Organocatalytic asymmetric nitroaldol reaction: cooperative effects of guanidine and thiourea functional groups.
Catalytic enantio- and diastereoselective nitroaldol reactions were explored by using designed guanidine-thiourea bifunctional organocatalysts under mild and operationally simple biphasic conditions. These catalytic asymmetric reactions have a broad substrate generality with respect to the variety of aldehydes and nitroalkanes. Based on this catalytic nitroaldol process, straightforward syntheses of cytoxazone and 4-epi-cytoxazone were achieved. These catalytic nitroaldol reactions require KI as an additive for highly asymmetric induction; it operates by inhibiting the retro mode of the reaction. On the basis of studies of structure and catalytic-activity relationships, a plausible guanidine-thiourea cooperative mechanism and a transition state of the catalytic reactions are proposed. Drastic substituent effects on the catalytic properties of this catalyst may lead to the development of new chiral surfactants.
Sohtome
Yoshihiro
Y
Graduate School of Pharmaceutical Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
Takemura
Nobuko
N
Takada
Keisuke
K
Takagi
Rika
R
Iguchi
Toshitsugu
T
Nagasawa
Kazuo
K
D000447:Aldehydes / Q000737:chemistry*; D002384:Catalysis; D002853:Chromatography, Liquid; D019791:Guanidine / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D013890:Thiourea / Q000737:chemistry*
D000447:Aldehydes; C116609:3-hydroxybutanal; D013890:Thiourea; D019791:Guanidine