Giant Energy Storage Density with Antiferroelectric-Like Properties in BNT-Based Ceramics via Phase Structure Engineering.

Driven by the information industry, advanced electronic devices require dielectric materials which combine both excellent energy storage properties and high temperature stability. These requirements hold the most promise for ceramic capacitors. Among these, the modulated Bi0.5 Na0.5 TiO3 (BNT)-based ceramics can demonstrate favorable energy storage properties with antiferroelectric-like properties, simultaneously, attaching superior temperature stability resulted from the high Curie temperature. Inspired by the above properties, a strategy is proposed to modulate antiferroelectric-like properties via introducing Ca0.7 La0.2 TiO3 (CLT) into Bi0.395 Na0.325 Sr0.245 TiO3 (BNST) ((1-x)BNST-xCLT, x = 0.10, 0.15, 0.20, 0.25). Combining both orthorhombic phase and defect dipole designs successfully achieve antiferroelectric-like properties in BNST-CLT ceramics. The results illustrate that 0.8BNST-0.2CLT presents superior recoverable energy storage density ≈8.3 J cm-3 with the ideal η ≈ 80% at 660 kV cm-1 . Structural characterizations demonstrate that there is the intermediate modulated phase with the coexistence of the antiferroelectric and ferroelectric phases. In addition, in situ temperature measurements prove that BNST-CLT ceramics exhibit favorable temperature stability over a wide temperature range. The present work illustrates that BNT-based ceramics with antiferroelectric-like properties can effectively enhance the energy storage performance, which provides novel perspectives for the subsequent development of advanced pulsed capacitors.

Asymmetric synthesis of chiral pyrazolo[3,4-b]pyridin-6-ones under carbene catalysis.

A structurally diverse set of chiral pyrazolo[3,4-b]pyridin-6-ones was efficiently prepared in excellent yields with excellent enantioselectivities via N-heterocyclic carbene-catalyzed oxidative [3 + 3] annulation of enals with pyrazol-5-amines. The reaction features mild reaction conditions, a broad substrate scope, and easy scale-up.

Bifunctional squaramide catalyzed asymmetric synthesis of chiral α-mercaptosilanes.

Bifunctional squaramide-catalyzed nucleophilic addition of thiophenols to easily available ß-silyl α,ß-unsaturated carbonyl compounds has been successfully developed. A structurally diverse set of chiral α-mercaptosilanes was efficiently prepared in good to excellent yields with acceptable enantioselectivities. The reaction features mild reaction conditions, a broad substrate scope, and easy scale-up.

N-Heterocyclic carbene-catalyzed [3 + 3] annulation of bromoenals with 2-aminochromones to access chromeno[2,3-b]pyridinones.

N-Heterocyclic carbene-catalyzed [3 + 3] annulation of bromoenals with 2-aminochromones has been successfully developed. A structurally diverse set of chromeno[2,3-b]pyridinones was efficiently constructed in acceptable to excellent yields. The reaction features mild reaction conditions, a broad substrate scope, and easy scale-up.

Formal [4 + 1] annulation of fluorinated sulfonium salt with cyclic unsaturated imines to access CF3-substituted pyrroles.

Formal [4 + 1] annulation of easily available fluorinated sulfonium salt with cyclic unsaturated imines has been successfully developed. A structurally diverse set of CF3-substituted dihydropyrroles was efficiently constructed in acceptable to excellent yields with excellent diastereoselectivities. The resulting CF3-containing dihydropyrroles from this transition metal-free strategy could be easily transformed to pyrroles in good yields under basic conditions.

Asymmetric Carbene-Catalyzed Oxidation of Functionalized Aldimines as 1,4-Dipoles.

The use of functionalized aldimines has been demonstrated as newly structural 1,4-dipole precursors under carbene catalysis. More importantly, enantiodivergent organocatalysis has been successfully developed using carbene catalysts with the same absolute configuration, leading to both (R)- and (S)- enantiomers of six-membered heterocycles with quaternary carbon centers. This strategy features a broad substrate scope, mild reaction conditions, and good enantiomeric ratio. DFT calculation results indicated that hydrogen bond C-H⋅⋅⋅F interactions between the catalyst and substrate are the key factors for controlling and even switching the enantioselectivity. These new 1,4-dipoles can also react with isatin and its imines under carbene catalysis, allowing for access to the spiro oxindoles with excellent enantiomeric ratios.

Access to Enantioenriched Spiro-ϵ-Lactam Oxindoles by an N-Heterocyclic Carbene-Catalyzed [4+3] Annulation of Flexible Oxotryptamines with Enals.

