Regioselective ortho-hydroxylation of 2-arylbenzothiazole via substrate directed C–H activation

Microwave-Assisted Ru(II)-Catalyzed Regioselective Methyl Acylation of 2-Arylbenzoazoles: Synthesis of Benzofuran Conjugates via C-H Activation/Annulation

An efficient Ru(II)-catalyzed C-H functionalization protocol for 2-arylbenzoazoles as the directing group and sulfoxonium ylide has been developed. Gratifyingly, concomitant annulation was observed when 3-(benzo[d]azol-2-yl) phenol was used, enabling the construction of benzofuran conjugates. Notably, the utilization of water as the solvent and an energy efficient approach makes the reaction greener, contributing to overall sustainability. This protocol exhibits excellent scalability up to the gram scale with a diverse array of substitutions. Furthermore, the mechanism was examined by ESI-MS, and photophysical studies were also performed.

Synthesis of Organosulfur and Related Heterocycles under Mechanochemical Conditions

In the last few decades, ball-milling has received tremendous attention as a "green tool" for conducting various challenging organic transformations under transition-metal-free and solvent-free conditions. Organosulfur and related heterocycles are ubiquitous in numerous biologically active molecules with potential applications, and those molecules could be synthesized from readily available starting materials under mechanochemical conditions without using any hazardous chemical or solvent. This synopsis highlights the green strategies developed in recent times to synthesize organosulfur and related heterocycles under ball-milling conditions.

Palladium-Catalyzed Weakly Coordinating Lactone-Directed C-H Bond Functionalization of 3-Arylcoumarins: Synthesis of Bioactive Coumestan Derivatives

A palladium-catalyzed highly regioselective ortho-selective C-H functionalization of 3-arylcoumarins has been developed. The method utilizes the weakly coordinating lactone as a directing group. The versatility of the strategy is highlighted by developing methodologies for alkenylation, halogenation, fluoroalkoxylation, and hydroxylation. Different functional groups were well tolerated, and functionalized coumarins were obtained in moderate to high yields. The method also showed good selectivity for monofunctionalization versus difunctionalization. The generated ortho-hydroxy derivatives were cyclized in the presence of DDQ, thus developing a simple and fast method for the synthesis of bioactive coumestan from 3-arylcoumarins.

Palladium-Catalyzed Regiospecific peri- and ortho-C-H Oxygenations of Polyaromatic Rings Mediated by Tunable Directing Groups

An efficient divergent approach of Pd-catalyzed C-H oxygenation of polyaromatic rings is described. Reversible directing groups enable regiospecific peri- and ortho-oxygenation to readily access a wide array of polyaromatic phenols without pre- and postmanipulation of directing groups. The systematic mechanistic investigation, including deuterium-labeling experiments, palladacycle trapping, and DFT calculations, reveals that the tunable ligand-assisted C-H bond cleavage played a crucial role during the reaction process.

Recent Advances in the Synthesis and Applications of 2-Arylbenzothiazoles

This review firstly covers the applications of 2-arylbenzothiazoles as amyloid imaging agents, antitumor agents, and organic luminescent materials. Then we review the recent advances in the synthesis of 2-arylbenzothiazole derivatives. On the one hand, we introduce the approaches for construction of the 2-arylbenzothiazole core, including the following categories: (i) classic condensation of 2-aminothiophenols, (ii) direct arylation of benzothiazoles, (iii) intramolecular cyclization of thiobenzanilides, and (iv) tandem cyclization of anilines/ nitroarenes­ with elemental sulfur or sulfides. On the other hand, the transition-metal-catalyzed direct C–H functionalizations of 2-aryl­benzothiazoles are also involved in this review.

1 Introduction

2 Applications of 2-Arylbenzothiazoles

3 Construction of the 2-Arylbenzothiazole Core

4 Synthesis 2-Arylbenzothiazoles via Direct C–H Functionalization

5 Conclusion

Copper Salts/TBAB-Catalyzed Chemo- and Regioselective β-C(sp3)-H Acyloxylation of Aliphatic Amides

An efficient Cu(II)-catalyzed and tetrabutylammonium bromide (TBAB)-promoted strategy for highly regioselective and chemoselective C(sp³)-H acyloxylation of aliphatic amides is described. Acyloxylation occurs selectively at the β position with a broad substrate scope of carboxylic acids and aliphatic amides and good functional group compatibility. Notably, the competing reaction of intramolecular dehydrogenative amidation and intermolecular acyloxylation could be efficiently controlled by the amount of copper salt and the addition of TBAB. The intramolecular dehydrogenative amidation product was obtained in high yield when the amount of copper salts was increased. However, when TBAB was used as an additive, a preference for acyloxylation over intramolecular amidation was observed and the acyloxylated products were obtained in good yield. Preliminary studies were carried out to gain insights into the mechanism.

