Nucleophilic Attack Of Methanol Research Articles

Investigation of the Influence of Functionalization Strategy on Urea 2D MOF Catalytic Performance.

Urea-functionalized MOFs with unique properties have recently been used as efficient platforms to conduct organocatalytic reactions. To gain more insight into the key factors which govern an efficient organocatalytic reaction in urea-MOFs, two different urea-containing 2D MOFs TMU-58 ([Zn(L1)(oba)].CH3CN) and TMU-83 ([Zn(L2)(oba)].DMF), where L1 = (1E,5E)-1,5-bis(1-(pyridine-4-ylethylidene)carbonohydrazide, L2 = (1E,5E)-1,5-bis(1-(pyridine-4-ylmethylene)carbonohydrazide, and oba = 4,4'-oxybisbenzoic acid, with abundant accessible active sites, were selected and examined in the methanolysis of styrene oxide. TMU-58 with the ability to form a two-point H-bond with different substrates revealed a high organocatalytic efficiency in the regioselective ring opening of styrene oxide. The catalytic activation of epoxide oxygen by the urea N-H functional sites, followed by the nucleophilic attack of methanol at the benzylic carbon led to the formation of 2-methoxy-2-phenylethanol as the major product. DFT calculations were also performed to investigate the acidic strength of the urea hydrogens in both TMU-58 and TMU-83 structures as a major factor to conduct an efficient catalytic reaction. The results indicated the more acidic nature of the urea hydrogens in TMU-83; however, its catalytic efficiency was remarkably reduced due to the inappropriate orientation of the active interaction sites within the framework revealing the importance of proper orientation of the urea hydrogens in conducting an efficient organocatalytic reaction. The current study provides a comparative study on the function-property relationship in 2D MOF assemblies which has not been explored so far.

The effect of ligand and acid promoter on hydroesterification of ethylene to methyl propionate and kinetic studies

A new palladium/tris(4-fluorophenyl)phosphine/p-toluenesulfonic acid catalytic system was developed to synthesize methyl propionate from ethylene hydroesterification. The influence of phosphine ligands and acid promoters on catalytic activity was systematically studied. A volcano relationship between the catalytic activity and the electric effect of phosphine ligand was achieved through the characterization of 31P NMR of selenium phosphine compounds. An acid strength range favorable to the hydroesterification of ethylene was found by characterizing the pKa value of Brønsted acid. Then, the effect of phosphine ligand/Pd(OAc)2 ratio, p-toluenesulfonic/Pd(OAc)2 ratio, temperature, time, and pressure on this reaction were investigated. Finally, the elementary reaction-based kinetic model was developed, which indicated that nucleophilic attack of methanol on the Pd-acyl intermediate to give methyl propionate is the rate-determining step. The activation barrier of rate-determining step is 83.1 kJ·mol−1.

Synthesis of Cu(II) complexes by N,O‐donor ligand transformation and their catalytic role in visible‐light‐driven alcohol oxidation

AbstractVisible‐light‐driven photoreactions using metal complexes as catalysts are currently a research hotspot in terms of the development of environmentally friendly sustainable processes. To develop potential copper‐based photocatalysts, a Mannich base ligand, namely, 2,4‐dichloro‐6‐((4‐(2‐hydroxyethyl)piperazin‐1‐yl)methyl)phenol (H2L), has been synthesized and characterized. Two copper complexes [Cu (HL1)] (1) and [Cu (HL2)] (2) have been obtained from H2L, where the ligand undergoes an unprecedented transformation plausibly via oxidation of piperazine ring to ketone, subsequent oxidation of enol and nucleophilic attack of methanol followed by hydrolysis of amide bond, resulting piperazine ring cleavage. Under the irradiation of visible light, these catalysts can oxidize primary alcohols into corresponding aldehydes with very good conversion and high selectivity in the presence of molecular oxygen. The photocatalysts could be recovered almost quantitatively after completion of the catalytic cycle and recycled at least four times without much depreciation of catalytic activity. A plausible mechanistic pathway for alcohol oxidation has been explored through electrospray ionization mass spectrometry (ESI‐MS) spectrometric, cyclic voltammetry, UV–vis, and computational study.

