Palladium‐Catalyzed Aza‐Wittig‐Type Condensation of Isoxazol‐5(4H)‐ones with Aldehydes

This paper describes the development of a palladium‐catalyzed decarboxylative inter‐ and intramolecular condensation reaction of isoxazol‐5(4 H)‐ones with carbonyl compounds in the presence of PPh₃, giving various 2‐azabuta‐1,3‐dienes or pyrroles in moderate to high yields.     

An approach for quinolines via palladium-catalyzed Heck coupling followed by cyclization

2-Iodoaniline reacts with α,β-unsaturated carbonyl compounds in DMF at 100 °C in the presence of a catalytic amount of a palladium catalyst along with a base to afford the corresponding quinolones or quinolines in moderate to good yields.     

Direct generation of nucleophilic chiral palladium enolate from 1,3-dicarbonyl compounds: catalytic enantioselective Michael reaction with enones

Generation of chiral palladium enolates from 1,3-dicarbonyl compounds with the palladium aqua complex and its application to the highly efficient catalytic enantioselective Michael reaction with enones are described. The palladium aqua complexes are likely to supply Br?nsted base and Br?nsted acid successively during the reaction. The former activates the carbonyl compounds to give chiral palladium enolates, and the latter cooperatively activates enones. Using a catalytic amount (2-10 mol %) of the palladium complexes, the various 1,3-dicarbonyl compounds including diketones and beta-ketoesters were converted to the desired Michael adducts in good yields (69-92%) with excellent enantiomeric excesses (89-99% ee).     

ZnCl2 and CuCl promoted aldol reactions of isocyanoacetate with α,β-unsaturated carbonyl compounds

Reaction of ethyl isocyanoacetate with α,β-unsaturated carbonyl compounds was promoted by a stoichiometric amount of ZnCl₂ or a catalytic amount of CuCl/Et₃N (1:1) to give 5-alkenyl-4-carboethoxyoxazolines (3) in moderate yields. The oxazolines (3) were converted by palladium catalyst to 2-formamino-2,4-alkadienoic acid ethyl esters (5).     

Reductive dehalogenation of α-halogenated carbonyl and cyano compounds with the hexamethyldisilane/tetrakis(triphenylphosphine)palladium system

Treatment of α-halogenated carbonyl or cyano compounds with hexamethyldisilane in the presence of catalytic amounts of tetrakis(triphenylphosphine)-palladium gives the corresponding parent carbonyl or cyano compounds in excellent yields via oxy-π-allyl(trimethylsilyl)palladium intermediates.     

Addition reaction of arylboronic acids to aldehydes and α,β-unsaturated carbonyl compounds catalyzed by conventional palladium complexes in the presence of chloroform

Arylboronic acids react with aldehydes and α,β-unsaturated carbonyl compounds in the presence of a base and a catalytic amount of a palladium(0) complex with chloroform, affording the corresponding addition products in good yields, and chiral benzhydrol was obtained with up to 43% e.e. using (S,S)-bppm as a ligand. General palladium complexes have no catalytic activity without chloroform. Because chloroform is essential for this reaction, these reactions would be promoted by dichloromethylpalladium(II) species.     

Rhenium-catalyzed reaction of carbonyl compounds with ketene silyl acetals

It was found that rhenium complex is an effective catalyst for the reaction of carbonyl compounds with ketene silyl acetals. A wide range of β-silyloxy esters is obtained by the treatment of carbonyl compounds with ketene silyl acetals in the presence of a catalytic amount of ReBr(CO)₅ in moderate to good yields.     

Asymmetric Synthesis of Multi-Substituted Tetrahydrofurans via Palladium/Rhodium Synergistic Catalyzed [3+2] Decarboxylative Cycloaddition of Vinylethylene Carbonates

Unlike the comprehensive development of tandem multi-metallic catalysis, bimetallic synergistic catalysis has been challenging to achieve high stereoselectivity with the generation of multi-stereogenic centers. Herein, an efficient synergistic catalysis for the diastereo- and enantioselective synthesis of multi-substituted tetrahydrofuran derivatives has been developed. Under mild reaction conditions, a series of target molecules with three consecutive stereocenters were synthesized by a palladium(0)/rhodium(III) bimetal-catalyzed asymmetric decarboxylative [3+2]-cycloaddition of vinylethylene carbonates with α,β-unsaturated carbonyl compounds. The corresponding adducts were obtained with moderate to high yields (67 %∼98 %) and excellent stereoselectivities (>20 : 1 d.r., up to 99 % ee).     

