Tian-Jun Gong

Palladium-Catalyzed Intermolecular Directed C−H Amidation of Aromatic Ketones

Pd-catalyzed directed ortho C-H amidation of aromatic ketones with both sulfonamides and amides has been accomplished. The use of an electron-deficient Pd complex, Pd(OTf)(2), is crucial for the success of this transformation. Some key intermediates of the reaction, that is, the cyclopalladation complexes of ketones, have been characterized by X-ray crystallography. Experimental analysis of these palladacycles and also the experimental results with N-methyl sulfonamides indicate that the new reaction does not seem to proceed through a nitrene intermediate. The utility of the newly developed reaction was demonstrated for the synthesis of useful organic intermediates such as 2- and 3-alkyl indoles and 2-aminophenyl ketones.

Pd(II)-Catalyzed C−H Activation/Aryl−Aryl Coupling of Phenol Esters

Although nitrogen-containing group-directed cyclopalladation reactions have been well-known, Pd(II) insertion into C-H bonds promoted by coordination of an oxygen-only group to the palladium remains rather rare. In the present study, the first cyclopalladation complex formed from a simple phenol ester was characterized by X-ray crystallography. A promising protocol for the ortho C-H activation/aryl-aryl coupling of phenol esters that was not sensitive to moisture or air was then established. The utility of the reaction was demonstrated for the synthesis of useful phenol derivatives.

Copper-catalyzed trifluoromethylation of terminal alkenes through allylic C-H bond activation.

An unprecedented type of reaction for Cu-catalyzed trifluoromethylation of terminal alkenes is reported. This reaction represents a rare instance of catalytic trifluoromethylation through C(sp(3))-H activation. It also provides a mechanistically unique example of Cu-catalyzed allylic C-H activation/functionalization. Both experimental and theoretical analyses indicate that the trifluoromethylation may occur via a Heck-like four-membered-ring transition state.

Synthesis of Dibenzofurans via Palladium-Catalyzed Phenol-Directed C–H Activation/C–O Cyclization

A practical, Pd(0)/Pd(II)-catalyzed reaction was developed for phenol-directed C-H activation/C-O cyclization using air as an oxidant. The turnover-limiting step of the process was found to be C-O reductive elimination instead of C-H activation. This reaction can tolerate a variety of functional groups and is complementary to the previous methods for the synthesis of substituted dibenzofurans.

Rhodium-catalyzed directed C-H cyanation of arenes with N-cyano-N-phenyl-p-toluenesulfonamide.

A Rh-catalyzed directed C-H cyanation reaction was developed for the first time as a practical method for the synthesis of aromatic nitriles. N-Cyano-N-phenyl-p-toluenesulfonamide, a user-friendly cyanation reagent, was used in the transformation. Many different directing groups can be used in this C-H cyanation process, and the reaction tolerates a variety of synthetically important functional groups.

Rhodium-Catalyzed Selective C–H Activation/Olefination of Phenol Carbamates

Rh(III)-catalyzed ortho C-H activation/olefination of phenol carbamates has been developed. High regioselectivity is observed with a range of phenol carbamates enabling efficient coupling with acrylates and styrenes. This reaction exhibits different reactivity as compared to the Pd-catalyzed ortho-arylation reaction of phenol esters and provides a new approach for the synthesis of ortho-substituted phenols.

Ligand‐Controlled Regiodivergent Copper‐Catalyzed Alkylboration of Alkenes

A novel copper-catalyzed regiodivergent alkylboration of alkenes with bis(pinacolato)diboron and alkyl halides has been developed. The regioselectivity of the alkylboration was controlled by subtle differences in the ligand structure. The reaction thus enables the practical, regiodivergent synthesis of two different alkyl boronic esters with complex structures from a single alkene.

Practical carbon-carbon bond formation from olefins through nickel-catalyzed reductive olefin hydrocarbonation

New carbon–carbon bond formation reactions expand our horizon of retrosynthetic analysis for the synthesis of complex organic molecules. Although many methods are now available for the formation of C(sp2)–C(sp3) and C(sp3)–C(sp3) bonds via transition metal-catalyzed cross-coupling of alkyl organometallic reagents, direct use of readily available olefins in a formal fashion of hydrocarbonation to make C(sp2)–C(sp3) and C(sp3)–C(sp3) bonds remains to be developed. Here we report the discovery of a general process for the intermolecular reductive coupling of unactivated olefins with alkyl or aryl electrophiles under the promotion of a simple nickel catalyst system. This new reaction presents a conceptually unique and practical strategy for the construction of C(sp2)–C(sp3) and C(sp3)–C(sp3) bonds without using any organometallic reagent. The reductive olefin hydrocarbonation also exhibits excellent compatibility with varieties of synthetically important functional groups and therefore, provides a straightforward approach for modification of complex organic molecules containing olefin groups.

Rh(III)-Catalyzed C–H Activation with Allenes To Synthesize Conjugated Olefins

Rh(III)-catalyzed C-H activation with allenes produces highly unsaturated conjugated olefins. The reaction is applicable to both olefin and arene C(sp(2))-H and is compatible with a variety of functional groups. The products can be further transformed into other important skeletons through Diels-Alder reaction and intramolecular transesterification.

Nickel-Catalyzed Defluorinative Reductive Cross-Coupling of gem-Difluoroalkenes with Unactivated Secondary and Tertiary Alkyl Halides

Herein, we described a nickel-catalyzed monofluoroalkenylation through defluorinative reductive cross-coupling of gem-difluoroalkenes with alkyl halides. Key to the success of this strategy is the combination of C-F cleavage with alkyl halides activation. This reaction enables the convenient synthesis of a large variety of functionalized monofluoroalkenes under mild reaction conditions with broad functional group compatibility and excellent Z-selectivity. The combination of Ni catalysis with (Bpin)2/K3PO4 as terminal reductant promoted the efficient C(sp2)-C(sp3) formation especially the generation of all-carbon quaternary centers with high chemoselectivity.