Search results for "Selectivity"

Photochemical Nitration by Tetranitromethane. Part XL. Regiochemistry of Trinitromethyl Attachment in the Photolysis of Benzofuran with Tetranitromet…

1997

(3RS,1SR)-3-Bromo-3-(1-phenylpropyl)chroman-2,4-dione

2005

The title compound, C18H15BrO3, was obtained by bromination of phenprocoumone with N-bromo­succin­imide. The X-ray structure confirms an earlier proposal concerning the regioselectivity of the reaction to introduce the Br atom at the 3-position.

ChemInform Abstract: Unique Regioselectivity in the C(sp3)-H α-Alkylation of Amines: The Benzoxazole Moiety as a Removable Directing Group.

2015

The benzoxazol-2-yl substituent is easily introduced by oxidative coupling or nucleophilic substitution and can be removed by hydroxide or by hydride reduction.

Homocalixpyridines: Ligands Exhibiting High Selectivity in Extraction and Sensor Processes

1998

A novel spherical host architecture, based on pyridine subunits, has been created. It exhibits selective complexing properties toward soft metal ions (right), which have been tested in extraction and sensor processes. The complex-forming behaviour can be tailored by variation of the size of the cavity and by substitution. Homocalixpyridines are interesting in view of their application as selective carriers in separation and sensing techniques.

A DFT study of the [3 + 2] versus [4 + 2] cycloaddition reactions of 1,5,6-trimethylpyrazinium-3-olate with methyl methacrylate.

2013

The reaction between 1,5,6-trimethylpyrazinium-3-olate and methyl methacrylate (MMA) yielding a lactone-lactam has been studied using the DFT method at the B3LYP/6-31G(d) level. It is concluded that formation of the lactone-lactam is a domino process involving three consecutive reactions: (i) a 1,3-dipolar cycloaddition (13DC) reaction between the pyrazinium-3-olate and MMA yielding a [3 + 2] cycloadduct (CA); (ii) a skeletal rearrangement, which converts the [3 + 2] CA into a formal [4 + 2] CA, possessing a diazabicyclo[2.2.2]octane structure; and finally, (iii) an S(N)2 reaction, promoted by halide anion, with concomitant nucleophilic attack of the created carboxylate anion on an iminium …

ChemInform Abstract: Selective “One-Pot” Synthesis of Functionalized Cyclopentenones.

2012

Reaction of squaric acid derivatives with vinyl magnesium bromide followed by treatment with trifluoroethanol allows a new and stereoselective access to functionalized cyclopentenones of type (III)/ (V).

ChemInform Abstract: Modular One-Pot Synthesis of Tetrasubstituted Pyrroles from α-(Alkylideneamino)nitriles.

2008

2,3,4,5-Tetrasubstituted pyrroles have been prepared with high regioselectivity by a formal cycloaddition of α-(alkylideneamino)nitriles and nitroolefins followed by elimination of HCN and HNO2. The reaction allows the convergent construction of the pyrrole ring in four steps from a nitroalkane and three aldehydes.

A new method for the regioselective synthesis of β-enamino acid derivatives

1993

Abstract A mild, simple and efficient route to β-enamino imidazole carbonilic derivatives 3 by reaction of ketimines with N,N′ -carbonyl diimidazole in the presence of boron triflouride as catalyst has been developed. The conversion of 3 to esters has also been explored.

Synthesis of 1,3-Oxazolidines and 1,3-Dioxolanes by Reaction of (2R, 3R)-3-Methylamino-3-phenyl-1,2-propanediol with Electrophiles

2003

Abstract The chemoselective reaction of (2R, 3R)-3-methylamino-3-phenyl-1,2-propanediol 1 with dimethoxypropane and dichloromethane under different conditions are reported as useful preparative procedures, for the synthesis 1,3-oxazolidines and 1,3-dioxolanes.

Influence of Reactant Polarity on the Course of the Inverse-Electron-Demand Diels−Alder Reaction. A DFT Study of Regio- and Stereoselectivity, Presen…

1999

The molecular mechanisms for the inverse-electron-demand Diels−Alder reactions between nitroethene and three substituted ethenes (propene, methyl vinyl ether, and dimethylvinylamine) to give the corresponding nitroso cycloadducts have been characterized with density functional theory methods using the B3LYP/6-31G* calculational level. On the basis of stability arguments and molecular orbital analysis relative rates, regioselectivity, and stereoselectivity, the presence of Lewis acid catalyst modeled by the BH3 system and the inclusion of solvent effects as a function of the nature of substituent in the dienophile fragment are analyzed and discussed. The ortho attack mode presents transition…