Herein, we report the palladium-catalyzed direct arylation of unactivated aliphatic C−H bonds in free primary amines. This method takes advantage of an exo-imine-type directing group (DG) that can be generated and removed in situ. A range of unprotected aliphatic amines are suitable substrates, undergoing site-selective arylation at the γ-position. Methyl as well as cyclic and acyclic methylene groups can be activated. Furthermore, when aniline-derived substrates were used, preliminary success with δ-C−H arylation was achieved. The feasibility of using the DG component in a catalytic fashion was also demonstrated.

Described is a new hydrazone-based exo-directing group (DG) strategy developed for the functionalization of unactivated primary β C−H bonds of aliphatic amines. Conveniently synthesized from protected primary amines, the hydrazone DGs are shown to site-selectively promote the β-acetoxylation and tosyloxylation via five-membered exo-palladacycles. Amines with a wide scope of skeletons and functional groups are tolerated. Moreover, the hydrazone DG can be readily removed, and a one-pot C−H acetoxylation/DG removal protocol was also discovered.

Direct arylation of cyclopentanones has been a long-standing challenge because of competitive self-aldol condensation and multiple arylations. Reported herein is a direct mono-α-C−H arylation of cyclopentanones with aryl bromides which is enabled by palladium/amine cooperative catalysis. This method is scalable and chemoselective with broad functional-group tolerance. Application to controlled sequential arylation of cyclopentanones has been also demonstrated.

Herein, we report the palladium-catalyzed direct arylation of unactivated aliphatic C−H bonds in free primary amines. This method takes advantage of an exo-imine-type directing group (DG) that can be generated and removed in situ. A range of unprotected aliphatic amines are suitable substrates, undergoing site-selective arylation at the γ-position. Methyl as well as cyclic and acyclic methylene groups can be activated. Furthermore, when aniline-derived substrates were used, preliminary success with δ-C−H arylation was achieved. The feasibility of using the DG component in a catalytic fashion was also demonstrated.

Described is a new hydrazone-based exo-directing group (DG) strategy developed for the functionalization of unactivated primary β C−H bonds of aliphatic amines. Conveniently synthesized from protected primary amines, the hydrazone DGs are shown to site-selectively promote the β-acetoxylation and tosyloxylation via five-membered exo-palladacycles. Amines with a wide scope of skeletons and functional groups are tolerated. Moreover, the hydrazone DG can be readily removed, and a one-pot C−H acetoxylation/DG removal protocol was also discovered.

Direct arylation of cyclopentanones has been a long-standing challenge because of competitive self-aldol condensation and multiple arylations. Reported herein is a direct mono-α-C−H arylation of cyclopentanones with aryl bromides which is enabled by palladium/amine cooperative catalysis. This method is scalable and chemoselective with broad functional-group tolerance. Application to controlled sequential arylation of cyclopentanones has been also demonstrated.

Reported herein is a palladium/norbornene-catalyzed ortho-arene acylation of aryl iodides by a Catellani-type CH functionalization. This transformation is enabled by isopropyl carbonate anhydrides, which serve as both an acyl cation equivalent and a hydride source.

Two complementary methods for catalytic intramolecular ketone alkylation reactions with unactivated olefins, resulting in Conia-ene-type reactions, are reported. The transformations are enabled by dual activation of both the ketone and the olefin and are atom-economical as stoichiometric oxidants or reductants are not required. Assisted by Kool’s aniline catalyst, the reaction conditions can be both pH- and redox-neutral. A broad range of functional groups are thus tolerated. Whereas the rhodium catalysts are effective for the formation of five-membered rings, a ruthenium-based system that affords the six-membered ring products was also developed.

Reported herein is a palladium/norbornene-catalyzed ortho-arene acylation of aryl iodides by a Catellani-type CH functionalization. This transformation is enabled by isopropyl carbonate anhydrides, which serve as both an acyl cation equivalent and a hydride source.

Two complementary methods for catalytic intramolecular ketone alkylation reactions with unactivated olefins, resulting in Conia-ene-type reactions, are reported. The transformations are enabled by dual activation of both the ketone and the olefin and are atom-economical as stoichiometric oxidants or reductants are not required. Assisted by Kool’s aniline catalyst, the reaction conditions can be both pH- and redox-neutral. A broad range of functional groups are thus tolerated. Whereas the rhodium catalysts are effective for the formation of five-membered rings, a ruthenium-based system that affords the six-membered ring products was also developed.

The first total syntheses of the proposed structure of cycloinumakiol (1) and its C5 epimer (18) are achieved in a concise and efficient fashion. Starting from the known 3-hydroxybenzocyclobutenone, 1 and 18 are obtained in nine and five steps with overall yields of 15 % and 33 %, respectively. The key for the success of this approach is the use of a catalytic CC activation strategy for constructing the tetracyclic core of 1 through carboacylation of a sterically hindered trisubstituted olefin with benzocyclobutenone. In addition, the structure of the natural cycloinumakiol was reassigned to 19-hydroxytotarol (7) through X-ray diffraction analysis. This work demonstrates the potential of CC activation for streamlining complex natural product synthesis.

The rhodium-catalyzed formation of all-carbon spirocenters involves a decarbonylative coupling of trisubstituted cyclic olefins and benzocyclobutenones through CC activation. The metal–ligand combination [{Rh(CO)₂Cl}₂]/P(C₆F₅)₃ catalyzed this transformation most efficiently. A range of diverse spirocycles were synthesized in good to excellent yields and many sensitive functional groups were tolerated. A mechanistic study supports a hydrogen-transfer process that occurs through a β-H elimination/decarbonylation pathway.

A tunable rhodium-catalyzed intramolecular alkyne insertion reaction proceeding through the CC cleavage of benzocyclobutenones is described. Selective formation of either the direct or decarbonylative insertion product can be controlled by using different catalytic systems. A variety of fused β-naphthol and indene scaffolds were obtained in good yields with high functional group tolerance. This work illustrates a divergent approach to synthesize fused-ring systems by CC activation/functionalization.

The first total syntheses of the proposed structure of cycloinumakiol (1) and its C5 epimer (18) are achieved in a concise and efficient fashion. Starting from the known 3-hydroxybenzocyclobutenone, 1 and 18 are obtained in nine and five steps with overall yields of 15 % and 33 %, respectively. The key for the success of this approach is the use of a catalytic CC activation strategy for constructing the tetracyclic core of 1 through carboacylation of a sterically hindered trisubstituted olefin with benzocyclobutenone. In addition, the structure of the natural cycloinumakiol was reassigned to 19-hydroxytotarol (7) through X-ray diffraction analysis. This work demonstrates the potential of CC activation for streamlining complex natural product synthesis.

The rhodium-catalyzed formation of all-carbon spirocenters involves a decarbonylative coupling of trisubstituted cyclic olefins and benzocyclobutenones through CC activation. The metal–ligand combination [{Rh(CO)₂Cl}₂]/P(C₆F₅)₃ catalyzed this transformation most efficiently. A range of diverse spirocycles were synthesized in good to excellent yields and many sensitive functional groups were tolerated. A mechanistic study supports a hydrogen-transfer process that occurs through a β-H elimination/decarbonylation pathway.

A tunable rhodium-catalyzed intramolecular alkyne insertion reaction proceeding through the CC cleavage of benzocyclobutenones is described. Selective formation of either the direct or decarbonylative insertion product can be controlled by using different catalytic systems. A variety of fused β-naphthol and indene scaffolds were obtained in good yields with high functional group tolerance. This work illustrates a divergent approach to synthesize fused-ring systems by CC activation/functionalization.