Between Oxirane and Phosphirane: The Spring‐loaded Oxaphosphirane Ring

AbstractDue to the potential interest of oxaphosphiranes in ring‐opening polymerizations, accurate ring strain energies (RSEs) of a wide variety of oxaphosphirane derivatives was computed, after validation of the optimization method by comparison with reported X‐ray structures. The parent oxaphosphirane exhibits a moderate RSE (22.44 kcal/mol) that is significantly enhanced by κ‐P‐complexation (especially with boranes), the introduction of P=O or P+‐Me groups as well as exocyclic double bonds at the ring carbon, such as 3‐methylene, 3‐imino and 3‐oxo functionalities. However, C3 alkyl substitution or pentacoordination at P in σ5λ5‐oxaphosphirane does not lead to significant variation of RSE. Bicyclic spiro‐oxaphosphirane derivatives show an RSE decrease when the size of the spiro ring increases. A moderate linear correlation between RSE and G(r)/ρ(r) values calculated at the ring critical points and also with the relaxed force constant (k0) for the P−C bond is observed for most oxaphosphiranes. The possibility of ring‐opening polymerization by using better (anionic) nucleophiles in the initiation step can be foreseen from the exergonicity and relatively low barrier of the endocyclic C−O cleavage by nucleophilic attack of methanol, thus underlining the effect of the RSE as driving force compared to acyclic analogs.

Deboronation of New Clarithromycin-Benzo[c][1,2]oxaborole Conjugates

<P>Background: The conjugates of antibiotics are new molecules that might show new antibacterial spectrum and overcome resistance of insusceptible bacterial strains. Modification of known antibiotics like Clarithromycin with active fragments is laborious and proven method to overcome resistance of such strains. Methods: The conjugates of Clarithromycin and Benzo[c][1,2]oxaboroles were synthesized using long linkers to extend antimicrobial spectrum of this antibiotic. Results and Discussion: Unexpected intramolecular deboronation of these bioconjugated was found to occur when the linker contained two or more CH2-groups. Molecular modeling was used to understand the source of instability and show a possibility of intramolecular complex of carbonyl group at C-9 in Clarithromycin core and hydroxy-borole moiety. This could facilitate nucleophilic attack of methanol used in reactions to destroy benzo[c][1,2]oxaboroles fragments and leave stable hydroxyl-aryl molecules. Conclusion: The loss of boron from benzo[c][1,2]oxoborole fragments leads to the significant decrease of antimicrobial activity of synthesized antibiotics.</P>

Rhenium complexes of di-2-pyridyl ketone, 2-benzoylpyridine and 2-hydroxybenzophenone: A structural and theoretical study

The reactions of di-2-pyridyl ketone (dpk), 2-benzoylpyridine (zpy) and 2-hydroxybenzophenone (Hbp) with [Re(CO)5Cl] (A) and trans-[ReOX3(PPh3)2] (B, X=Cl, Br) were studied. The complex fac-[Re(CO)3(dpk·OCH3)] was isolated from the reaction of A with dpk in methanol. The monoanionic tridentate chelate dpk·OCH3 was formed by the nucleophilic attack of methanol at the carbonylic carbon atom of dpk. A similar attack of water on dpk was observed in the compound cis-[ReOBr2(dpk·OH)]·2(dpkH+Br−), which was formed from dpk and [ReOBr3(PPh3)2] in acetone. The reaction of zpy with B in acetonitrile produced the complexes [ReIIIX3(zpy)(PPh3)], but in methanol as solvent the compounds [ReOX2(zpyH)(PPh3)] were isolated, where zpyH coordinates bidentately as the monoanionic ligand [C6H5(HC-O)C5H4N]−. With A as starting material the complex fac-[Re(CO)3(zpy)Cl] was isolated. The complexes cis-[ReOX2(bp)(PPh3)] were the products of the reaction of Hbp with B in acetonitrile; however, in methanol cis-[ReIIIBr2(bp)(PPh3)2] was isolated. All these complexes were characterized by conductance measurements, elemental analyses, UV–Vis, IR and NMR spectroscopy and by single crystal X-ray diffraction. DFT calculations regarding the electronic ground states show single states for all the complexes, except for the rhenium(III) complexes [ReIIIX3(zpy)(PPh3)] and [ReBr2(bp)(PPh3)2], in which the states are triplet. The DFT and experimental results are in agreement in all cases, especially the anisotropy of the Re–N bond length of fac-[Re(CO)3(dpk·OCH3)] and exact O(1)–Re–O(3) angles for [ReOX2(bp)(PPh3)].

