Synthesis of (-)-centrolobine by Prins cyclizations that avoid racemization |
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Authors: | Marumoto Shinji Jaber James J Vitale Justin P Rychnovsky Scott D |
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Institution: | Department of Chemistry, 516 Rowland Hall, University of California-Irvine, Irvine, California 92697-2025, USA. |
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Abstract: | formula: see text] The segment-coupling Prins cyclization avoids two of the problems common to other Prins cyclization protocols: side-chain exchange and partial racemization by reversible 2-oxonia Cope rearrangement. Model studies demonstrate the stereochemical fidelity of Prins cyclizations using alpha-acetoxy ethers compared with direct aldehyde-alcohol Prins reactions. Furthermore, we propose a mechanism for the racemization observed in some intermolecular Prins cyclizations. Two straightforward syntheses of optically pure (-)-centrolobine highlight the utility of Prins cyclizations. |
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