title: Annulation approach to doubly linked (A-type) oligocatechins: syntheses of (+)-procyanidin A₂ and (+)-cinnamtannin B₁.
abstract: The first stereoselective syntheses of doubly linked (A-type) oligocatechins, (+)-procyanidin A2 and (+)-cinnamtannin B1, have been achieved. Ethylenedioxy-bridged flavans served as excellent platforms, thus allowing annulation with nucleophilic catechin units in a stereoselective manner. An additional key was the new synthetic approach to selectively protected nucleophilic catechin, thus enabling regioselective construction of the key dioxabicyclo skeleton of the A-type oligocatechins.
authors: Department of Chemistry, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro-ku, Tokyo 152-8551 (Japan).
authors: Yuji
authors: Y
authors: Ito
authors: Ken
authors: K
authors: Ohmori
authors: Keisuke
authors: K
authors: Suzuki
mesh_terms: D044946:Biflavonoids / Q000138:chemical synthesis* / Q000737:chemistry; D002392:Catechin / Q000138:chemical synthesis / Q000737:chemistry*; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D015394:Molecular Structure; D044945:Proanthocyanidins / Q000138:chemical synthesis* / Q000737:chemistry; D013237:Stereoisomerism
chemical_list: D044946:Biflavonoids; D044945:Proanthocyanidins; C542735:procyanidin A2; C479579:procyanidin B1; D002392:Catechin
keywords: annulation; heterocylces; natural products; structure elucidation; total synthesis