A Selective, Efficient and Environmentally Friendly Method for the Oxidative Cleavage of Glycols

A catalytic methodology for the oxidative cleavage of vicinal diols is described as an advantageous alternative in terms of the environmental impact on classical methods involving toxic oxidants. The novel strategy is based on the use of dioxomolybdenum(VI) complexes as catalysts and dimethyl sulfoxide (DMSO) as an oxidant and displays high selectivity and a broad scope for glycol cleavage. In addition, the developed system is also useful for the oxidation of acyloins to diketones.Ministerio de Economía y Competitividad (MINECO) and FEDER (CTQ2013-48937-C2-1-P) and Junta de Castilla y León (BU237U13

Oxidation of benzoin catalyzed by oxovanadium (IV) schiff base complexes

BACKGROUND: The oxidative transformation of benzoin to benzil has been accomplished by the use of a wide variety of reagents or catalysts and different reaction procedures. The conventional oxidizing agents yielded mainly benzaldehyde or/and benzoic acid and only a trace amount of benzil. The limits of practical utilization of these reagents involves the use of stoichiometric amounts of corrosive acids or toxic metallic reagents, which in turn produce undesirable waste materials and required high reaction temperatures. In recent years, vanadium complexes have attracted much attention for their potential utility as catalysts for various types of reactions. RESULTS: Active and selective catalytic systems of new unsymmetrical oxovanadium(IV) Schiff base complexes for the oxidation of benzoin is reported. The Schiff base ligands are derived between 2-aminoethanol and 2-hydroxy-1- naphthaldehyde (H2L1) or 3-ethoxy salicylaldehyde (H2L3); and 2-aminophenol and 3-ethoxysalicylaldehyde (H2L2) or 2-hydroxy-1-naphthaldehyde (H2L4). The unsymmetrical Schiff bases behave as tridentate dibasic ONO donor ligands. Reaction of these Schiff base ligands with oxovanadyl sulphate afforded the mononuclear oxovanadium(IV) complexes (VIVOLx.H2O), which are characterized by various physico-chemical techniques. The catalytic oxidation activities of these complexes for benzoin were evaluated using H2O2 as an oxidant. The best reaction conditions are obtained by considering the effect of solvent, reaction time and temperature. Under the optimized reaction conditions, VOL4 catalyst showed high conversion (>99%) with excellent selectivity to benzil (~100%) in a shorter reaction time compared to the other catalysts considered. CONCLUSION: Four tridentate ONO type Schiff base ligands were synthesized. Complexation of these ligands with vanadyl(IV) sulphate leads to the formation of new oxovanadium(IV) complexes of type VIVOL.H2O. Elemental analyses and spectral data of the free ligands and their oxovanadium(IV) complexes were found to be in good agreement with their structures, indicating high purity of all the compounds. Oxovanadium complexes were screened for the oxidation of benzoin to benzil using H2O2 as oxidant. The effect of time, solvent and temperature were optimized to obtain maximum yield. The catalytic activity results demonstrate that these catalytic systems are both highly active and selective for the oxidation of benzoin under mild reaction conditions.Web of Scienc

Lewis Acid Catalyzed Reactions of Aziridino-Olefins

Electrophilic reactions resulting in the formation of new carbon-carbon bonds are important tools in organic synthesis. For example, the acid catalyzed cyclization of epoxy olefins has been well documented, while similar cyclizations with aziridines have been largely unexplored. The aim of this project is to develop and demonstrate the formation of a carbocyclic compound from aziridino-olefins utilizing a Lewis acid to catalyze the cyclization. In working toward this goal, a number of aziridino-olefins were synthesized from isoprenoid start materials. These aziridino-olefins were then reacted with both Lewis and protic acids in an attempt to induce cyclization. As a result, we have demonstrated the formation of both the desired carbocyclic products as well as competing cyclizations to oxazoline products

Palladium-Catalyzed Cross-Coupling Reactions of Organosilanols: I. New Methods That Employ Alkynylsilanols and Bissilyl Reagents. II. Mechanistic Analysis of the Cross-Coupling of Aryldimethylsilanolates

587 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007.Mechanistic investigations of the palladium-catalyzed cross-coupling of aryldimethylsilanolates demonstrated that transmetalation proceeds directly from an arylpalladium(II) silanolate intermediate without external activation. Arylpalladium(II) silanolate complexes bearing phosphine ligands were isolated and characterized. These complexes produce biaryl products via ligand dissociation and transmetalation.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD

Oxidation of Benzoins to Benzils using Bismuth(III) Nitrate-Copper(II) Acetate

Benzoins are oxidized to benzils in excellent yields by 0.4 equivalents of Bi(NO3)3.5H20 and 4 mol% of Cu(OAc)23)3.5H20 is a stable, inexpensive, commercially available solid. The relatively low cost and low toxicity of bismuth(Ill) nitrate makes this procedure a particularly attractive method for oxidation of benzoins

Mechanistic Significance of the Si–O–Pd Bond in the Palladium-Catalyzed Cross-Coupling Reactions of Alkenylsilanolates

Through the combination of reaction kinetics (both catalytic and stoichiometric) and solid-state characterization of arylpalladium­(II) alkenyl­silanolate complexes, the intermediacy of covalent adducts containing Si–O–Pd linkages in the cross-coupling reactions of organo­silanolates has been unambiguously established. Two mechanistically distinct pathways have been demonstrated: (1) transmetalation via a neutral 8-Si-4 intermediate that dominates in the cross-coupling of potassium alkenyl­silanolates, and (2) transmetalation via an anionic 10-Si-5 intermediate that dominates in the cross-coupling of cesium alkenyl­silanolates. Arylpalladium­(II) alkenyl­silanolate complexes bearing various phosphine ligands (both bidentate and monodentate) have been isolated, fully characterized, and evaluated for their kinetic competence under thermal (stoichiometric) and anionic (catalytic) conditions. Comparison of the rates for thermal and anionic activation demonstrates that intermediates containing the Si–O–Pd linkage are involved in the cross-coupling process