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Biomimetic Synthesis of Fused Polypyrans:  Oxacyclization Stereo- and Regioselectivity Is a Function of the Nucleophile

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journal contribution
posted on 2003-05-21, 00:00 authored by Fernando Bravo, Frank E. McDonald, Wade A. Neiwert, Bao Do, Kenneth I. Hardcastle
The stereoselectivity of Lewis acid-induced endo-regioselective oxacyclizations of 1,4-diepoxides is dependent upon the nature of the terminating nucleophile. For instance, the tert-butyl carbonate-substituted diepoxide of 3,6-dimethylhepta-2,5-dien-1-ol provides a cis-fused bicyclic product, whereas the N,N-dimethylcarbamate derivative affords the trans-fused diastereomer. Stereospecific and regioselective conversion of the tertiary carbamate-terminated 1,4,7-triepoxide (I) to tricyclic all-trans-fused polypyran (II) is also demonstrated.

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