Catalytic Pauson-Khand-type reaction using aldehydes as a CO source

[reaction: see text]. Rhodium complex-catalyzed carbonylative alkene-alkyne coupling proceeds using aldehydes as a CO source. Cinnamaldehyde is the best CO donor, and various cyclopentenones were provided in high isolated yields by a solvent-free system.     

Rhodium complex-catalyzed Pauson-Khand-type reaction with aldehydes as a CO source

With aldehydes as a CO source under solvent-free conditions, rhodium complex efficiently catalyzed an intramolecular carbonylative alkene-alkyne coupling (Pauson-Khand-type reaction) and various bicyclic enones were obtained in high yield. Experiments under argon flow and a 13C-labeling experiment suggested that almost no free carbon monoxide was generated in this reaction. When noncationic rhodium complex with chiral phosphine was used as a chiral catalyst, the reaction proceeded enantioselectively to give various chiral cyclopentenones in up to 90% ee under solvent-free conditions.     

Cyclohydrocarbonylation of substituted alkynes and tandem cyclohydrocarbonylation-CO insertion of alpha-keto alkynes catalyzed by immobilized Co-Rh heterobimetallic nanoparticles

The use of cobalt-rhodium (Co(2)Rh(2)) heterobimetallic nanoparticles in the cyclohydrocarbonylation of substituted alkynes and tandem cyclohydrocarbonylation-CO insertion of alpha-keto alkynes to give 2(3H)- or 2(5H)-furanones is described.     

CO-transfer carbonylation reactions. A catalytic Pauson-Khand-type reaction of enynes with aldehydes as a source of carbon monoxide

The reaction of enynes with aldehydes in the presence of a catalytic amount of [RhCl(cod)](2)/dppp results in the Pauson-Khand-type reaction without the use of gaseous carbon monoxide to give bicyclic cyclopentenones in high yields (14 examples). Aldehydes serve as a source of carbon monoxide, and their carbonyl moiety is transferred to enynes, resulting in the formation of the carbonylated products. This reaction represents the first example of a CO-transfer carbonylation.     

New coupling reaction of secondary amines, aldehydes, and alkynes catalyzed by an iridium complex

A new reductive coupling reaction of secondary amines, aldehydes, and alkynes using an iridium complex as catalyst has been developed. For example, dibutylamine was allowed to react with butyraldehyde and 1-octyne in 1,4-dioxane at 50 degrees C under the influence of a catalytic amount of [IrCl(cod)](2) to give the corresponding allylamines such as N,N-dibutyl-2-butylideneoctylamine and N,N-2-tributyl-2-octenylamine in excellent yields. [reaction: see text]     

Cobalt/rhodium heterobimetallic nanoparticle-catalyzed carbonylative [2+2+1] cycloaddition of allenes and bisallenes to Pauson-Khand-type reaction products

The first catalytic intra- and intermolecular [2+2+1] cocyclization reactions of allenes and carbon monoxide have been developed. In the Co(2)Rh(2) heterobimetallic nanoparticle-catalyzed carbonylative [2+2+1] cycloaddition of allenes and carbon monoxide, the allenes formally serve both as an excellent alkene- and alkyne-like moiety within a Pauson-Khand-type process.     

Direct asymmetric aldol reaction of acetophenones with aromatic aldehydes catalyzed by chiral Al/Zn heterobimetallic compounds

Chiral Al/Zn heterobimetallic complexes are effective catalysts for the direct highly enantioselective aldol reaction of acetophenones with aromatic aldehydes. The Al site in the complex acts as a Lewis acid to activate aldehyde, whereas ethylzinc alkoxide plays a role of a Brønsted base to form a reactive zinc enolate with acetophenone. Distinct nature of two different metals contributes to the efficient direct asymmetric aldol reaction.     

Addition reaction of dialkyl disulfides to terminal alkynes catalyzed by a rhodium complex and trifluoromethanesulfonic acid

[reaction: see text]. Addition of dialkyl disulfides to terminal alkynes is catalyzed by a rhodium-phosphine complex and trifluoromethanesulfonic acid giving (Z)-bis(alkylthio)olefins stereoselectively.     

Mannich reaction of secondary amines,aldehydes and alkynes in water using Cu/C nanoparticles as a heterogeneous catalyst

The use of 2 mol% of Cu/C nanoparticles, as an easily accessible and inexpensive heterogeneous catalyst, promoted a one-pot three-component condensation of an amine, aldehyde, and an alkyne in water to produce the corresponding propargylamine in good to high yields. This method was proved to be applicable to a wide range of substrates and is especially practical for the synthesis of new azacrown ether derivatives. The catalyst was quantitatively recovered from the reaction by a simple filtration and reused for at least ten times with almost consistent activity.     

Innovative synthesis of 4-carbaldehydepyrrolin-2-ones by zwitterionic rhodium catalyzed chemo- and regioselective tandem cyclohydrocarbonylation/CO insertion of alpha-imino alkynes

The tandem cyclohydrocarbonylative/CO insertion of alpha-imino alkynes employs CO, H(2), and catalytic quantities of zwitterionic rhodium complex (eta(6)-C(6)H(5)BPh(3))(-)Rh(+)(1,5-COD) and triphenyl phosphite affording aldehyde substituted pyrrolinones in 67-82% yields. This unique transformation is readily applied to imino alkynes containing alkyl, alkoxyl, vinyl, and aryl substituents. The ability to prepare highly functionalized pyrrolinones makes this an attractive route to these important and versatile pharmaceuticals.     

