Synthesis of novel chiral bisoxazoline ligands with a spiro[4,4]-1,6-nonadiene skeleton
【摘要】：A new type of chiral bisoxazoline ligands 1 based on spiro[4,4]-1,6-nonadiene backbone was easily prepared in six steps from racemic spiro[4,4]-nonane-1,6-dione,with the Pd-catalyzed coupling of the enol triflates with CO and amino alcohols as the key steps for the construction of the oxazoline moiety. The structure of the ligand (R,S,S)-1b was unambiguously established by X-ray crystallographic analysis. The chiral Cu(II) complex generated in situ from the combination of spiro bisoxazoline ligand (S,S,S)-1c and Cu(OTf)2 was effective in the catalysis of asymmetric chlorination of the β-ketoester,methyl 1-oxo-2,3-dihydro-1H-indene-2-carboxylate,affording the corresponding chlorinated derivative in 99% yield with 17% ee.
【基金】：supported by the National Natural Science Foundation of China (20821002 and 20972176) the Chinese Academy of Sciences, the National Basic Research Program of China (2010CB833300),the Science and Technology Commission of Shanghai Municipality,and Merck Research Laboratories