Supported-amine-catalyzed cascade synthesis of spiro-thiazolone-tetrahydrothiophenes: assessing HSA binding activity

We have devised a supported-amine-catalyzed efficient synthesis of spiro-thiazolone-tetrahydrothiophenes via a sulfa-Michael/aldol cascade approach. The catalyst demonstrated sustained efficacy over 21 cycles. These derivatives were found to exhibit excellent binding abilities with purified human serum albumin as indicated by both in silico and in vitro-based experiments.

α-Functionalisation of Cyclic Sulfides Enabled by Lithiation Trapping

A general and straightforward procedure for the lithiation trapping of cyclic sulfides such as tetrahydrothiophene, tetrahydrothiopyran and a thiomorpholine is described. Trapping with a wide range of electrophiles is demonstrated, leading to more than 50 diverse α-substituted saturated sulfur heterocycles. The methodology provides access to a range of α-substituted cyclic sulfides that are not easily synthesised by the currently available methods.

(Thiolan-2-yl)diphenylmethanol Benzyl Ether-Catalyzed Asymmetric Cyclopropanation of Chalcones

We devised a new method for asymmetric cyclopropanation by employing (S)-(thiolan-2-yl)diphenylmethanol benzyl ether as an organocatalyst. Under optimal conditions, an in situ generated sulfur ylide reacts with (E)-chalcones via a Johnson-Corey-Chaykovsky reaction to afford a variety of cyclopropanes in excellent yields and stereoselectivities. This strategy employs low-environmental-risk reaction conditions and reusable catalysts. Hence, it is a green and efficient method for constructing cyclopropane scaffolds.

Multifunctional Catalysts in the Asymmetric Mannich Reaction of Malononitrile with N-Phosphinoylimines: Coactivation by Halogen Bonding versus Hydrogen Bonding

A multifunctional (noncovalent) catalyst containing halogen-bond donor, hydrogen-bond donor, and Lewis basic sites was developed and applied in an enantioselective Mannich reaction between malononitrile and diphenylphosphinoyl-protected aldimine affording products in high yields (up to 98%) and moderate to high enantiomeric purities (ee up to 89%). Typically, noncovalent catalysts rely on several weak interactions to activate the substrate, with one or two of these giving the most notable contribution to activation. In this instance, instead of the initially proposed coactivation by halogen bonding, it was revealed that hydrogen bonding plays a key role in determining the enantioselectivity.

Stereoselective synthesis of tri-substituted tetrahydrothiophenes and their in silico binding against mycobacterial protein tyrosine phosphatase B

A facile approach to tri-substituted tetrahydrothiophenes via thia-Michael/aldol has been developed. The cascade reaction was carried out in the presence of 5 mol% of DABCO in ethyl acetate to afford diversely functionalized tetrahydrothiophenes (THTs) with excellent diastereoselectivity. The present methodology has broad substrate tolerance. Gram-scale reaction proceeds with equal efficiency. Functional group transformations further highlight the synthetic potential of the THTs. An asymmetric version of the cascade reaction has also been investigated and a maximum of 72% ee was observed with cinchonidine derived squaramide. Moreover, in silico based molecular docking followed by deep learning based affinity prediction and molecular dynamics simulation analysis indicate the synthesized THT derivatives can act as potent competitive inhibitors of MptpB at low micromolar to nanomolar concentrations. In silico ADME analysis further suggests the plausibility of these compounds to act as future anti-mycobacterial therapeutic leads.

Oxathiaborolium-catalyzed enantioselective [2 + 2] cycloadditions

The one-pot-prepared oxathiaborolium pentachlorostannate is an excellent Lewis acid and is successfully used to catalyze the [2 + 2] cycloadditions of N-substituted maleimides and silyl enol ethers with excellent enantioselectivities.

