Photoinduced Metal- and Photosensitizer-Free Decarbonylative C-H Alkylation of Cyclic Sulfamidate Imines

Condensation of carboxylic acids with amines using the Boc2O/DMAP system under solvent-free conditions

The present study describes the use of the di-tert-butyl dicarbonate (Boc2O)/4-(N,N-dimethylamino)pyridine (DMAP) system for the amidation of carboxylic acids under neat conditions without heating. A set of carboxylic acids was explored, such as non-steroidal anti-inflammatory drugs (NSAIDs), fatty acids and protected prolines in the presence of aromatic, benzylic and aliphatic amines as nucleophilic partners. The scope of this easy approach was extended to the preparation of thirty-two diverse carboxylic amides, which were recovered with isolated yields varying from moderate to excellent. To increase the value of this protocol, a scalable chemoselective amidation of oleic acid with ethanolamine was successfully established. The corresponding fatty carboxylic amide, N-oleoylethanolamide (OEA), was recovered with 73% yield. This study highlights the potency of the use of mixed anhydrides formed in situ and the pursuit of the reaction profile reveals sequential steps rather than a one-pot process.

Solvent-controlled silver catalyzed radical transformation of α-imino-oxy acids with cyclic aldimines

A silver-catalyzed cross coupling of cyclic aldimines and α-imino-oxy acids has been developed. The solvent-dependent reaction could selectively deliver either cyclic imine moiety retained nitriles or ring-opened oxonitriles in moderate yields. The mechanistic studies show that the reaction undergoes a radical pathway.

CeCl3-Catalyzed C-H Alkylation of N-Sulfonyl Ketimines with Alkanes and Ether via Photoinduced Ligand-to-Metal Charge Transfer

A cerium-catalyzed C-H alkylation of N-sulfonyl ketimines with low-cost and readily available alkanes as alkyl sources was developed. This transformation proceeded through the synergy of photoinitiated ligand-to-metal charge transfer (LMCT) using a chlorine radical as an HAT reagent and air as a green oxidant. A series of alkylated N-sulfonyl ketimines were synthesized with moderate to good yields in a highly atom-economic manner under chemical oxidant-free conditions.

Self-Catalyzed Sono-Photoinduced Arylation of Quinoxalin-2(1H)-ones with Arylhydrazines

Herein, the first example of self-catalyzed sono-photoinduced carbon-carbon bond formation was described. Combining the advantages of phototriggered self-catalysis and ultrasonic catalysis, a wide range of 3-arylquinoxalin-2(1H)-ones can be efficiently synthesized in good yields with high functional-group compatibility under mild and eco-friendly conditions.

Photocatalyst-free light-promoted carbohydrate synthesis and modification

Photoredox catalysis has recently emerged as a powerful approach for preparing oligosaccharides because it uses mild conditions, is compatible with partially or completely unprotected carbohydrate substrates, and exhibits impressive regio- and stereo-selectivity and high functional group tolerance. However, most catalytic photoredox reactions require an external photocatalyst (organic dye or expensive transition-metal complex) to deliver key glycosyl radicals. Several photocatalyst-free photocatalytic reactions that avoid the use of expensive metal salts or organic-dye additives have received significant attention. In this review, we highlight the most recent developments in photocatalyst-free light-promoted carbohydrate synthesis and modification, which is expected to inspire broad interest in further innovations in the green synthesis of saccharides.

COAP-Pd Catalyzed Asymmetric Formal [3+2] Cycloaddition for Optically Active Multistereogenic Spiro Cyclopentane-Indandiones Bearing Cyclic N-Sulfonyl Ketimine Skeletons

We reported a chiral oxamide-phosphine ligand (COAP-Ph)-Pd-catalyzed asymmetric [3+2] cycloaddition reaction between vinyl cyclopropane compounds derived from 1,3-indanedione and 2-vinylcyclopropane-1,1-dicarboxylates with cyclic sulfonyl 1-azadienes. The corresponding reactions provided a series of enantiomerically active spiro cyclopentane-indandione and cyclopentane structures bearing three consecutive stereogenic centers in good yields with good diastereo- and enantioselectivity. The COAP-Pd complex serves not only to promote generation of chiral π-allyl-palladium intermediates and induce the asymmetry of the reaction, but also depress the background reaction.

Organophotoelectrocatalytic C(sp2)-H alkylation of heteroarenes with unactivated C(sp3)-H compounds

An organophotoelectrocatalytic method for the C(sp2)-H alkylation of heteroarenes with unactivated C(sp3)-H compounds through dehydrogenation cross-coupling has been developed. The C(sp2)-H alkylation combines organic catalysis, photochemistry and electrochemistry, avoiding the need for external metal-reagents, HAT-reagents, and oxidants. This protocol exhibits good substrate tolerance and functional group compatibility, providing a straightforward and powerful pathway to access a variety of alkylated heteroarenes under green conditions.

Organocatalyzed Photoelectrochemistry for the Generation of Acyl and Phosphoryl Radicals through Hydrogen Atom-Transfer Process

An organocatalyzed photoelectrochemical method for the generation of acyl and phosphoryl radicals from formamides, aldehydes, and phosphine oxides has been developed. This protocol utilizes 9,10-phenanthrenequinone (PQ) as both a molecular catalyst and a hydrogen atom-transfer (HAT) reagent, eliminating the requirement for external metal-based reagents, HAT reagents, and oxidants. The generated acyl radicals can be applied to a range of radical-mediated transformation reactions, including C-H carbamoylation of heteroarenes, intermolecular tandem radical cyclization of CF3-substituted N-arylacrylamides, as well as intramolecular cyclization reactions. The use of acyl radicals in these transformations offers an efficient and sustainable approach to accessing structurally diverse carbonyl compounds.

Light-Driven Access to Selenium-Substituted Thiazole-2-imine Derivatives

The thiazole-2-imine derivatives with interesting pharmacological activities have attracted significant attention. However, previously reported synthesis strategies usually suffered from some drawbacks, such as the use of metals/additive and harsh reaction conditions. Herein, we developed a metal- and photoinitiator-free photocatalytic strategy for the synthesis of various selenium-substituted thiazole-2-imine derivatives for the first time. The reaction displayed mild reaction conditions, simple operation, a broad substrate scope (37 examples), and good to excellent yields.

Photodriven Radical-Polar Crossover Cyclization Strategy: Synthesis of Pyrazolo[1,5-a]pyridines from Diazo Compounds

This work demonstrates the synthesis of a variety of perfluoroalkyl heterocycles via a visible-light-driven radical-polar crossover cyclization strategy. In this process, single-electron reduction/SNV-type/cyclization sequences follow the radical addition reaction of a diazoester, which differs from the current role of diazoesters as radical precursors/acceptors. This transformation demonstrates excellent functional group compatibility and allows for the modification of many bioactive molecules with diazoesters. Such a reaction could represent a novel approach to the photochemical transformation of diazo compounds.