Friedländer condensation of 5‐aminopyrazole‐4‐carbaldehydes with reactive α‐methylene ketones: Synthesis of pyrazolo[3,4‐b]pyridines

A series of 1,3,6‐trisubstituted and 1,3,5,6‐tetrasubstituted pyrazolo[3,4‐b]pyridines 5 has been synthesized by Friedlander condensation of 5‐arninopyrazole‐4‐carbaldehydes 3 with α‐methylene ketones such as acetone (4a) or acetophenones 4b‐f with potassium hydroxide as basic catalyst. Condensation of 5‐aminopyrazole‐4‐carbaldehydes 3 and unsymmetric dialkylketones 6 yielded mixtures of isomeric pyra‐zolo[3,4‐b]pyridine derivatives 7 and 8 . Condensation of 5‐aminopyrazole‐4‐carbaldehydes 3 with CH‐acidic acylacetonitriles 9 and acylacetates 11 with piperidine as basic catalyst yielded pyrazolo[3,4‐b]pyri‐dine‐5‐carbonitriles 10 and pyrazolo[3,4‐b]pyridine‐5‐carboxylates 12 ; with diethyl malonate 13 as CH‐acidic component, pyrazolo[3,4‐b]pyridin‐6‐ones 14 were obtained.     

Directly Knitted Hierarchical Porous Organometallic Polymer-Based Self-Supported Single-Site Catalyst for CO2 Hydrogenation in Water

In recent times, heterogenization of homogeneous molecular catalysts onto various porous solid support structures has attracted significant research focus as a method for combining the advantages of both homogeneous as well as heterogeneous catalysis. The design of highly efficient, structurally robust and reusable heterogenized single-site catalysts for the CO₂ hydrogenation reaction is a critical challenge that needs to be accomplished to implement a sustainable and practical CO₂-looped renewable energy cycle. This study demonstrated a heterogenized catalyst [Ir-HCP-(B/TPM)] containing a molecular Ir-abnormal N-heterocyclic carbene (Ir-aNHC) catalyst self-supported by hierarchical porous hyper-crosslinked polymer (HCP), in catalytic hydrogenation of CO₂ to inorganic formate (HCO₂⁻) salt that is a prospective candidate for direct formate fuel cells (DFFC). By employing this unique and first approach of utilizing a directly knitted HCP-based organometallic single-site catalyst for CO₂-to-HCO₂⁻ in aqueous medium, extremely high activity with a single-run turnover number (TON) up to 50816 was achieved which is the highest so far considering all the heterogeneous catalysts for this reaction in water. Additionally, the catalyst featured excellent reusability furnishing a cumulative TON of 285400 in 10 cycles with just 1.6 % loss in activity per cycle. Overall, the new catalyst displayed attributes that are important for developing tangible catalysts for practical applications.     

Study of ion–solvent interactions of some tetraalkylammonium halides in THF + CCl4 mixtures by conductance measurements

Conductivities of some tetraalkylammonium halides, viz. tetrapentylammonium chloride (Pen₄NCl), tetrahexylammonium chloride (Hex₄NCl), tetraheptylammonium chloride (Hep₄NCl), and tetraoctylammonium chloride (Oct₄NCl) were measured at 298.15 K in THF + CCl₄ mixtures with 40, 60 and 80 mass% of THF. A minimum in the conductometric curves (molar conductance, Λ vs. square root of concentration, √c) was observed at concentrations which is dependent both on the salt and the solvent. The observed molar conductivities were explained by the formation of ion-pairs (M⁺ + X⁻ ↔ MX, K_P) and triple-ions (2M⁺ + X⁻ ↔ M₂X⁺; M⁺ + 2X⁻ ↔ MX₂⁻, K_T). A linear relationship between the triple-ion formation constants [log(K_T/K_P)] and the salt concentrations at the minimum conductivity (log C_min) was given for all salts in THF + CCl₄ mixtures. The formation of triple-ions might be attributed to the ion sizes in solutions in which coulombic interactions and covalent bonding forces act as the main forces between the ions (R₄N⁺X⁻).     

Investigations in the transition metal catalyzed aziridination of olefins, amination, and other insertion reactions with Bromamine-T as the source of nitrene.

