Catalytic Asymmetric Transfer Hydrogenation of Acylboronates: BMIDA as the Privileged Directing Group.

Developing a general, highly efficient, and enantioselective catalytic method for the synthesis of chiral alcohols is still a formidable challenge. We report in this article the asymmetric transfer hydrogenation (ATH) of N-methyliminodiacetyl (MIDA) acylboronates as a general substrate-independent entry to enantioenriched secondary alcohols. ATH of acyl-MIDA-boronates with (het)aryl, alkyl, alkynyl, alkenyl, and carbonyl substituents delivers a variety of enantioenriched α-boryl alcohols. The latter are used in a range of stereospecific transformations based on the boron moiety, enabling the synthesis of carbinols with two closely related α-substituents, which cannot be obtained with high enantioselectivities using direct asymmetric hydrogenation methods, such as the (R)-cloperastine intermediate. Computational studies illustrate that the BMIDA group is a privileged enantioselectivity-directing group in Noyori-Ikariya ATH compared to the conventionally used aryl and alkynyl groups due to the favorable CH-O attractive electrostatic interaction between the η6-arene-CH of the catalyst and the σ-bonded oxygen atoms in BMIDA. The work expands the domain of conventional ATH and shows its huge potential in addressing challenges in symmetric synthesis.

Asymmetric Transfer Hydrogenation of Cyclobutenediones.

Four-membered carbocycles are fundamental substructures in bioactive molecules and approved drugs and serve as irreplaceable building blocks in organic synthesis. However, developing efficient protocols furnishing diversified four-membered ring compounds in a highly regio-, diastereo-, and enantioselective fashion remains challenging but very desirable. Here, we report the unprecedented asymmetric transfer hydrogenation of cyclobutenediones. The reaction can selectively afford three types of four-membered products in high yields with high stereoselectivities, and the highly functionalized products enable a series of further transformations to form more diversified four-membered compounds. Asymmetric synthesis of di-, tri-, and tetrasubstituted bioactive molecules has also been achieved. Systematic mechanistic studies and theoretical calculations have revealed the origin of the regioselectivity, the key hydrogenation transition state models, and the sequence of the double and triple hydrogenation processes. The work provides a new choice for the catalytic asymmetric synthesis of cyclobutanes and related structures and demonstrates the robustness of asymmetric transfer hydrogenation in the accurate selectivity control of highly functionalized substrates.

Copper-Catalyzed Umpolung Reactivity of Propargylic Carbonates in the Presence of Diboronates: One Stone Four Birds.

Allylation and propargylation are two powerful synthetic strategies for making new substances that have been of significant importance in chemistry, medicine, and material fields. Conventional tactics employ various preformed allylation and propargylation reagents. In this study, a conceptually novel copper-catalyzed and B2pin2-mediated Umpolung reactivity of propargylic carbonates has been achieved for the first time, realizing both allylation and propargylation of aldehydes and ketones without additional reductants. Three types of allylation products and one type of propargylation product are generated efficiently, and all allylation products are formed with syn-configurations predominantly. The choice of ligands plays a vital role in modulating the Umpolung modes. The synthetic applications have been demonstrated in a myriad of further transformations including natural product synthesis, and systematic mechanistic studies have been conducted to reveal detailed insights into the Umpolung processes.

Copper-Catalysed Rearrangement of Cyclic Ethynylethylene Carbonates: Synthetic Applications and Mechanistic Studies.

Transition-metal-catalysed reactions of cyclic ethynylethylene carbonates have been intensively studied because of their robustness in new bond formation and diversified molecule construction. Known reaction modes usually involve a substitution step occurring at either the propargylic or terminal alkyne positions. Here, we report an unprecedented reaction pattern in which cyclic ethynylethylene carbonates first undergo a rearrangement to release allenal intermediates, which subsequently react with diverse nucleophiles to furnish synthetically useful allylic and propargylic allenols, phosphorus ylides, and cyclopropylidene ketones through an addition process rather than a substitution pathway. The products enable various further transformations, and mechanistic studies and theoretical calculations reveal that the reaction does not proceed via a semipinacol type [1,2]-hydride shift, but through base-mediated deprotonation as the key step to induce the rearrangement.

