Asymmetric Catalysis Stereocontrolled by Entropy : A New Aspect for Chiral Tethered Reactions

基于手性拴系反应开发不对称催化体系的研究结果如下：1)研究了2，4-戊二醇(PD)及其类似物与间芳烃-烯烃的光环加成反应、类若卡宾与烯烃或芳烃的加成反应、以及与烯烃-烯烃的环加成反应。通过对它们的立体选择性的分析，发现Pd系链上的两个甲基中的任何一个是严格的立体控制所必需的因素，并且手性源上的甲基可以被转移到比异丙基更小的另一个，而不会损失分子内反应的效率。2)引入了一个新的动力学参数手性微扰因子来阐明系链上的取代基与由此引起的微分活化熵之间的关系。通过对具有手性扰动因子的类铑与芳烃的加成反应的分析，发现Pd-Tether上的一个甲基加速了主要的反应过程，而减慢了次要的反应速度，产生了30cal/molK，这被认为是手性系链反应严格立体控制的主要原因。3)研究了环糊精(CDS)存在下的苯氧基自由基二聚反应。4)Pd系留反应扩展到气相热解，在严格的立体控制下，即使在400℃与Pd相连的重氮酯反应也能生成烯烃。与Pd系留重氮酯的反应产生许多光学活性产物，这些产物被转化为不同的化合物，如昆虫信息素、亚精氨酮和几种聚酮。

The studies to develop asymmetric catalytic system basing on the chiral tethered reaction brought us the following results.1)The chiral tethered reactions with 2,4-pentanediol (PD) and its analogues were studied for meta-arene-alkene photocycloaddition, rhodium carbenoid addition to olefin or arene, and ketene-olefin cycloaddition. By the analysis of their stereoselectivities, either of the two methyl groups in PD tether was found to be indispensable factor for the strict stereocontrol, and the methyl group of the chiral source can be displaced to the other smaller than isopropyl group without loosing the efficiency of the intramolecular reaction.2)A new kinetic parameter, chiral perturbation factor, was introduced to clarify the relation between the substituents on the tether and differential activation entropy caused by them. By the analysis of the rhodium carbenoid addition to arene with chiral perturbation factor, one of the methyl groups on the PD-tether was found to accelerate the major process in entropy term, while decelerate the minor one to result in 30 cal/mol K, which is assumed to be a major reason of the strict stereocontrol of the chiral tethered reaction.3)Dimerization reaction of phenoxyl radical was studied in the presence of cyclodextrins (CDs). The stereoselectivity of 1 to 1 in the absence of CD in 42% yield becomes 47% diastereomeric excess when the tether has a benzoyloxy substituent at the 2 position.4)The PD tethered reaction was extended to a vapor phase pyrolysis, where ketene generated adds to olefin under strict stereocontrol even at 400 The reactions with PD-tethered diazo esters resulted in many optically active products, which were converted to varied compounds such as an insect pheromone, sperapyrone, and several polyketides.