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

基于手性系链反应开发不对称催化体系的研究带来了以下结果：1)研究了与2,4-戊二醇（PD）及其类似物的手性系链反应，包括间芳烃-烯烃光环加成反应、类碳铑与烯烃或芳烃的光环加成反应和烯酮-烯烃环加成反应。通过对它们的立体选择性分析，发现PD系链中两个甲基中的任何一个都是严格立体控制的不可或缺的因素，手性源的甲基可以转移到比异丙基小的另一个甲基上，而不会失去分子内反应的效率。2)引入了新的动力学参数手性扰动因子，阐明了系链上取代基与它们引起的微分激活熵之间的关系。用手性扰动因子对芳烃加成的类羰基铑进行了分析，发现pd -系链上的一个甲基在熵项上加速了主要过程，而在熵项上减慢了次要过程，导致30 cal/mol K，这可能是手性系链反应严格立体控制的主要原因。3)研究了苯氧基在环糊精（CDs）存在下的二聚化反应。在42%产率下，当链链在2位上有一个苯甲酰取代基时，1对1的立体选择性变为47%的非对映体过剩。4)将PD系链反应扩展为气相热解，在严格的立体控制下生成烯烃，即使在400℃时，PD系链的重氮酯也能生成许多光学活性产物，这些产物可转化为各种化合物，如昆虫信息素、sperapyrone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.