ORGN 307 |
| Cyclohexa-2,4-dienone derivatives, such as ortho-quinone monoketals (e.g., 2) and ortho-quinols (e.g., 3), have proven extremely useful in the construction of many complex natural product architectures. Nevertheless, obtention of these functionalized building blocks in an enantiomerically pure form keeps challenging organic chemists. Our interest in the hypervalent iodine-mediated dearomatization of phenols led us to accomplish an asymmetric synthesis of ortho-quinone monoketals 2 in quantitative yields and diastereomeric ratios up to 95:5 according to the nature of the R alkyl group. A rationalization of this stereochemical control can be made on the basis of an iodine-centered ligand coupling mechanism. The chiral ketal unit of 2 was then used to induce asymmetry in subsequent reactions, and was finally removed to afford enantiopure synthons (e.g., 3). Their exploitation for the total synthesis of natural products, such as Amaryllidaceae lycorine-type alkaloids and carvacrol-based dimer, will be also discussed.
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Asymmetric Reactions and Syntheses
1:00 PM-5:00 PM, Monday, 11 September 2006 Moscone Center -- Room 131, Oral
Division of Organic Chemistry |
