Vanessa Kar-Yan Lo

Selective functionalisation of saturated C–H bonds with metalloporphyrin catalysts

The recent surge of interest in metal-catalysed C-H bond functionalisation reactions reflects the importance of such reactions in biomimetic studies and organic synthesis. This critical review focuses on metalloporphyrin-catalysed saturated C-H bond functionalisation reported since the year 2000, including C-O, C-N and C-C bond formation via hydroxylation, amination and carbenoid insertion, respectively, together with a brief description of previous achievements in this area. Among the metalloporphyrin-catalysed reactions highlighted herein are the hydroxylation of steroids, cycloalkanes and benzylic hydrocarbons; intermolecular amination of steroids, cycloalkanes and benzylic or allylic hydrocarbons; intramolecular amination of sulfamate esters and organic azides; intermolecular carbenoid insertion into benzylic, allylic or alkane C-H bonds; and intramolecular carbenoid C-H insertion of tosylhydrazones. These metalloporphyrin-catalysed saturated C-H bond functionalisation reactions feature high regio-, diastereo- or enantioselectivity and/or high product turnover numbers. Mechanistic studies suggest the involvement of metal-oxo, -imido (or nitrene), and -carbene porphyrin complexes in the reactions. The reactivity of such metal-ligand multiple bonded species towards saturated C-H bonds, including mechanistic studies through both experimental and theoretical means, is also discussed (244 references).

Gold-Catalyzed Highly Enantioselective Synthesis of Axially Chiral Allenes

Axially chiral allenes are synthesized from chiral propargylamines catalyzed by KAuCl4 in high yields (up to 93% yield) and excellent enantioselectivities (up to 97% ee) in CH3CN at 40 degrees C. The reaction has been applied to the synthesis of novel allene-modified artemisinin derivatives with the delicate endoperoxide moieties remaining intact. A tentative mechanism regarding gold(I)-catalyzed intramolecular hydride transfer was proposed on the basis of deuterium-labeling experiments and ESI-MS analysis of the reaction mixture.

Gold-mediated selective cysteine modification of peptides using allenes

A new approach for selective modification of cysteine-containing peptides through gold-mediated oxidative allene-thiol coupling reaction in aqueous medium is developed.

7.02 Oxidation by Metals (Nitrene)

Recent surge of interest in metal-catalyzed nitrene transfer reactions reflects the high importance of such reactions in organic synthesis. Nitrene transfer reaction, the analogous to carbene and oxo transfer reactions, involves the formation of a new covalent X–N bond, where X is mainly C atom for most of the metal-catalyzed nitrene transfer and insertion reactions. This class of reactions can also be viewed as oxidation due to the higher electronegativity of nitrogen atom than carbon atom. In this chapter, the focus is on the transition metal-catalyzed nitrene transfer and insertion reactions reported since the year 2000. A brief description of earlier studies is provided. Mechanistic studies including the preparation and characterization of the reaction intermediates and the identification of short-lived reactive species are discussed. The recent important findings in transition metal-catalyzed alkene aziridination, C–H amidation/amination, and sulfimidation reactions are highlighted in this chapter.