Oxotryptamines were firstly used as flexible four-atom synthons in an NHC-catalyzed formal [4+3] annulation, providing a novel enantioselective method to access structurally diverse spiro-ϵ-lactam oxindoles with excellent enantioselectivities. This metal-free reaction features a broad substrate scope, excellent functional-group tolerance and proceeds under mild reaction conditions. Importantly, enantiopure privileged hexahydropyrroloindoles could be easily constructed by a one-pot process from the resulting spiro-ϵ-lactam oxindoles.

Asymmetric Synthesis of Enantioenriched 6-Hydroxyl Butyrolactams Promoted by N-Heterocyclic Carbene.

Herein, an efficient route to synthesize 6-hydroxyl butyrolactams has been successfully developed via an N-heterocyclic carbene-catalyzed formal [3 + 2] annulation of bromoenals with α-amino ketones, followed by reduction. Remarkably, enantioenriched epi-neoclausenamide, which is one of the clausenamide derivatives, could be efficiently prepared by this strategy.

Carbene-Catalyzed Construction of Carbazoles from Enals and 2-Methyl-3-oxoacetate Indoles.

Direct and rapid construction of carbazoles has been successfully developed via carbene-catalyzed oxidative formal [4 + 2] annulation of enals with 2-methyl-3-oxoacetate indoles. This metal-free reaction features a broad substrate scope, features good functional-group tolerance, proceeds under mild conditions, and can be easily scaled up.

Access to Enantioenriched Organosilanes from Enals and ß-Silyl Enones: Carbene Organocatalysis.

Herein, an efficient route to enantioenriched organosilanes, containing two consecutive stereogenic centers, from enals and ß-silyl enones under carbene organocatalysis is described. Under mild reaction conditions, this transition-metal-free strategy exhibits a broad substrate scope, and excellent diastereo- and enantioselectivity.

Nucleophilic ß-Carbon Activation of Propionic Acid as a 3-Carbon Synthon by Carbene Organocatalysis.

Direct ß-carbon activation of propionic acid (C2H5CO2H) by carbene organocatalysis has been developed. This activation affords the smallest azolium homoenolate intermediate (without any substituent) as a 3-carbon nucleophile for enantioselective reactions. Propionic acid is an excellent raw material because it is cheap, stable, and safe. This approach provides a much better solution to azolium homoenolate synthesis than the previously established use of acrolein (enal without any substituent), which is expensive, unstable, and toxic.

Access to oxoquinoline heterocycles by N-heterocyclic carbene catalyzed ester activation for selective reaction with an enone.

Organocatalytic ester activation is developed for a highly selective cascade reaction between saturated esters and amino enones. The reaction involves activation of the ß-carbon atom of the ester as a key step. This method allows a single-step access to multicyclic oxoquinoline-type heterocycles with high enantiomeric ratios.

Ruthenium-catalyzed redox-neutral and single-step amide synthesis from alcohol and nitrile with complete atom economy.

A completely atom-economical and redox-neutral catalytic amide synthesis from an alcohol and a nitrile is realized. The amide C-N bond is efficiently formed between the nitrogen atom of nitrile and the α-carbon of alcohol, with the help of an N-heterocyclic carbene-based ruthenium catalyst, without a single byproduct. A utility of the reaction was demonstrated by synthesizing (13)C or (15)N isotope-labeled amides without involvement of any separate reduction and oxidation step.

Desymmetrization of N-Cbz glutarimides through N-heterocyclic carbene organocatalysis.

Over the past decade, the catalysis of N-heterocyclic carbenes has achieved significant advances. In this area, aldehydes, enals, and esters, are commonly employed as starting materials through various catalytic activation modes. However, NHC-activated strategy of amide and its derivatives remains elusive. Described herein is the realization of asymmetric desymmetrization of N-Cbz glutarimides with alcohols through an imide C-N bond cleavage under NHC organocatalysis. A structurally diverse set of enantioenriched 4-amido esters is generated with acceptable yields and high enantioselectivities. This method features mild reaction conditions, excellent substrate scope, and excellent atom economy. DFT calculations have been performed to explore the detailed reaction mechanism and the origin of the enantioselectivity, which indicate that the strength of the C-H···O hydrogen bond and C-H⋯π interactions should be responsible for the stereoselectivity. The current strategy could open a door for efficient construction of (R)-Rolipram with excellent stereoselectivity.

