The straightforward synthesis of polystyrene-supported Chinchona alkaloids and their application in the asymmetric dimerization of ketenes is reported. Six different immobilized derivatives, consisting of three dimeric and two monomeric 9-O ethers, were prepared by “click” anchoring of soluble alkaloid precursors on to azidomethyl resins. The resulting insoluble polymer-bound (IPB) organocatalysts were employed for promoting the dimerization of in-situ generated ketenes. After opening of the ketene dimer intermediates with N,O-dimethylhydroxylamine, valuable Weinreb amides were eventually obtained in good yield (up to 81 %) and excellent enantiomeric purity (up to 96 % ee). All of the IPB catalysts could be recycled effectively without significant loss of activity and enantioselectivity. The extension to other asymmetric transformations (meso-anhydride desymmetrization and α-amination of 2-oxindoles) is also briefly discussed.
|Autori:||Jumde R.P. ; Di Pietro A.; Manariti A.; Mandoli A.|
|Titolo:||New Polymer-Supported Mono- and Bis-Cinchona Alkaloid Derivatives: Synthesis and Use in Asymmetric Organocatalyzed Reactions|
|Anno del prodotto:||2015|
|Digital Object Identifier (DOI):||10.1002/asia.201402924|
|Appare nelle tipologie:||1.1 Articolo in rivista|