Asymmetric induction in the Michael reaction by means of chiral phase-transfer catalysts derived from cinchona and ephedra alkaloids
作者:Stefano Colonna、Alberto Re、Hans Wynberg
DOI:10.1039/p19810000547
日期:——
Asymmetricinduction in the Michaelreaction has been achieved using alkaloidonium salts in a two-phase system with optical yields of up to 36 and 26% in the addition to αβ-unsaturated ketones of thiols and nitroalkanes respectively. The presence of a hydroxy-group β to the 'onium function is essential to achieve substantial asymmetric syntheses.
New nitrocyclohexanols 3a-f are synthesized by a clean and original method from nitromethane 1 and unsaturated ketones 2a-f in the presence of solid potassium fluoride-alumina under solvent-free conditions coupled with microwave irradiation. The reaction involves a double and diastereoselective Michael addition followed by ring closure. Another diastereomer 3', which differs by the configuration of C-4, is obtained in the presence of piperidine and EtOH at room temperature. (C) 2003 Elsevier Ltd. All rights reserved.