Metal-Free Construction of the C(sp3)-CF3 Bond: Trifluoromethylation of Hydrazones with Togni's Reagent under Mild Conditions

Stereoselective Reductive Coupling Reactions Utilizing [1,2]-Phospha-Brook Rearrangement: A Powerful Umpolung Approach

[1,2]-Phospha-Brook rearrangement entails the generation of α-oxygenated carbanions via the umpolung process. Recently, these anionic species have been widely utilized for several C-C bond forming strategies, providing various useful frameworks that are difficult to access through conventional approaches. However, the application of this powerful methodology in the development of chiral strategies is still at the nascent stage due to challenges involved in controlling chemoselectivity and enantioselectivity. This synopsis provides a detailed summary of diastereo- and/or enantioselective chemical transformations using [1,2]-phospha-Brook rearrangement.

HOME-Chemistry: hydrazone as organo-metallic equivalent

The modern synthetic chemistry heavily relies on the use of stoichiometric organometallic reagents to react with various electrophiles. The dependence on stoichiometric quantities of metals and often organic halides as precursors, in turn both produces copious amounts of metal halide wastes as well as leads to concerns on future metal sustainability. Inspired by the classical Wolff-Kishner reduction, our lab has recently developed a general strategy of HOME-Chemistry , directly using naturally abundant alcohols/aldehydes and ketones as feedstocks with the releasing of innocuous water and nitrogen gas. These reactions include 1,2-carbonyl/imine addition, conjugate addition, carboxylation, olefination, cross-coupling arylation/allylation, alkylation, hydroalkylation and C-heteroatom formations. This article provides a brief summary on this chemistry.

Copper-Catalyzed Thiolation of Hydrazones with Sodium Sulfinates: A Straightforward Synthesis of Benzylic Thioethers

A facile and sustainable protocol for the thiolation of hydrazones with sodium sulfinates has been developed in the presence of CuBr₂ and DBU in DMF to afford diverse benzylic thioethers. Control experiments reveal a radical pathway involving a thiyl radical as a key intermediate.

Visible Light Promotes Cascade Trifluoromethylation/Cyclization, Leading to Trifluoromethylated Polycyclic Quinazolinones, Benzimidazoles and Indoles

Efficient visible-light-induced radical cascade trifluoromethylation/cyclization of inactivated alkenes with CF₃Br, which is a nonhygroscopic, noncorrosive, cheap and industrially abundant chemical, was developed in this work, producing trifluoromethyl polycyclic quinazolinones, benzimidazoles and indoles under mild reaction conditions. The method features wide functional group compatibility and a broad substrate scope, offering a facile strategy to pharmaceutically produce valuable CF₃-containing polycyclic aza-heterocycles.

Trifluoromethylation of Carbonyl and Unactivated Olefin Derivatives by C(sp3 )-C Bond Cleavage

Herein, we report a Cu-mediated trifluoromethylation of carbonyl-type compounds and unactivated olefins enabled by visible-light irradiation via σ C(sp³ )-C bond-functionalization. The reaction is distinguished by its modularity, mild conditions and wide scope-even in the context of late-stage functionalization-thus offering a complementary approach en route to valuable C(sp³ )-CF₃ architectures from easily accessible precursors.

Visible-light-induced cross-coupling of aryl iodides with hydrazones via an EDA-complex

A visible-light-induced, transition-metal and photosensitizer-free cross-coupling of aryl iodides with hydrazones was developed. In this strategy, hydrazones were used as alternatives to organometallic reagents, in the absence of a transition metal or an external photosensitizer, making this cross-coupling mild and green. The protocol was compatible with a variety of functionalities, including methyl, methoxy, trifluoromethyl, halogen, and heteroaromatic rings. Mechanistic investigations showed that the association of the hydrazone anion with aryl halides formed an electron donor–acceptor complex, which when excited with visible light generated an aryl radical via single-electron transfer.

Visible-light-induced catalyst-free cross-coupling of aryl iodides with hydrazones via single-electron-transfer was reported. The mechanistic investigations showed that the association of hydrazone anion with aryl iodides formed an EDA complex.

Deoxygenative Functionalizations of Aldehydes, Ketones and Carboxylic Acids

Conversion of carbonyl compounds, including aldehydes, ketones and carboxylic acids, into functionalized alkanes via deoxygenation would be highly desirable from a sustainability perspective and very enabling in chemical synthesis. This review covers the recent methodology development in carbonyl and carboxyl deoxygenative functionalizations, highlighting some typical and significant contributions in this field. These advances will be categorized based on types of bond formation, and in each part, selected examples will be discussed from their generalized mechanistic perspectives. Four summarized reactivity modes of aldehydes and ketones during the deoxygenation, namely, bis-electrophile, carbenoid, bis-nucleophile and alkyl radical, are presented, while the carboxylic acids are deoxygenated mainly via activated carbonyl or acetal intermediates.

