Formal aromatic C-H phosphinylation of [2.2]paracyclophanes was efficiently achieved via their arylsulfonium salts with secondary phosphine oxides under nickel(0) catalysis. The reaction selectively cleaved the aromatic C(sp2)-S bond over the aliphatic C(sp3)-S bond in the aryl(alkyl)sulfonium salts of [2.2]paracyclophanes with Ni(COD)2 as the catalyst and CuBr as the promoter, affording the corresponding P-[2.2]paracyclophanylated products in good to excellent yields. The applicability of the present protocol was established through scalable preparation of the typical target product and its application as a potentially useful phosphine ligand for transition-metal-catalyzed carbene insertion to X-H (X = C, N) bonds.

Base-enabled aromatic C-H functionalization of [2.2]paracyclophanes was achieved by thioalkylphosphinylation via sulfonium salts. Cross-coupling between [2.2]paracyclophane tetrahydro-1H-thiophen-1-ium trifluoromethanesulfonates and secondary phosphine oxides afforded thioalkylphosphinylated [2.2]paracyclophane derivatives through selective C(sp3)-S bond cleavage of the arylsulfonium salts under mild conditions. The protocol features broad substrate scopes, good functional group tolerance from readily available reagents, and decent efficiency in up to 96% yields. The practicability of this method was demonstrated by scale-up preparation of the target products and their transformations to potential P,S-ligands for Suzuki and Sonogashira cross-coupling reactions.

Palladium‐catalyzed stereoselective olefinic C−H alkynylation of gem‐diarylsubstituted ethylenes with propargylic alcohols was achieved to access diverse unsymmetrical 1,3‐enynes. The regio‐ and stereoselectivities were established through a 1,4‐palladium migration from aryl to vinyl in the presence of 2‐FC6H4OH as additive. Mechanistic investigations suggest that cleavage of the olefinic C−H bond might not be involved in the rate‐determining step of the catalytic process.

Formal olefinic C-P cross-coupling between alkenyl sulfonium salts and secondary phosphine oxides and H-phosphinates has been developed. A base enables construction of alkenyl C-P bonds as well as aliphatic C-P bonds at ambient temperature under an air atmosphere. This protocol provides an alternative access to multisubstituted alkenyl phosphine oxides and phosphinates in 40-99% yield from functionalized alkenes through an interrupted Pummerer activation/base-promoted olefinic C-S bond phosphinylation sequence. Gram-scale preparation and feasible derivatization demonstrated the applicability of the resultant alkenylphosphine oxides.

Efficient palladium-catalyzed regioselective vinylic C-H polyfluoroarylation of gem-disubstituted ethylenes with polyfluoroarenes was realized to access a variety of polyfluorinated triarylethenes. An aryl to vinyl 1,4-palladium migration is proposed to achieve high regio- and stereoselectivities for the target products. This strategy features broad substrate scopes and good functional group tolerance. Mechanistic studies have suggested that a protonation-deprotonation process reversibly occurs between a five-membered palladacycle and the vinyl-palladium intermediates, and aromatic C-H cleavage of polyfluoroarenes contributes to the rate-limiting step in the overall catalytic cycle. Efficient palladium-catalyzed regioselective vinylic C-H polyfluoroarylation of gem-disubstituted ethylenes with polyfluoroarenes was realized via an aryl to vinyl 1,4-palladium migration process to access various polyfluorinated triarylethenes.

A chemo- and regioselective olefinic C–H cyanation strategy was developed via alkenyl sulfonium salts with CuCN, affording alkenyl nitriles by a site-selective interrupted Pummerer activation/palladium-catalyzed olefinic C(sp 2 )–S cyanation sequence.

The Pd(cod)Cl2-catalyzed alkoxycarbonylation of conjugated dienes to β,γ-unsaturated esters was approached by both intramolecular phosphinesulfonate L1 and intermolecular PPh3/PTSA in this study. However, the poor solubility of the Pd/L1 complex and the labile monodentate Pd/PPh3 structure restricts the system efficiency, especially for the scale-up application. By contrast, the stable and well-soluble bidentate Xantphos system allows for the quantitative formation of 3-pentenoate (96%) on a gram scale within 6 h in weakly alkaline N-methylpyrrolidone (NMP), which also functions as a basic site to promote the rate-limiting alcoholysis step while reducing the dosage of ligand to a theoretical value.

