title: Enantioselective total syntheses of citrinadins A and B. Stereochemical revision of their assigned structures.
abstract: The concise, enantioselective total syntheses of (-)-citrinadin A and (+)-citrinadin B in a total of only 20 and 21 steps, respectively, from commercially available starting materials are described. Our strategy, which minimizes refunctionalization and protection/deprotection operations, features the highly diastereoselective, vinylogous Mannich addition of a dienolate to a chiral pyridinium salt to set the first chiral center. The absolute stereochemistry of this key center was then relayed by a sequence of substrate-controlled reactions, including a highly stereoselective epoxidation/ring opening sequence and an oxidative rearrangement of an indole to furnish a spirooxindole to establish the remaining stereocenters in the pentacyclic core of the citrinadins. An early stage intermediate in the synthesis of (-)-citrinadin A was deoxygenated to generate a dehydroxy compound that was elaborated into (+)-citrinadin B by a sequence of reaction identical to those used to prepare (-)-citrinadin A. These concise syntheses of (-)-citrinadin A and (+)-citrinadin B led to a revision of their stereochemical structures.
authors.affiliation: Department of Chemistry, The University of Texas , Austin, Texas 78712, United States.
authors.forename: Zhiguo
authors.initials: Z
authors.lastname: Bian
authors.forename: Christopher C
authors.initials: CC
authors.lastname: Marvin
authors.forename: Martin
authors.initials: M
authors.lastname: Pettersson
authors.forename: Stephen F
authors.initials: SF
authors.lastname: Martin
mesh_terms: D060326:Chemistry Techniques, Synthetic; D026121:Indole Alkaloids / Q000138:chemical synthesis* / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D013237:Stereoisomerism
chemical_list: D026121:Indole Alkaloids; C503673:citrinadin A