title: New polymer-supported mono- and bis-Cinchona alkaloid derivatives: synthesis and use in asymmetric organocatalyzed reactions.
abstract: 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.
authors.affiliation: Dipartimento di Chimica e Chimica Industriale, Università di Pisa and Istituto di Chimica dei Composti Organometallici del CNR (Sez. di Pisa), Via G. Moruzzi 3, Pisa 56124 (Italy), Fax: (+39) 050-2219260; Istituto di Scienze e Tecnologie Molecolari del CNR, Via Golgi 19, Milano 20133 (Italy).
authors.forename: Ravindra P
authors.initials: RP
authors.lastname: Jumde
authors.forename: Anila
authors.initials: A
authors.lastname: Di Pietro
authors.forename: Antonella
authors.initials: A
authors.lastname: Manariti
authors.forename: Alessandro
authors.initials: A
authors.lastname: Mandoli
mesh_terms: D000480:Alkynes / Q000737:chemistry; D002384:Catalysis; D002930:Cinchona Alkaloids / Q000138:chemical synthesis / Q000737:chemistry*; D057930:Click Chemistry; D003300:Copper / Q000737:chemistry; D061565:Cycloaddition Reaction; D019281:Dimerization; D005030:Ethylenes / Q000737:chemistry; D007659:Ketones / Q000737:chemistry; D011108:Polymers / Q000737:chemistry*; D011137:Polystyrenes / Q000737:chemistry; D013237:Stereoisomerism
chemical_list: D000480:Alkynes; D002930:Cinchona Alkaloids; D005030:Ethylenes; D007659:Ketones; D011108:Polymers; D011137:Polystyrenes; D003300:Copper; C008223:ketene
keywords: Cinchona alkaloids; asymmetric catalysis; click chemistry; desymmetrization; ketenes; supported catalysts