Iron-Catalyzed Oxidative Radical Cross-Coupling/Cyclization between Phenols and Olefins

Benzothiadiazole-Based Ordered Mesoporous Polymer as a Versatile, Metal-Free Heterogeneous Photocatalyst

Visible-light active heterogeneous organophotocatalysts have recently gained considerable interest in organic synthetic community. Ordered mesoporous polymers (OMPs) are highly promising as heterogeneous alternative to traditional precious metal/organic dyes-based photocatalysts. Herein, we report the preparation of a benzothiadiazole functionalized OMPs (BT-MPs) through a "bottom-up" strategy. High ordered periodic porosity, large surface area, excellent stability and rational energy-band structures guarantee the high catalytic activity of BT-MPs. As a result, at least six conversions, e. g., the [3+2] cycloaddition of phenols with olefins, the selective oxidation of sulfides, the C-3 thiocyanation of indole and the aminothiocyanation of β-keto ester, could be promoted smoothly by BT-MPs. In addition, BT-MPs was readily recovered with well maintaining its photocatalytic activity and could be reused for at least eight times. This study highlights the potential of exploiting photoactive OMPs as recyclable, robust and metal-free heterogeneous photocatalysts.

Mechanistic Study on AgI-Catalyzed Oxidative Cross-Coupling/Cyclization between Terminal Alkynes and β-Enamino Esters under Base Conditions

A combined computational and experimental study was performed to elucidate the mechanism of the Ag^I-catalyzed oxidative cross-coupling/cyclization of terminal alkynes with β-enamino esters. The results indicated a more favorable Ag^I/Ag⁰-catalyzed radical mechanism (than cationic mechanism) which involves three key stages: (i) the initiation of radical species, (ii) the cyclization, and (iii) the formal 1,2-H shift. Meanwhile, the Ag^I species was found to be the active initiator for the delocalized nitrogen radical species generation, and Ag₂CO₃ acts as an effective oxidant to initiate the β-enamino ester radical formation. Furthermore, it was shown that the silver acetylide is the key intermediate in the title reaction and that the coordination of solvent dimethyl sulfoxide (DMSO) regulates the electronic properties of the Ag center better as compared with base 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), thereby enhancing the negative charge of the reaction sites and promoting the cyclization process. Finally, the DBU was revealed to play a key role in the final 1,2-H shift process through the formation of [DBU-H]⁺, acting as a proton shuttle to assist the proton migration process. The theoretical results provide key insights into the Ag^I/Ag⁰-catalyzed radical mechanism and guidelines for further development of Ag-catalyzed synthetic methods.

Concise Synthesis of Polysubstituted Carbohelicenes by a C-H Activation/Radical Reaction/C-H Activation Sequence

Disclosed herein is the merging of C-H activation and radical chemistry, enabling rapid access to a structurally diverse family of fused carbohelicenes through the fusion of α-acetylnaphthalenes with alkynes under oxidative conditions. This cascade process exhibits exquisite chemoselectivity and regioselectivity. The reaction pathway was analyzed by intermediate separations, control experiments, radical trapping, EPR, MALDI-TOF-MS, and ESI-HRMS experiments, and shown to involve a C2-H activation/radical reaction/C8-H activation relay.

Copper/P(tBu)3 -Mediated Regiospecific Synthesis of Fused Furans and Naphthofurans

A novel [3+2] cycloaddition between a variety of cyclic ketones and diverse olefins or alkynes can be effectively promoted by copper in combination with the tri-tert-butylphosphine [P(tBu)₃ ] ligand. This protocol exhibits excellent selectivity and provides an exemplary set of fused heterocycles in good to excellent yields. Present strategy also represents an extremely simple and atom-economic way to construct substituted fused furans and naphthofurans from readily available starting materials under mild reaction conditions. The utility of the method is further demonstrated by the synthesis of chiral furans from (R)-(-)-carvone and (S)-(+)-carvone. A plausible mechanism involving the oxidative radical cyclization has been suggested based on experimental observations.

A Catalyst-Controlled Aerobic Coupling of ortho-Quinones and Phenols Applied to the Synthesis of Aryl Ethers

ortho-Quinones are underutilized six-carbon-atom building blocks. We herein describe an approach for controlling their reactivity with copper that gives rise to a catalytic aerobic cross-coupling with phenols. The resulting aryl ethers are generated in high yield across a broad substrate scope under mild conditions. This method represents a unique example where the covalent modification of an ortho-quinone is catalyzed by a transition metal, creating new opportunities for their utilization in synthesis.

Direct oxidative coupling of N-acetyl indoles and phenols for the synthesis of benzofuroindolines related to phalarine

Inspired by the biogenetic synthesis of benzofuroindoline-containing natural products, we designed an oxidative coupling between phenol and N-acetyl indoles. This straightforward and direct radical process, mediated by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone and FeCl3 allowed the regioselective synthesis of benzofuro[3,2-b]indolines, whose structure is found in the natural product phalarine.