Chiral Diene Ligands for Catalytic Asymmetric Reactions

手性配体的设计和制备是发展催化不对称反应的重要课题之一，它能在催化活性和对映体选择性方面与给定的反应有效地匹配。一些含磷和/或氮原子的手性分子已被制备并用于过渡金属催化的不对称反应，但由于它们的催化活性或对映体选择性较低，作为手性配体并不总是有用的。在本研究项目中，作为概念上的新型手性配体，我们引入了一系列手性二烯类化合物，为不对称催化领域开辟了一个新的维度。手性二烯是基于双环[2.2.1]庚二烯(NBD^*)、双环[2.2.2]辛二烯(BOD^*)或双环[3.3.1]壬二烯(BND^*)骨架的。手性双烯配体对催化芳基硼试剂与缺电子烯烃的不对称1，4-加成反应、与N-磺酰亚胺的1，2-加成反应等反应都非常有效。与手性双膦等其他类型的手性配体相比，手性双烯配体具有很高的对映体选择性。值得注意的是，与双烯配体配位的Rh催化剂的催化活性远高于与常规磷配体配位的催化剂，这使得用很少的催化剂(~lt；0.005摩尔%)实现催化不对称反应成为可能。

One of the most significant subjects for developing catalytic asymmetric reactions is the design and preparation of a chiral ligand which will fit in with a given reaction efficiently in catalytic activity and enantioselectivity. A number of chiral molecules containing phosphorus and/or nitrogen atoms have been prepared and used for transition metal-catalyzed asymmetric reactions, but they are not always useful as chiral ligands because of their low catalytic activity or enantioselectivity. In this research project, as conceptually new chiral ligands, we have introduced a series of chiral dienes which opened up a new dimension in the field of asymmetric catalysis. The chiral dienes are based on bicyclo[2.2.1]heptadiene (nbd^*), bicyclo[2.2.2]octadiene (bod^*), or bicyclo[3.3.1]nonadiene (bnd^*) skeleton. The chiral diene ligands were found to be very effective for rhodium-catalyzed asymmetric 1,4-addition of arylboron reagents to electron deficient olefins, 1,2-addition to N-sulfonylimines, and so on. The enantioselectivities observed with the chiral diene ligands are very high compared with those observed with other types of chiral ligands such as chiral bisphosphines. It is remarkable that the catalytic activity of the rhodium catalysts coordinated with the diene ligands is much higher than with conventional phosphorus ligands, which made it possible to realize the catalytic asymmetric reactions with a very small amount (<0.005 mol %) of the catalyst.