Search results for "SELE"

Aqueous selective photocatalytic oxidation of salicyl alcohol by TiO2 catalysts: Influence of some physico-chemical features

2021

Abstract Partial photocatalytic oxidation of salicyl alcohol (2-hydroxybenzyl alcohol) to salicylaldehyde in water was investigated under environmental friendly conditions in the presence of home-prepared and commercial TiO2 (Merck and Aeroxide P25) samples under UVA irradiation. The photocatalysts were characterized by using BET, XRD, SEM and/or TEM techniques. The effects of crystallinity degree, pH (3–11) and presence of a hole trap (ethanol) on the photocatalytic activity and product selectivity were investigated. 4-Hydroxybenzyl alcohol was also used to study the influence of the position of the substituent group in the aromatic ring. High alcohols conversion and product selectivity va…

Nanostructured rutile TiO2 for selective photocatalytic oxidation of aromatic alcohols to aldehydes in water

2008

WOS: 000253100100022

Photocatalytic oxidation of trans-ferulic acid to vanillin on TiO2 and WO3-loaded TiO2 catalysts

2015

Abstract The photocatalytic oxidation of trans-ferulic acid to vanillin in water has been studied by using various TiO2 and WO3-loaded TiO2 samples as catalysts. Different values of selectivity were obtained depending on the physico-chemical properties of the single samples and a vanillin selectivity of 10% was reached in the presence of the commercial TiO2 Merck. Higher selectivity values were obtained by impregnation of TiO2 with H2WO4 followed by calcination. The increased production of vanillin exhibited by the obtained WO3-loaded TiO2 powders was attributed to a reduced further oxidation of the aldehyde caused by the presence of the practically inactive tungsten trioxide hydrate on the…

ChemInform Abstract: Toward an Understanding of the Mechanisms of the Intramolecular [5 + 2] Cycloaddition Reaction of γ-Pyrones Bearing Tethered Alk…

2000

The molecular mechanism for the intramolecular [5 + 2] cycloaddition reaction of β-silyloxy-γ-pyrones bearing tethered alkenes has been characterized using ab initio methods. A comparative study for this sort of cycloaddition carried out at different computational levels points out that the B3LYP/6-31G* calculations give similar barriers to those obtained with the MP3/6-31G* level. Analysis of the energetic results shows that the reaction takes place along a stepwise process:  first, the migration of the neighboring silyl group to the carbonyl group of the γ-pyrone takes place to give a weak oxidopyrylium ylide intermediate, which by a subsequent concerted intramolecular [5 + 2] cycloadditi…

ChemInform Abstract: Asymmetric Synthesis Using Polymer-Immobilized Proline Derivatives

2012

Stereoselective Combinatorial Ugi-Multicomponent Synthesis on Solid Phase

2000

Solvent-free ruthenium-catalysed triflate coupling as a convenient method for selective azole-o-C-H monoarylation.

2019

Metal-catalysed ortho-directed C–H functionalization usually faces selectivity issues in the competition between mono- and disubstitution processes. We report herein the ruthenium-catalysed N-directed C–H monoarylation of arylpyrazoles with a selectivity of up to 96% or that generally reaches values above 80%. This selectivity is an effect of solvent-free conditions associated with sulfonate reagents, in the absence of frequently used acidic additives.

ChemInform Abstract: Highly Enantioselective Protonation of the 3,4-Dihydro-2-methylnaphthalen-1(2H)-one Li-Enolate by TADDOLs.

2001

A series of nine TADDOLs (=α,α,α′,α′-tetraaryl-1,3-dioxolane-4,5-dimethanols) 1a – 1i, have been tested as proton sources for the enantioselective protonation of the Li-enolate of 2-methyl-1-tetralone (=3,4-dihydro-2-methylnaphthalen-1(2H)-one). The enolate was generated directly from the ketone (with LiN(i-Pr)2 (LDA)/MeLi) or from the enol acetate (with 2 MeLi) or from the silyl enol ether (with MeLi) in CH2Cl2 or Et2O as the solvent (Scheme). The Li-enolate (associated with LiBr/LDA, or LiBr alone) was combined with 1.5 – 3.0 equiv. of the TADDOL at −78° by addition of the latter or by inverse addition. 2-Methyl-1-tetralone of (S)-configuration is formed (≤80% yield) with up to 99.5% sele…

Asymmetric Synthesis of Spiro Tetrahydrothiophene-indan-1,3-diones via a Squaramide-Catalyzed Sulfa-Michael/Aldol Domino Reaction

2016

Synthesis 48(08), 1131-1138(2016). doi:10.1055/s-0035-1560412

Stereoselective synthesis of 7,11-guaien-8,12-olides from santonin. Synthesis of podoandin and (+)-zedolactone A.

2000

Photochemical rearrangement of hydroxy ester 2, easily obtained from santonin (1), afforded butenolide 4, a good starting material for the synthesis of 7,11-guaien-8,12-olides. Compound 4 has been transformed into compound 10, which has been used for the synthesis of podoandin (5) and (+)-zedolactone A (ent-6). Regioselective elimination of the acetyl group on C10 afforded directly podoandin (5). For the synthesis of ent-6, a hydroxyl group has been regio- and stereoselectively introduced at the 4alpha-position through the 3alpha,4alpha-epoxide 15. The basic hydrolysis of the 10-acetyl group in compound 18 took place with concomitant intramolecular conjugated addition of the alkoxide to the…