Urazoles as Heterocyclic Directing Groups in Ru(II)-Catalyzed Annulation of N-H/C-H Bonds with Vinylene Carbonate

The development of novel directing groups is a valuable strategy to secure the advancement of catalytic C-H functionalization. To illustrate the feasibility of urazoles as heterocyclic directing groups, we herein present the ruthenium(II)-catalyzed annulation of N-H/C-H bonds on N-aryl urazoles with vinylene carbonate. This transformation provides the rapid construction of triazolocinnoline derivatives as hemiaminal and dehydrated forms. A series of mechanistic investigations and post-transformations highlighted the amenability of the developed method.

Ruthenium(ii) catalyzed C-3 site selective alkenylation of indole derivatives via C-H activation

An efficient synthetic method has been developed for C-3 site-selective alkenylation of indole derivatives under ruthenium(ii) catalysis with an ester as a directing group. Besides the presence of two potential C(sp2)-H sites available for functionalization in the substrates, exclusive C3 selectivity was achieved in a selective manner as only mono-functionalized products were formed. The high site selectivity is attributed to the formation of an uncommon six-membered metallacycle intermediate between the ruthenium catalyst and ester directing group, enabled by the selective alkenylation at the C3 position of indole derivatives. This protocol features high site selectivity, operational simplicity, broad substrate scope, and moderate to high yields.

Ru(II)-Catalyzed C-H Alkenylation of Benzimidates with Unactivated Olefins: A Route to ortho-Alkenylated Benzonitriles

A Ru(II)-catalyzed C-H alkenylation of benzimidates with unactivated alkenes providing ortho-alkenylated benzonitriles in good to excellent yields in a highly regio- and stereoselective manner is described. In the reaction, an imidate group converted into a nitrile under the reaction conditions. The alkenylation reaction was compatible with various substituted benzimidates as well as functionalized unactivated olefins, including ibuprofen-, neproxen-, coumarin-, and cholesterol-substituted alkenes. A feasible reaction mechanism was proposed to account for the present alkenylation reaction.

Ru(II)-Catalyzed regioselective carbene insertion into β-carbolines and isoquinolines

A protocol for carbene insertion into the inert C(sp²)-H bond has been established wherein β-carbolines and isoquinolines are explored as intrinsic directing groups. The Ru(II)-catalyzed strategy employing sulfoxonium ylides as the carbene precursor offers an effective and atom-economical functionalization of substrates of biological interest with only DMSO as the sole by-product. The strategy is scalable to gram scale, and it also showcases a wide range of functional group tolerance. ESI-MS studies assisted in the identification of intermediates and consolidation of a probable mechanistic pathway. Furthermore, investigations revealed that the functionalized molecules not only displayed selective inhibition against cancer cell lines, but also demonstrated promising photophysical properties.

Iridium(I)-Catalyzed Isoindolinone-Directed Branched-Selective Aromatic C-H Alkylation with Simple Alkenes

We report an iridium(I)-catalyzed branched-selective C–H alkylation of N-arylisoindolinones with simple alkenes as the alkylating agents. The amide carbonyl group of the isoindolinone motif acts as the directing group to assist the ortho C–H activation of the N-aryl ring. With this atom-economic and highly branched-selective protocol, an array of biologically relevant N-arylisoindolinones were obtained in good yields. Asymmetric control was achieved with up to 87:13 er when a BiPhePhos-like chiral ligand was employed.

Silver-Catalyzed Regioselective 1,6-Hydroarylation of para-Quinone Methides with Anilines and Phenols

A simple and efficient method for the silver-catalyzed regioselective 1,6-hydroarylation of para-quinone methides (p-QMs) with anilines and phenols has been established. Without the need for pre-protection, a broad range of...

Enantioselective Thiolysis and Aminolysis of Cyclic Anhydrides Using a Chiral Diamine-Derived Thiourea Catalyst

Catalytic desymmetrization of cyclic anhydrides has been widely investigated in the field of organocatalysis. Using this approach, many stereocenters can be established in a single, symmetry-breaking transformation. Herein, a thiourea organocatalyst was prepared in a single step from a chiral diamine, (R,R)-1,2-diphenylethylenediamine, and used for the desymmetrization of various cyclic anhydrides through double hydrogen-bonding activation. The asymmetric ring-opening reaction of the cyclic anhydride proceeded via the enantioselective addition reaction catalyzed by diamine thiourea. Thiolysis afforded the desired products in the yields of 86-98% and enantioselectivities of 60-94%, while aminolysis afforded the yields of 90-94% and enantioselectivities of 90-95%.

One-Pot Tandem Access to Phenothiazine Derivatives from Acetanilide and 2-Bromothiophenol via Rhodium-Catalyzed C-H Thiolation and Copper-Catalyzed C-N Amination

A one-pot and step economic reaction involving Rh(III)-catalyzed C-H thiolation and relay Cu(II)-catalyzed C-N amination of acetanilide and 2-bromothiophenol is reported here, with several valuable phenothiazine products obtained. This synthesis protocol proceeds from easily starting materials, demonstrating high atom economy, broad substrate scope, and good yield. Furthermore, the directing group can be easily eliminated, and chlorpromazine is provided in a large scale; thus this synthesis protocol could be utilized to construct phenothiazine scaffolds.

