ORGN 36 |
| Asymmetric catalysis is recognized to be a powerful tool in bringing about selective asymmetric transformations in many organic reactions. It has also been recognized that the presence of an additional element of symmetry like C2-axis brings about constraints that restrict the number of available diastereomeric transition states in the resting state of the intermediating chiral complex. This results in enhancement of enantiomeric excess in the product formed. We have employed the chiral amino-diol (shown below) that has been used for making complexes that act as promoters in asymmetric Diels-Alder, inverse-electron-demand Diels-Alder, Ene and Michael addition reactions. We have recently discovered that, for the first time, asymmetric 1,4-addition of various malonates to cyclic enones can be carried out using tetrabutylammoniumtetrahydroborate (TBATB) in the presence of a chiral ligand. The Michael adducts were formed in reasonably good yields (61 – 67%) with moderate ee's at 0 °C. 11B NMR spectroscopic studies explain this unexpected reactivity through the predominant formation of an aminodiol modified borate complex in the presence of a hydride acceptor.
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Asymmetric Reactions and Syntheses
8:00 AM-11:40 AM, Sunday, 26 March 2006 Georgia World Congress Center -- C302, Oral
Division of Organic Chemistry |