The direct synthesis of triazole 2-oxides has posed a challenge in the field of N-heterocyclic chemistry. A novel copper(I)-catalyzed nitrosylation/annulation cascade of enaminones provides a straightforward route to 1H-1,2,3-triazole 2-oxides by forming new C-N, N=N, and N-N bonds using noncorrosive tert-butyl nitrite (TBN) as both the N and NO sources. The synthetic protocol features easily accessible starting materials, wide substrate scopes, and good tolerance toward various functional groups while avoiding use of explosive azides.

Multinuclear porphyrin-based ruthenium(II)-NNNN complexes were efficiently assembled by means of coordinatively unsaturated 16-electron mononuclear ruthenium(II)-pyrazolyl-imidazolyl-pyridine complex, zinc(II) meso-tetra(4-pyridyl)-porphyrin (ZnTPyP), and 4,4 '-linked bipyridines. The resultant multinuclear (Ru-4 and Ru-8) porphyrin-based ruthenium(II)-NNNN complexes exhibited exceptionally high catalytic activity at as low as 0.008 mol % Ru loading for the transfer hydrogenation reaction of ketones in refluxing 2-propanol, reaching up to 99 % yields and 5.7x10(6) h(-1) TOFs.

Zinc(II)-catalyzed [2+2+1] annulation of internal alkenes, diazooxindoles, and isocyanates was successfully developed for the construction of multisubstituted spirooxindoles. This multicomponent transformation involves in situ generation of a sulfur-containing spirocyclic intermediate from the [4+1] annulation of diazooxindole to sulfonyl isocyanate, which subsequently reacts as a 1,3-dipole with the internal alkene, that is, α-oxo ketene dithioacetal, to furnish a formal [2+2+1] annulation in a one-pot manner. This synthetic protocol features a low-toxicity main group metal catalyst, readily available reagents, and ≤96% yields, offering an efficient route to multisubstituted spirooxindole derivatives.

Various pincer-type ruthenium(II) complexes were developed from our laboratories and herein the relevant advance is summarized from a viewpoint of their synthesis and organic synthetic applications as homogeneous catalysts. The investigated Ru(II)-NNN and Ru(II)-NNNN-type complexes exhibited highly catalytic activities in the transfer hydrogenation of ketones, C-C bond formation from alcohols and ketones, and dehydrogenation. RuH complexes were identified or considered as the catalytically active intermediates for these transformations. This review deals with the following subjects: (i) mononuclear ruthenium(II) pincer complexes with high catalytic activity in (asymmetric) transfer hydrogenation of ketones; (ii) multinuclear ruthenium(II) complexes for transfer hydrogenation of ketones; (iii) mononuclear ruthenium(II) complexes for other reactions such as Oppenauer-type oxidation, beta-alkylation of secondary alcohols, synthesis of multisubstituted heterocycles, acceptorless dehydrogenation of N-heterocycles and secondary alcohols.

Carbene insertion into the C(sp(2))-H bonds of internal alkenes was enabled in air by HFIP (1,1,1,3,3,3-hexafluoro-2-propanol) as both the mediator and solvent through its cooperation with borane B(C6F5)(3) as the catalyst. 3-Diazooxindoles and 3-diazoindolin-2-imines were amenable to work as the carbene precursors, and alpha-oxo ketene dithioacetals acted as the internal alkenes at ambient temperature. The present synthetic protocol features metal-free conditions, diverse substituent tolerance, and 47-84% yields, offering an efficient route to 3-vinylated oxindole and indole derivatives.

A concise synthetic route to spiroindoline-fused S-heterocycles was developed through copper-catalyzed [4 + 1] annulation using enaminothiones as donor-acceptor synthons. Both 3-diazoindolin-2-imines and 3-diazooxindoles were amenable to work as effective C1 building blocks. The reaction proceeds via a copper-catalyzed cascade process involving the in situ generation of copper(I) carbene and C-S/C-C bond formation. This synthetic protocol features the use of readily available substrates, diverse substituent tolerance, and good to excellent yields.