Equivalent Loading of Directed Arenes in Pd(II)-Catalyzed Oxidative Cross-Coupling of Aryl C-H Bonds at Room Temperature

The unsymmetrical biaryls (Ar¹-Ar²) produced by the catalytic cross-couplings of aryl halides (Ar¹-halo) with aryl metallics (Ar²-M) in the loading ratio of 1:1 are popular in chemical synthesis. In contrast, there has been less precedence on the same biaryls produced effectively from two normal aryl C-H bonds with equivalent loading. Here, we report that, in a palladium/oxidant/acid catalytic system at room temperature, one arene (Ar¹-H, 1 equiv) can highly selectively couple with the other one (Ar²-H, 1 equiv) to afford the target Ar¹-Ar² just by controlling the directing groups and the substituted groups on their phenyl rings. The utility of this one-one cross-coupling is also demonstrated by synthesis of a few bioactive molecules.

Ruthenium (II) Catalyzed C(sp2 )-H Bond Alkenylation of 2-Arylbenzo[d]oxazole and 2-Arylbenzo[d]thiazole with Unactivated Olefins

Functionalization of the bio-relevant heterocycles 2-arylbenzo[d]oxazole and 2-arylbenzo[d]thiazole has been achieved through Ru(II)-catalyzed alkenylation with unactivated olefins leading to selective formation of the mono-alkenylated products. This approach has a broad substrate scope with respect to the coupling partners, affords high yields, and works for gram scale synthesis using a readily available Ru-based catalyst. Mechanistic studies reveal a C-H activation pathway for the dehydrogenative coupling leading to the alkenylation. However, the results of the ESI-MS-guided deuterium kinetic isotope effect studies indicate that the C-H activation stage may not be the rate-determining step of the reaction. The use of a radical scavenging agent such as TEMPO did not show any detrimental effect on the reaction outcome, eliminating the possibility of the involvement of a free-radical pathway.

Rh(iii)-Catalyzed multi-site-selective C–H bond functionalization: condition-controlled synthesis of diverse fused polycyclic benzimidazole derivatives

Multi-site-selective C–H activation: Diverse novel fused polycyclic- and multi-substituted 2-oxyl naphthalene benzimidazole derivatives were selectively synthesized via Rh(iii)-catalyzed tandem C–H activation/cyclization.

Ruthenium-catalysed oxidative coupling of vinyl derivatives and application in tandem hydrogenation

The first ruthenium-catalyzed oxidative homo- and cross-coupling of exclusive vinyl derivatives giving highly valued 1,3-diene building blocks is reported. In situ ruthenium-catalyzed hydrogenation afforded relevant adipic acid ester derivatives.

Ruthenium-Catalyzed C(sp2)-H Bond Bisallylation with Imidazopyridines as Directing Groups

A Ru(II)-catalyzed bisallylation of imidazopyridines with vinylcyclopropanes or vinyl cyclic carbonate has been successfully realized. Notably, pharmacophore imidazopyridine was utilized as an intrinsic directing group, which gave access to value-added bisallylated products in high yields via double tandem C-H and C-C/C-O activation. The current methodology was featured with broad substrate scope, good functional group compatibility, and operational simplicity.

Directing Group Assisted Unsymmetrical Multiple Functionalization of Arene C-H Bonds

Multiple C-H bond functionalizations promptly install diverse groups on the molecular framework and consequently fabricate complex molecular entities. This review briefly surveys the conceptual development of directing group assisted unsymmetrical multiple functionalization of arene C(sp² )-H bonds, which is exceedingly appealing and highly important.

Steering Site-Selectivity in Transition Metal-Catalyzed C-H Bond Functionalization: the Challenge of Benzanilides

Selective C-H bond functionalization catalyzed by metal complexes have completely revolutionized the way in which chemical synthesis is conceived nowadays. Typically, the reactivity of a transition metal catalyst is the key to control the site-, regio- and/or stereo-selectivity of a C-H bond functionalization. Of particular interests are molecules that contain multiple C-H bonds prone to undergo C-H bond activations with very similar bond dissociation energies at different positions. This is the case of benzanilides, relevant chemical motifs that are found in many useful fine chemicals, in which two C-H sites are present in chemically different aromatic fragments. In the last years, it has been found that depending on the metal catalyst and the reaction conditions, the amide motif might behave as a directing group towards the metal-catalyzed C-H bond activation in the benzamide site or in the anilide site. The impact and the consequences of such subtle control of site-selectivity are herein reviewed with important applications in carbon-carbon and carbon-heteroatom bond forming processes. The mechanisms unraveling these unique transformations are discussed in order to provide a better understanding for future developments in the field of site-selective C-H bond functionalization with transition metal catalysts.

Ru(II)-Catalyzed C-H Hydroxyalkylation and Mitsunobu Cyclization of N-Aryl Phthalazinones

Ruthenium(II)-catalyzed C(sp²)-H functionalization of N-aryl phthalazinones with a range of aldehydes and activated ketone is described. Initial formation of hydroxyalkylated phthalazinones and subsequent Mitsunobu cyclization provided facile access to biologically relevant indazolophthalazinones. The utility of this method is highlighted by synthetic transformations into a series of potentially bioactive scaffolds.

Direct oxidative coupling of N-acyl pyrroles with alkenes by ruthenium(ii)-catalyzed regioselective C2-alkenylation

Ruthenium(ii)-catalyzed oxidative coupling by C2-alkenylation of N-acyl pyrroles with alkenes has been described. The acyl unit was found to be an effective chelating group for the activation of aryl C-H bonds ortho to the directing group. The alkenylation reaction of benzoyl pyrroles occurred regioselectively at the C2-position of the pyrrole ring, without touching the benzene ring. The reaction provides exclusively monosubstituted pyrroles under the optimized conditions. Disubstituted pyrroles could be obtained using higher loadings of the ruthenium(ii)-catalyst and the additives.

Revisiting the mechanism of the Fujiwara–Moritani reaction

A new perspective of the Fujiwara–Moritani reaction is presented, including its kinetic profile and catalyst deactivation studies.