Investigations into the transition metal catalyzed aziridination of olefins with Bromamine-T as a new source of nitrene is presented in this account. Comparison of Chloramine-T and Bromamine-T in this reaction indicates that the latter is superior as the source of nitrene. Systematic study with several transition metal based catalysts suggests that Cu-halides are the best catalysts. A first report of aziridination under microwave and ultrasound irradiation conditions is also presented. Copper-catalyzed aziridination of methyl cinnamate with Bromamine-T did not proceed at ambient temperature but was effected smoothly under ultrasound irradiation to furnish trans-aziridine selectively, while under microwave irradiation, a mixture of cis and trans isomers, was obtained. It has been demonstrated that aziridination of olefins proceeds smoothly with inexpensive bleaching powder. Preliminary results of Rh-catalyzed benzylic insertion reactions with Bromamine-T are included in this account.     

Enantiodivergent synthesis of N-protected azetidine-2-carboxylic acid

A new route to both enantiomers of N-tosyl-azetidine-2- carboxylic acid has been developed from (R)-2-cyclohexylideneglyceraldehyde which proceeded with good overall yield and excellent enantiomeric purity.     

Molar volumes,viscosity, and isentropic compressibility of some primary monoalkanols in aqueous N,N-dimethylformamide solutions

The densities (ρ) and viscosities (η) for the ternary liquid mixtures of water + N,N-dimethylformamide + monoalkanols, have been measured as a function of the composition at 298.15, 308.15, and 318.15 K. From the experimental measurements excess molar volumes (V ^E), Viscosity deviation (Δη), and synergy index (I _s) have been evaluated. The speeds of sound have been also measured and excess isentropic compressibilities (K _s^E) are calculated al 298.15 K. The results are discussed and interpreted in terms of molecular package and specific interaction predominated by hydrogen bonding, been investigated.     

Quantum dynamics of H + LiH reaction and its isotopic variants

Time-dependent quantum wave packet dynamics study is carried out to investigate the initial state selected channel specific reactivity of H + LiH collisional system on a new and more accurate ab initio potential energy surface developed by Wernli et al. [J. Phys. Chem. A 113, 1121 (2009)]. The H + LiH reaction proceeds through LiH depletion and H-exchange paths. While the former path is highly exoergic (by ～2.258 eV), the latter path is thermoneutral. State selected and energy resolved integral reaction cross sections and thermal rate constants are reported and compared with the literature data. The reactivity of the LiH depletion channel is found to be greater than the H-exchange channel. Rotational excitation of the reagent LiH molecule causes a decrease of reactivity of both the channels. On the other hand, the vibrational excitation of the reagent LiH decreases the reactivity of the LiH depletion channel and increases the reactivity of the H-exchange channel. The effect of isotopic substitution (H by D) on the reaction dynamics is also examined.     

Non-radiative depletion of the excited electronic states of 9-cyanoanthracene in presence of tetrahydronaphthols

Both steady state and time resolved spectroscopic measurements reveal that the prime process involved in quenching mechanism of the lowest excited singlet (S1) and triplet (T1) states of the well known electron acceptor 9-Cyanoanthracene (9CNA) in presence of 5,6,7,8-tetrahydro-1-naphthol (TH1N) or 5,6,7,8-tetrahydro-2-naphthol (TH2N) is H-bonding interaction. It has been confirmed that the fluorescence of 9CNA is not at all affected in presence of 5,6,7,8-tetrahydro-2-methoxy naphthalene (TH2MN) both in non-polar n-heptane (NH) and highly polar acetonitrile (ACN) media. This indicates that the H-bonding interaction is crucial for the occurrence of the quenching phenomenon observed in the present investigations with TH1N (or TH2N) donors and 9CNA acceptor. In ACN solvent both contact ion-pair (CIP) and solvent-separated (or dissociated) ions are formed due to intermolecular H-bonding interactions in the excited electronic states (both singlet and triplet). In NH environment due to stronger H-bonding interactions, the large proton shift within excited charge transfer (CT) or ion-pair complex, 1 or 3(D+-H...A-), causes the formation of the neutral radical, 3(D+H-A)*, due to the complete detachment of the H-atom. It is hinted that both TH1N and TH2N due to their excellent H-bonding ability could be used as antioxidants.     

Solvent- or temperature-controlled diastereoselective aldol reaction of methyl phenylacetate

Unlike the enolboration-aldolization of methyl propanoate, the choice of either the solvent or temperature determines the diastereoselectivity during the enolboration-aldolization of methyl phenylacetate. In CH(2)Cl(2), the reaction favors the anti-pathway at -78 °C and the syn-pathway at rt. Conversely, the reaction produces the anti-isomer up to rt and the syn-isomer at refluxing temperatures in nonpolar solvents.