Acid‐Free Nickel Catalyst for Stereo‐ and Regioselective Hydrophosphorylation of Alkynes: Synthetic Procedure and Combined Experimental and Theoretical Mechanistic Study

The nickel catalyst prepared in situ from nickel bis(acetylacetonate) [Ni(acac)₂] precursor and bis(diphenylphosphino)ethane (DPPE) ligand has shown excellent performance in the hydrophosphorylation of alkynes. Markovnikov‐type regioselective addition to terminal alkynes and stereoselective addition to internal alkynes were carried out with high selectivity without an acidic co‐catalyst (in contrast to the palladium/acid catalytic system). Various H‐phosphonates and alkynes reacted smoothly in the developed catalytic system with up to 99% yield. The mechanisms of catalyst activation and C P bond formation were revealed by experimental (NMR, ESI‐MS, X‐ray) and theoretical (density functional calculations) studies. Two different pathways of the alkyne insertion in the coordination sphere of the metal are reported for the first time.     

Ruthenium‐Catalyzed Oxidative Annulation of 6‐Anilinopurines with Alkynes via C?H Activation: Synthesis of Indole‐Substituted Purines/Purine Nucleosides

Indole‐substituted purine nucleobases have been synthesized by Ru‐catalyzed oxidative annulation of 6‐anilinopurines with internal alkynes that involves C H activation. Unsymmetrical aryl(alkyl)alkynes led to high regioselectivity. The reaction was also successful with nucleosides by delivering unprotected indole‐substituted nucleosides. In the presence of [RuCl₂(p‐cymene)]₂ and copper(II) acetate hydrate [Cu(OAc)₂⋅H₂O], in some cases, we have observed two‐fold C H activation products that exhibit fluorescence. A ruthenacycle intermediate was characterized by crystallography, which suggests that the N‐1 nitrogen atom of the purine acts as a directing group for the present transformation.

     

Efficient Addition Reaction of Dibutylphosphane Oxide with Alkynes: New Mechanistic Proposal Involving a Duo of Palladium and Brønsted Acid

The addition reaction of dibutylphosphane oxide [Bu₂P(O)H] with alkynes proceeds efficiently in the presence of palladium‐chelating phosphane–Brønsted acid catalyst systems. Terminal alkynes afford branched‐structured products selectively. On the other hand, the same reaction using monodentate phosphane ligands or the reaction run in the absence of a Brønsted acid affords a much lower yield. A mechanistic study has revealed that Brønsted acids (XOH) interact with oxygen in M P(O)R₂ species (M=Pd, Pt) through hydrogen bonding to transform them to ionic M⁺←PR₂(OH⋅⋅⋅O⁻X) species, which was confirmed by NMR spectroscopy and X‐ray crystallography. The phosphane‐like PR₂(OH⋅⋅⋅O⁻X) moiety is coordinatively labile, as substantiated by the ligand exchange reaction with tert‐butyl isocyanide. A new mechanism that accommodates these observations has been proposed to rationalize the enhancement of catalytic activity and the regioselectivity induced by the Brønsted acid.     

Synthesis of Isoquinolines via Rhodium(III)‐Catalyzed Dehydrative C?C and C?N Coupling between Oximines and Alkynes

Isoquinolines have been synthesized from the redox‐neutral dehydrative C N and C C cross‐coupling between oximines and alkynes using a catalytic amount of (pentamethylcyclopentadiene)rhodium dichloride dimer {[RhCp*Cl₂]₂} and cesium acetate (CsOAc), a process that involves ortho C H activation of oximines and subsequent functionalization with alkynes. This redox‐neutral catalytic isoquinoline synthesis operates under mild conditions, and is insensitive to moisture or air. A broad scope of coupling partners has been established, and a likely mechanism has been suggested.     

Iron‐Catalyzed Oxidative Cleavage of Olefins and Alkynes to Carboxylic Acids with Aqueous tert‐Butyl Hydroperoxide

A new method for the oxidation of aromatic olefins and alkynes has been developed using inexpensive iron(III) chloride hexahydrate (FeCl₃⋅6 H₂O, 5 mol%) catalyst in combination with commercially available aqueous 70% tert‐butyl hydroperoxide (TBHP) as oxidant. The present system works well for aromatic alkenes and alkynes with both electron‐donating and electron‐withdrawing substituents being tolerated. The protocol is free from chromatographic purification and the carboxylic acids are obtained in high yields by simple filtration.     

