New polymer-supported mono- and bis-Cinchona alkaloid derivatives: synthesis and use in asymmetric organocatalyzed reactions.
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.
['Jumde|Ravindra P|RP|', 'Di Pietro|Anila|A|', 'Manariti|Antonella|A|', 'Mandoli|Alessandro|A|']
D000480:Alkynes D002384:Catalysis D002930:Cinchona Alkaloids D057930:Click Chemistry D003300:Copper D061565:Cycloaddition Reaction D019281:Dimerization D005030:Ethylenes D007659:Ketones D011108:Polymers D011137:Polystyrenes D013237:Stereoisomerism
ketenes desymmetrization Cinchona alkaloids asymmetric catalysis click chemistry supported catalysts