Practical aldol reaction of trimethylsilyl enolate with aldehyde catalyzed by N-methylimidazole as a Lewis base catalyst

Aldol reaction of trimethylsilyl enolate with aldehyde proceeded in the presence of a catalytic amount of a Lewis base, N-methylimidazole, and lithium chloride in DMF at room temperature. Not only aryl aldehyde but also alkyl aldehyde provided the aldol product in satisfactory yields. The reaction was mild enough to apply to the aldehyde having HO, AcO, THPO, TBDMSO, MeS, pyridyl or olefinic group. Microwave irradiation accelerated the reaction.     

A theoretical study on the mechanisms of intermolecular hydroacylation of aldehyde catalyzed by neutral and cationic rhodium complexes

In this paper, we used density functional theory(DFT) computations to study the mechanisms of the hydroacylation reaction of an aldehyde with an alkene catalyzed by Wilkinson's catalyst and an organic catalyst 2-amino-3-picoline in cationic and neutral systems. An aldehyde's hydroacylation includes three stages: the C–H activation to form rhodium hydride(stage I), the alkene insertion into the Rh–H bond to give the Rh-alkyl complex(stage II), and the C–C bond formation(stage III). Possible pathways for the hydroacylation originated from the trans and cis isomers of the catalytic cycle. In this paper, we discussed the neutral and cationic pathways. The rate-determining step is the C–H activation step in neutral system but the reductive elimination step in the cationic system. Meanwhile, the alkyl group migration-phosphine ligand coordination pathway is more favorable than the phosphine ligand coordination-alkyl group migration pathway in the C–C formation stage. Furthermore, the calculated results imply that an electron-withdrawing group may decrease the energy barrier of the C–H activation in the benzaldehyde hydroacylation.     

Nickel-catalyzed addition of dimethylzinc to aldehydes across alkynes and 1,3-butadiene: an efficient four-component connection reaction

In the presence of 10 mol % of Ni(acac)(2), four components comprising Me(2)Zn, alkynes, 1,3-butadiene, and carbonyl compounds combine in this order in 1:1:1:1 ratio to furnish (3E,6Z)-octadien-1-ols 1 in good yields. Similarly, the coupling reaction of Me(2)Zn, 1,omega-dienynes 5, and carbonyls furnishes 1-alkylidene-2-(4'-hydroxy-(1'E)-alkenyl)cyclopentanes and -cyclohexanes 6 and their oxygen and nitrogen heterocycle derivatives in good yield and an excellent level of 1,5-diastereoselectivity with respect to the cycloalkane methine carbon and the OH-bearing carbon of the C2 side chain. The reaction is completed in most cases within 1 h at room temperature under nitrogen, tolerates an ester, a hydroxy, an allyl and propargyl ethers, an allylamino, and a pyridyl functionalities, and accommodates a variety of aromatic and aliphatic alkynes and carbonyls (aldehydes and ketones).     

Conversion of alpha,beta-unsaturated aldehydes into saturated esters: an Umpolung reaction catalyzed by nucleophilic carbenes

N-Heterocyclic carbenes derived from benzimidazolium salts are effective catalysts for generating homoenolate species from alpha,beta-unsaturated aldehydes. These nucleophilic intermediates can be protonated, and the resulting activated carbonyl unit is trapped with an alcohol nucleophile, thereby promoting a highly efficient conversion of an alpha,beta-unsaturated aldehyde into a saturated ester. A kinetic resolution of secondary alcohols can be achieved using chiral imidazoylidene catalysts. [reaction: see text]     

Colloid and nanosized catalysts in organic synthesis: XI. Hydrogenation of alkynes catalyzed by nickel nanoparticles

The reaction of alkynes with hydrogen under atmospheric pressure in the presence of nickel nanoparticles as a catalyst led to the exhaustive hydrogenation of the triple bond.     

L-Proline catalyzed aldol reactions between acetone and aldehydes in supercritical fluids: An environmentally friendly reaction procedure

The direct asymmetric aldol reaction between various aldehydes and acetone catalyzed by l-proline catalyst was successfully carried out in supercritical CO₂ (scCO₂) and 1,1,1,2-tetrafluoroethane (R-134a) fluids. The enantioselectivity of 84% ee to the targeted product was achieved under 20 MPa, 40 °C, and 15 mol% of the catalyst in supercritical CO₂ (scCO₂) fluid. The effects of reaction parameters, such as temperature, pressure, catalyst loading and different substituted aldehydes on both enantioselectivity and aldol yield were discussed. The titled reaction was also performed in 1,1,1,2-tetrafluoroethane, and the obtained results were compared with those in scCO₂. This new reaction procedure provides an environmental asymmetric aldol reaction system as compared with that in organic solvents.     

Reaction between carbon dioxide and propylene oxide catalyzed by cobalt and chromium porphyrin complexes: The effect of reaction conditions on the reaction rate

The effect of the conditions (time, temperature, pressure, and cocatalyst/catalyst ratio) on the rate and selectivity of the reaction between СО₂ and propylene oxide catalyzed by TPPCrCl and TPPCoCl (TPP is 5,10,15,20-tetraphenylporphyrin) has been studied. The time variation of the reaction rate has been analyzed by measuring the СО₂ uptake during the reaction. The observed dependences of the reaction rate on the temperature and cocatalyst/catalyst ratio are similar for TPPCrCl and TPPCoCl. In the presence of TPPCoCl, the reaction yields a mixture of poly(propylene carbonate) and a cyclic carbonate, while when TPPCrCl is used, only the cyclic carbonate is synthesized.     

Sequential catalytic process: synthesis of quinoline derivatives by AuCl3/CuBr-catalyzed three-component reaction of aldehydes, amines, and alkynes

A sequential catalytic process has been developed based on gold-catalyzed nucleophilic addition of terminal alkynes to imines, and gold-catalyzed intramolecular reaction of aromatic ring to alkynes. This one-pot reaction of aldehydes, amines, and alkynes gives quinoline derivatives in good yields.