Chiral NCN Pincer Rhodium(III) Complexes with Bis(imidazolinyl)phenyl Ligands: Synthesis and Enantioselective Catalytic Alkynylation of Trifluoropyruvates with Terminal Alkynes

A series of new chiral C₂‐symmetrical NCN pincer rhodium(III) complexes with bis(imidazolinyl)phenyl ligands have been conveniently synthesized from easily available materials. The complexes were subsequently applied in the enantioselective addition of terminal alkynes to trifluoropyruvates. With catalyst loading of 1.5–3.0 mol%, the alkynylation of ethyl or methyl trifluoropyruvate with a variety of electronically and structurally diverse terminal alkynes gave the optically active trifluoromethyl‐substituted tertiary propargylic alcohols with enantioselectivities of up to >99% ee and high yields. Although good to excellent enantioselectivities (85–98% ee) could be achieved only for some of the aliphatic terminal alkynes under the optimized conditions, the enantioselectivities were consistently excellent (94% to >99% ee) in the case of aromatic as well as heteroaromatic alkynes and enynes.     

Vapour phase hydrogenolysis of biomass‐derived diethyl succinate to tetrahydrofuran over CuO?ZnO/solid acid bifunctional catalysts

BACKGROUND: Catalytic upgrading of fermentation‐derived succinic acid or its derivates (succinic acid esters and succinic anhydride) to value added chemicals has received great attention recently. The aim of this work is to provide a process for the production of tetrahydrofuran from succinic acid esters. RESULTS: The hydrogenolysis of biomass‐derived diethyl succinate was investigated over CuO? ZnO and CuO? ZnO/solid acid (HY, HZSM‐5, SAPO‐11 and Al₂O₃) catalysts in a fixed‐bed reactor. Over CuO? ZnO, gamma‐butyrolactone and 1,4‐butanediol can be selectively produced under appropriate reaction conditions, while the selectivity of tetrahydrofuran is relatively low due to the weak acidity of CuO? ZnO. Over CuO? ZnO/HZSM, both the formed 1,4‐butanediol and ethanol can be further converted to tetrahydrofuran and diethyl ether, while tetrahydrofuran is selectively produced over CuO? ZnO/HY. CuO? ZnO/Al₂O₃ and CuO? ZnO/SAPO exhibit slight improvements in terms of selectivity to tetrahydrofuran when compared with CuO? ZnO. CONCLUSION: CuO? ZnO/HY is an appropriate catalyst to produce tetrahydrofuran from biomass‐derived diethyl succinate with high activity, selectivity and stability. Furthermore, Brønsted acid sites with appropriate acid strength are responsible for the selective formation of tetrahydrofuran under the applied reaction conditions. Copyright © 2010 Society of Chemical Industry     

Iron‐Catalyzed Oxidation of Cycloalkanes and Alkylarenes with Hydrogen Peroxide

An iron‐catalyzed process for the oxidation of saturated hydrocarbons (cycloalkanes and alkylarenes) to alcohols and ketones with aqueous H₂O₂ in acetonitrile at room temperature is reported. Addition of a carboxylic acid increases the selectivity towards the ketone formation. Best results were obtained with ethylbenzene as substrate and acetic acid as additive, affording acetophenone as the main product.     

On the Use of Non‐Symmetrical Mixed PCN and SCN Pincer Palladacycles as Catalyst Precursors for the Heck Reaction

The mixed pincer palladacycles (Me₂NCH₂(Cl)CCCH₂CH₂Y‐κN,κC,κY)PdCl ( 1 , Y=PPh₂; 2 , OPPh₂) and (t‐BuSCH₂CH₂CC(Cl)(o‐NC₅H₄)‐κS,κC,κN)PdCl 3 have been obtained in high yields by chloropalladation of heterosusbstituted alkynes Me₂NCH₂CCCH₂CH₂PPh₂, Me₂NCH₂CCCH₂CH₂OPPh₂ and t‐BuSCH₂CH₂CC(o‐NC₅H₄), respectively. The molecular structures of 1 and 3 have been ascertained by means of X‐ray diffraction analysis. The catalytic properties of these mixed donor group pincer‐type palladacycles have been evaluated in the arylation of olefins (Heck reaction). The pincer palladacycle 1 is highly active for the coupling of aryl iodides and aryl bromides with n‐butyl acrylate. In contrast it is only moderately active for the coupling of aryl chlorides substituted with electron‐withdrawing groups and inactive for the coupling of electron neutral and electron deactivated aryl chlorides.     

