Chiral Lewis Acid Catalysis in Nitrile Oxide Cycloadditions
作者:Mukund P. Sibi、Kennosuke Itoh、Craig P. Jasperse
DOI:10.1021/ja0318636
日期:2004.5.1
examples of highly regio- and enantioselective nitrileoxidecycloadditions to unsaturated alkenes using substoichiometric amounts of a chiral Lewis acid. Pyrazolidinones proved to be effective achiral templates in the cycloadditions providing C-adducts typically in >30:1 selectivity and 80-99% ee. To avoid potential problems involving coordination of the Lewis acid by amine bases, we have devised a novel
oxides and nitrones in the presence of Mg(II) cation as catalyst were evaluated. The presence of acetonitrile as co-solvent was found to be fundamental for the Lewis acid catalysis on solid-phase. The regio- and stereochemical outcome of nitrile oxide cycloadditions is influenced by nearly stoichiometric quantities of the cation, whilst catalytic amounts of Mg(II) influence both the reactivity and the
Catalytic efficiency, ligand acceleration, and concentration effect in magnesium ion mediated 1,3-dipolar cycloadditions of mesitonitrile oxide to allylic alcohols
Magnesium ion catalysis in nitrile oxide cycloadditions to allylic alcohols has been studied by use of stable mesitonitrile oxide. Moderate catalytic efficiency, ligand acceleration effect, and concentration effect have been observed to provide a promising access to a catalytic version of 1,3-dipolar cycloaddition reactions. (C) 1997 Elsevier Science Ltd.