Usui Kazuteru
Graduate School of Pharmaceutical Sciences, Kyushu University.
Yakugaku Zasshi. 2017;137(11):1381-1390. doi: 10.1248/yakushi.17-00151.
The design and development of new chiral ligands to enable precise stereocontrol in a wide variety of reactions is one of the most important branches of organic synthesis. To date, the development of hybrid ligands containing both σ-donating and π-donating groups has attracted considerable attention, with unprecedented reactivities and stereoselectivities being observed. Therefore to develop efficient hybrid chiral ligands with novel structural motifs, we envisage that helicene would be a suitable π-donor efficiently to construct a helical environment around a metal center. In this context, we herein describe our recent efforts to develop a series of novel chiral [5]helicene-derived phosphine ligands (L1, with a 7,8-dihydro[5]helicene core structure, and L2, with a fully aromatic [5]helicene core structure). The prepared ligands, and in particular L1, were found highly effective in the asymmetric allylation of 1,3-diphenylallyl acetate with indoles and etherification with alcohols. Furthermore, in the asymmetric Suzuki-Miyaura coupling reaction, L2 exhibited excellent enantioselectivities. Finally, density functional theory studies were employed to propose a model that accounts for the origin of such high enantioselectivity in these reactions.
设计和开发新型手性配体以在各种反应中实现精确的立体控制是有机合成最重要的分支之一。迄今为止，同时含有σ供体基团和π供体基团的杂化配体的开发已引起了相当大的关注，观察到了前所未有的反应活性和立体选择性。因此，为了开发具有新颖结构 motif 的高效杂化手性配体，我们设想并苯将是一种合适的π供体，能够在金属中心周围有效地构建螺旋环境。在此背景下，我们在此描述了我们最近开发一系列新型手性[5]并苯衍生的膦配体（L1，具有7,8-二氢[5]并苯核心结构，以及L2，具有全芳族[5]并苯核心结构）的努力。所制备的配体，特别是L1，在1,3-二苯基烯丙基乙酸酯与吲哚的不对称烯丙基化反应以及与醇的醚化反应中被发现非常有效。此外，在不对称铃木-宫浦偶联反应中，L2表现出优异的对映选择性。最后，采用密度泛函理论研究提出了一个模型，该模型解释了这些反应中如此高的对映选择性的起源。