Solubility of propane in N-formyl morpholine

N-formyl morpholine (NFM) is a solvent that has been used to separate acid gases from gas streams. An advantage of NFM is the high solubility of acid gases compared with the low solubility of light hydrocarbons. The solubility of the light hydrocarbons in NFM is important, as the hydrocarbons constitute a loss to the process, and result in hydrocarbon emissions to the atmosphere. However, there are only a few experimental data sets dealing with the solubility of hydrocarbons in NFM. To provide data to be used in the design of plants in the natural gas processing industry, the solubility of propane (C₃H₈) in NFM was measured at 298.15, 313.15, and 343.15 K at pressures up to 20.15 MPa. The Peng-Robinson equation of state was employed to correlate the experimental data and to obtain binary interaction parameters. The binary interaction parameters were used to obtain the parameters of the Krichevsky-Ilinskaya equation and Henry's law constants for propane were calculated. Henry's law constants for propane were compared with those of hydrogen sulphide, carbon dioxide, methane, and ethane in NFM.     

Copper(I)-catalyzed homocoupling reaction of terminal alkynes in supercritical CO2

An efficient method for CuCl-catalyzed homocoupling reaction of terminal alkynes in the synthesis of symmetric 1,3-diynes has been developed in supercritical CO₂ (ScCO₂) without organic solvent. Homocoupling of various terminal alkynes (solid or liquid) could afford the corresponding products in moderate to excellent yields. In addition, ScCO₂ play the role of reactive solvent, and DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) acts as the key additive for homocoupling reactions of terminal alkynes, which enhanced the reaction rate and the solubility of copper(I) catalyst in ScCO₂.     

Nickel(II) Chloride‐Catalyzed Regioselective Hydrothiolation of Alkynes

Regioselective Markovnikov‐type addition of PhSH to alkynes (HC≡C‐R) has been performed using easily available nickel complexes. The non‐catalytic side reaction leading to anti‐Markovnikov products was suppressed by addition of γ‐terpinene to the catalytic system. The other side reaction leading to the bis(phenylthio)alkene was avoided by excluding phosphine and phosphite ligands from the catalytic system. It was found that catalytic amounts of Et₃N significantly increased the yield and selectivity of the catalytic reaction. Under optimized conditions high product yields of 60–85% were obtained for various alkynes [R=n‐C₅H₁₁, CH₂NMe₂, CH₂OMe, CH₂SPh, C₆H₁₁(OH), (CH₂)₃CN]. The X‐ray structure of one of the synthesized products is reported.     

Aerobic Oxidative Iodination of Organic Compounds with Iodide Catalyzed by Sodium Nitrite

Selective and efficient iodinations of organic compounds were achieved by an aerobic oxidative process catalyzed by sodium nitrite using potassium iodide in acidic media. Using the potasasium iodide (KI)/air/sodium nitrite (NaNO₂; cat.)/sulfuric acid (H₂SO₄) iodinating system, activated and moderately deactivated aromatic compounds were exclusively or preferentially iodinated at the para position. In protic solvents ketones and 1,3‐dicarbonyl compounds were iodofunctionalized at the α carbonyl position, while in the case of aryl methyl ketones bearing an activated aromatic ring, the regioselectivity of iodination could be directed by the solvent used. In acetonitrile (MeCN) the aromatic ring was selectively iodinated, while in aqueous rethanol (EtOH) functionalization of the methyl carbon atom took place. Alkenes were transformed to vicinal iodohydrins or vicinal iodoalkoxy derivatives following Markovnikov‐type regioselectivity and anti stereoselectivity, while 1,2‐diiodoalkenes with preferentially E orientation were formed from alkynes.     

A High‐Yield,Liquid‐Phase Approach for the Partial Oxidation of Methane to Methanol using SO3 as the Oxidant

A direct approach for producing methanol from methane in a three‐step, liquid phase process is reported. In the first step, methane is reacted with SO₃ to form methanesulfonic acid (MSA) at 75 °C using a free‐radical initiator and MSA as the solvent. Urea‐H₂O₂ in combination with RhCl₃ is found to be the most effective initiator (57% conversion of SO₃; 7.2% conversion of CH₄). MSA is then oxidized by SO₃ at 160 °C in a second step to produce a mixture containing methyl bisulfate and some methyl methanesulfonate (87% conversion of MSA). In the third step, the mixture of methyl bisulfate and methyl methanesulfonate is hydrolyzed in the presence of an organic solvent, to produce an organic phase containing methanol and an aqueous phase containing sulfuric acid and some MSA (63% conversion of methyl bisulfate; 72% conversion of methyl methanesulfonate). Overall, 58% of the MSA (of which 23% is derived from methane) is converted to methanol.     

