We report herein a mild and catalytic intramolecular aminofluorination of unactivated alkenes. Thus, with the catalysis of AgNO3, the reactions of various N-arylpent-4-enamides with Selectfluor reagent in CH2Cl2/H2O led to the efficient synthesis of 5-fluoromethyl-substituted γ-lactams. A mechanism involving silver-catalyzed oxidative generation of amidyl radicals and silver-assisted fluorine atom transfer was proposed.
The first total syntheses of (-)-penicipyrone and (-)-tenuipyrone were accomplished enantioselectively in 12 steps with an 11% yield and 6 steps with a 28% yield from the known 4-((tert-butyldimethylsilyl)oxy)-cyclopent-2-enone, respectively, by developing a biomimetic bimolecular cascade cyclization featuring an intermolecular Michael addition/cyclo-(spiro-)ketalization sequence. The relative, absolute stereochemistry and carbon connectivity of penicipyrone was further confirmed by X-ray crystallographic analysis and comparison of optical rotations.
Cephalosporolide B (Ces-B) was efficiently synthesized and exploited for the first time as a versatile biomimetic synthetic precursor for the chemical syntheses of not only cephalosporolides C, G, and (4-OMe-) G via a challenging diastereoselective oxa-Michael addition but also the structurally unprecedented cephalosporolides E and F via a novel biomimetic ring-contraction rearrangement. These findings provide the first direct chemical evidence that Ces-B may be the true biosynthetic precursor of cephalosporolides.
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