Visible Light-Mediated Direct C-H Aroylation and Alkylation of Heteroarenes

BPO-promoted [4 + 2] cyclization of enaminones and o-phenylenediamines to 2-acyl quinoxalines via a cascade transamination and C-H amination

Rapid assembly of quinoxalines in a single step from readily available precursors has been recognized as an ideal platform in terms of efficiency and operation. Herein, we report a BPO-promoted metal-free approach to 2-acyl quinoxalines from enaminones and o-phenylenediamines via cascade transamination and C-H amination. This methodology demonstrates excellent compatibility with various substrates, including o-hydroxy enaminones, drug derivatives and natural products under mild reaction conditions.

Organo-photoredox-Catalyzed Selective Mono- and Bis-C-H Alkylation of Electron-Rich (Hetero)Arenes

Herein, we disclose a simple strategy for the C-H alkylation of electron-rich (hetero)arenes with alkyl bromides employing visible-light-mediated organo-photocatalytic SET processes. The generality of this method has been evidenced by the inclusion of a variety of alkyl radicals (α-alkyl-carbonyl, benzyl, cyanomethyl) as well as diverse biologically active electron-rich arenes and (hetero)arenes under mild conditions. The extent of alkylation with alkyl bromides was found to be controlled by introducing Zn(OAc)2 as a bromide scavenger, ensuring the blocking of potential bromo-arene byproduct formation under photoredox conditions. In addition, a sequential C-H alkylation strategy for selective bis-alkylation has also been developed via chronological incorporation of different alkyl radical precursors in one pot quite efficiently.

Photoredox Minisci-Type Hydroxyfluoroalkylation of Isoquinolines with N-Trifluoroethoxyphthalimide

A straightforward photocatalytic approach has been demonstrated to incorporate a trifluoroethanol unit onto the isoquinolines. Herein, we report N-trifluoroethoxyphthalimide as a hydroxyfluoroalkyl radical precursor, enabling efficient synthesis of trifluoroethanol-substituted heteroarenes. Radical quenching experiments confirmed the involvement of a free-radical pathway under developed photocatalytic conditions. The DFT calculations confirmed the intramolecular 1,2-HAT reactivity of the O-centered trifluoroethoxy radical (generated from N-trifluoroethoxyphthalimide under photocatalytic condition) to the C-centered trifluoroethanol radical. Fluorescence quenching studies suggested that isoquinoline was responsible for the quenching of Ir-photocatalyst emission. A catalytic cycle involving trifluoroethanol radical reaction with isoquinolines has been proposed.

Organic-acid catalysed Minisci-type arylation of heterocycles with aryl acyl peroxides

A metal-free method for the Minisci-type arylation of heterocycles with aryl acyl peroxides has been reported. This strategy enables the rapid and simple synthesis of a series of Minisci-type adducts...

Photo-Induced Cross-Dehydrogenative Alkylation of Heteroarenes with Alkanes under Aerobic Conditions

We report a Minisci-type cross-dehydrogenative alkylation in an aerobic atmosphere using abundant and inexpensive cerium chloride as a photocatalyst and air as an oxidant. This photoreaction exhibits excellent tolerance to functional groups and is suitable for both heteroarene and alkane substrates under mild conditions, generating the corresponding products in moderate-to-good yields. Our method provides an alternative approach for the late-stage functionalization of valuable substrates.

Alkyl Halides as Substrates for Photocatalytic Minisci-Type C–H Alkylation of Hetarenes

Alkyl halides are readily available starting materials for various synthetic transformations, including Minisci-type C–H functionalizations of hetarenes. The existing methods, however, often require harsh reaction conditions, such as the use of acids, sacrificial electron donors, or radical precursors in excess amounts. Here, we outline recent developments in this field and we highlight our group̓s efforts to achieve fully catalytic photoredox Minisci-type alkylations supported by noncovalent interactions under mild aqueous conditions.

Ag-Catalyzed Remote Unactivated C(sp3)-H Heteroarylation of Free Alcohols in Water

Catalyzed by silver salt, the unactivated C(sp³)-H heteroarylation of free alcohol at the δ position is realized under gentle thermal conditions in water through a radical procedure. Both protonic acids and Lewis acids are found to be efficient for activating pyridines for this Minisci-type reaction. The reaction enjoys a good functional group tolerance and substrate scope. Terminal secondary and tertiary alcohols are suitable substrates. With either electron-donating or -withdrawing groups, the electron-deficient heteroarene substrates generate the target products in moderate to good yields. A gram-scale experiment can be successfully operated. A radical blocking experiment and a radical clock experiment are studied to support the radical mechanism.

Minisci aroylation of N-heterocycles using choline persulfate in water under mild conditions

A modified Minisci aroylation of isoquinoline using arylglyoxylic acids in the presence of choline persulfate or pre-composition (choline acetate and K2S2O8) in water at ambient temperature affording aroylated isoquinolines is reported.