporting coordination

The ansa -metallocene complexes Me 2 Si(η 5 -C 5 H 4 )(η 5 -C 5 Me 4 )MCl 2 [M=Ti ( 1 ), Zr ( 2 ), Hf ( 3 )] were prepared by the reaction of [Me 2 Si(η 5 -C 5 H 4 )(η 5 -C 5 Me 4 )]Li 2 with MCl 4 ·2THF. Complexes Me 2 Ge(η 5 -C 5 H 4 )(η 5 -C 5 Me 4 )MCl 2 [M=Ti ( 4 ), Zr ( 5 )] were synthesized using similar method from the germyl-bridged ligand. The molecular structures of 1 – 3 and 5 have been determined by X-ray diffraction. Complexes 1 – 3 and 5 in combination with MAO were studied as catalysts for ethylene polymerization and it was found that zirconocene catalysts show much higher activities than the titanocene and hafnocene and the activities reach the maximum at high temperature. This indicates that the zirconocene system based upon [Me 2 E(C 5 H 5 )(C 5 Me 4 )] 2 (E=Si, Ge) supporting coordination is a highly stable ethylene polymerization catalyst system. The relationship between structures and catalytic properties of catalysts is discussed.