Novel vanadium-catalyzed oxidation of alcohols to aldehydes and ketones under atmospheric oxygen

[reaction: see text] Oxidation of alcohols to aldehydes and ketones has been studied in high yields using atmospheric oxygen and a catalytic amount of V2O5 in toluene under heating (ca. 100 degrees C). Secondary alcohols can be chemoselectively converted into ketones in the presence of primary hydroxy groups.     

Fluorescent non-linear chiral polymer chemosensor bonded alternatively with 1,4-diethynyl-2,5-dioctyloxybenzene and (R,R)-salen for Zn2+recognition

Stereoregular non-linear chiral main chain polymers 1a–b bonded alternatively with (R,R)-salen and 1,4-diethynyl-2,5-dioctyloxybenzene moieties have been synthesized using palladium catalyzed C–C cross-coupling and Schiff base formation reactions as the key steps. These polymers are soluble in common organic solvents, and act as an effective chemosensor for the detection of Zn²⁺ with respect to other metal ions with enhanced fluorescence. The CD spectra observed for the polymers 1a–b could be attributed to the helical secondary structure with a low degree of inter-strand interactions. This reduced inter-strand interaction has been ascertained from the titration of pyridine to the Zn(II)-polymer 1b complex, which results in minor changes in the fluorescence emission.     

Copper(II)-catalyzed CH oxidation of alkylbenzenes and cyclohexane with hydrogen peroxide

Copper(II) complex 1 efficiently catalyses the oxidation of alkylbenzenes and cyclohexane into the corresponding ketones in moderate to high yields in the presence of 30% H₂O₂. This protocol is simple, clean and generates water as the only by-product.     

Copper(II)-catalyzed conversion of bisaryloxime ethers to 2-arylbenzoxazoles via C-H functionalization/C-N/C-O bonds formation

A copper(II)-catalyzed conversion of bisaryloxime ethers to 2-arylbenzoxazoles has been developed. The reaction involves a cascade C-H functionalization and C-N/C-O bond formation under oxygen atmosphere.     

Cobalt(II)-catalyzed oxidation of alcohols into carboxylic acids and ketones with hydrogen peroxide

The oxidation of aliphatic and aromatic alcohols into the corresponding carboxylic acid analogues and ketones has been carried out using 30% H₂O₂ and cobalt(II) complex 1 in good to high yields. The reaction is safe, clean and functions in the absence of additives.     

Formation and reactivity of cobalt(III)-dioxygen complexes promoted by 2-methylpropanal: Oxidation of alkenes and alcohols

2-Methylpropanal promotes the formation of cobalt(III)-dioxygen species from catalysts1 or2 and dioxygen. The cobalt(III)-dioxygen complexes efficiently catalyse the oxidation of various alcohols to carbonyl compounds in the presence of dioxygen and 2-methylpropanal. Similarly substituted alkenes are smoothly transformed to the corresponding monoepoxides under these reaction conditions. EPR study of these reactions indicates that different activated dioxygen species are formed in the presence of catalysts1 and2.     

Copper(II)‐Catalyzed Nitroaldol (Henry) Reactions: Recent Developments

Self‐assembled copper(II) complexes are described as effective catalysts for nitroaldol (Henry) reactions on water. The protocol involves a heterogeneous process and the catalysts can be recovered and recycled without loss of activity. Further, C2‐symmetric N,N′‐substituted chiral copper(II) salan complexes are found to be more effective catalysts than chiral copper(II) salen complexes for reactions in homogeneous catalysis, with high enantioselectivities. The reactions involve bifunctional catalysis, bearing the properties of a Brønsted base, as well as a Lewis acid, to effect the reaction in the absence of external additives.     

Synthesis, structure and application of chiral copper(II) coordination polymers for asymmetric acylation

Chiral copper(II) coordination polymers 1a-c have been prepared by one-pot synthesis in high yield. Their single-crystal X-ray analysis showed that repeating units are connected to each other by carboxylate linker and copper(II) atoms are pentacoordinated with distorted square-pyramidal geometry for 1a-b and square-planar geometry for 1c. These polymers have catalyzed the kinetic resolution of secondary alcohols by acylation with up to 90% ee ( s = 50).     

Copper(II)-catalyzed aerobic oxidative synthesis of substituted 1,2,3- and 1,2,4-triazoles from bisarylhydrazones via C-H functionalization/C-C/N-N/C-N bonds formation

An unprecedented copper(II)-catalyzed aerobic oxidative synthesis of 2,4,5-triaryl-1,2,3-triazoles and 1,3,5-triaryl-1,2,4-triazoles from bisarylhydrazones as the common starting precursor has been achieved via cascade C-H functionalization/C-C/N-N/C-N bonds formation under mild reaction conditions. One of the enthralling outcomes of this strategy is the copper(II)-catalyzed room temperature C-H functionalization/C-N bond formation in presence of air, which has been accomplished during the synthesis of substituted 1,2,4-triazoles. This new class of compounds could give prospective luminescence as an iconic component in the area of pharmaceutical and biological sciences. The intermediates for both the processes have been isolated to elucidate the mechanistic scenario.