Organocatalytic asymmetric nitroaldol reaction: cooperative effects of guanidine and thiourea functional groups
摘要:
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.
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关键词:
chemoselectivity guanidine nitroaldol reaction organocatalysis surfactants BAYLIS-HILLMAN REACTION ENANTIOSELECTIVE HENRY REACTION ALPHA-AMINO-ACIDS DYNAMIC KINETIC RESOLUTION PHASE-TRANSFER CATALYSIS BIFUNCTIONAL CINCHONA ORGANOCATALYSTS QUATERNARY AMMONIUM-SALTS CHIRAL BICYCLIC GUANIDINE DIRECT CONJUGATE ADDITION HETERO-MICHAEL REACTION
DOI:
10.1002/asia.200700145
年份:
2007
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