Dynamic Kinetic Resolution of ß-Substituted α-Diketones via Asymmetric Transfer Hydrogenation.

Developing innovative dynamic kinetic resolution (DKR) modes and achieving the highly regio- and enantioselective semihydrogenation of unsymmetrical α-diketones are two formidable challenges in the field of contemporary asymmetric (transfer) hydrogenation. In this work, we report the highly regio- and stereoselective asymmetric semi-transfer hydrogenation of unsymmetrical α-diketones through a unique DKR mode, which features the reduction of the carbonyl group distal from the labile stereocenter, while the proximal carbonyl remains untouched. Moreover, the protocol affords a variety of enantioenriched acyclic ketones with α-hydroxy-α'-C(sp2)-functional groups, which represent a new product class that has not been furnished in known arts. The utilities of the products have been demonstrated in a series of further transformations including the rapid synthesis of drug molecules. Density functional theory calculations and plenty of control experiments have also been conducted to gain more mechanistic insights into the highly selective semihydrogenation.

Oxa-Nazarov Cyclization-Michael Addition Sequence for the Rapid Construction of Dihydrofuranones.

The Nazarov cyclization has been established as a powerful tool in constructing cyclopentenone skeletons. In sharp contrast, oxa-Nazarov cyclization that affords dihydrofuranones, a new type of product, has been less explored. In this work, we report the I2-catalyzed oxa-Nazarov cyclization-Michael addition cascade between vinyl α-diketones and enones. The protocol allows access to a range of functionalized dihydrofuranones with good to high yields, and diverse further transformations on the products have been achieved. Furthermore, the mechanistic studies reveal that the 1,2-hydride shift occurs simultaneously during the dihydrofuranone formation.

Access to enantioenriched compounds bearing challenging tetrasubstituted stereocenters via kinetic resolution of auxiliary adjacent alcohols.

Contemporary asymmetric catalysis faces huge challenges when prochiral substrates bear electronically and sterically unbiased substituents and when substrates show low reactivities. One of the inherent limitations of chiral catalysts and ligands is their incapability in recognizing prochiral substrates bearing similar groups. This has rendered many enantiopure substances bearing several similar substituents inaccessible. Here we report the rationale, scope, and applications of the strategy of kinetic resolution of auxiliary adjacent alcohols (KRA*) that can be used to solve the above troubles. Using this method, a large variety of optically enriched tertiary alcohols, epoxides, esters, ketones, hydroxy ketones, epoxy ketones, ß-ketoesters, and tetrasubstituted methane analogs with two, three, and four spatially and electronically similar groups can be readily obtained (totally 96 examples). At the current stage, the strategy serves as the optimal solution that can complement the inability caused by direct asymmetric catalysis in getting chiral molecules with challenging fully substituted stereocenters.

N-Heterocyclic Carbene-Catalyzed Asymmetric Synthesis of Cyclopentenones.

N-Heterocyclic carbene-catalyzed asymmetric construction of cyclopentenones using enals and α-diketones is achieved, furnishing a series of highly functionalized cyclopentenones in a highly diastereo- and enantioselective manner. The protocol tolerates substrates with both aromatic and aliphatic groups, and further transformations of the products delivered a range of value-added molecules.

Mechanistic Studies on N-Heterocyclic Carbene-Catalyzed Umpolung of ß,γ-Unsaturated α-Diketones.

The mechanism of N-heterocyclic carbene-catalyzed umpolung of ß,γ-unsaturated α-diketone was studied using both density functional theory (DFT) calculations and experimental methods. In contrast to the originally proposed mechanism, the calculations revealed a more complicated process involving both nucleophilic O-acylated homoenolate and electrophilic α,ß-unsaturated acyl azolium intermediates. The experimental studies confirmed the existence of the aforementioned two key intermediates. A revised mechanism has been proposed to demonstrate the detailed mechanistic insights into the product formation.