Organoselenium-Catalyzed Asymmetric Cyclopropanations of (E)-Chalcones

We report a new class of chiral tetrahydroselenophene based on (S)-diphenyl(tetrahydroselenophen-2-yl)methanol, which was prepared from (R)-3-(3-bromopropyl)-2,2-diphenyloxirane and sodium selenide. These chiral tetrahydroselenophene-based compounds were used to catalyze asymmetric cyclopropanation reactions; the selenonium ylide intermediates formed from these selenium-containing catalysts and benzyl bromide efficiently react with (E)-chalcones to give various cyclopropanes (27 examples) with excellent enantioselectivities of ≤99% ee and are the first examples of organoselenium-catalyzed asymmetric cyclopropanations.

Oxathiaborolium-Catalyzed Enantioselective [4 + 2] Cycloaddition and Its Application in Lewis Acid Coordinated and Chiral Lewis Acid Catalyzed [4 + 2] Cycloaddition

The nascency of second-generation sulfur-stabilized borenium cations by halophilic Lewis acid SnCl₄ leads to highly active chiral Lewis acids that are very effective catalysts for [4 + 2] cycloaddition. Oxathiaborolium pentachlorostannate (5-10 mol %) successfully catalyzed cycloaddition of various dienes and dienophiles to afford cycloadducts with excellent enantioselectivity (20 examples, up to 99% ee). This super Lewis acid also exhibited good enantioselectivity for the first Lewis acid coordinated and chiral Lewis acid catalyzed [4 + 2] cycloaddition to α,β-unsaturated mixed ester amide.

Chiral bifunctional sulfide-catalyzed asymmetric bromoaminocyclizations

A BINOL-derived chiral bifunctional sulfide catalyst bearing a phenylurea moiety was applied to enantioselective bromoaminocyclization reactions of 2-allylaniline derivatives, which provide optically active 2-substituted indoline products as important motifs for biologically active compounds. A protecting group on the nitrogen of the 2-allylaniline substrate was carefully optimized, and highly enantioselective reactions were achieved by employing the p-biphenylsulfonyl-protected substrates. The origin of the good level of enantioselectivity for the present bromoaminocyclization was also investigated on the basis of DFT calculations. The resultant optically active 2-(bromomethyl)indoline products could be transformed to various 2-substituted indolines with no loss of the optical purity.

Sulfur-Mediated Allylic C-H Arylation, Epoxidation, and Aziridination

Transition-metal-free, sulfur-mediated allylic C-H arylation, epoxidation, and aziridination were realized through one-pot procedures. The reaction design involved initial addition between olefins and triflic anhydride activated sulfoxides, followed by subsequent reactions of the allylic sulfur ylides generated under basic conditions with arylboronic acids, aldehydes, or aldimines, to give allylic arylation, epoxidation, or aziridination products, respectively.

Iron-Catalyzed Asymmetric Nitro-Mannich Reaction

The first enantioselective addition of nitroalkanes to imines (nitro-Mannich reaction), mediated by an iron(II) catalyst assembled by a hindered hydroxyethyl-pybox ligand, is described. This valuable carbon-carbon bond-forming reaction proceeds smoothly at room temperature to afford enantioenriched β-nitro amines in good yields and high enantioselectivity, up to 98% with unprecedentedly low iron catalyst loading (5 mol %).

An unprecedented base-promoted domino reaction of methyleneindolinones and N-tosyloxycarbamates for the construction of bispirooxindoles and spiroaziridine oxindoles

An efficient and unprecedented domino reaction of methyleneindolinones andN-tosyloxycarbamates was realized to construct bispirooxindoles and spirooxindole aziridines.

Yb(OTf)3 catalyzed [3 + 2] annulations of D–A cyclopropanes with β-oxodithioesters: a regioselective synthesis of tetrahydrothiophenes

An efficient approach to synthesis tetrahydrothiophenes was developed through the reaction of β-oxodithioesters and D–A cyclopropanes catalyzed by Yb(OTf)₃. This methodology was highly regioselective.