Carbonyl umpolung as an organometallic reagent surrogate

Construction of new carbon-carbon bonds is the cornerstone of organic chemistry. Organometallic reagents are amongst the most robust and versatile nucleophiles for this purpose. Polarization of the metal-carbon bonds in these reagents facilitates their reactions with a vast array of electrophiles to achieve chemical diversification. The dependence on stoichiometric quantities of metals and often organic halides as feedstock precursors, which in turn produces copious amounts of metal halide waste, is the key limitation of the classical organometallic reactions. Inspired by the classical Wolff-Kishner reduction converting carbonyl groups in aldehydes or ketones into methylene derivatives, our group has recently developed strategies to couple various alcohols, aldehydes, and ketones with a broad range of both hard and soft carbon electrophiles in the presence of catalytic amounts of transition metals, via the hydrazone derivatives: i.e., as organometallic reagent surrogates. This Tutorial Review describes the chronological development of this concept in our research group, detailing its creation in the context of a deoxygenation reaction and evolution to a more general carbon-carbon bond-forming strategy. The latter is demonstrated by the employment of carbonyl-derived alkyl carbanions in various transition-metal catalyzed chemical transformations, including 1,2-carbonyl/imine addition, conjugate addition, carboxylation, olefination, cross-coupling, allylation, alkylation and hydroalkylation.

Structure-based design, synthesis, and biological evaluation of novel piperine-resveratrol hybrids as antiproliferative agents targeting SIRT-2

A series of novel piperine–resveratrol hybrids 5a–h was designed, synthesized, and structurally elucidated by IR, and ¹H, ¹³C, and ¹⁹F NMR. Antiproliferative activities of 5a–h were evaluated by NCI against sixty cancer cell lines. Compound 5b, possessing resveratrol pharmacophoric phenolic moieties, showed a complete cell death against leukemia HL-60 (TB) and Breast cancer MDA-MB-468 with growth inhibition percentage of −0.49 and −2.83, respectively. In addition, 5b recorded significant activity against the other cancer cell lines with growth inhibition percentage between 80 to 95. New 5a–h hybrids were evaluated for their inhibitory activities against Sirt-1 and Sirt-2 as molecular targets for their antiproliferative action. Results showed that compounds 5a–h were more potent inhibitors of Sirt-2 than Sirt-1 at 5 μm and 50 μm. Compound 5b showed the strongest inhibition of Sirt-2 (78 ± 3% and 26 ± 3% inhibition at 50 μM and 5 μM, respectively). Investigation of intermolecular interaction via Hirschfeld surface analysis indicates that these close contacts are mainly ascribed to the O–H⋯O hydrogen bonding. To get insights into the Sirt-2 inhibitory mechanism, a docking study was performed where 5b was found to fit nicely inside both extended C-pocket and selectivity pocket and could compete with the substrate acyl-Lys. Another possible binding pattern showed that 5b could act by partial occlusion of the NAD⁺ C-pocket. Collectively, these findings would contribute significantly to better understanding the Sirt-2 inhibitory mechanism in order to develop a new generation of refined and selective Sirt-2 inhibitors.

A series of novel piperine–resveratrol hybrids 5a–h was designed, synthesized, and structurally elucidated by IR, and ¹H, ¹³C, and ¹⁹F NMR.

Umpolung Difunctionalization of Carbonyls via Visible-Light Photoredox Catalytic Radical-Carbanion Relay

The combination of photoredox catalysis with the Wolff-Kishner (WK) reaction allows the difunctionalization of carbonyl groups by a radical-carbanion relay sequence (photo-Wolff-Kishner reaction). Photoredox initiated radical addition to N-sulfonylhydrazones yields α-functionalized carbanions following the WK-type mechanism. With sulfur-centered radicals, the carbanions are further functionalized by reaction with electrophiles including CO2 and aldehydes, whereas CF3 radical addition furnishes a wide range of gem-difluoroalkenes through β-fluoride elimination of the generated α-CF3 carbanions. More than 80 substrate examples demonstrate the broad applicability of this reaction sequence. A series of investigations including radical inhibition, deuterium labeling, fluorescence quenching, cyclic voltammetry, and control experiments support the proposed radical-carbanion relay mechanism.

A metal-free visible-light-promoted phosphorylation/cyclization reaction in water towards 3-phosphorylated benzothiophenes

A metal-free visible-light-induced phosphorylation/cyclization reaction was developed in water at room temperature for the synthesis of 3-phosphorylated benzothiophenes.