Synthesis of Novel Chiral Bipyridine-tertiary Amine and Their Derived N-Oxides
The synthesis of chiral bipyridine ligands and chiral N-oxide ligands derived from tertiary a-mines remains an important topic in the field of asymmetric catalysis.In this paper,using optically pure various substituted prolamides(1)as the chiral source,the eight chiral bipyridine-tertiary amines 3a～3h were synthesized by condensation cyclization with bipyridyl-6-formaldehyde(2)in 75％～80％yield and dr＞20/1.Then the nitrogen atom in the compounds(3)were oxidized under the action of chloro perbenzoic acid,an oxidant,to provide eight chiral bipyridine-tertiary amine-derived N-oxides 4a～4h in 45％～51％overall yield and dr 14/1～＞20/1.The structures of products 3 and 4 were characterized by 1H NMR,13C NMR and HR-MS(ESI-TOF).The absolute configuration(3R,7aS)of compound 3h was further determined by the single crystal X-ray diffraction.Chiral bipyridine and chiral N-oxide serve as privileged ligands,and the synthesis of their skeleton compounds 3 and 4 can provide new ligand screening for asymmetric Lewis acid catalysis in the future.
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