Study on reactive intermediates and solvent participation by means of interplay of photochemical and thermochemical reactions

光学活性的4-甲基亚环己基甲基碘鎓盐的溶剂分解得到重排的环庚烯基产物，其光学纯度完全保留，表明没有形成伯乙烯基阳离子。甚至在1，1，1，3，3，3-六氟-2-丙醇（HFIP）和离子液体以及高离子强度的溶液中也是如此。然而，光溶剂分解通过形成伯乙烯基阳离子导致产物的外消旋化。相同的碘鎓盐在HFIP中碱的存在下导致外消旋取代产物。外消旋化通过与环庚炔中间体的消除-加成机理发生。苯乙烯基碘鎓盐的热反应通过β-苯基参与苯阳离子中间体而发生。苯乙烯基底物的光反应也通过伯乙烯基阳离子而不参与。利用激光光解技术在纳秒时间尺度内观察到了通过光生乙烯基伯阳离子形成的中间体苯阳离子，但没有发现这种桥阳离子的形成.带有手性侧链的萘衍生物与邻四氯对苯醌的光诱导环加成反应是立体选择性的.该溶液在355 nm处的激光光解显示萘基质的阳离子自由基的形成。铁盐在HFIP溶液中热生成相同的阳离子自由基，观察到圆二色性光谱，显示吸收波长附近的Cotton效应。这一结果表明，萘环和手性侧链之间存在着一定的相互作用，这被认为是环加成反应的立体选择性的原因。带有手性羧酸酯侧链的类似萘衍生物与单线态氧反应，合成了光学活性的氢过氧化物。

Solvolysis of optically active 4-methylcyclohexylidenemethyl iodonium salt gives a rearranged cycloheptenyl product with complete retention of optical purity, indicating that primary vinyl cation is not formed. This was also the case even in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), and ionic liquids as well as in a solution of high ionic strength. However, the photosolvolysis leads to racemization of the products via formation of the primary vinylic cation. The same iodonium salt leads to racemized substitution products in the presence of a base in HFIP. The racemization takes place via elimination-addition mechanism with the cycloheptyne intermediate. Thermal reaction of styryl iodonium salt occurs via beta-phenyl participation with a benzenium ion intermediate. Photoreaction of the styryl substrate also takes place via the primary vinyl cation without participation. Observation of intermediate benzenium ion via photo-generated primary vinyl cation was attempted by laser photolysis in a nanosecond time scale, but there found no indication of formation of this bridged cation.Photo-induced cycloaddition of naphthalene derivatives carrying a chiral side chain with o-chloranil took place stereoslectively.. Laser photolysis of this solution at 355 nm showed formation of a cation radical of the naphthalene substrate. The same cation radical was thermally generated with ferric salt in HFIP solution, and circular dichroic spectra were observed showing the Cotton effects around the wavelength of absorption. This result suggests that there is some interaction between the naphthalene ring and the chiral side chain, which is considered to be responsible for the stereoselectivity of the cycloaddition. Similar naphthalene derivatives carrying a chiral carboxylate side chain were subjected to the reaction with singlet oxygen, which led to synthesis of optically active hydroperoxides.