Synthesis of new dendritic chiral binol ligands and their applications in enantioselective lewis acid catalyzed addition of diethylzinc to aldehydes

Abstract

报道了树状结构的手性联二萘酚 ( BINOL)配体的合成及其在二乙基锌对醛的不对称加成反应中的应用 .( R) -2 ,2′-二羟基 -1 ,1′-联萘 -3,3′-二羧酸与末端为氨基的 Frechet聚芳醚型树状分子经缩合反应 ,以中等产率得到 0～ 3代的树状分子配体 ,用 1 H NMR,IR和 MALDI-TOF质谱进行了结构表征 .这些树状手性配体与 Ti( OPri) 4在无水甲苯溶液中形成的配合物是二乙基锌对醛不对称加成反应的高效催化剂 ,树状分子载体的体积对催化剂的对映选择性没有明显的影响 .以邻氯苯甲醛为底物时 ,反应的对映选择性随树状分子代数的增加而有所提高 . The series of new dendritic chiral BINOL ligands(3) were synthesized by condensation reaction of (R)-2,2′-dihydroxy-1,1′-binaphthyl-3,3′-dicarboxylic acid(1) and Fréchet-type poly(aryl ether) dendrons(2) with an amino group at the focal point in moderate reaction yields. All ligands were characterized by 1H NMR, IR and MALDI-TOF-MS spectra, which clearly demonstrated the formation of monodispersed dendritic BINOLs. The titanium complexes of these dendritic ligands obtained by mixing(3) with Ti(OPr i) 4 in dry toluene were found to be efficient catalysts in asymmetric addition of diethylzinc to aldehydes. The size of the dendritic wedges did not significantly influence the enantioselectivity of the catalyst. Most interestingly, when ortho-chlorobenzaldehyde was used as substrate, we found that enantioselectivity increased slightly with increasing generation of the dendrimers.