Tributylphosphine catalyzed addition of diphenylphosphine oxide to unsubstituted and substituted electron-deficient alkenes

The PBu₃-catalyzed conjugate addition of diphenylphosphine oxide to unsubstituted and substituted electron-deficient alkenes is reported. β-Substituted α,β-unsaturated esters, trans-methyl crotonate and trans-methyl cinnamate, known for their reluctance to participate in phosphine-catalyzed transformations, also react well under the developed conditions. Mild reaction conditions, simple work-up and the ease of catalyst recovery make the proposed methodology useful for the preparation of functionalized tertiary phosphine oxides. The utility of this method was demonstrated by the gram-scale reactions of diphenylphosphine oxide with electron-deficient alkenes.     

Homogeneous gold-catalyzed hydrosilylation of aldehydes

The catalytic hydrosilylation of aldehydes in the presence of PBu₃ modified Au(I)-complexes was investigated. In situ IR and NMR experiments have revealed that both, the ligand PBu₃ and the substrate aldehyde play an important role in stabilizing the gold catalyst and/or forming the catalytically active species. In their absence the reducing power of silane destabilizes the gold (I) catalyst giving rise to gold clusters or particles. Several side reactions involving water and oxygen were also investigated. A plausible reaction pathway as an alternative to the well-accepted mechanism for the transition-metal homogeneously catalyzed hydrosilylation of aldehydes has been proposed to accommodate the experimental observations.     

Studies of poly-yne polymers containing transition metals in the main chain : III. Synthesis and characterization of a poly-yne polymer containing mixed metals in the main chain,

By the reaction of trans-(PBu₃)₂Pt(CCCCH)₂ with trans-(PBu₃)₂PdCl₂, the title polymer,

(II), has been prepared and characterized by spectral and analytical data. The alternating regularity of the metal arrangement in II was confirmed by the selective formation of the trinuclear complex trans,trans,trans-ClPd(PBu₃)₂?CCC CPt(PBu₃)₂?CC-CCPd(PBu₃)₂(XXIII), in the depolymerization by trans- (PBu₃)₂PdCl₂ using CuI as catalyst in XXNEt₂.     

Elucidating the Mechanism and Chemoselectivity in the PBu3-Catalyzed Rauhut-Currier Reaction of Chalcone with Ethyl Acrylate

Disclosing the chemoselectivity and regioselectivity of phosphine-catalyzed Rauhut-Currier (R−C) reaction remains a challenge. Here, a comprehensive study on the possible mechanisms and origins of the chemoselectivity and regioselectivity of PBu₃-catalyzed R−C reactions between ethyl acrylate and chalcone is performed by DFT. Both cross and homo R−C reactions are investigated and compared. The computational results show that the cross R−C reaction is energetically favorable than the homo R−C reaction, with head-to-tail product being generated preferentially. Moreover, the C−C bond formation process is identified to be the regioselectivity- and chemoselectivity-determining step. The CDFT and Parr function analyses are successfully used to predict the origins of chemoselectivity and regioselectivity, respectively. This work would provide a valuable case for exploring the origins of the chemoselectivity and regioselectivity of the phosphine catalyzed reactions, which should be helpful to understand and control the selectivities by rational design.     

A mechanistic investigation of the decacarbonyldimanganese-catalyzed carbonylation of amines

The Mn₂(CO)₁₀-catalyzed reactions of n-butylamine and cyclohexylamine with CO to give the corresponding ureas have been examined under a variety of conditions of temperature, CO pressure, reaction time, solvent and potential co-catalysts. With the diamines, ethylenediamine and 1,4-diaminobutane, there was no catalyzed reaction with CO. On the other hand, 1,3-diaminopropane gave 1,4,5,6-tetrahydropyrimidine, and 1,6-diaminohexane yielded a polyurea. In an effort to elucidate the mechanism of these reactions, several stoichiometric reactions were carried out. The reaction of Mn₂(CO)₁₀ with primary aliphatic amines proceeds to give a carbamoyl complex as follows: Mn₂(CO)₁₀ + 3 RNH₂ ? cis-Mn(CO)₄(NH₂R)(CONHR) + RNH₃⁺ + Mn(CO)₅^? Under CO pressure the isolated carbamoyl complex reacted to give the urea as follows: cis-Mn(CO)₄(NH₂R)(CONHR) + CO → (RNH)₂CO + HMn(CO)₅ The mechanism of this latter reaction is proposed to involve the intermediate formation of the organic isocyanate RNCO. These reactions are discussed as part of an overall mechanism for the Mn₂(CO)₁₀-catalyzed formation of ureas. The mechanism successfully accounts for factors which affect the yields of the reaction. Other metal carbonyl complexes, Re₂(CO)₁₀, (η-CH₃C₅H₄)Mn(CO)₃ and [η-C₅H₅Cr(CO)₃]₂, did not catalyze the reactions.     

