Studies on asymmetric reaction catalized by optically active metallocenes

高度立体选择性和催化反应的发展已经合成了天然产物、药物和其他有用的材料。茂金属如二氯化二茂钛和二氯化二茂锆已被用作聚合（Zieglar-Natta催化剂）、碳化和加氢的催化剂。由于茂金属具有两个空间要求配体环戊腺苷基，因此在茂金属催化反应中引入手性会引起高的不对称诱导。用光学分辨方法制备了一些取代的环戊二烯基与烷基链连接的光学活性异新烃。然而，先前在茂金属的烷基链中引入手性似乎消除了麻烦的分解步骤，并为合成各种光学活性的后第三系打开了一个机会。以(2S, 3S)-酒石酸二乙酯、(S)-乳酸乙酯、(S)- 1,3 -丁二醇、(2S, 3S)- 2,3 -丁二醇、(2S, 4S)- 2,4 -戊二醇为原料制备手性烷基烯链。另一方面，由于其化学稳定性高于普通的烷基环戊二烯，因此采用茚一基作为取代环戊二烯部分。然后，通过这两部分的偶联，合成了几种具有有效活性的二茚二基配体。发现配体与钛或四氯化锆的下一步络合是困难的，并且几乎在每种情况下都得到复杂的分解产物。经过多次实验，用(R)- 1,3 -二（1 -独立基）丁烷或(2R, 4R)- 2,4 -二（1 -独立基）戊烷处理四氯化钛，然后加氢，产率为9- 1.1%，制得两种晶型二茂钛。结构分析表明，结晶产物为取代基排列方向相同的重叠配合物。令人失望的是，在重叠配合物催化反应中不能期望高度不对称的诱导。最近，R. L. Halterman等人报道了一种具有光学活性的二茂钛的合成，其在烷基链上具有双烷基轴向不对称[有机金属，10,2998(1991)]。由于目前我们的结果与Halterman的结果存在差异的原因尚不清楚，因此需要进一步的实验。少

The development of highly stereoselective and catalytic reactions has syntheses of natural products, pharmaceuticals, and other useful materials. Metallocenes such as titanocene dichloride and zirconocene dichloride have been used as a catalyst for polymerization (Zieglar-Natta catalyst), carbonetallation, and hydrogenation. Since metaflocenes have two sterically demanded ligands of cyclopentadenyl group, inmkuction of chirality on metahocenes may bring high asymmetric induction in the metallocene catalyzed reactions. Some optically active metahocenes whose substituted cyclopentadienyl groups were connected with alkylene chain had already been prepared by optical resolution. However, prior introduction of chirality into the alkylene chain of metallocenes seemed to eliminate the troublesome resolution step and to open an opportunity for the synthesis of various Kinds of optically active metahocenes.The chiral alkylene chains were prepared from easily available (2S, 3S)-diethyl tartrate, … More (S)-ethyl lactate, (S)-1, 3-butanediol, (2S, 3S)-2, 3-butanediol, (2S, 4S)-2, 4-pentanediol. On the other hand, indenyl group was employed as the substituted cyclopentadienyl part due to its higher chemical stability than ordinary'alkylcyclopentadienes. Then, several o]fftically active diindenyl ligands were synthesized by coupling of the two parts. Next complexation of the ligands with titanium or zirconium tetrachloride was found to be difficult and complex decomposition products were obtained in almost every case. After numerous experimentations, two crystalline titanocenes were produced by a treatment of titanium tetrachloride with (R)-1, 3-di(1 -indenyl) butane or (2R, 4R)-2, 4-di(l-indenyl) pentane and subsequent hydrogenation in 9-1 1% yield. The structure elucidation revealed that the crystalline products were eclipsed complex whose substituent arranged to same direction. Disappointingly, highly asymmetric induction could not be expected in the eclipsed complex catalyzed reaction. Quite recently, R. L. Halterman et al. reported a synthesis of optically active titanocene having binaphthyl axial asymmetry on the alkylene chain [Organometallics, 10, 2998(1991)]. Since it is not clear a reason for the difference between our result and Halterman's result at present, further experimentations are required. Less