Search results for "Tandem"

ChemInform Abstract: Multifaceted Palladium Catalysts Towards the Tandem Diboration-Arylation Reactions of Alkenes.

2009

Novel Pd(2) (6+) compounds have been synthesized in high yield. These compounds and their Pd(2) (4+) counterparts as synthetic precursors mediate the diboration of vinylarenes and aliphatic 1-alkenes, and under mild and basic reaction conditions they produce a variety of 1,2-diboronate esters with excellent conversions and chemoselectivities. The presence of bis(catecholato)diboron (B(2)cat(2)) favours the reduction of Pd(III) to Pd(II), while the catalytic precursor of Pd(II) is transformed into Pd(0)-nanoparticles. An "in situ" catalytic tandem reaction has been designed to transform the diboronate intermediates into the monoarylated product, which after oxidative workup, provides the car…

ChemInform Abstract: Tandem Asymmetric Michael Reaction-Intramolecular Michael Addition. An Easy Entry to Chiral Fluorinated 1,4-Dihydropyridines.

2010

The sequential treatment of optically active sulfoxide (I) with fluorinated nitriles and alkyl propiolates affords (sulfinylmethyl)dihydropyridines of type (IV) as single diastereomers in most cases.

β-Branched α-Halo Carboxylic Acid Derivatives via Stereoselective 1,4 Addition of Dialkylaluminum Chlorides to α,β-Unsaturated N-Acyloxazolidinones

1997

The stereoselective synthesis of β-branched α-halo carboxylic acids containing two newly formed chiral centers is accomplished by a reaction cascade consisting of the 1,4 addition of dialkylaluminum chlorides to α,β-unsaturated N-acyloxazolidinones and subsequent reaction of the intermediate aluminum enolates with N-halosuccinimide. The most efficient stereocontrol in these tandem processes has been achieved with oxazolidinones derived from glucosamine. Not only aryl substituted but also purely aliphatic β-branched α-halo carboxylic acids can be stereoselectively synthesized by this method. However, the reactions of β-aryl α,β-unsaturated N-acyloxazolidinones show the highest diastereoselec…

Monitoring Alternaria mycotoxins and pesticide residues in tomato by dispersive liquid–liquid microextraction coupled to gas chromatography–tandem ma…

2013

1,7-Octadiene-Assisted Tandem Multicomponent Cross-Enyne Metathesis (CEYM)-Diels-Alder Reactions: A Useful Alternative to Mori’s Conditions

2012

The use of 1,7-octadiene as an in situ source of ethylene led us to develop a novel multicomponent tandem cross-enyne metathesis (CEYM)-Diels-Alder reaction. The process can be considered a relay metathesis, in which the ethylene liberated in the ring-closing metathesis (RCM) of 1,7-octadiene initiates the tandem sequence. Aliphatic, aromatic, and fluorinated alkynes and several dienophiles are compatible with the process, which is particularly efficient with aromatic alkynes. This methodology constitutes a useful variant of Mori's conditions in CEYM-related reactions.

ChemInform Abstract: 1,7-Octadiene-Assisted Tandem Multicomponent Cross-Enyne Metathesis (CEYM)-Diels-Alder Reactions: A Useful Alternative to Mori′s…

2013

The protocol relies on a relay metathesis process, in which 1,7-octadiene acts as an in situ source of ethylene.

A New Tandem Cross Metathesis-Intramolecular Aza-Michael Reaction for the Synthesis of α,α-Difluorinated Lactams

2012

A new tandem cross metathesis–intramolecular aza-Michael­ reaction in which an α,α-difluorinated amide serves as a source of nucleophilic nitrogen is described. This process gives rise to a new family of fluorinated γ- and δ-lactams. The tandem protocol is catalyzed by the Hoveyda–Grubbs second-generation ruthenium catalyst with titanium(IV) tetraisopropoxide as a co-catalyst and it is highly efficient when conjugated ketones are used as the Michael acceptors. With conjugated esters, however, it is necessary to perform a step-by-step procedure in which the cyclization event is activated by the addition of a base. An asymmetric version of the process is also evaluated.

ChemInform Abstract: Tandem Nucleophilic Addition-Intramolecular Aza-Michael Reaction: Facile Synthesis of Chiral Fluorinated Isoindolines.

2011

A highly stereoselective synthesis of fluorinated 1,3-disubstituted isoindolines is described. To this end, a tandem reaction consisting of a diastereoselective addition of fluorinated nucleophiles to Ellman’s N-(tert-butanesulfinyl)imines followed by an intramolecular aza-Michael reaction has been developed. This strategy allows for the construction of isoindolines bearing several degrees of fluorination (mono-, di-, or trifluoromethyl as well as heavier fluorinated groups). In the majority of all cases, the products are formed as single isomers.

ChemInform Abstract: Catalytic Aminomercuration of Olefins in a Tandem Aminomercuration-Deoxymercuration; One-Step Synthesis of Secondary N-Arylallyl…

1990

Abstract Allyl alcohols react with primary aromatic amines and stoichiometric amounts of mercury(II) tetrafluoroborate to give mixtures of mono- and diallyl anilines. However, the use of the tandem aminomercuration-deoxymercuration promoted by catalytic mercury(II) tetrafluoroborate allows to perform regiospecifically the monoallylation reaction with very high yields. A mechanism is proposed to account for the observed results.

ChemInform Abstract: A New Tandem Cross Metathesis-Intramolecular Aza-Michael Reaction for the Synthesis of α,α-Difluorinated Lactams.

2012

Difluorinated amides are treated with methyl vinyl ketone or analogous esters to produce the desired γ- and δ-lactam units including optically active versions.