| Indole ring is one of the most widely heterocycles and ubiquitous substructural motifs found in many biologically active molecules and natural products,thus the synthesis of indole derivatives has been a focused interest for organic chemists.Asymmetric Friedel-Crafts reaction of indole with nitroalkenes is an important method for the synthesis of indole derivatives.The nitro-group containing indole derivatives obtained from the reaction can be further converted to some active compounds.Therefore,it’s highly important to realize such catalytic and stereoselective Friedel-Crafts reactions.1.The enantioselective alkylation reaction of indoles with a-substituted-β-nitroacrylates was studied and the optimal reaction conditions were found after the scanning of Lewis acid,bisoxazoline ligand,solvent,temperature and so on.With 1 mol%of Ni-bisoxazoline complex,the reaction proceeds efficiently in toluene at 50℃,giving the yield from 43%to 98%and the enantioselectivity from 54%to 97%,and providing a reliable access to the potential biologically active β-tryptophan derivatives bearing all-carbon quaternary stereocenters.2.Highly enantioselective alkylation reaction of 3-methyl indole with nitroolefins was studied.The optimal reaction conditions were found after the screening of Lewis acid,chiral ligand,solvent as well as the temperature,the optimal condition is discovered.With 6 mol%bisoxazoline ligand L3-8 and 5 mol%Zn(OTf)2,the reaction proceeds efficiently in toluene at 80℃,giving the yield from 70%to 99%and the enantioselectivity up to 93%. |