钌1,2-萘醌-1-肟配合物对aldol C—C成键反应的催化作用

在钌1,2-萘醌-1-肟(1-nqo)配合物cis,cis-[Ru(1-nqo)₂(CO)(NCMe)] (1)或trans,trans-[Ru(1-nqo)₂(PBu₃)₂] (2)的作用下, 氰基乙酸乙酯与取代苯甲醛发生aldol C—C成键反应. 根据GC-MS检测及HPLC分离结果, 对二苯甲醛的二个醛基可分别或同时与氰基乙酸乙酯发生aldol反应. ¹H NMR表征结果证明, 二种产物的双键构型均为反式. 其它取代苯甲醛的反应均给出单一反式aldol产物, 这表明该催化反应具有立体选择性. 配合物1的催化活性稍差, 产率不超过60%, 而配合物2的催化活性要高于1, 最高产率达99%.     

Facile activation of hydrogen by unsaturated platinum-osmium carbonyl cluster complexes

The electronically unsaturated cluster complex Os₃Pt₂(CO)₁₀(PBu^t₃)₂ (10) was obtained from the reaction of Os₃(CO)₁₀(NCMe)₂ with Pt(PBu^t₃)₂. Three side products: PtOs₃(CO)₁₀(PBu^t₂)CMe₂CH₂(μ-H) (13), Os₃(CO)₁₀(PBu^t₃)₂ (14) and Pt₂Os₃(CO)₁₀(PBu^t₃)(PBu^t₂)CMe₂CH₂(μ-H) (15) were also obtained from this reaction. The three osmium atoms in 10 lie in the equatorial plane of a trigonal bipyramid. The platinum atoms occupy the apical positions. When heated, compound 10 was converted to 15 by metallation of one of the methyl groups of one of the PBu^t₃ ligands at the platinum atom to which it is coordinated. The platinum atom then shifted to an edge of the Os₃ triangle by cleaving one of its Pt-Os bonds. Compound 13 also contains a metallated PBu^t₃ ligand attached to the platinum atom of the tetrahedral PtOs₃ cluster. Compound 10 reacts with hydrogen at 0 °C to yield the di- and tetra-hydrido compounds Os₃Pt₂(CO)₁₀(PBu^t₃)₂(μ-H)₂ (11) and Os₃Pt₂(CO)₁₀(PBu^t₃)₂(μ-H)₄ (12) with the hydrido ligands bridging Os-Pt and Os-Os bonds. With each addition of hydrogen, one of the platinum atoms in the cluster was shifted to an edge of the Os₃triangle. When solutions of 12 at 25 °C were purged with nitrogen, hydrogen was eliminated and the compounds 10 and 11 were regenerated. The electronic structures of 10 and 11 were also investigated by Fenske-Hall molecular orbital theory. When compound 10 was exposed to hydrogen for 2.5 h, compound 12 was formed together with the new tetranuclear metal cluster complexes PtOs₃(CO)₁₀(PBu^t₃)(μ-H)₂ (16), PtOs₃(CO)₉(PBu^t₃)(μ-H)₄ (17) and PtOs₃(CO)₈(PBu^t₃)₂(μ-H)₄ (18). Compounds 16-18 contain tetrahedrally shaped clusters of four metal atoms with bridging hydrido ligands. All new compounds were characterized structurally by single-crystal X-ray diffraction methods.     