Ruthenium(II)-Catalyzed Regioselective C-8 Hydroxylation of 1,2,3,4-Tetrahydroquinolines

Ru(II)-catalyzed chelation-assisted highly regioselective C8-hydroxylation of 1,2,3,4-tretrahydroquinolines has been developed. Various 1,2,3,4-tetrahydroquinolines underwent smooth C8-H hydroxylation with cheap and safe K₂S₂O₈ as the oxidant and oxygen source to furnish the corresponding products in good to excellent yields with high tolerance of the functional groups. The choice of a readily installable and removable N-pyrimidyl directing group is the key to catalysis. Mechanistic studies suggest the involvement of a six-membered ruthenacycle intermediate in the catalytic cycle. The method can also be extended to the direct hydroxylation of other (hetero)arene C-H bonds.

Effects of intramolecular hydrogen bonding and sterically forced non-coplanarity on organic donor/acceptor two-photon-absorbing molecules

Excited-state decay rate constant is controlled by hydrogen bonding, which is switched from intramolecular to intermolecular by choice of solvent.

Transition-metal-catalyzed synthesis of phenols and aryl thiols

Phenols and aryl thiols are fundamental building blocks in organic synthesis and final products with interesting biological activities. Over the past decades, substantial progress has been made in transition-metal-catalyzed coupling reactions, which resulted in the emergence of new methods for the synthesis of phenols and aryl thiols. Aryl halides have been extensively studied as substrates for the synthesis of phenols and aryl thiols. In very recent years, C-H activation represents a powerful strategy for the construction of functionalized phenols directly from various arenes. However, the synthesis of aryl thiols through C-H activation has not been reported. In this review, a brief overview is given of the recent advances in synthetic strategies for both phenols and aryl thiols.

A diversity-oriented synthesis of bioactive benzanilides via a regioselective C(sp2)-H hydroxylation strategy

A diversity-oriented synthesis of bioactive benzanilides via C(sp2)-H hydroxylation has been studied. Different regioselectivity was observed with Ru(ii) and Pd(ii) catalysts. The reaction demonstrates excellent regioselectivity, good tolerance of functional groups, and high yields. A wide range of ortho-hydroxylated-benzanilides can be readily synthesized with excellent regioselectivity via this new synthetic strategy. Computational investigations revealed that the regioselectivity was controlled mainly by both steric and electronic factors. Steric effects determine the regioselective outcomes in the Ru-catalyzed reaction, while electronic effects are dominant in the Pd-catalyzed reaction.

Advances in Synthetic Applications of Hypervalent Iodine Compounds

The preparation, structure, and chemistry of hypervalent iodine compounds are reviewed with emphasis on their synthetic application. Compounds of iodine possess reactivity similar to that of transition metals, but have the advantage of environmental sustainability and efficient utilization of natural resources. These compounds are widely used in organic synthesis as selective oxidants and environmentally friendly reagents. Synthetic uses of hypervalent iodine reagents in halogenation reactions, various oxidations, rearrangements, aminations, C-C bond-forming reactions, and transition metal-catalyzed reactions are summarized and discussed. Recent discovery of hypervalent catalytic systems and recyclable reagents, and the development of new enantioselective reactions using chiral hypervalent iodine compounds represent a particularly important achievement in the field of hypervalent iodine chemistry. One of the goals of this Review is to attract the attention of the scientific community as to the benefits of using hypervalent iodine compounds as an environmentally sustainable alternative to heavy metals.

Palladium catalyzed ortho-halogenation of 2-arylbenzothiazole and 2,3-diarylquinoxaline

A Pd-catalysed mono and di-o-halogenation strategy has been demonstrated selectively using benzothiazoles and quinoxalines as the directing substrates.

Palladium catalyzed Csp2–H activation for direct aryl hydroxylation: the unprecedented role of 1,4-dioxane as a source of hydroxyl radicals

Direct aryl hydroxylation has been achieved via palladium-catalysed C_sp2–H activation using versatile directing groups through unprecedented hydroxyl transfer from 1,4-dioxane.