Reaction of carbonyl compounds with trialkylsilyl phenylselenide and tributylstannyl hydride under radical conditions

A novel method for the hydrosilylation of carbonyl compounds has been developed. When carbonyl compounds were allowed to react with trimethylsilyl phenylselenide and tributylstannyl hydride in the presence of a catalytic amount of AIBN as the radical initiator, hydrosilylation of the carbonyl compounds efficiently proceeded to give the corresponding silyl ethers in moderate to good yields. In the absence of carbonyl compounds, the triethylsilyl hydride was obtained by the reaction of PhSeSiEt(3) with Bu(3)SnH. Although the tributylgermyl phenylselenide instead of PhSeSiMe(3) was treated with tributylstannyl hydride in the presence of a benzaldehyde under radical conditions, hydrogermylated product was not obtained and tributylgermyl hydride was mainly formed.     

The six-membered annulation reaction involving sequential palladium-catalyzed allylic alkylation and Michael addition: scope and limitations

The palladium-catalyzed condensation of a variety of active methylene compounds with methyl 6-acetoxymethyl-hepta-2,6-dienoate was investigated. The six-membered adducts resulting from a η³ palladium complex alkylation-Michael addition sequence were obtained with moderate to good yields. In some cases, further evolution of the primary adduct was observed. The process has been expanded to access nitrogen heterocycles by using sodium p-toluenesulfonamide as the nucleophilic partner.     

FeCl3催化羰基化合物的还原卤代反应

在甲基二氯硅烷作用下, FeCl₃能催化羰基化合物(醛、酮)的还原氯代反应, 得到相应的氯代产物; 在甲基二氯硅烷、PBr₃或NaI作用下, FeCl₃可以催化羰基化合物(醛、酮)的还原溴代或碘代反应, 分别以良好的收率得到相应的溴代烷或碘代烷.     

Coordination of Lewis acid to eta(2)-enonepalladium(0) leading to continuous structure variation from eta(2)-olefin type to eta(3)-allyl type.

The reaction of alpha,beta-unsaturated carbonyl compounds, a palladium(0) complex, and Lewis acids led to the formation of a new class of complexes showing a wide variety of structures with eta(2)-type and eta(3)-type coordination of the carbonyl compounds. The reaction of Pd(PhCH=CHCOCH(3))(PPh(3))(2) with BF(3).OEt(2) or B(C(6)F(5))(3) quantitatively gave palladium complexes 1a,b having BX(3)-coordinated eta(2)-enonepalladium structure, as revealed by X-ray structure analysis of the B(C(6)F(5))(3) adduct 1b. On the other hand, the reaction of Pd(PhCH=CHCHO)(PPh(3))(2) with BF(3).OEt(2) or B(C(6)F(5))(3) gave distorted zwitterionic eta(3)-allylpalladium complexes 3a,b, where the Pd-carbonyl carbon distance in 3a (2.413(4) A) is much shorter than that (2.96(1) A) in 1b. The values of the P-P coupling constant and (13)C chemical shift for carbonyl carbon are useful criteria for predicting how the eta(3)-coordination mode contributes to the structure of the enone-palladium-Lewis acid system. Molecular orbital calculations on the series of model complexes suggest that orbital overlap in the highest occupied molecular orbital between the palladium and carbonyl carbon is enlarged by coordination of the Lewis acid to the carbonyl group. Palladium-catalyzed conjugate addition of R-M (R-M = AlMe(3), AlEt(3), ZnEt(2)) and its plausible reaction path are also reported.     

Palladium‐Catalyzed Decarbonylative Dehydration for the Synthesis of α‐Vinyl Carbonyl Compounds and Total Synthesis of (−)‐Aspewentins A,B, and C

The direct α‐vinylation of carbonyl compounds to form a quaternary stereocenter is a challenging transformation. It was discovered that δ‐oxocarboxylic acids can serve as masked vinyl compounds and be unveiled by palladium‐catalyzed decarbonylative dehydration. The carboxylic acids are readily available through enantioselective acrylate addition or asymmetric allylic alkylation. A variety of α‐vinyl quaternary carbonyl compounds are obtained in good yields, and an application in the first enantioselective total synthesis of (?)‐aspewentins A, B, and C is demonstrated.     

