PMID: 11312959Apr 21, 2001Paper

Studies in polyphenol chemistry and bioactivity. 3.(1,2) stereocontrolled synthesis of epicatechin-4alpha,8-epicatechin, an unnatural isomer of the B-type procyanidins

The Journal of Organic Chemistry
Alan P KozikowskiY Hu

Abstract

Oligomeric procyanidins containing 4alpha-linked epicatechin units are rare in nature and have hitherto not been accessible through stereoselective synthesis. We report herein the preparation of the prototypical dimer, epicatechin-4alpha,8-epicatechin (6), by reaction of the protected 4-ketones 11a,b with aryllithium reagents derived by halogen/metal exchange from the aryl bromides 26a,b. Removal of the 4-hydroxyl group from the resulting tertiary benzylic alcohols 27a,b was effected by tri-n-butyltin hydride and trifluoroacetic acid in a completely stereoselective manner, resulting in hydride delivery exclusively from the beta face. If benzyl was chosen for protection of the 3-hydroxyls, all protective groups could subsequently be removed in a single step by hydrogenolysis. tert-Butyldimethylsilyl groups, on the other hand, permitted selective deprotection of the 3-hydroxyls in preparation for their subsequent acylation with tri-O-benzylgalloyl chloride. Only monogalloylation at the "bottom" 3-hydroxyl took place when 28c was acylated under the previously reported conditions, reflecting the increased steric hindrance of the "top" 3-hydroxyl group in 28c compared with its 4beta,8-isomer 3. The preparation of compounds 14 and 17...Continue Reading

Citations

May 14, 2004·Proceedings of the National Academy of Sciences of the United States of America·Ken OhmoriKeisuke Suzuki
Apr 21, 2006·Organic Letters·David J MaloneySidney M Hecht
Feb 26, 2003·Organic Letters·Giovanni AppendinoGian Cesare Tron
Jun 8, 2017·Journal of Agricultural and Food Chemistry·Wayne E Zeller, Paul F Schatz
Dec 5, 2008·Molecules : a Journal of Synthetic Chemistry and Natural Product Chemistry·Fei HeChang-Qing Duan
Sep 30, 2010·Chemical Record : an Official Publication of the Chemical Society of Japan ... [et Al.]·Keisuke Suzuki
Dec 10, 2009·Angewandte Chemie·Shin-ya HayashiAtsuhiro Osuka
May 24, 2008·The Journal of Organic Chemistry·Yongxiang LiuZhen Yang
Jun 20, 2020·The Journal of Organic Chemistry·Bin ZhouGuido F Pauli
Mar 24, 2005·Journal of the American Chemical Society·David J MaloneySidney M Hecht

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