Oxidative conversion of propane to acrylic acid and acetic acid over mixed oxide catalysts

The oxidative conversion of propane to acrylic acid and acetic acid over Mo? V? Sb? R? O (R?La, Ce, Nd and Sm) catalysts at different reaction conditions (viz. temperature, C₃H₈/O₂ ratio, H₂O/C₃H₈ ratio, space velocity, etc.) was investigated. The catalytic activity and selectivity of the Mo? V? Sb catalyst are strongly influenced by the addition of rare earth metals to the catalyst. The addition of water vapour to the feed of propane and oxygen enhances greatly the formation of oxygenated products, particularly acrylic acid and acetic acid. The ratio of selectivities of acrylic acid to acetic acid was found to depend on the rare earth metal used in the catalyst's preparation and the reaction conditions. High contact times, i.e. high degrees of propane conversion, are detrimental to the formation of acrylic acid but beneficial for acetic acid formation. Copyright © 2005 Society of Chemical Industry     

Impurity control in the production of boric acid from colemanite in the presence of propionic acid

The most important problem in boric acid production from colemanite ores with H₂SO₄ is the formation of MgSO₄ impurity due to the partial decomposition of clay minerals in the reaction media. Increase of MgSO₄ concentration in solution may be balanced by the discharge of mother liquor which leads to decrease the efficiency of the process. Therefore, the intake rate of MgSO₄ should be lowered for obtaining high purity product in a high yield process. In order to control the intake rate of MgSO₄ impurity, propionic acid, which does not decompose the clay minerals, is used in an acid mixture with H₂SO₄. Batch wise laboratory experiments showed that the higher the propionic acid in reacting acid mixture, the lower the magnesium intake rate. When 10% of required H₂SO₄ replaced by propionic acid, magnesium intake concentration decreased to approximately half of the value obtained in the reaction with H₂SO₄.     

A novel palladium complex catalyst for carbonylation of alkynes under mild conditions

Carbonylation of alkynes has been carried out using a catalyst system consisting of Pd(OAc)₂, a monophosphine, p‐toluene sulphonic acid and semilabile anionic bidentate ligands such as pyridine or piperidine carboxylic acids. Turnover frequencies (TOF) upto 3500 h⁻¹ and 98% selectivity to 2‐substituted 2‐propenoic acid/ester have been achieved under mild CO pressures of 1–3 atm at 373 K. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ruthenium(II)‐Catalyzed Regioselective Synthesis of Allyl Ketones from Alkynes and their Silver(I)‐Catalyzed Hydroarylation into γ‐Functionalized Ketones

The regioselective synthesis of β,γ‐unsaturated ketones from terminal alkynes is achieved by cooperative action of tris(acetonitrile)pentamethylcyclopentadieneruthenium hexafluorophosphate [Cp*Ru(NCMe)₃⁺ PF₆⁻] and para‐toluenesulfonic acid catalysts. These allyl ketones undergo direct regioselective hydroarylation/Friedel–Crafts reaction to introduce an electron‐rich aryl group at the γ‐position in the presence of ligand‐free silver triflate (AgOTf) catalyst. Both catalytic reactions take place with atom economy and provide an alternative to the synthesis of a variety of allyl ketones and γ‐arylated ketones.     

Oxidative Alkoxycarbonylation of Alkynes by Means of Aryl α‐Diimine Palladium(II) Complexes as Catalysts

The straightforward in situ synthesized bis(2,6‐diisopropyl)acenaphthenequinonediimine palladium triflate catalyst was generally employed for both the mono‐alkoxycarbonylation of terminal alkynes, and the bis‐alkoxycarbonylation of 1,2‐disubstituted alkynes by using mild reaction conditions [carbon monoxide pressure (P_CO)=4 bar, temperature=20 °C]. Utilizing low catalyst loading (down to 0.5 mol%), a variety of propiolic esters were synthesized with good to excellent isolated yields. Most importantly the system was very efficient not only with methanol but also with a range of different alcohols, starting from the less hindered benzyl alcohol to the most hindered ones, such as isopropyl alcohol and tert‐butyl alcohol. In addition, aromatic and aliphatic 1,2‐disubstituted alkynes were converted into maleic acid derivatives, together with an acid‐catalyzed isomerization reaction, showing modest to good selectivity and excellent combined yields. In particular 3‐hexyne showed a satisfactory degree of selectivity for the maleic diesters of methanol and benzyl alcohol, obtaining the corresponding products with good isolated yields.