Gold-Catalyzed One-Pot Synthesis of Polyfluoroalkylated Oxazoles from N-Propargylamides Under Visible-Light Irradiation

Activation of metal-involved halogen bonds and classical halogen bonds in gold(I) catalysis

In gold(I) catalysis, the activation of Au(I) chloride catalysts via chloride abstraction and noncovalent interactions has become a research focus in organometallic catalysis. In this work, taking halogen bond donors (C₄H₂INO₂, C₆F₅I, C₈H₉O₂I) as activators for a Au(I) chloride catalyst (Ph₃PAuCl), the mechanism of the cyclization reaction of propargylic amide was investigated. It was found that there are two activation modes as design principles to obtain the catalytically active species Ph₃PAu⁺: the halogen bond donors activate the Cl atoms of Ph₃PAuCl to form X-I⋯Cl (X = C, N) classical halogen bonds and activate the Au atoms of Ph₃PAuCl to form X-I⋯Au (X = C, N) metal-involved halogen bonds. For the two activation modes, the mechanism of the cyclization reaction of propargylic amide has pathways: the chloride abstraction process of the first step and the 5-exo/6-endo cyclization process of the second step. Both activation modes show good activity for the cyclization reaction with the activation ability of classical halogen bonds being slightly stronger than that of the metal-involved halogen bonds, which is consistent with the strength of the X-I⋯Cl halogen bonds being slightly stronger than that of the X-I⋯Au halogen bonds. Therefore, both metal-involved halogen bonds and classical halogen bonds have important development prospects for the activation of catalysts in gold(I) catalysis.

Visible light-induced carbene reactivity of acceptor diazoalkanes: deconstructive difunctionalizations of cyclic ethers with nucleophiles

A visible light-induced carbene reactivity of acceptor diazoalkanes has been developed for the synthesis of difunctionalized ethers from cyclic ethers and various N/O/S nucleophiles.

Photocatalytic Regioselective Difunctionalization of Alkenes with Diazo Compounds and tert-Butyl Nitrite: Access to γ-Oximino Esters

A visible-light photocatalytic regioselective difunctionalization of alkenes with diazo compounds and tert-butyl nitrite has been developed. The protocol provides an efficient approach to γ-oximino esters under mild conditions. Significantly, this transformation not only shows the good compatibility of nucleophilic diazo compounds and electrophilic tert-butyl nitrite but also displays diazo compounds generating alkyl radicals that preferred addition to alkenes over nitroso radicals.

Visible Light-Promoted Radical-Mediated Ring-Opening/Cyclization of Vinyl Benzotriazoles: An Alternative Approach to Phenanthridines

A visible light-promoted radical-mediated ring-opening/cyclization of vinyl benzotriazoles has been developed. The method provides an efficient and practical approach to synthesize functionalized phenanthridines from vinyl benzotriazoles with alkyl bromides under mild conditions. Significantly, the readily available and bench-stable vinyl benzotriazoles can serve as valuable alternative radical acceptors during the synthesis of phenanthridines.

Visible Light-Promoted Diazoacetates and Nitriles Generating Nitrilium Ions Trapped by Benzotriazoles and Carboxylic Acids

A visible light-promoted generation of nitrilium ions from diazoacetates and nitriles has been developed. The reaction utilized visible light transformation of diazoacetates to the free carbene that could be trapped by nitriles to generate nitrilium ions, followed by nucleophilic attack on the benzotriazoles and carboxylic acids. This protocol provides an efficient and practical approach to N-imidoylbenzotriazoles and diacylglycine esters in good to excellent yields.

Palladium-Catalyzed Carbonylative [5+1] Cycloaddition of N-Tosyl Vinylaziridines: Solvent-Controlled Divergent Synthesis of α,β- and β,γ-Unsaturated δ-Lactams

A palladium-catalyzed carbonylative [5+1] cycloaddition of N-tosyl vinylaziridines with CO has been developed. This protocol affords an efficient and practical approach for solvent-controlled divergent synthesis of α,β-unsaturated δ-lactams in dimethylformamide and β,γ-unsaturated δ-lactams in tetrahydrofuran in good to excellent yields. Significantly, the step- and atom-economical reactions are more regioselective toward [5+1] cycloaddition than toward [3+1] cycloaddition.

Visible-Light-Induced 1,6-Enynes Triggered C-Br Bond Homolysis of Bromomalonates: Solvent-Controlled Divergent Synthesis of Carbonylated and Hydroxylated Benzofurans

Visible-light-induced 1,6-enyne-triggered C-Br bond homolysis of bromomalonates has been developed. This transition-metal-free, photocatalyst-free, and oxidant- and additive-free protocol affords an efficient approach for divergent synthesis of carbonylated and hydroxylated benzofurans from 1,6-enynes and bromomalonates under mild conditions. Significantly, mechanistic studies reveal that the homolysis of C-Br bonds appears to experience an energy-transfer pathway, and the atom-transfer radical addition products are the key intermediates to generate carbonylated and hydroxylated benzofurans.

Reactivity of Vinyl Epoxides/Oxetanes/Cyclopropanes toward Arynes: Access to Functionalized Phenanthrenes

The reactivity of vinyl epoxides/oxetanes/cyclopropanes toward arynes has been demonstrated under mild conditions to give the corresponding phenanthrenes in moderate to good yields. This transition-metal-free cascade process involves a series of Diels-Alder reaction, ring-opening aromatization, and ene reaction. Various functionalized phenanthrenes could be synthesized utilizing the versatile hydroxy group. Interestingly, vinyl epoxides/oxiranes experience preferentially the Diels-Alder reaction toward arynes over nucleophilic attack of epoxides/oxiranes.

Merging Gold/Copper Catalysis and Copper/Photoredox Catalysis: An Approach to Alkyl Oxazoles from N-Propargylamides

Here, we report a mild and highly efficient approach to alkyl oxazoles through merging gold/copper catalysis and copper/photoredox catalysis. Various alkyl oxazoles are synthesized from N-propargylamides with alkyl halides in good to excellent yields with wide functional-group compatibility under blue-light irradiation. Significantly, a copper catalyst plays a dual role in this transformation: as a powerful cocatalyst to accelerate protodeauration of vinyl gold intermediates and improve photoredox catalysis.