A number of α-hydroxy-3-benzylbenzophenones 7–11 have been synthesized for the purpose of studying the effect of a phenyl substituent on the intramolecular photoredox reaction of 3-(hydroxymethyl)benzophenone (5) discovered in our laboratory. This latter compound was found to undergo a unimolecular (formal) intramolecular redox reaction upon photolysis in aqueous acid that results in clean reduction of the benzophenone ketone (to secondary alcohol) and oxidation of the alcohol to aldehyde. Three of the phenyl-substituted compounds with simple phenyl (7), p-methylphenyl (8), and p-methoxyphenyl (9) were found to undergo the acid-catalyzed intramolecular photoredox reaction with the observation that 9 also undergoes a residual photoredox reaction that is not acid-mediated and may involve initial photoinduced electron transfer, which is supported by LFP data. The m-methoxyphenyl (10) compound did not undergo the reaction. The trend in observed relative reactivity may be partially rationalized by examining changes in molecular orbital coefficients observed in the calculated HOMOs and LUMOs. The photoredox reaction has also been applied twice in succession in a single compound 11, demonstrating that the photoredox reaction may be useful for sequential photoredox reactions in a multifunctional compound.Key words: intramolecular photoredox, acid catalysis, meta effect, benzophenone photochemistry.
为了研究苯基取代基对我们实验室发现的 3-(羟甲基)二苯甲酮(5)的分子内光氧化反应的影响,我们合成了一些 α-羟基-3-苄基二苯甲酮 7-11。研究发现,3-(羟甲基)二苯甲酮 (5) 在水酸中光解时会发生单分子(形式)分子内氧化还原反应,使二苯甲酮酮还原成仲醇,仲醇氧化成醛。研究发现,单苯基(7)、对甲基苯基(8)和对甲氧基苯基(9)的三种苯基取代化合物会发生酸催化的分子内光氧化反应,同时还观察到 9 还会发生非酸介导的残余光氧化反应,可能涉及初始光诱导电子转移,这一点得到了 LFP 数据的支持。间甲氧基苯基(10)化合物没有发生这种反应。通过研究在计算的 HOMO 和 LUMO 中观察到的分子轨道系数的变化,可以部分合理地解释观察到的相对反应性趋势。光氧化反应还在单个化合物 11 中连续应用了两次,这表明光氧化反应可用于多功能化合物中的连续光氧化反应。