PPh3O as an Activating Reagent for One-Pot Stereoselective Syntheses of Di- and Polybrominated Esters from Simple Aldehydes

Selective 1,1- and 1,2-dibromination of phenylethanes in the presence of NaBr/NaBrO3/H2SO4 as the bromination reagent

Selective 1,1- and 1,2-dibromination of phenylethanes by simply adjusting the reaction conditions has been developed. Mixtures of NaBr/NaBrO3/H2SO4 are employed as green bromination reagents, which can release Br2 or BrOH in situ as required without polluting the environment. Both the resulting 1,1- and 1,2-dibromoethyl arenes can be easily transformed to phenylacetylenes via elimination under basic conditions, demonstrating great potential for industrial applications.

Enantioselective anti-Dihalogenation of Electron-Deficient Olefin: A Triplet Halo-Radical Pylon Intermediate

The textbook alkene halogenation reaction establishes straightforward access to vicinal dihaloalkanes. However, a robust catalytic method for dihalogenizing electron-deficient olefins in an enantioselective manner is still under development, and its mechanism remains controversial. Herein, we disclose efficient regio-, anti-diastereo-, and enantioselective dibromination, bromochlorination, and dichlorination reactions of enones catalyzed by a chiral N,N'-dioxide/Yb(OTf)₃ complex. With the combination of electrophilic halogen and halide salts as halogenating agents, an array of homo- and heterodihalogenated derivatives is achieved in moderate to good enantioselectivities. Moreover, DFT calculations reveal that a novel triplet halo-radical pylon intermediate is probable in accounting for the exclusive regio- and anti-diastereoselectivity.

Mo-Catalyzed One-Pot Synthesis of N-Polyheterocycles from Nitroarenes and Glycols with Recycling of the Waste Reduction Byproduct. Substituent-Tuned Photophysical Properties

A catalytic domino reduction-imine formation-intramolecular cyclization-oxidation for the general synthesis of a wide variety of biologically relevant N-polyheterocycles, such as quinoxaline- and quinoline-fused derivatives, and phenanthridines, is reported. A simple, easily available, and environmentally friendly dioxomolybdenum(VI) complex has proven to be a highly efficient and versatile catalyst for transforming a broad range of starting nitroarenes involving several redox processes. Not only is this a sustainable, step-economical as well as air- and moisture-tolerant method, but also it is worth highlighting that the waste byproduct generated in the first step of the sequence is recycled and incorporated in the final target molecule, improving the overall synthetic efficiency. Moreover, selected indoloquinoxalines have been photophysically characterized in cyclohexane and toluene with exceptional fluorescence quantum yields above 0.7 for the alkyl derivatives.

Modular synthesis of chiral 1,2-dihydropyridines via Mannich/Wittig/cycloisomerization sequence that internally reuses waste

1,2-Dihydropyridines are valuable and reactive synthons, and particularly useful precursors to synthesize piperidines and pyridines that are among the most common structural components of pharmaceuticals. However, the catalytic enantioselective synthesis of structurally diverse 1,2-dihydropyridines is limited to enantioselective addition of nucleophiles to activated pyridines. Here, we report a modular organocatalytic Mannich/Wittig/cycloisomerization sequence as a flexible strategy to access chiral 1,2-dihydropyridines from N-Boc aldimines, aldehydes, and phosphoranes, using a chiral amine catalyst. The key step in this protocol, cycloisomerization of chiral N-Boc δ-amino α,β-unsaturated ketones recycles the waste to improve the yield. Specifically, recycling by-product water from imine formation to gradually release the true catalyst HCl via hydrolysis of SiCl₄, whilst maintaining a low concentration of HCl to suppress side reactions, and reusing waste Ph₃PO from the Wittig step to modulate the acidity of HCl. This approach allows facile access to enantioenriched 2-substituted, 2,3- or 2,6-cis-disubstituted, and 2,3,6-cis-trisubstituted piperidines.

A General Method for the Dibromination of Vicinal sp3 C-H Bonds Exploiting Weak Solvent-Substrate Noncovalent Interactions

A general procedure of 1,2-dibromination of vicinal sp³ C-H bonds of arylethanes using N-bromosuccinimide as the bromide reagent without an external initiator has been established. The modulation of the strength of the intermolecular noncovalent interactions between the solvent and arylethane ethanes, quantitatively evaluated via quantum chemical calculations, allows us to circumvent the fact that arylethane ethane cannot be dibrominated through traditional methods. The mechanism was explored by both experiments and quantum chemical calculations, revealing a radical chain with HAA process.

Catalytic selective mono- and difluoroalkylation using fluorinated silyl enol ethers

This feature article highlights our recent achievements in catalytic selective mono- and difluoroalkylation using fluorinated silyl enol ethers (FSEEs).

Identification and Structure-Activity Relationship (SAR) of potent and selective oxadiazole-based agonists of sphingosine-1-phosphate receptor (S1P1)

Agonism of S1P₁ receptor has been proven to be responsible for peripheral blood lymphopenia and elicts the identification of various S1P₁ modulators. In this paper we described a series of oxadiazole-based S1P₁ direct-acting agonists disubstituted on terminal benzene ring, with high potency for S1P₁ receptor and favorable selectivity against S1P₃ receptor. In addition, two representative agents named 16-3b and 16-3g demonstrated impressive efficacy in lymphocyte reduction along with reduced effect on heart rate when orally administered. Furthermore, these compounds have been shown to possess desired pharmacokinetic (PK) and physicochemical profiles. The binding mode between 16-3b and the activated S1P₁ model was also studied.

Experimental and computational studies on H2O-promoted, Rh-catalyzed transient-ligand-free ortho-C(sp2)–H amidation of benzaldehydes with dioxazolones

We develop an efficient and convenient ligand-free, rhodium-catalyzed ortho-C(sp²)–H amidation of benzaldehydes with dioxazolones using H₂O as the key promoter.

Directed C–C bond cleavage of a cyclopropane intermediate generated fromN-tosylhydrazones and stable enaminones: expedient synthesis of functionalized 1,4-ketoaldehydes

An efficient method to construct functionalized 1,4-ketoaldehydes bearing all-carbon α-quaternary centersviaregioselective C–C bond activation has been described.

Organoselenium-catalyzed vicinal dichlorination of unsaturated phosphonates

An efficient organoselenium-catalyzed vicinal dichlorination of unsaturated phosphonates was developed under mild conditions.