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showing 10 items of 4721 documents
Asymmetric Tandem Reactions: New Strategies and Applications
2013
Abstract The application of allylic sulphoxides and, particularly, the chiral amine reagent tert-butanesulphinamide has been extended to three different tandem processes. The condensation of (R)-(+)-allyl p-tolyl sulphoxide, fluorinated nitriles and alkyl propiolates led to a new family of enantiomerically pure fluorine-containing 1,4- dihydropyridines. A diastereoselective nucleophilic addition of fluorinated nucleophiles onto (R)-(tert-butanesulphinyl) imines, followed by an intramolecular aza-Michael reaction gave rise to either fluorinated isoindolines or 3-substituted indanones in a stereoselective manner.
New Strategies for the Synthesis of Fluorinated Vinylogous Amidines and β-Enamino Ketones
2001
Reaction of fluorinated imidoyl chlorides 3 with ketimines 1a provides fluorinated 1,3-diimines, which were exclusively isolated as vinylogous amidine tautomers 2beta, with good yields. Fluorinated beta-enamino ketones 4 are obtained by regioselective hydrolysis of 2. Complementary methods for the synthesis of regioisomeric beta-enamino ketones 4 and 5 are also reported. These methods include the reaction of azaenolates of ketimines with fluorinated esters 6 and reactions of ketone enolates with fluorinated imidoyl chlorides 3. The behavior of these systems in hydrolysis reactions was also tested.
ChemInform Abstract: A Novel Synthesis of Chain-Extended Amino Sugar Derivatives Through Aza-Cope Rearrangement of N-Galactosyl-N-homoallylamines.
2010
Abstract Chain-extended amino sugars are synthesized via stereocontrolled Lewis acid-catalyzed aza-Cope rearrangement of N-glycosyl homoallylamines in high yield and stereoselectivity.
A novel synthesis of chain-extended amino sugar derivatives through aza-Cope rearrangement of N-galactosyl-N-homoallylamines
1998
Abstract Chain-extended amino sugars are synthesized via stereocontrolled Lewis acid-catalyzed aza-Cope rearrangement of N-glycosyl homoallylamines in high yield and stereoselectivity.
Photocatalytic oxidation of aromatic alcohols to aldehydes in aqueous suspension of home prepared titanium dioxide
2008
In this paper some intrinsic electronic properties of home prepared (HP) TiO2 catalysts were investigated by diffuse reflectance spectroscopy and quasi-Fermi level measurements. These powders were used for carrying out the photocatalytic oxidation of benzyl alcohol to benzaldehyde and CO2 in water; the selectivity for aldehyde formation was enhanced by the addition of small amounts of ethanol, a typical hole trap. The values of band gap, valence band and conduction band edges are almost identical for all the HP samples in which anatase phase is predominant, whereas appreciable differences can be noticed for an HP sample containing high amount of rutile phase. A comparative ATR-FTIR study of…
A DFT study of the mechanism of NHC catalysed annulation reactions involving α,β-unsaturated acyl azoliums and β-naphthol.
2016
The mechanism of NHC catalysed annulation reactions involving an α,β-unsaturated acyl azolium and β-naphthol has been studied using DFT methods at the MPWB1K/6-311G(d,p) level in toluene. For the C-C bond formation step, which corresponds to the rate- and stereo-determining step of this NHC catalysed reaction, the two competitive addition modes, i.e. the 1,2- and the 1,4-additions, have been studied. In toluene, acyl azolium forms an ion pair (IP) with the counterion chloride anion. Interestingly, β-naphthol forms a hydrogen bond with the chloride anion of IP, increasing the nucleophilic character of β-naphthol and the electrophilic character of the acyl azolium moiety. For the first time, …
Total Synthesis of (-)-C/D-cis-Dehydro-3-O-methyl-estradiols
2015
A convergent synthesis of (–)-dehydro-3-O-methyl-C/D-cis-estradiol started from stereochemically defined substituted optically active 3-(2-arylethyl)-γ-butyrolactones. Regioselective bromination of the anisyl moiety, reductive ring opening of the iodolactone, and protecting-group changes led to a Weinreb amide. This then underwent an intramolecular Grignard reaction closing the B-ring to give a tetralone with defined configuration. Introduction of C-11 through an allyl Grignard addition and subsequent ring-closing metathesis gave a tetrahydro phenanthrene derivative. Oxidation of the side-chain alcohol resulted in the key aldehyde group, and a final samarium-diiodide-mediated reductive D-ri…
Asymmetric Synthesis of Spirobenzazepinones with Atroposelectivity and Spiro-1,2-Diazepinones by NHC-Catalyzed [3+4] Annulation Reactions
2016
A strategy for the NHC-catalyzed asymmetric synthesis of spirobenzazepinones, spiro-1,2-diazepinones, and spiro-1,2-oxazepinones has been developed via [3+4]-cycloaddition reactions of isatin-derived enals (3C component) with in-situ-generated aza-o-quinone methides, azoalkenes, and nitrosoalkenes (4atom components). The [3+4] annulation strategy leads to the seven-membered target spiro heterocycles bearing an oxindole moiety in high yields and excellent enantioselectivities with a wide variety of substrates. Notably, the benzazepinone synthesis is atroposelective and an all-carbon spiro stereocenter is generated.
Reductive transformations - 11. stereoselective cycloannelation and bridging of the cyclooctatetraene dianionMakromol. Chem., Rapid. Commun. 1988, 9,…
1988
Abstract Bifunctional electrophiles with C4-, C6-, and C8-chains are reacted with the cyclooctatetraene dianion to selectively give novel cycloannelation and bridging products which possess a surprising stereochemistry and are useful starting compounds for further syntheses.
N-Glycosylamines of 4,6-O-ethylidene-alpha-D-glucopyranose: synthesis, characterisation and structure of CO2H, Cl and F ortho-substituted phenyl deri…
2000
A saccharide based ligand suitable for metal binding (HLCOOH) has been synthesized using 4,6-O-ethylidene-alpha-D-glucopyranose (4,6-O-EGP) and anthranilic acid. A few analogous glycosylamines with chloro and fluoro ortho substitutions have also been synthesized and characterised. Complexes of HLCOOH with Na+, K+, Mg2+, Ca2+, Ba2+, Cd2+ and Hg2+ have been isolated and characterised fully. The crystal structures of 4,6-O-EGP, the chloro analogue of HLCOOH and the K+ complex of L-COOH are established. The anomeric nature, orientation of the binding core and the co-ordination aspects of K+ have been derived from these structures.