Preparation of chiral bipyridine bis-N-oxides by oxidative dimerization of chiral pyridine N-oxides |
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| Institution: | 1. Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hong Kong;2. Department of Chemistry, Faculty of Science, Kyoto University, Japan;1. Department of Chemistry and Biochemistry, The University of Texas at Arlington, Arlington, TX 76019-0065, USA;2. Seoul Center, Korea Basic Science Institute, 126-16 Anam-dong, Sungbuk-gu, Seoul 136-713, South Korea;3. AZYP LLC, Arlington, TX USA;4. Department of Organic Chemistry, University of Geneva, Quai Ernest Ansermet 30, 1211 Geneva 4, Switzerland;1. Institut de Chimie, UMR 7177, CNRS, Université de Strasbourg, 4, Rue Blaise Pascal, 67000, Strasbourg, France;2. Inserm UMR_S 1113, Université de Strasbourg, 3 av. Molière, 67200, Strasbourg, France |
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| Abstract: | The direct preparation of chiral 2,2′-bipyridine bis-N-oxides has been developed. The method involves two stages, first, the deprotonation of substituted chiral pyridine N-oxides and second, the oxidative dimerization of the resulting 2-lithiopyridine N-oxides. Optimization of the reaction conditions led to the selection of LiTMP in THF for the deprotonation and molecular iodine as the oxidant. The corresponding 2-iodopyridine N-oxide is invariably formed as a by-product. A series of 11 chiral pyridine N-oxides was prepared that bear substituents at the C(2) and C(5) positions. Oxidative dimerization of these mono-N-oxides proceeded in 33–77% yield. In all cases, the dimerization was highly diastereoselective for the formation of the P-configuration of the chiral axis. |
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