A density functional theory study of the stereoselectivity of Cu(OTf)2-catalyzed [3+2] cycloaddition of trifluoromethylated N-acylhydrazones and isoprene: A concerted asynchronous mechanism

Here we employ density functional theory calculations to systematically investigate the underlying mechanism of Cu(OTf)₂-catalyzed [3+2] cycloaddition reactions in the synthesis of CF₃-substituted pyrazolidines. About eight possible initial configurations of the [3+2] reaction is considered, and all relevant reactants, transition states, and products are optimized. Based on these structures, internal reaction coordinate paths, and wavefunction analysis results, we conclude that the Cu(OTf)₂-catalyzed [3+2] cycloaddition follows a concerted asynchronous mechanism. The C N bond forms immediately after the formation of the C C bond. Among the eight reaction paths, the energy barrier for the [3+2] reaction that leads to the CF₃-substituted syn-pyrazolidine is the lowest, ∼5.4 kcal/mol, which might result in the diastereoselectivity that is observed in the experiment. This work not only gives the detailed mechanism of the Cu(OTf)₂-catalyzed [3+2] cycloaddition but can also be helpful for the future designation of Cu(OTf)₂-based cycloaddition processes.     

Cyclometallation of a pyrrole ring of 2-(1-pyrrolyl)pyridine with palladium(II) and rhodium(III)

2-(1-Pyrrolyl)pyridine (Hplp) is cyclometallated with lithium tetrachloropalladate(II) and hexahalogenotetrakis(tri-n-butylphosphine)dirhodium(III) to give [PdCl(plp)]₂ and [RhX₂(plp(PBu₃)₂] (X = Cl, Br; PBu₃ = tri-n-butylphosphine), respectively, where deprotonated plp is coordinated via the pyridine-N and pyrrole-2C atoms forming a five-membered metallacycle. [PdCl(plp)]₂ reacts with pyridine (py) and with PBu₃ to form the adducts [PdCl(plp)L] (L = py, PBu₃) and with acetylacetone (Hacac) to afford the complex [Pd(plp)(acac)]. Metathesis of [RhCl₂(plp)(PBu₃)₂] with excess lithium iodide gives a mixed halogeno complex [RhClI(plp)(PBu₃)₂]. These complexes are characterized spectroscopically.     

Mn(III)-based reaction of alkenes with quinolinones. Formation of peroxyquinolinones and quinoline-related derivatives

The reactions of 1,1-disubstituted alkenes with 4-hydroxyquinolin-2(1H)-ones under both Mn(III)-catalyzed aerobic oxidation conditions at room temperature and Mn(III)-mediated oxidation conditions at reflux temperature are described. The Mn(III)-catalyzed aerobic oxidation afforded bis(hydroperoxyethyl)quinolinones and azatrioxa[4.4.3]propellanes, while the oxidation with Mn(OAc)₃·2H₂O produced furo[3,2-c]quinolin-4-one analogues. The existence of a substituent at the 3-position of the 4-hydroxyquinolin-2(1H)-ones prevented a double reaction with the alkenes, and (endoperoxy)quinolinones and/or (hydroperoxyethyl)quinolinones were obtained under the Mn(III)-catalyzed aerobic conditions, while furo[3,2-c]quinolinone hemiacetals and vinylquinolinones were selectively produced under the Mn(III)-mediated oxidation conditions depending on the reaction temperature and times. Cyclic assembly of quinolinone-related 1,3-dicarbonyl compounds such as dihydropyridinones, pyranones, and dimedone derivatives was also examined under elevated temperature conditions.     

A concise synthesis of substituted stilbenes and styrenes from propargylic phosphonium salts by a cobalt-catalyzed Diels-Alder/Wittig olefination reaction sequence

The cobalt(I)-catalyzed Diels-Alder reaction of propargylic phosphonium salts and longer chained alkyne-functionalized phosphonium salts with 1,3-dienes led to dihydroaromatic phosphonium salt intermediates which were directly used in a one-pot Wittig-type olefination reaction with aldehydes. Subsequent oxidation led to styrene- and stilbene-type products under formation of three new carbon-carbon bonds in a single synthetical step starting from three variable starting materials. The E/Z stereoselectivities of the products revealed that the dihydroaromatic phosphonium ylides behave as semistabilized ylides giving predominantly the E-configured products. The application of unsymmetrical 1,3-dienes as well as internal phosphonium functionalized alkynes is also described.     

