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DOI: 10.1055/s-0028-1083396
Resin-Bound Pyrrolidine Catalysts for Enamine-Mediated Reactions
Contributor(s):Yasuhiro Uozumi, Yoichi M. A. Yamada, Hidetoshi OhtaUniversity of California - Davis and University of California - Davis Cancer Center, Sacramento, USA
Asymmetric Catalysis: Resin-Bound Hydroxyprolylthreonine Derivatives in Enamine-Mediated Reactions
Angew. Chem. Int. Ed. 2008, 47: 6407-6410
Publication History
Publication Date:
23 October 2008 (online)
Key words
organocatalysis - pyrrolidine catalyst - asymmetric catalysis - enamine-mediated reaction
Significance
Tentagel-bound asymmetric pyrrolidine catalysts 1 and 2 are reported for the preparation of optically active chromanones 5. The catalysts mediated the asymmetric tandem aldol-Michael reactions with high enantioselectivity and complete diastereoselectivity. Thus, the reaction of 3 and cycloalkanones (4 and 6) was carried out with 1 in MeOH. The reaction mixture was then heated under microwave irradiation to give 5a-h in 71-90% yield with up to 97% ee (8 examples). The reaction with 2 under similar conditions afforded ent-5b-g and 5h in 77-94% yield with up to 99% ee (7 examples).
Comment
The polymeric catalysts were also effective for kinetic resolution of racemic 3-methylcycloalkanones 4 with 3 (2 equiv) to give the unreacted 3-methylcycloalkanone in 35-43% yield with 95-99% ee. Enantioselective aldol, Michael, and Robinson annulations, as well as Mannich reactions with catalysts 1 and 2 are also described.