ORGN 751 |
| Alkaloids of the sparteine group are versatile chiral ligands with a range of useful applications in asymmetric synthesis. Only (–)-sparteine is conveniently obtained from lupine extracts and a practical stereocontrolled entry to this entire class of quinolizidines is desired. Previously, we demonstrated the transformation of an easily prepared C2V-symmetric tetraoxobispidine, representing the central B,C-rings of the sparteine skeleton, into racemic alpha-isosparteine. A variety of asymmetric methods could potentially be applied to such bisimides to effect their enantioselective desymmetrization into materials ideally suited for further conversion to enantioenriched sparteine bases. Ongoing efforts to achieve an asymmetric synthesis of sparteine along these lines will be presented. To date, N,N'-dibenzyl tetraoxobispidine 1 has been successfully desymmetrized in an enantioselective fashion by the agency of (S)-methyl-CBS-oxazaborolidine. Subsequent elaboration of the mono-reduced product from this transformation (2), via sequential Sakurai and Grignard allylations, has provided 4 and set the stage for advance on sparteine.
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Total Synthesis, Materials, Molecular Recognition, Process R&D, and Physical Organic Chemistry
8:00 PM-10:00 PM, Wednesday, 13 September 2006 Moscone Center -- Hall D, Poster
Division of Organic Chemistry |