Synthesis of a chiral phosphonium salt for the preparation of α-substituted alaninol derivatives

We herein report the synthesis of a chiral phosphonium salt, {[(4S)-4-methyl-2-oxo-1,3-oxazolidin-4-yl]methyl}(triphenyl)phosphonium iodide 13 to provide a new Wittig reagent for the general method of synthesizing α-substituted alaninol derivatives. Our method described here is widely applicable to reactions with various types of aldehyde to afford olefin products with high E-selectivity, enabling us to provide a new approach to the synthesis of chiral S1P₁ agonists including our key intermediates, and of the trace amine-associated receptor 1 (TAAR1) agonist.     

An ESR study of photochemical reactions of Co2(CO)6(PBu3)2 with quinones and phenothiazine

The photochemical reactions of Co₂(CO)₆(PBu₃)₂ with various quinones and phenothiazine were studied by ESR. The results indicate that the photolysis of Co₂(CO)₆(PBu₃)₂ in the presence of o-quinones led to the observation of an ESR spectrum, showing a broad 8 or 12 groups of hyperfine lines due to interaction with cobalt (Co, 1 = 7/2). The results show that with o-quinones the cobalt radical adducts are formed via metal chelation to the carbonyl oxygens. However, when Co₂(CO)₆(PBu₃)₂ was irradiated in the presence of p-quinones, only the para-semiquinone radicals were observed. The photolysis of Co₂(CO)₆(PBu₃)₂ with phenothiazine in toluene yields phenothiazine radical. The sixteen and eighteen electrons rule have been used to account for these observations.     

Pd(OAc)2-catalyzed domino reactions of 1,2-dihaloarenes and 2-haloaryl arenesulfonates with Grignard reagents: efficient synthesis of substituted fluorenes

Pd(OAc)₂-catalyzed domino reactions of 1,2-dihalobenzenes and 2-haloaryl arenesulfonates with hindered Grignard reagents to form substituted fluorenes, which are believed to occur through palladium associated aryne intermediates, are described. Such palladium associated aryne reaction pathway was found to be favored by omitting the use of phosphine and N-heterocyclic carbene ligands for palladium catalysts and with better leaving groups. Our study suggested that Pd(leaving group)X associated arynes should be formed first and the sp³ C-H activation preferentially occurred at benzylic C-(1°)H bonds. The work described here provides a high yield, one-step access to substituted fluorenes from readily available 1,2-dihalobenzenes and 2-haloaryl arenesulfonates and hindered Grignard reagents, and this substituted fluorene-making method may find applications in the preparation of substituted fluorene-containing molecules including polymers.     

An improved Ullmann-Ukita-Buchwald-Li conditions for CuI-catalyzed coupling reaction of 2-pyridones with aryl halides

An effective CuI-trans-N,N′-dimethylcyclohexane-1,2-diamine (DMCDA)-K₂CO₃-catalyzed coupling reaction of 2-pyridones with aryl halides is described. Under our conditions, DMCDA was found to be an effective catalyst that facilitates the coupling reactions even in toluene, a common industrial solvent. In addition, 3-bromopyridine could also be coupled effectively under these conditions, indicating that the catalytic reactivity of this system is high. The reaction could be applied for polymer modification and iterative oligo-pyridone synthesis.     

Copper-catalyzed imination of sulfoxides and sulfides

Sulfoximines and sulfilimines have attracted considerable interest among organic chemists. The Cu(II)-catalyzed imination of sulfoxides and sulfides using various N-fluoro benzenesulfonamides was investigated in this study. The scope of the reaction was demonstrated by using several substituted sulfides and sulfoxides. The flow strategy for the preparation of NH-sulfoximines was also examined. By trapping nitrene intermediates through triphenylphosphine, we found that the reaction was conducted through a metal-nitrene intermediate mechanism.     

