Study for Highly Stereocontrolled Reactions by Liquid Crystalline Mesophases

探讨了热致液晶介质中的光二聚反应和热环加成反应，以说明液晶在有机反应中的应用，并阐明了液晶相的化学意义.一个有据可查的尿嘧啶的光二聚化似乎是一个合适的反应，本研究，并提供有关高度优先的液晶介质中的溶质的取向的信息。因此，甲基尿嘧啶在各向同性和各向异性介质（包括冷冻溶液）中用高压汞灯照射。的光二聚体的分布和转化率被确定为温度和溶剂相的函数。近晶相液晶介质显著提高了光二聚反应的立体选择性和速率，与各向同性相反应的二聚选择性和产率差形成强烈对比.合成了胆固醇酯烷基酯和芳基酯，作为Diels-Alder反应中的液晶亲双烯体。在适宜环加成反应的温度范围内，有些化合物表现出非晶态的液态晶相。正己基胆甾醇胆甾醇富马酸酯在介晶相中作为亲双烯体与环戊二烯反应，得到光学活性的环加合物，对映体过量为10%。另一方面，胆甾醇甲酯富马酸酯与2，6-二甲氧基蒽反应生成2，6-二甲氧基-9，10-二氢-9，10-乙醇基-蒽-11（顺），12（顺）-二羧酸和11（反），12（反）-异构体，比例为96：4（92% d.e.）。这些结果清楚地表明，一个中间相可以立体化学控制的Diels-Alder反应在相当大的程度上。

Photodimerizations and thermal cycloadditions in thermotropic liquid crystalline media were explored in order to show the utility of liquid crystals in organic reaction and chemical significance of the liquid crystalline phases was clarified.1. A well documented photodimerization of uracils seemed to be a suitable reaction for the present study, and provided information regarding highly preferred orientations of solutes in liquid crystalline media. Thus methyluracils were irradiated with a high pressure HG-lamp in isotropic and anisotropic media including frozen solutions. The photodimer distribution and conversion yields were determined as a function of temperature and solvent phase. Smectic liquid crystalline medium significantly enhanced the stereoselectivity and the rate in photodimerization, in strong contrast to the isotropic phase reaction which gave poor dimer-selectivity and yield.2. Alkyl and aryl cholesteryl fumarates were prepared to serve as a liquid crystalline dienophile in Diels-Alder reaction. Some of them showed cholesteric liquid crystial phases in temperature ranges suitable to the cycloaddition. The reaction of n-hexyl cholesteryl cholesteryl fumarate in mesomorphic phase as a dienophile with cyclopentadiene gave the optically active cycloadducts in 10% enantiomeric excess. On the other hand, the reaction of methyl cholesteryl fumarate with 2,6-dimethoxyanthracene gave 2,6-dimethoxy-9,10-dihydro-9,10-ethano-anthracene-11(syn),12(syn)-dicarboxylic acid and the 11(anti),12(anti)-isomer in a ratio of 96 : 4 (92% d.e.). These results clearly showed that a cholesteric mesophase could stereochemically control the diels-Alder reaction to a considerable extend.