Para-substituted Benzaldehydes Research Articles

A facile synthesis of new coumarin-3,4-dihydropyrimidin-2(1H)-ones/thiones dyads

A new series of 4-aryl-6-methyl-5-(2-oxo-2H-chromene-3-carbonyl)-3,4-dihydropyrimidin-2(1H)-ones/thiones (DHPMs) have been synthesized through multicomponent Biginelli reactions, involving 3-(acetoacetyl)coumarin derivatives, para-substituted benzaldehydes, and urea/thiourea in refluxing acetonitrile, in the presence of a catalytic amount of sulfuric acid. The structure of all newly synthesized compounds has been established by 2D NMR spectroscopic spectra (HSQC, HMBC, and NOESY), elemental analysis, and mass spectrometry.

Amine oxidative N-dealkylation via cupric hydroperoxide Cu-OOH homolytic cleavage followed by site-specific fenton chemistry.

Copper(II) hydroperoxide species are significant intermediates in processes such as fuel cells and (bio)chemical oxidations, all involving stepwise reduction of molecular oxygen. We previously reported a Cu(II)-OOH species that performs oxidative N-dealkylation on a dibenzylamino group that is appended to the 6-position of a pyridyl donor of a tripodal tetradentate ligand. To obtain insights into the mechanism of this process, reaction kinetics and products were determined employing ligand substrates with various para-substituent dibenzyl pairs (-H,-H; -H,-Cl; -H,-OMe, and -Cl,-OMe), or with partially or fully deuterated dibenzyl N-(CH2Ph)2 moieties. A series of ligand-copper(II) bis-perchlorate complexes were synthesized, characterized, and the X-ray structures of the -H,-OMe analogue were determined. The corresponding metastable Cu(II)-OOH species were generated by addition of H2O2/base in acetone at -90 °C. These convert (t1/2 ≈ 53 s) to oxidatively N-dealkylated products, producing para-substituted benzaldehydes. Based on the experimental observations and supporting DFT calculations, a reaction mechanism involving dibenzylamine H-atom abstraction or electron-transfer oxidation by the Cu(II)-OOH entity could be ruled out. It is concluded that the chemistry proceeds by rate limiting Cu-O homolytic cleavage of the Cu(II)-(OOH) species, followed by site-specific copper Fenton chemistry. As a process of broad interest in copper as well as iron oxidative (bio)chemistries, a detailed computational analysis was performed, indicating that a Cu(I)OOH species undergoes O-O homolytic cleavage to yield a hydroxyl radical and Cu(II)OH rather than heterolytic cleavage to yield water and a Cu(II)-O(•-) species.

ChemInform Abstract: Chemoselective N‐Heterocyclic Carbene‐Catalyzed Cross‐Benzoin Reactions: Importance of the Fused Ring in Triazolium Salts.

Morpholinone- and piperidinone-derived triazolium salts are shown to catalyze highly chemoselective cross-benzoin reactions between aliphatic and aromatic aldehydes. The reaction scope includes ortho-, meta-, and para-substituted benzaldehyde derivatives with a range of electron-donating and -withdrawing groups as well as branched and unbranched aliphatic aldehydes. Catalytic loadings as low as 5 mol % give excellent yields in these reactions (up to 99%).

Probing the evolution of an Ar-BINMOL-derived salen–Co(iii) complex for asymmetric Henry reactions of aromatic aldehydes: salan–Cu(ii) versus salen–Co(iii) catalysis

A new type of chiral salen–Co catalyst that features aromatic π-walls and an active Co(III) center has been developed for enantioselective Henry/nitroaldol reactions on the basis of salen–Cu catalysis. The asymmetric Henry reaction of aromatic aldehydes and nitromethane catalyzed by an Ar-BINMOL-derived salen–Co(III) complex was achieved with high yields (up to 93%) and excellent enantioselectivities (up to 98% ee). And more interestingly, it was supposed that either salan–Cu(II) or salen–Co(III) complex-catalyzed Henry reaction was an ideal model reaction for providing direct evidence of noncovalent interaction due to the distinguishable ortho-substituted aromatic aldehydes from meta- or para-substituted benzaldehydes in terms of enantioselectivities and yields.

Chemoselective N-heterocyclic carbene-catalyzed cross-benzoin reactions: importance of the fused ring in triazolium salts.