Photogeneration of quinone methide-type intermediates from pyridoxine and derivatives

The photochemical generation of novel quinone methide-type intermediates has been observed upon photolysis of Vitamin B 6 (pyridoxine, 1) and its derivatives 7 and 8. Irradiation of 1 or 7 in 1:1 CH 3OH/H 2O gives the corresponding methyl ethers ( Φ p=0.18 and 0.21, respectively), consistent with nucleophilic attack of methanol on o-quinone methide-type intermediates. Similarly, photolysis in aqueous CH 3CN with ethyl vinyl ether resulted in the regioselective formation of the respective chroman products through [4+2] cycloaddition. Although laser flash photolysis (LFP) studies point to formation of two different o-quinone methide-type intermediates upon irradiation of either 7 or 8 in neutral aqueous solution, only one such reactive species is observed in alkaline solutions. These intermediates necessarily arise from formal loss of water. The mechanism by which this occurs is dependent upon the pH of the solution. In alkaline solution formation of the quinone methide-type intermediate occurs by dehydroxylation of the excited state phenolate. In neutral solution the reactive species may be formed either by ESPT or by excited state intramolecular proton transfer (ESIPT) between the phenol and the benzylic alcohol, followed by loss of water.

Electron transfer photochemistry of quadricyclanone: Stereospecific nucleophilic capture of a radical cation and singular rearrangement

The electron transfer photo-sensitized reaction of quadricyclanone (1) with methanol produces a single product, 7- syn-methoxybicyclo[2.2.1]hept-5-en-2-one (2) via nucleophilic attack of methanol on the radical cation of 1. The structure of the product and the stereochemistry of the methoxy group reveal that the radical cation is captured by backside attack of methanol on one cyclopropane function followed by a specific cyclopropylcarbinyl to butenyl rearrangement.

Silicenium ions: A gas-phase radiolytic approach.

The gas-phase protonation of vinyltrimethylsilane was carried out, using γ -radiolysis of methane. The ionic species, involved in the process, were trapped by nucleophilic attack of methanol.

ChemInform Abstract: PHOTOCHEMICAL REACTIONS OF AROMATIC COMPOUNDS. XXXIII. PHOTOREACTIONS OF 1‐CYANONAPHTHALENE WITH INDENE IN VARIOUS SOLVENTS

AbstractDie Photoreaktion von 1‐Cyan‐naphthalin (II) mit Inden (III) wird stark von Polarität und Natur der Solvenzien beeinflußt: In nicht stark polaren Solvenzien, wie Et2O, Benzol, Cyclohexan, THF oder Ethylacetat verläuft die Photolyse stereospezifisch zu dem Kopfan‐Kopf‐1:1‐endo‐Cycloaddukt (I).

Photochemical Reactions of Aromatic Compounds. XXXIII. Photoreactions of 1-Cyanonaphthalene with Indene in Various Solvents

Abstract The stereospecific photocycloaddition of 1-cyanonaphthalene to indene occured in cyclohexane, benzene, diethyl ether, tetrahydrofuran, and ethyl acetate, giving the endo head-to-head cycloadduct as the sole 1:1-adduct. The mechanism was discussed in terms of the exciplex intermediacy. In methanol or in acetonitrile in the presence of water, the photoreaction gave the dihydrocycloadduct (8), accompanied by the formation of 2-methoxyindan and 2,2′-dimethoxy-1,1′-biindanyl or 2-indanol and 1-hydroxy-2,2′-biindanyl. In these solvents, the reactions were suggested to be initiated by photochemical electron transfer; the methoxylated or hydroxylated compounds are formed by the nucleophilic attack of methanol or water on the indene cation. Anionic species, including the 1-cyanonaphthalene anion, were suggested to play important roles in the formation of 8.

