Development of Highly Selective Asymmetric Reactions

作为手性刘易斯，钛试剂是通过将衍生自酒石酸二甲酯的1，4-手性二醇部分引入钛化合物来制备的。手性钛试剂在各种不对称反应中有着广泛的应用.丙烯酸和富马酸衍生物与双烯反应，通过催化量的手性钛和分子筛4A的组合使用，得到高对映选择性的[4+2]环加合物。通过分子内Diels-Alder反应与手性钛反应合成了几乎光学纯形式的双环碳环。手性钛试剂还促进丙烯酸衍生物和烯酮二硫代缩醛（或烯基或炔基硫化物）之间的[2+21]环加成。环丁烷和环丁烯的制备具有高的对映选择性.手性钛催化不对称分子内烯反应，对映选择性地得到环戊酮和环己酮.在手性钛的存在下，不同类型的醛与三甲基氰基硅烷反应，得到了90%ee以上的相应氰醇.手性钛醇盐作为手性催化剂有效地用于外消旋羧酸衍生物的动力学拆分。α-芳基乙酸以高选择性被拆分。从由此制备的光学活性中间体开始，以光学纯形式合成了氧杂环丁烷的C-类似物、grandisol和ε-杜松烯。

As a chiral Lewis, titanium reagents have been prepared by introducing a 1,4-chiral diol moiety derived from dimethyl tartrate to titanium compounds. The chiral titanium reagents have found a wide application to various asymmetric reactions.1. Acrylic acid and fumaric acid derivatives react with dienes to afford the [4+2] cycloadducts with high enantioselectivity by the combined use of a catalytic amount of the chiral titanium and Molecular Sieves 4A. Bicyclic carbocycles are synthesized in almost optically pure forms by intramolecular Diels-Alder reactions with the chiral titanium.2. The chiral titanium reagent also promotes [2+21 cycloadditions between acrylic acid derivatives and ketene dithioacetals (or alkenyl or alkynyl sulfides). Cyclobutanes and cyclobutenes are prepared in high enantioselectivity.3. Asymmetric intramolecular ene reaction is catalyzed with the chiral titanium, and cyclopentanone and cyclobexanones are obtained enantioselectively.4. Various types of aldehydes react with cyanotrimethylsilane in the presence of the chiral titanium to give the corresponding cyanohydrins in more than 90%ee.5. The chiral titanium alkoxide is efficiently employed in the kinetic resolution of racemic carboxylic acids derivatives as a chiral catalyst. alpha-Arylacetic acids are resolved in high selectivity.6. Starting from the optically active intermediates thus prepared, C-analogue of oxetanocin, grandisol and epsilon-cadinene are synthesized in optically pure forms.