Morpholinone- and piperidinone-derived triazolium salts are shown to catalyze highly chemoselective cross-benzoin reactions between aliphatic and aromatic aldehydes. The reaction scope includes ortho-, meta-, and para-substituted benzaldehyde derivatives with a range of electron-donating and -withdrawing groups as well as branched and unbranched aliphatic aldehydes. Catalytic loadings as low as 5 mol % give excellent yields in these reactions (up to 99%).

Facile Si–H bond activation and hydrosilylation catalysis mediated by a nickel–borane complex

Metal–borane complexes are emerging as promising systems for study in the context of bifunctional catalysis. Herein we describe diphosphineborane nickel complexes that activate Si–H bonds and catalyze the hydrosilylation of aldehydes. Treatment of [MesDPBPh]Ni (1) ([MesDPBPh] = MesB(o-Ph2PC6H4)2) with organosilanes affords the complexes [MesDPBPh](μ-H)NiE (E = SiH2Ph (3), SiHPh2 (4)). Complex 4 is in solution equilibrium with 1 and the thermodynamic and kinetic parameters of their exchange have been characterized by NMR spectroscopy. Complex 1 is a catalyst for the hydrosilylation of a range of para-substituted benzaldehydes. Mechanistic studies on this reaction via multinuclear NMR spectroscopy are consistent with the intermediacy of a borohydrido-Ni-siloxyalkyl species.

ChemInform Abstract: Para Substituted Benzaldehydes as Expedient Reagents for the Oxidative Aromatization of Hydroquinoline.

AbstractThe reaction proceeds through an unprecedented hydride transfer from tetrahydroquinoline to arylaldehydes.

Para Substituted Benzaldehydes as Expedient Reagents for the Oxidative Aromatization of Hydroquinoline

A Cannizzaro-type reaction of tetrahydro-5(1H)-quinolinones with para substituted benzaldehydes in the presence of a base formed the corresponding quinoline and aryl methanol rather than arylidene derivatives because of the oxidation of tetrahydroquinoline and reduction of benzaldehydes as a result of unprecedented hydride transfer from tetrahydroquinoline to arylaldehydes. The reaction proceeds best with the participation of substituents with +M effect in substrate molecule.

CORRELATION ANALYSIS OF REACTIVITY IN THE OXIDATION OF SUBSTITUTED BENZALDEHYDES BY QUINOLINIUM FLUOROCHROMATE

Oxidation of thirty six monosubstituted benzaldehydes by quinolinium fluorochromate (QFC) in dimethylsulphoxide (DMSO), leads to the formation of corresponding benzoic acids. The reaction is of first order with respect to QFC. A Michaelis-Menten type kinetics was observed with respect to the reactants. The reaction is promoted by hydrogen ions; the hydrogen‑ion dependence has the form k obs =a +b[H + ]. The oxidation of [ 2 H]benzaldehyde (PhCDO) exhibited a substantial primary kinetic isotope effect. The reaction was studied in nineteen different organic solvents and the effect of solvent was analysed using Taft's and Swain's multi-parametric equations. The rates of the oxidation of para‑ and meta‑substituted benzaldehydes showed excellent correlation in terms of Charton’s triparametric LDR equation, whereas the oxidation of ortho-substituted benzaldehydes were correlated well with tetraperametric LDRS equation. The oxidation of para-substituted benzaldehydes is more susceptible to the delocalized effect than is the oxidation of ortho- and meta- substituted compounds, which display a greater dependence on the field effect. The positive value of h suggests the presence of an electron-deficient reaction centre in the rate-determining step. The reaction is subjected to steric acceleration by the ortho-substituents. A suitable mechanism has been proposed.

DC Electrical Conductivity of Some Oligoazomethines Doped with Nanotubes

Three aromatic oligoazomethines containing seven benzene rings each were synthesized. The terminal rings were substituted with different organic groups; namely, OH, H, and NO2. Synthesis was carried out according to the literature by condensing the para-substituted benzaldehydes with benzidine to give the three rings compound, which is then condensed with terephthaldehyde to give the respective seven benzene rings oligomer. The oligomers were used to investigate the effects of molecular structure on the electronic structure, as well as electronic and electrical properties. DC electrical conductivity variation of oligoazomethines is studied in the temperature range 300–500 K after annealing for 24 h at 100°C and after doping with 25 and 50 wt% Multi Wall Nanotubes (MWNTs). An attempt is made to relate DC electrical conductivity and electronic properties to chain length, substituted groups and coplanarity. The different groups attached to the ends showed a small effect on conductivity of the different oligomers in the following order: electron donating > neutral > electron withdrawing groups. Oligoazomethines-MWNTs gave a value of (10−4 Scm−1) as the highest electrical conductivity at higher temperatures. DC electrical conductivity was interpreted using the band energy model. The narrow-gap activation energies noted suggest its application in formulation of photovoltaic panels.

