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Selective Transformation (selective + transformation)

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Chemistry	100%

Selected Abstracts

A Selective Transformation of Flavanones to 3-Bromoflavones and Flavones Under Microwave Irradiation

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1-2 2006
Zhongzhen Zhou
Abstract This paper presents the first report of a highly selective transformation of flavanones to 3-bromoflavones or flavones by microwave irradiation of the corresponding flavanone reactants and N -bromosuccinimide (NBS) in the presence of a catalytic amount of 2,2,-azobis(isobutyronitrile) (AIBN). The combination of good to excellent yields, shorter reaction time (10,min), and high levels of functional group compatibility make this an attractive synthetic approach to 3-bromoflavones and flavones. [source]

Synthesis of Pyrrole Derivatives through Functionalization of 3,4-Bis(lithiomethyl)dihydropyrroles

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 4 2003
José Barluenga
Abstract Bis(2-lithioallyl)amines 2, substituted at the double bonds, undergo intramolecular carbolithiation of a lithiated double bond in different solvents to afford dilithiated dihydropyrroles 3. Treatment of these dianions with electrophiles allows the preparation of functionalized pyrrole derivatives 5 and 6. Interestingly, treatment of these dianions with carboxylic esters selectively affords either keto or hydroxy compounds (9 or 10), depending on the conditions. Several experiments have been carried out in order to clarify the mechanism of this selective transformation. Finally, dilithiated dihydropyrrole 3a could be transformed in a three-step procedure into the corresponding 3,4-bis(bromomethyl) derivative 31, which can easily be converted into bicyclic pyrrole compounds 32,33 by treatment with different nucleophiles. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

Regioselective Reactions on a Chiral Substrate Controlled by the Configuration of a Chiral Catalyst

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 2-3 2010
Raju Ranjith Kumar
Abstract A racemic mixture may be partially transformed in the presence of a chiral catalyst by kinetic resolution and formation of products with new structural features. If the starting material is fully consumed the products may still be enantiomerically enriched. The situation is summarized in the Introduction. A brief discussion on the regioselective transformations occurring on a racemic mixture under the influence of a chiral catalyst is presented in Section 2. Often stereo-differences occur, each enantiomer of the starting material resulting in a different product. It allows one to predict what the behaviour of some enantiopure substrates should be in presence of each of the enantiomers of a chiral catalyst. Many examples are presented in Section 3. The chiral substrates under consideration have two different reacting sites, usually of the same nature (OH, CC, allylic positions, CH for carbene insertion, epoxide fragment, etc.). In some cases the absolute configuration of the catalyst allows an excellent control of the regioselectivity. This approach is promising for the selective transformation of chiral molecules. [source]