The enantioselective [2+2+2] cycloisomerisation of the aromatic triynes under nickel(0) catalysis to afford nonracemic [6]- and [7]helicene derivatives has been systematically studied. A collection of mono- and bidentate phosphines, phosphites, phosphinites and phosphinous amides possessing stereogenic units such as chiral centre, axis or plane (or their combinations) has been tested and axially chiral binaphthyl-derived monodentate MOP-type phosphine ligands were the optimal class of ligands. Nickel complexes of these ligands afforded nonracemic tetrahydro[6]helicene in up to 64% ee in a model reaction.
芳香族三
炔烃在
镍(0)催化下进行立体选择性的[2+2+2]环异构化反应,生成非拉克米的[6]-和[7]螺
芴衍
生物已经被系统研究。一系列具有手性中心、轴或平面(或它们的组合)的单齿和双齿膦、
膦酸酯、
膦酸酯和膦酰胺已经被测试,其中轴手性的双齿MOP型
膦配体是最佳的
配体类别。这些
配体的
镍配合物在模型反应中生成非拉克米的四氢[6]螺
芴,其对映选择性可高达64% ee。