期刊
EUROPEAN JOURNAL OF ORGANIC CHEMISTRY
卷 2012, 期 21, 页码 3978-4017出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/ejoc.201200207
关键词
Acylation; Natural products; Total synthesis; 1; 3-Dienes; Furanones; Self-reproduction of stereocenters; Stereoselectivity; Structure elucidation
资金
- International Research Training Group 1038 Catalysts and Catalytic Reactions for Organic Synthesis of the Deutsche Forschungsgemeinschaft
Comprehensive comparisons of 1H and 13C NMR chemical shift values in the furanone cores a, b, and c provide plausible support for a reassessment of the furanone nuclei of the title compounds from b to c. Total syntheses via enantiomerically pure lactic esters were based on the Seebach-Frater self-reproduction of stereocenters methodology. Attachment of the hexadienyl side-chain in a trans,trans-selective manner was achieved by addition of the SeebachFrater enolate to trans-hex-4-en-1-al rather than to trans-hex-3-en-1-al. The type-c furanone cores of the synthetic materials were reached by single or double acylation of a model gamma-hydroxy-beta-oxo ester (compound 50) and its hexadiene-containing counterpart 29. Our syntheses confirmed the novel connectivities in six compounds. In addition, they required revision of the configuration of a quaternary carbon atom in five cases. Moreover, they allowed elucidation of the configurations of four previously unassigned stereocenters. Hindsight analyses of why the furanone cores of the title compounds had been misinterpreted as a and/or b instead of c are given. Why the stereocenters in the heterocycles had been incorrectly configured, on the bases (a) of relay studies in the 1960s, and (b) of a 1984 total synthesis of gregatin B, is also discussed.
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