Palladium‐Catalyzed Decarbonylative Dehydration for the Synthesis of α‐Vinyl Carbonyl Compounds and Total Synthesis of (−)‐Aspewentins A,B, and C

The direct α‐vinylation of carbonyl compounds to form a quaternary stereocenter is a challenging transformation. It was discovered that δ‐oxocarboxylic acids can serve as masked vinyl compounds and be unveiled by palladium‐catalyzed decarbonylative dehydration. The carboxylic acids are readily available through enantioselective acrylate addition or asymmetric allylic alkylation. A variety of α‐vinyl quaternary carbonyl compounds are obtained in good yields, and an application in the first enantioselective total synthesis of (−)‐aspewentins A, B, and C is demonstrated.     

AuBr(3)-catalyzed [4 + 2] benzannulation between an enynal unit and enol

The reaction of enynals 1, including o-alkynylbenzaldehydes, and carbonyl compounds 2 in the presence of a catalytic amount of AuBr3 in 1,4-dioxane at 100 degrees C gave the functionalized aromatic compounds 3 in high yields. The AuBr3-catalyzed formal [4 + 2] benzannulation proceeds most probably through the coordination of the triple bond of 1 to AuBr3, the formation of a pyrylium auric ate complex via the nucleophilic addition of the carbonyl oxygen atom, the reverse electron demand-type Diels-Alder addition of the enols, derived from 2, to the auric ate complex, and subsequent dehydration and bond rearrangement. Similarly, the AuBr3-catalyzed reactions of 1 with acetal compounds afforded the corresponding aromatic compounds in good yields.     

Enantioselective Palladium‐Catalyzed Cross‐Coupling of α‐Bromo Carboxamides and Aryl Boronic Acids

We herein report an enantioselective palladium‐catalyzed cross‐coupling between α‐bromo carboxamides and aryl boronic acids, generating a series of chiral α‐aryl carboxamides in good yields and excellent enantioselectivities. The development of a chiral P,P=O ligand was critical in overcoming the second transmetalation issue and allows the first asymmetric palladium‐catalyzed coupling of α‐bromo carbonyl compounds.     

Rhenium complex-catalyzed allylation of aldehydes with allyltributylstannane

It was confirmed that the rhenium complex, ReBr(CO)₅, catalyzed the allylation of aldehydes with allyltributylstannane to give the corresponding homoallylic alcohols in moderate to good yields. Similarly, the reaction of aldehydes with enol silyl ether was efficiently promoted by the rhenium catalyst to afford the corresponding β-hydroxy carbonyl compounds.     

A novel metal-free synthesis of thiazole-substituted α-hydroxy carbonyl compounds and 2-alkenylthiazoles from thiazole N-oxides and olefins

A metal-free and highly atom-economic synthesis of thiazole-substituted α-hydroxy carbonyl compounds has been developed. Catalyzed by 5 mol% of p-toluenesulfonic acid (TsOH), a variety of thiazole-substituted α-hydroxy carbonyl compounds were obtained in moderate to good yields via 1,3-dipolar cycloaddition of thiazole N-oxides with olefins, followed by a ring-opening reaction. Furthermore, the corresponding 2-alkenylthiazoles could be produced in excellent yields from synthesized α-hydroxy carbonyl compounds through a one-pot, two-step dehydration process.     

Efficient method for the reduction of carbonyl compounds by triethylsilane catalyzed by PdCl2

The versatility of the palladium(II) chloride and triethylsilane system has been tested in the reduction of aromatic carbonyl compounds. The reaction takes place under mild conditions. This facile and efficient method affords high yields for the reduction of aldehydes and ketones to the corresponding alkanes.     

Palladium catalyzed mild reduction of α,β-unsaturated compounds by triethylsilane

The palladium(II) chloride/triethylsilane system has been successfully applied for the selective hydrogenation of the carbon-carbon double bond of α,β-unsaturated ketones to yield the corresponding saturated carbonyl compounds. The reaction takes place under mild conditions and affords high yields.