Preparation and antibacterial activity of Schiff bases from O-carboxymethyl chitosan and para-substituted benzaldehydes

Seven Schiff bases were synthesized from O-carboxymethyl chitosan (CMC) and para-substituted benzaldehydes. The Schiff bases were characterized through Fourier Transform Infrared Spectroscopy, Carbon-13 Nuclear Magnetic Resonance (13C NMR), Distortionless Enhancement of Polarization Transfer (DEPT) 135 NMR, elemental analysis, and acid–base titration. Antibacterial activities of the Schiff bases against Escherichia coli (E. coli, ATCC 35218) and Staphylococcus aureus (S. aureus, ATCC 25923) were measured through the optical density method. Antibacterial activity of the Schiff bases differs from the substituent at the para position of benzaldehyde, and decreases as the sequence OCH3 > CH3 > H > F > Cl > Br > NO2. The IC50 of the Schiff base from 4-methoxylbenzylaldehyde against E. coli and S. aureus is 30 and 34 ppm, respectively, much lower than that of chitosan (53, 48 ppm) and CMC (58, 60 ppm).

Synthesis and E/Z Configuration Determination of Novel Derivatives of 3-Aryl-2-(benzothiazol-2'-ylthio) Acrylonitrile, 3-(Benzothiazol-2'-ylthio)-4-(furan-2''-yl)-3-buten-2-one and 2-(1-(Furan-2''-yl)-3'-oxobut-1''-en-2-ylthio)-3-phenylquinazolin-4(3H)-one

Knoevenagel condensation of 2-(benzothiazol-2-ylthio) acetonitrile (2) with either furan-2-carbaldehyde or thiophene-2-carbaldehydes leads to E-isomers 4a–b exclusively, while the condensation of the compound 2 with benzaldehyde or para-substituted benzaldehydes with an electron-donating group afforded E/Z mixtures 4c–e with preferentially formation of the E-isomer. Condensation of furan-2-carbaldehyde (3a) with either 1-(benzothiazol-2'-ylthio) propan-2-one (5) or 2-(2'-oxo propylthio)-3-phenyl-quinazolin-4(3H)-one (9) leads exclusively to the Z-isomers of 6 and 10, respectively. The structures of the newly synthesized compounds were elucidated by elemental analyses, 1H-NMR and 13C-NMR spectra, COSY, HSQC, HMBC, NOE, MS and X-ray crystallographic investigations.

Mechanism and electronic effects in nitrogen ylide-promoted asymmetric aziridination reaction

The mechanism and stereoselectivity of the aziridination reaction between guanidinium ylide and a series of para-substituted benzaldehydes have been studied by using density functional theory methods. The mechanistic details and analyses of the key elementary steps involved in (a) the addition of nitrogen ylide to benzaldehydes and (b) subsequent fragmentation of the resulting oxaspirocyclic intermediate are presented. The relative energies of important transition states and intermediates are found to be useful toward rationalizing reported diastereoselective product formation. The relative energies of the key transition states could be rationalized on the basis of the differences in steric, electrostatic, and other stabilizing weak interactions. The deformation analysis of the transition state geometries exhibited good correlation with the predicted activation barriers. The changes in cis/trans diastereoselectivity preferences upon changes in the electron donating/withdrawing abilities of the para substituents on benzaldehyde are identified as arising due to vital differences in the preferred pathways. The large value of reaction constant (ρ > 4.8) estimated from the slope of good linear Hammett plots indicated high sensitivity to the electronic nature of substituents on benzaldehyde. The formation of trans-aziridine in the case of strong electron donating groups and cis-aziridines with weakly electron donating/withdrawing group has been explained by the likely changes in the mechanistic course of the reaction. In general, the predicted trends are found to be in good agreement with the earlier experimental reports.