Rhodium(III)-catalyzed triple C-H bond activation of aryl enaminones was achieved to access naphtho[1,8-bc]pyrans by oxidative annulation to internal alkynes. 1-Naphthols might be formed as the only products, depending on the steric and/or electronic environment around the aroyl moiety of the aryl enaminones or the electronic impact from the alkynes. With propargyl alcohols as the masked terminal alkynes, aryl enaminones underwent rhodium(III)-or rhodium(I)-catalyzed internal alkenyl C-H bond activation to afford functionalized but-2-ene-1,4-diones. The resultant naphtho[1,8-bc]pyrans are highly fluorescent and can be further transformed by chlorination, bromination, and difluoromethylation, demonstrating potential practicability of the synthetic protocol.

Efficient palladium-catalyzed vinylic C-H alkenylation and allenylation of gem-disubstituted ethylenes with N-tosylhydrazones of aryl alkyl and diaryl ketones were achieved to access trisubstituted 1,3-dienes and tetrasubstituted allenes, respectively. An aryl to vinyl 1,4-palladium migration/carbene insertion/β-hydride elimination sequence proceeded to switch the chemo- and regioselectivities to give structurally diverse products. Use of 2-FC6H4OH additive enables enhancement of the reaction efficiency through accelerating the key 1,4-palladium migration process.

C-H functionalization has been emerging as a powerful method to establish carbon-carbon and carbon-heteroatom bonds. Many efforts have been devoted to transition-metal-catalyzed direct transformations of C-H bonds. Metal carbenes generated in situ from transition-metal compounds and diazo or its equivalents are usually applied as the transient reactive intermediates to furnish a catalytic cycle for new C-C and C-X bond formation. Using this strategy compounds from unactivated simple alkanes to complex molecules can be further functionalized or transformed to multi-functionalized compounds. In this area, transition-metal-catalyzed carbene insertion to C-H bonds has been paid continuous attention. Diverse catalyst design strategies, synthetic methods, and potential applications have been developed. This critical review will summarize the advance in transition-metal-catalyzed carbene insertion to C-H bonds dated up to July 2021, by the categories of C-H bonds from aliphatic C(sp3)-H, aryl (aromatic) C(sp2)-H, heteroaryl (heteroaromatic) C(sp2)-H bonds, alkenyl C(sp2)-H, and alkynyl C(sp)-H, as well as asymmetric carbene insertion to C-H bonds, and more coverage will be given to the recent work. Due to the rapid development of the C-H functionalization area, future directions in this topic are also discussed. This review will give the authors an overview of carbene insertion chemistry in C-H functionalization with focus on the catalytic systems and synthetic applications in C-C bond formation.

Methods for the Ru(dppbsa)-catalyzed hydrodeoxygenation and reductive etherification of ketones and aldehydes were developed. Mechanistic studies suggest two paths with respective rate-limiting step to distinct carbonyl substrates.

A transition-metal-free olefinic C-H azidoalkylthiolation protocol was developed through C(sp(3))-S bond cleavage of vinylsulfonium salts with sodium azide in air under aqueous conditions. An interrupted Pummerer/nucleophilc azidoalkylation cascade was developed for such a process. The practicability of the synthetic protocol was demonstrated by scale-up preparation of the azidoalkylthiolated tetrasubstituted alkene products and their transformations to diverse triazole and tetrazole derivatives as well as azidoalkylthio-funtionalized N-heterocyclic compounds. The present synthetic methodology features broad substrate scopes and good functional group tolerance under mild conditions.

The ligand-free Co-catalyzed chemoselective reductive cyclization cascade of enone-tethered aldehydes with i-PrOH as the environmentally benign hydrogen surrogate is developed by this study. Mechanistic studies disclosed that such a protocol is initiated by an ortho-enone-assisted Co(I)-catalyzed reduction of the aldehyde functionality with i-PrOH. Meanwhile, the selectivity from the Michael-Aldol cycloreduction cascade to the oxa-Michael cascade is feasible and readily adjusted by the addition of steric Lewis bases, such as TEMPO and DABCO, delivering substituted 1H-indenes and dihydroisobenzofurans, respectively.