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

光学活性的4-甲基环己亚甲基碘盐的溶剂分解得到重排的环庚烯基产物，完全保持了光学纯度，表明没有形成初级乙烯基阳离子。即使在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，光解导致产物通过形成初级乙烯基阳离子而外消旋。在HFIP中存在碱的情况下，相同的碘盐会导致外消旋取代产物。外消旋反应是通过与环庚炔中间体的消除加成反应进行的。苯乙基碘盐的热反应是通过β-苯基参与苯离子中间体进行的。苯乙烯基底物的光反应也通过初级乙烯基阳离子进行，无需参与。在纳秒时间尺度上，激光光解尝试通过光生初级乙烯基阳离子观察中间苯离子，但没有发现这种桥联阳离子的形成迹象。带有手性侧链的萘衍生物与邻氯苯胺光诱导环加成反应发生在立体选择性上。该溶液在355 nm处的激光光解表明，在萘基质上形成了阳离子自由基。同样的阳离子自由基在HFIP溶液中与铁盐热生成，在吸收波长附近观察到了Cotton效应。这一结果表明，萘环和手性侧链之间存在一定的相互作用，这被认为是导致环加成反应立体选择性的原因。类似的含手性羧酸侧链的萘衍生物与单线态氧反应，合成了具有光学活性的过氧化氢。

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.