Optically active allylic sulphides 10–13, bearing two different leaving groups, react with organocopper reagents by selective substitution of the heterocyclic moiety leading to optically active homoallylic pivalates with chemo-, regio- and enantio- control. This selectivity seems to be related to the coordination exerted by the heterocyclic nucleus towards the organometal.
Cross-benzoin condensation catalyzed by NHC, prepared from chiral triazolium salts bearing a pyridine ring, afforded α-hydroxy ketones with reasonable chemical yields and enantioselectivities. A wide range of aliphatic and aromatic aldehydes were successfully used in the reaction.
5-aza-semicorrins: A new class of bidentate nitrogen ligands for enantioselective catalysis
作者:Urs Leutenegger、Gisela Umbricht、Christoph Fahrni、Peter von Matt、Andreas Pfaltz
DOI:10.1016/s0040-4020(01)88880-3
日期:1992.1
C2-symmetric 5-aza-semicorrins are readily prepared in enantiomerically pure form starting from pyroglutamic acid. Methylation at N(5) leads to neutral bidentate nitrogen ligands. Copper(I) and palladium(II) complexes of these ligands have proved to be efficient enantioselective catalysts for the cyclopropanation of olefins and for allylic nucleophilic substitutions.
C 2对称的5-氮杂-半corrins很容易从焦谷氨酸开始以对映体纯的形式制备。N(5)处的甲基化导致中性双齿氮配体。这些配体的铜(I)和钯(II)配合物已被证明是用于烯烃环丙烷化和烯丙基亲核取代的有效对映选择性催化剂。