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Modular Stereoselective Synthesis of (1→2)‐C‐Glycosides based on the sp2–sp3 Suzuki–Miyaura Reaction
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Beata Oroszova Jan Choutka Dr. Radek Pohl Dr. Kamil Parkan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(19):7043-7047
This work reports a modular and rapid approach to the stereoselective synthesis of a variety of α‐ and β‐(1→2)‐linked C‐disaccharides. The key step is a Ni‐catalyzed cross‐coupling reaction of D ‐glucal pinacol boronate with alkyl halide glycoside easily prepared from commercially available D ‐glucal. The products of this sp2–sp3 cross‐coupling reaction can be converted to glucopyranosyl, mannopyranosyl, or 2‐deoxy‐glucopyranosyl C‐mannopyranosides by one‐ or two‐step stereoselective oxidative–reductive transformations. To the best of our knowledge, we demonstrated the first synthetic application of a challenging sp2–sp3 Suzuki‐Miyaura cross‐coupling reaction in carbohydrate chemistry. 相似文献
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Co(CH3)(PMe3)4 forms 100 % regioselectively with (2‐(2‐diphenylphosphanyl)phenyl)‐1,3‐dioxalane and 2‐diphenylphosphanyl‐pyridine, by elimination of methane, the four‐membered metallacycles Co{(C3O2HC6H3)P(C6H5)2}(PMe3)3 ( 1 ) and Co{(CNC4H3)P(C6H5)2}(PMe3)3 ( 4 ). The regioselectivity is independent of the steric requirement of the ortho substituent in the 2‐diphenylphosphanylaryl‐ligands. Oxidative addition with iodomethane transforms 1 and 4 into octahedral, diamagnetic low‐spin d6 complexes Co(CH3)I‐{(C3O2HC6H3)P(C6H5)2}(PMe3)2 ( 2 ) and Co(CH3)I‐{(CNC4H3)P(C6H5)2}(PMe3)2 ( 5 ). Under an atmosphere of carbon monoxide, insertion into the Co‐C bond results in ring expansion by forming the new assembled phosphanylbenzoyl complexes Co{(C4O3HC6H3)‐P(C6H5)2}CO(PMe3)2 ( 3 ) and Co{(OCNC4H3)P(C6H5)2}CO(PMe3)2 ( 6 ). The three different types of cobaltacycles are supported by X‐ray diffraction of 1 , 3 , 5 and 6 . 相似文献
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