Mechanism of the formation of palladium complexes serving as catalysts in hydrogenation reactions : II. Reactivity of palladium phosphine halides towards molecular hydrogen

[(PPh₃)₃(PPh₂)₂Pd₃Cl] Cl, benzene and aniline hydrochloride were isolated as products of the reactions of (PPh₃)₂PdCl₂]₂ or [(PPh₃)PdCl₂]₂ with H₂ in organic amines (Am). Similar products were obtained when (Ph₃P)₂Pd(Ph)Br was treated with H2₃ Both in amines and aromatic solvents. The reaction between H₂ and [(PBu₃)PdCl₂]₂ resulted in the formation of [(PBu₃(PBu_2)PdCl2 ·. 2 Am The kinetic data for H₂ absorption by solutions of palladium(II) complexes are consistent with the heterolytic mechanism of cleavage fo hte HH bond in the coordination sphere of palladium(II); the function of the H⁺ acceptor being performed by the bases (e.g. Am or Ph). The reaction between the palladium complexes and H₂ is autocatalytic. Reduction of the initial Pd^II complexes leads to lower oxidation state palladium complexes, which catalyse the reduction of Pd^II complexes. In the coordination sphere of the lower oxidation state palladium complexes, the oxidative addition of PR₃ to Pd takes place with formation of compounds containing a Pd-R bond. It is the reaction between these complexes and H₂ that yields palladium compounds with PR₂ ligands.     

InCl3-catalyzed synthesis of C-pyrrolyl glycosides via tandem condensation of aminosugars and 1,3-dicarbonyl compounds in water

Various C-pyrrolyl glycosides were obtained through tandem condensation of aminosugars (d-glucosamine and d-galactosamine) and 1,3-dicarbonyl compounds under green conditions in moderate to good yields. The reactions were carried out in the presence of 10 mol % InCl₃ in water at 50 °C. A reaction mechanism through carbocation intermediates was proposed.     

Co-Catalyzed Metal-Ligand Cooperative Approach for N-alkylation of Amines and Synthesis of Quinolines via Dehydrogenative Alcohol Functionalization

Herein we report a cobalt-catalyzed sustainable approach for C−N cross-coupling reaction between amines and alcohols. Using a well-defined Co-catalyst 1 a bearing 2-(phenyldiazenyl)-1,10-phenanthroline ligand, various N-alkylated amines were synthesized in good yields. 1 a efficiently alkylates diamines producing N, N′-dialkylated amines in good yields and showed excellent chemoselectivity when oleyl alcohol and β-citronellol, containing internal carbon-carbon double bond were used as alkylating agents. 1 a is equally compatible with synthesizing N-heterocycles via dehydrogenative coupling of amines and alcohols. 1H-Indole was synthesized via an intramolecular dehydrogenative N-alkylation reaction, and various substituted quinolines were synthesized by coupling of 2-aminobenzyl alcohol and secondary alcohols. A few control reactions and spectroscopic experiments were conducted to illuminate the plausible reaction mechanism, indicating that the 1 a -catalyzed N-alkylation proceeds through the borrowing hydrogen pathway. The coordinated arylazo ligand participates actively throughout the reaction; the hydrogen eliminated during dehydrogenation of alcohols was set aside in the ligand backbone and subsequently gets transferred in the reductive amination step to imine intermediates yielding N-alkylated amines. On the other hand, 1 a -catalyzed quinoline synthesis proceeds through dehydrogenation followed by successive C−C and C−N coupling steps forming H₂O₂ as a by-product under air.     

Aromatic nucleophilic substitution reaction of 2,4-dinitrohalogenobenzene and ethyl α-cyano-phenylacetate benzyl anion

The aromatic nucleophilic substitution reaction of 2,4-dinitrohalogenobenzene (DNHB; halogeno =F, Cl, Br) with ethyl α-cyanophenylacetate (ECPA) benzyl anion has been studied by means of UV and IR spectrophotometry as well as gas chromatography. The rates of intermediate formation and product formation were determined respectively. In contrast with common S _N Ar reactions, the formation rate constant of the intermediates, substituted cyclohexadienates, was in the order of halogen =F>Br>Cl, whereas the rate constant of product formation was in the order F>Cl>Br, which revealed that the departure of the halogen atom was the rate-limiting step for the overall reaction in the presence of a sterically hindered nucleophile. These reactions could be catalyzed by the solvated electrons. The corresponding reaction intermediates, radical species, were detected by ESR and the reactions were proved to proceed mainly by a solvated-electron induced radical chain reaction mechanism.