Ti(OiPr)4-Facilitated Formal Deoxygenative Annulation of Alkynyl 1,2-Diketones for the Synthesis of Highly Functionalized Furans.

A unique deoxygenative cyclodimerization of alkynyl 1,2-diketones facilitated by Ti(OiPr)4 is achieved, affording a series of highly functionalized furan products. An unusual C-C bond and C═O bond cleavage of the substrates is observed, and Ti(OiPr)4 plays triplicate roles in the reaction. Furthermore, the products show uncommon fluorescent emission in the solid state, indicating the potential practical applications of this work.

Divergent Synthesis of Bicyclo[3.2.1]octenes and Cyclohexenes via Catalytic Annulations of Nazarov Reagent and Vinyl 1,2-Diketones.

Bicyclo[3.2.1]octanes and related structures are unique units that widely exist in natural products, but the rapid and stereoselective construction of this skeleton is a challenging issue. We report the stereodivergent synthesis of bicyclo[3.2.1]octenes using Nazarov reagents and alkenyl 1,2-diketones with Brønsted base catalysis under mild conditions. Both stereoisomers of the bridged products can be obtained by tuning the reaction conditions, and cyclohexene product can also be selectively formed.

Lewis-Acid-Catalyzed Asymmetric Alkynylation of Alkynyl 1,2-Diketones: Controllable Formation of 3(2H)-Furanones and α-Hydroxy Ketones.

We report the highly regio- and enantioselective alkynylation of alkynyl 1,2-diketones under Lewis acid catalysis, leading to the formation of a series of biologically important 3(2H)-furanones with high to excellent ee values. Moreover, a slight change of the reaction conditions produces a range of highly functionalized α-hydroxy ketones with a high level of enantioselectivity. A variety of further transformations can be easily achieved, demonstrating the synthetic potential of this protocol.

Catalytic Annulation of Alkynyl 1,2-Diketone Leading to Hydroxy Spirocyclopenteneindenedione: An Organic Dye with Strong Crystallization-Induced Emission and Data Storage Application.

An unprecedented cascade annulation between alkynyl 1,2-diketones and indene-1,3-diones is achieved for the first time, leading to a series of propeller-like large conjugated compounds in ≤99% yield. The products show strong crystallization-induced emission, with the colors changing from green to red. The fluorescence of the dye can be switched on and off by external acid/alkali stimuli, which can be utilized to develop a practical technology for rewritable information storage and security ink.

Regioselectivity-Switchable Catalytic Annulations of Alkynyl α-Diketones and α-Cyanoketones.

Regioselectivity-switchable reactions hold irreplaceable importance in the construction of diversified architectures. In this work, Brønsted base-catalyzed regioselectivity-switchable annulations between alkynyl α-diketones and α-cyanoketones have been achieved for the first time, delivering a series of skeletally thoroughly different dihydrofurofuran and furan derivatives. A range of novel transformations of the products can be realized. The work also demonstrates the unique features of alkynyl α-diketone chemistry, which are in sharp contrast to the current understanding of ynone-related chemistry.

Stereodivergent Access to Enantioenriched Epoxy Alcohols with Three Stereogenic Centers via Ruthenium-Catalyzed Transfer Hydrogenation.

The resolution technique of stereodivergent reaction on racemic mixtures (stereodivergent RRM) was employed for the first time in ruthenium complex catalyzed transfer hydrogenation of racemic epoxy ketones, providing a new and very simple method that allows access to enantioenriched epoxy alcohols with three stereogenic centers in a one-step fashion. The protocol features simple reaction conditions, practical operation, ability to scale up, and broad group tolerance.

Trifluoperazine as an alternative strategy for the inhibition of tumor growth of colorectal cancer.

