Studies of Copper−Bisoxazoline-Catalyzed Asymmetric Cyclopropanation of 2,5-Dimethyl-2,4-hexadiene
作者:Makoto Itagaki、Katsuhisa Masumoto、Katsuhiro Suenobu、Yohsuke Yamamoto
DOI:10.1021/op050203d
日期:2006.3.1
In the [bis(4R)-(1-naphthyl)-5,5-diniethyloxazoline}/copper]catalyzed asymmetric cyclopropanation of 2,5-dimethyl-2,4-hexadiene with tert-butyl diazoacetate, the effects of a counterion of the copper complex were studied. The[CuCl/bisoxazoline/ Ph3CPF6] catalyst was found to enhance both the catalytic efficiency and the stereoselectivity (the catalyst 0.2 mol %, yield 92%, trans/cis = 88/12, 96% ee for the trans product), compared to our previously reported CuOTf/bisoxazoline catalyst. The density functional calculations were performed to elucidate the effects of the counterion as well as the effects of the gem-dimethyl groups at the 5-position on the bisoxazoline ligand.