Photoinduced Oxidation of Secondary Alcohols Using 4-Benzoylpyridine as an Oxidant

Oxidative Cleavage of Csp3-Csp2 and Csp3-H Bonds with KOtBu: Highly Robust and Practical Synthesis of Diaryl/(het-Ar) Ketones

Herein, we report an efficient and practical approach for synthesizing diaryl(het) ketones from R-CO-CHR-Ar through a simultaneous oxidative cleavage of C-C and C-H bonds using KO^tBu. This method enables synthesizing a variety of unsymmetrical and symmetrical (hetero)aryl ketones in excellent yields, which are otherwise difficult to make. Besides, we synthesized natural products using this method.

Electrochemical Aerobic Oxidative Cleavage of (sp3)C-C(sp3)/H Bonds in Alkylarenes

An electrochemistry-promoted oxidative cleavage of (sp³)C-C(sp³)/H bonds in alkylarenes was developed. Various aryl alkanes can be smoothly converted into ketones/aldehydes under aerobic conditions using a user-friendly undivided cell setup. The features of air as oxidant, scalability, and mild conditions make them attractive in synthetic organic chemistry.

Photocatalytic, site-selective oxidations of carbohydrates

Site-selective oxidations of carbohydrates, employing acridinium photocatalysis and quinuclidine hydrogen atom transfer catalysis, are presented. Protocols have been developed for oxidations of all-equatorial carbohydrates as well as those containing cis-1,2-diols. Site-selectivity reflects the relative rates of hydrogen atom transfer from the carbohydrate C-H bonds, and can be enhanced using a phosphate hydrogen-bonding or boronic acid catalyst.

Neutral-Eosin-Y-Photocatalyzed Silane Chlorination Using Dichloromethane

Chlorosilanes are versatile reagents in organic synthesis and material science. A mild pathway is now reported for the quantitative conversion of hydrosilanes to silyl chlorides under visible-light irradiation using neutral eosin Y as a hydrogen-atom-transfer photocatalyst and dichloromethane as a chlorinating agent. Stepwise chlorination of di- and trihydrosilanes was achieved in a highly selective fashion assisted by continuous-flow micro-tubing reactors. The ability to access silyl radicals using photocatalytic Si-H activation promoted by eosin Y offers new perspectives for the synthesis of valuable silicon reagents in a convenient and green manner.

Synthesis of Alkylated Pyrimidines via Photoinduced Coupling Using Benzophenone as a Mediator

The synthesis of alkylated pyrimidines was achieved via benzophenone-mediated photoinduced coupling between saturated heterocycles and sulfonylpyrimidines. The pyrimidine ring was selectively introduced at the nonacidic C(sp³)-H bond proximal to heteroatoms including oxygen, nitrogen, and sulfur. This is a coupling reaction mediated solely by photoexcited benzophenone, an organic molecule, without the aid of any metallic catalysts or reagents.

An Unexpected Controlled New Oxidant: SO4(·-)

A controlled new oxidant sulfate radical anion (SO₄^.–) was found and it can be easily prepared by mixing Na₂S₂O₄ and TBHP with stirring. In this new metal-free oxidation system (Na₂S₂O₄/TBHP), SO₄^.– can be used as a controllable oxidant to oxidize various aromatic alcohols to the corresponding aldehydes in good yields without any acid formation at room temperature. SO₄^.– was determined by a DMPO (5,5-dimethyl-1-pyrroline-N-oxide) spin-trapping EPR method at room temperature on a Bruker E500 spectrometer and the results suggested that SO₄^.– was generated in this transformation.

Base metal-catalyzed benzylic oxidation of (aryl)(heteroaryl)methanes with molecular oxygen

The methylene group of various substituted 2- and 4-benzylpyridines, benzyldiazines and benzyl(iso)quinolines was successfully oxidized to the corresponding benzylic ketones using a copper or iron catalyst and molecular oxygen as the stoichiometric oxidant. Application of the protocol in API synthesis is exemplified by the alternative synthesis of a precursor to the antimalarial drug Mefloquine. The oxidation method can also be used to prepare metabolites of APIs which is illustrated for the natural product papaverine. ICP-MS analysis of the purified reaction products revealed that the base metal impurity was well below the regulatory limit.

Radical-mediated dehydrogenation of bile acids by means of hydrogen atom transfer to triplet carbonyls

The aim of the present paper is to explore the potential of radical-mediated dehydrogenation of bile salts (BSs), which is reminiscent of the enzymatic action of hydroxysteroid dehydrogenase enzymes (HSDH).