The development of cancer in patients with schizophrenia is affected by genetic and environmental factors and antipsychotic medication. Several studies found that schizophrenia was associated with decreased risk of some cancers, and the neuroleptic medication might help to reduce the risk of colorectal cancer (CRC). Phenothiazine drugs including trifluoperazine (TFP) are widely used antipsychotic drugs and showed some antitumor effects, we here investigated the potential application of TFP in the treatment of colon cancer. A series doses of TFP were treated to the colon cancer cell line HCT116 and the inhibitory concentration (IC50 ) of TFP for HCT116 was determined by cell counting kit-8. The results indicated that the treatment of TFP impaired the cell vitality of HCT116 in a dose- and time-dependent manner. Meanwhile, the Edu assay demonstrated that the proliferation was also inhibited by TFP, which was accompanied with the induction of apoptosis and autophagy. The expression of CCNE1, CDK4, and antiapoptosis factor BCL-2 was downregulated but the proapoptosis factor BAX was upregulated. The autophagy inhibitor chloroquine could significantly reverse the TFP-induced apoptosis. Moreover, the ability of migration and invasion of HCT116 was found to be suppressed by TFP, which was associated with the inhibition of epithelial-mesenchymal transition (EMT). The function of TFP in vivo was further confirmed. The results showed that the administration of TFP remarkably abrogated the tumor growth with decreased tumor volume and proliferation index Ki-67 level in tumor tissues. The EMT phenotype was also confirmed to be inhibited by TFP in vivo, suggesting the promising antitumor effects of TFP in CRC.

Bifunctional Thiourea-Catalyzed Asymmetric Inverse-Electron-Demand Diels-Alder Reaction of Allyl Ketones and Vinyl 1,2-Diketones via Dienolate Intermediate.

Inverse-electron-demand Diels-Alder reactions have attracted intense research focus. However, enolate and enamine are the most employed intermediates to realize such transformation, and the use of dienolate intermediate remains elusive. Reported herein is the asymmetric inverse-electron-demand oxa-Diels-Alder reaction between allyl ketones and alkenyl 1,2-diketones using a bifunctional thiourea catalyst. The reaction afforded various highly functionalized dihydropyrans with good to excellent enantioselectivities under mild conditions, and further novel transformations on the products have also been realized.

Kinetic resolution of ß-ketoesters with quaternary stereocenters via a carbene-catalyzed benzoin reaction.

Chiral ß-ketoesters bearing fully substituted carbon centers are important building blocks in organic synthesis. Mono-substituted ketoesters have been widely used to synthesize the above compounds through asymmetric additions or substitutions. The limitations of these protocols mainly exist in the substrate scopes, and α-methyl or α-fluoro-substituted ß-ketoesters or acetyl acetates are frequently used owing to their relatively higher reactivity. To break through this limitation, we employed N-heterocyclic carbene-catalyzed kinetic resolution to achieve the access to enantioenriched ß-ketoesters with quaternary stereocenters. Sterically more bulky groups such as benzyl, allyl, phenyl and cyclopropyl groups are all tolerated using this method.

Design and activity study of a melittin-thanatin hybrid peptide.

The unique antimicrobial mechanism of antimicrobials make them a promising substitute for antibiotics for fighting drug-resistant bacteria. Both melittin and thanatin have antimicrobial bioactivity. However, thanatin does not inhibit the growth of Staphylococcus aureus. Melittin can inhibit S. aureus and has strong hemolytic activity. In the present study, the mutant fragments of melittin and thanatin were combined by flexible peptides to form a novel hybrid peptide, which was synthesized based on the secondary and tertiary structure prediction. The hybrid peptide inhibited S. aureus with a hemolytic concentration of above 45 µmol/L and inhibition rate in SMMC-7721 cells of 19.14%. The hybrid antimicrobial peptide, which was designed by the combination of α-helix and ß-lamellar antimicrobial peptides, showed that both types of peptides did not interact with each either on spatial structure or biological activities, thereby providing a novel idea for the design of artificial antimicrobial peptides.