Desymmetrization of Cyclic 1,3-Diketones under N-Heterocyclic Carbene Organocatalysis: Access to Organofluorines with Multiple Stereogenic Centers.

Symmetric 1,3-diketones with fluorine or fluorinated substituents on the prochiral carbon remain to be established. Herein, we have developed a novel prochiral fluorinated oxindanyl 1,3-diketone and successfully applied these substrates in carbene-catalyzed asymmetric desymmetrization. Accordingly, a versatile strategy for asymmetric generation of organofluorines with fluorine or fluorinated methyl groups has been developed. Multiple stereogenic centers were selectively constructed with satisfactory outcomes. Structurally diverse enantioenriched organofluorines were generated with excellent results in terms of yields, diastereoselectivities, and enantioselectivities. Notably, exchanging fluorinated methyl groups to fluorine for this prochiral 1,3-diketones leads to switchable stereoselectivity. Mechanistic aspects and origin of stereoselectivity were studied by DFT calculations. Notably, some of the prepared organofluorines demonstrated competitive antibacterial activities.

Carbene-Catalyzed Enantioselective Synthesis of γ-Keto-ß-silyl Esters and Amides.

A variety of γ-keto-ß-silyl esters and amides, most with extremely high enantioselectivities, were efficiently prepared via a carbene-catalyzed formal [4 + 2] annulation followed by ring opening with nucleophiles. The resulting compounds from this one-pot strategy can be easily converted into enantioenriched ß,σ-dihydroxyl esters.

Facile Synthesis of Polysubstituted Indolizines via One-Pot Reaction of 1-Acetylaryl 2-Formylpyrroles and Enals.

An efficient method for the synthesis of polysubstituted indolizines has been developed based on formal [4+2] annulation of 1-acetylaryl 2-formylpyrroles with enals, followed by oxidative aromatization. Pyridine-type six-membered rings were constructed in this transformation. This transition metal-free reaction features mild reaction conditions, a broad substrate scope, and excellent functional group tolerance. Notably, the formyl group is well tolerated under reaction conditions.

Organocatalytic asymmetric N-sulfonyl amide C-N bond activation to access axially chiral biaryl amino acids.

Amides are among the most fundamental functional groups and essential structural units, widely used in chemistry, biochemistry and material science. Amide synthesis and transformations is a topic of continuous interest in organic chemistry. However, direct catalytic asymmetric activation of amide C-N bonds still remains a long-standing challenge due to high stability of amide linkages. Herein, we describe an organocatalytic asymmetric amide C-N bonds cleavage of N-sulfonyl biaryl lactams under mild conditions, developing a general and practical method for atroposelective construction of axially chiral biaryl amino acids. A structurally diverse set of axially chiral biaryl amino acids are obtained in high yields with excellent enantioselectivities. Moreover, a variety of axially chiral unsymmetrical biaryl organocatalysts are efficiently constructed from the resulting axially chiral biaryl amino acids by our present strategy, and show competitive outcomes in asymmetric reactions.

Direct synthesis of highly substituted 2-cyclohexenones and sterically hindered benzophenones based on a [5C + 1C] annulation.

The regiospecific [5C + 1C] annulation of readily available alpha-alkenoyl ketene (S,S)-acetals 1 with aryl methyl ketones 2, the less active methylene compounds, has been developed. Upon treatment of 1 with 2 in the presence of t-BuOK in DMF at room temperature, highly substituted 2-cyclohexenones 3 were synthesized in high to excellent diastereoselectivities with high yields. On the basis of this strategy, sterically hindered benzophenones 4 were conveniently prepared via the iodonation-aromatization of 2-cyclohexenones 3 with I(2) in MeONa/MeOH basic medium. Furthermore, benzophenones 4 were also obtained directly from 1 and 2 following a sequential [5 + 1] annulation-iodonation-aromatization procedure in a one-pot operation.

Facile Synthesis of 2,2-Diacyl Spirocyclohexanones via an N-Heterocyclic Carbene-Catalyzed Formal [3C + 3C] Annulation.

A novel strategy for the construction of 2,2-diacyl spirocyclohexanones 3 has been demonstrated on the basis of an NHC-catalyzed [3C + 3C] annulation of potassium 2-oxo-3-enoates with 2-ethylidene 1,3-indandiones. Furthermore, enantioenriched 3 was obtained in good to excellent yields with good enantioselectivities when chiral N-heterocyclic carbene (NHC) was employed. Notably, ring opening of the resulting 2,2-diacyl spirocyclohexanones 3 with hydrazine led to the formation of phthalazinones in good to excellent yields.