Structure–Reactivity Correlation in the Oxidation of Substituted Benzaldehydes by Pyridinium Bromochromate

Oxidation of 36 monosubstituted benzaldehydes by pyridinium bromochromate (PBC) in dimethyl sulfoxide (DMSO), leads to the formation of corresponding benzoic acids. The reaction is first order with respect to both PBC and aldehydes. The reaction is promoted by hydrogen ions; the hydrogen–ion dependence has the form kobs = a + b[H+]. The oxidation of [2H]benzaldehyde (PhCDO) exhibited a substantial primary kinetic isotope effect. The reaction was studied in 19 different organic solvents and the effect of solvent was analysed using Taft's and Swain's multi-parametric equations. The rates of oxidation of para- and meta-substituted benzaldehydes showed excellent correlation in terms of Charton's triparametric LDR equation, whereas the oxidation of ortho-substituted benzaldehydes were correlated well with the tetraperametric LDRS equation. The oxidation of para-substituted benzaldehydes is more susceptible to the delocalized effect than is that of ortho- and meta-substituted compounds, which display a greater dependence on the field effect. The positive value of η suggests the presence of an electron-deficient reaction centre in the rate-determining step. The reaction is subjected to steric acceleration by the ortho-substituents. A suitable mechanism has been proposed.

ChemInform Abstract: The Aldol Reaction of Lithiopinacolonate with Substituted Benzaldehydes. Solvent and Structure Effects on Aggregation, Electrochemistry, and Heat of Reaction

The reaction of lithium pinacolonate with seven para-substituted benzaldehydes has been examined in tetrahydrofuran and acetonitrile. Reactions were clean, complete, and instantaneous at 25 o C, and heats of reaction were determined by titration calorimetry. Fairly good (R=0.96) correlations between heats of reaction and the usual Hammett σp substituent parameters were obtained although the ionization of substituted benzoic acids is scarcely an appropriate model for the aldol reaction in nonpolar media

ChemInform Abstract: Efficient Catalytic Activity of Polymerized Micelle-Forming Surfactants.

Abstract Micellar catalysis in the hydrolysis of para-substituted benzaldehyde diethylacetals by sodium 10-undecenyl sulfate is enhanced by polymerization of the surfactant aggregates.

Reaction of (−)-cis-verbenol epoxide with aromatic aldehydes over montmorillonite K10 clay

Reactions of (−)-cis-verbenol epoxide with a series of para-substituted benzaldehydes in the presence of montmorillonite K10 gave mixtures of products of intra- and intermolecular transformations, whose composition depended on the initial aldehyde.

New Conjugated Benzothiazole-N-oxides: Synthesis and Biological Activity

Eleven new 2-styrylbenzothiazole-N-oxides have been prepared by aldol – type condensation reactions between 2-methylbenzothiazole–N-oxide and para-substituted benzaldehydes. Compounds with cyclic amino substituents showed typical push-pull molecule properties. Four compounds were tested against various bacterial strains as well as the protozoan Euglena gracilis as model microorganisms. Unlike previously prepared analogous benzothiazolium salts, only weak activity was recorded.

Salivary Aldehyde Dehydrogenase: Activity towards Aromatic Aldehydes and Comparison with Recombinant ALDH3A1

A series of aromatic aldehydes was examined as substrates for salivary aldehyde dehydrogenase (sALDH) and the recombinant ALDH3A1. Para-substituted benzaldehydes, cinnamic aldehyde and 2-naphthaldehydes were found to be excellent substrates, and kinetic parameters for both salivary and recombinant ALDH were nearly identical. It was demonstrated that for the fluorogenic naphthaldehydes the only produced reaction product after incubation in saliva is the carboxylate.

Kinetics and Mechanism of the Oxidation of Substituted Benzaldehydes by [Bis(Trifluoroacetoxy)Iodo]Benzene

The oxidation of monosubstituted benzaldehydes by [bis(trifluoroacetoxy)iodo]-benzene (TFAIB), in acidic solution, leads to the formation of the corresponding benzoic acids. The reaction is first-order with respect to each the aldehydes, TFAIB and hydrogen ions. The reaction failed to induce the polymerization of acrylonitrile. The oxidation of [2H]benzaldehyde (PhCDO) indicated the presence of a substantial kinetic isotope effect. The effect of solvent composition indicated that the reaction rate increases with a decrease in the polarity of the medium. The rates of oxidation of meta- and para-substituted benzaldehydes showed excellent correlations in terms of Charton's triparametric LDR equation whereas the oxidation of ortho-substituted benzaldehydes correlated well with tetraparametric LDRS equation. The oxidation of para-substituted benzaldehydes is more susceptible to the delocalization effect but the oxidation of ortho- and meta-substituted compounds displayed a greater dependence on the field effect. The positive value of η suggests the presence of an electron-deficient reaction centre in the rate-determining step. The reaction is subjected to steric acceleration when ortho-substituents are present.