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Advanced Synthesis & Catalysis
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Wiley Online Library : Advanced Synthesis & Catalysis
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Catalytic Epoxidation of Alkenes by the Manganese Complex of a Reduced Porphyrinogen Macrocycle
The present paper details the first application of a fully reduced meso-octamethylporphyrinogen macrocycle as an effective ligand for simple operative manganese-catalyzed alkene epoxidation. The efficiency of the novel catalyst was determined in the presence of various oxidants, apical ligands and acidic/basic additives. Higher reactivity was found in favour of electron-rich alkenes, whereas an electron-deficient conjugated alkene appeared as a poor substrate in the screening. Sulfur additives were active as apical ligands, whereas nitrogen-containing additives influenced the reactivity only moderately. cis-Stilbene and 3β-acetoxy-5-cholestene were epoxidized in a stereoselective manner. The X-ray structures of the new manganese complexes were determined and showed a rigid planar coordination geometry of the saturated macrocyclic ligand to the metal centre.
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Biocatalysis of Cycloastragenol by Filamentous Fungi to Produce Unexpected Triterpenes
The biocatalysis of cycloastragenol, a natural tetracyclic triterpenoid with anti-aging activity, by cultured whole cells of three strains of filamentous fungi, namely Cunninghamella elegans AS 3.1207, Syncephalastrum racemosum AS 3.264 and Doratomyces stemonitis AS 3.1411 produced 15 metabolites. Thirteen of them are new compounds. The structures of these metabolites were fully characterized on the basis of HR-ESI-MS analyses together with 1D and 2D NMR spectroscopy. The three fungal strains exhibited significant biocatalytic preferences: C. elegans enabled hydroxylation reactions, particularly on the 28- and 29-CH3 groups; S. racemosum efficiently catalyzed a complicated rearrangement reaction to form the unusual ranunculane skeleton, which was further substituted with diverse side chains at C-19; D. stemonitis mainly led to carbonylation reactions, especially on 3-OH. It is particularly noteworthy that S. racemosum also catalyzed an unexpected ring expansion reaction to generate the rare 9(10)a-homo-19-nor-cycloartane skeleton. Biocatalysis was proved powerful in the structural diversification of cycloastragenol for future structure-activity relationship studies.
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Palladium-Catalyzed Oxidative CC Bond Cleavage Cyclization of Biaryl-2-amines with Alkenes Involving CH Olefination and Carboamination
A new, general method for the synthesis of phenanthridines has been developed by palladium-catalyzed oxidative remote CH olefination–carboamination–CC bond cleavage tandem reaction. It is noteworthy that alkenes are used as the one-carbon resources for this tandem reaction.
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Palladium-Catalyzed Direct and Site-Selective Desulfitative Arylation of Indoles with Sodium Sulfinates
An efficient method was developed for the desulfitative arylation of indoles with sodium sulfinates using palladium as catalyst and copper chloride dihydrate as oxidant. The direct arylation occurred exclusively in the C-2 position of indoles and proceeded well for a range of different substrates.
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Enantioselective α-Arylation of Cyclic Ketones Catalyzed by a Combination of an Unmodified Cinchona Alkaloid and a Palladium Complex
A palladium/Cinchona alkaloid-catalyzed α-arylation between cyclic ketones and aryl halides under phosphine-free conditions is presented. The use of a simple, unmodified Cinchona alkaloid results in high levels of activity and selectivity with up to 93% ee. These enantioinduction levels are comparable or even higher than the ones reported using palladium/BINAP complexes. To the best of our knowledge, this represents the first use of unmodified Cinchona alkaloids as ligands/catalysts in asymmetric transition metal complex-catalyzed cross-coupling reactions.
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