CdS Quantum Dot Gels as a Direct Hydrogen Atom Transfer Photocatalyst for C-H Activation.

Here, we report CdS quantum dot (QD) gels, a three-dimensional network of interconnected CdS QDs, as a new type of direct hydrogen atom transfer (d-HAT) photocatalyst for C-H activation. We discovered that the photoexcited CdS QD gel could generate various neutral radicals, including α-amido, heterocyclic, acyl, and benzylic radicals, from their corresponding stable molecular substrates, including amides, thio/ethers, aldehydes, and benzylic compounds. Its C-H activation ability imparts a broad substrate and reaction scope. The mechanistic study reveals that this reactivity is intrinsic to CdS materials, and the neutral radical generation did not proceed via the conventional sequential electron transfer and proton transfer pathway. Instead, the C-H bonds are activated by the photoexcited CdS QD gel via a d-HAT mechanism. This d-HAT mechanism is supported by the linear correlation between the logarithm of the C-H bond activation rate constant and the C-H bond dissociation energy (BDE) with a Brønsted slope α = 0.5. Our findings expand the currently limited direct hydrogen atom transfer photocatalysis toolbox and provide new possibilities for photocatalytic C-H activation.

Revisiting Alternating Current Electrolysis for Organic Synthesis.

This review summarizes the recent advancements in alternating current (AC)-driven electroorganic synthesis since 2021 and discusses the reactivities AC electrolysis provides to achieve new and unique organic transformations.

Quantum dot gels as efficient and unique photocatalysts for organic synthesis.

Here we report CdS quantum dot (QD) gels as highly efficient and unique photocatalysts for organic synthesis. We found that the photocatalytic activity of CdS QD gel was superior to phosphine oxide- and thiolate-capped CdS QDs for dehalogenation and α-amine arylation reactions because of the high accessibility of its surface sites to the substrates. In addition, we discovered the unique reactivity of CdS QD gel for ring-opening during α-amine arylation of tetrahydroisoquinoline via the reductive cleavage of C-N bonds. QD gels provide new opportunities in photocatalysis due to their unique surface interactions with the substrates or intermediates.

DBU-Mediated Addition of α-Nitroketones to α-Cyano-enones and α,ß-Unsaturated α-Ketoesters: Synthesis of Dihydrofurans and Conjugated Dienes.

1,8-Diazabicyclo[5.4.0]undec-7-ene-mediated reactions of α-nitroketones with α-cyano-enones and α,ß-unsaturated α-ketoesters have been developed. The products, namely, dihydrofurans and conjugated dienes, were isolated in moderate to good yields, and a range of substitutions were tolerated.

α-Nitro-α,ß-Unsaturated Ketones: An Electrophilic Acyl Transfer Reagent in Catalytic Asymmetric Friedel-Crafts and Michael Reactions.

Herein, we introduce α-nitro-α,ß-unsaturated ketones as efficient electrophilic acyl transfer reagents, and they were employed in Friedel-Crafts as well as in Michael reactions. The desired acyl transfer products of these reactions were obtained in high yields with high to excellent enantioselectivities with t-leucine-derived squaramide catalyst under mild reaction conditions. Few applications including a synthesis of the isoxazoline motif have been demonstrated.

Highly Diastereo- and Enantioselective Synthesis of Spiro-tetrahydrofuran-pyrazolones via Organocatalytic Cascade Reaction between γ-Hydroxyenones and Unsaturated Pyrazolones.

The first diastereo- and enantioselective synthesis of spiro-tetrahydrofuran-pyrazolones is reported via organocatalytic asymmetric cascade oxa-Michael/Michael reaction between γ-hydroxyenones and unsaturated pyrazolones. Bifunctional squaramide catalyst was found to be effective for this reaction. With 10 mol % of catalyst, excellent results were attained for a variety of spiropyrazolones under mild reaction conditions.

Organocatalytic asymmetric Michael/hemiacetalization/acyl transfer reaction of α-nitroketones with o-hydroxycinnamaldehydes: synthesis of 2,4-disubstituted chromans.

An organocatalytic asymmetric cascade Michael/hemiketalization/acyl transfer reaction between o-hydroxycinnamaldehydes and α-nitroketones is developed. Prolinol TMS ether catalyst in combination with benzoic acid was found to be the most effective for this reaction which proceeds through an equilibrium of lactols to provide a single diastereomer of enantiopure 2,4-disubstituted chromans.

Enantioselective aminocatalytic synthesis of tetrahydropyrano[2,3-c]pyrazoles via a domino Michael-hemiacetalization reaction with alkylidene pyrazolones.

An enantioselective organocatalytic domino Michael-hemiacetalization reaction between alkylidene pyrazolones and cyclic ketones/pentanal has been revealed. The fused tetrahydropyranopyrazole products having three contiguous stereocentres were obtained with perfect diastereoselectivities and in moderate to good yields with good to high enantioselectivities. Also, few synthetic transformations of the product including the formation of a spiro derivative have been demonstrated.

Organocatalytic Asymmetric Michael/Hemiketalization/Retro-aldol Reaction of α-Nitroketones with Unsaturated Pyrazolones: Synthesis of 3-Acyloxy Pyrazoles.

An organocatalytic asymmetric cascade Michael/hemiketalization/retro-aldol reaction between unsaturated pyrazolones and α-nitroketones is described. A bifunctional thiourea catalyst was found to be efficient for this reaction. With 10 mol % of catalyst, high yields as well as excellent enantioselectivities are attained for a variety of 3-acyloxy pyrazoles under mild reaction conditions.

Organocatalytic asymmetric intramolecular aza-Henry reaction: facile synthesis of trans-2,3-disubstituted tetrahydroquinolines.

An enantio- and diastereoselective organocatalytic intramolecular aza-Henry (nitro-Mannich) reaction has been developed. The trans-2-aryl-3-nitro-tetrahydroquinoline products are obtained in high yields and in good enantioselectivities with a bifunctional tertiary amine-thiourea catalyst. Excellent enantioselectivities were obtained after single recrystallization of some products.