- Enantioselective total syntheses of citrinadins A and B. Stereochemical revision of their assigned structures
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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.
- Bian, Zhiguo,Marvin, Christopher C.,Pettersson, Martin,Martin, Stephen F.
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supporting information
p. 14184 - 14192
(2015/02/18)
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- Palladium-catalyzed kumada coupling reaction of bromoporphyrins with silylmethyl grignard reagents: Preparation of silylmethyl-substituted porphyrins as a multipurpose synthon for fabrication of porphyrin systems
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We have developed an efficient method for preparing silylmethyl-substituted porphyrins via the palladium-catalyzed Kumada cross-coupling reaction of bromoporphyrins with silylmethyl Grignard reagents. We demonstrated the synthetic utility of these silylmethylporphyrins as a multipurpose synthon for fabricating porphyrin derivatives through a variety of transformations of the silylmethyl groups, including the DDQ-promoted oxidative conversion to CHO, CH2OH, CH2OMe, and CH2F functionalities and the fluoride ion-mediated desilylative introduction of carbona-carbon single and double bonds.
- Sugita, Noriaki,Hayashi, Satoshi,Hino, Fumio,Takanami, Toshikatsu
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p. 10488 - 10497
(2013/02/22)
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