Anodic functionalisation in synthesis. Part 1. Methoxylation of methyl-substituted benzene and anisole derivatives, and the synthesis of aromatic aldehydes by anodic oxidation

The anodic oxidation in methanol of a series of alkylanisoles and hydroquinone ethers, and of p-xylene has been studied. It was established that the initial step in the product formation always involves direct anodic oxidation of the aromatic compound to the corresponding cation radical. If the electrolysis is conducted under conditions where formation of methoxyl radicals also takes place (platinum anode, supporting electrolyte NaOMe) nuclear methoxylation dominates. Substitution in the nucleus of the aromatic compound presumably occurs either by nucleophilic attack of a methoxide ion on the anodically generated cation radical or by a coupling reaction between the latter and an anodically generated methoxyl radical. If the electrolysis is conducted under conditions where formation of methoxyl radicals does not take place (carbon or platinum anode with supporting electrolyte LiBF4) side-chain oxidation of p-alkylanisoles and p-xylene, with the formation of benzyl ethers, benzaldehyde dimethyl acetals, or ortho-esters of benzoic acids becomes important. This side-chain oxidation occurs via nucleophilic attack of methanol on a benzyl cation formed by deprotonation–anodic oxidation of the initially formed cation radical. Phenol ether cation radicals without p-alkyl substituents under these conditions either dimerise or undergo nuclear methoxylation via nucleophilic attack of methanol on the cation radical.

Anodic oxidation of phenolic compounds. Part 5. Anodic methoxylation of phenols. A simple synthesis of quinones, quinone acetals, and 4-methyl-α-methoxycyclohexa-2,5-dienones

The products and yields obtained on anodic oxidation in methanol of a series of phenols (1a–h) have been investigated as a function of anode material, anode potential, methanol concentration, supporting electrolyte, temperature, and substituents. ortho- and para-Methoxylated and dimeric products were observed. However, experimental conditions were found which, in favourable cases, allow selective formation of para-methoxylated products (isolated as a para-dienone or para-benzoquinone), ortho-methoxylated products (isolated as an ortho-dienone or the Diels–Alder adduct of this dienone), or dimeric products. The methoxylated products are formed via nucleophilic attack of methanol on an anodically generated phenoxylium ion; the dimeric products are probably formed by dimerisation of anodically generated phenoxyl radicals.

Reaction of Chlorohydrocarbons. VI. Co-pyrolysis of Chloroethanes and Methanol on Activated Alumina

Abstract Co-pyrolysis of chloroethanes and methanol on activated alumina was carried out in order to elucidate the reaction mechanism. The reaction rate was of first order in chloroethanes in the presence of excess methanol. A linear free energy relationship was found to exist between the reactivities of chloroethanes (at 230°C) and Taft’s σ* constants, ρ* values for reactions of RCH3, RCH2Cl and RCHCl2 series were 0.24, 0.45 and 0.70, respectively. It could be assumed that a β-hydrogen of chloroethanes was abstracted by the nucleophilic attack of methanol, chlorine being removed at the same time. E2 reaction seems to dominate in co-pyrolysis of chloroethanes and methanol on activated alumina.

Mechanism of formation of π-allyl complexes: The reaction of PdCl 42− with 1,3-cyclohexadiene in methanol

The results of a kinetic study of the reaction between PdCl 4 2− and 1,3,-cyclohexadiene hexadiene are interpreted in terms of intermediate formation of a π-complex of palladium(II) with 1,3-cyclohexadiene, having only one double bond coordinated to the metal. Nucleophilic attack of methanol, from outside the coordination sphere of the metal, on the coordinated olefinic double bond, then gives the methoxy-π-allyl complex.