REGIOSELECTIVITY IN THE PHOTOCYCLIZATION OF STILBENES

该提案的目的是开发合成潜力的 光环化反应，其中紫外线照射 在没有溶解氧的情况下邻甲氧基芪得到4 α-甲氧基-4 α， 4b-二氢菲作为瞬时中间体， 进行甲醇的消除以得到菲。 除了几 这种消除性光环化的实例由其他人报道， 在1974年，这种反应在很大程度上被忽视了。 研究 将进行与母体邻甲氧基芪，以建立最佳的 反应条件;特别是，假设将被测试，这 在酸化的甲醇中，消除性光环化将比在酸化的甲醇中进行得更好。 它在环己烷中。 将对这一做法的可行性进行研究 反应作为一种方法，以克服区域化学问题，有时 限制了公知的氧化光环化的合成价值 法 例如，间位取代的 芪类得到2-和4-取代菲的混合物，通常与 几乎没有区域选择性。 的消除性光环化反应 2-甲氧基-5-甲基芪和2-甲氧基-3-甲基芪将被携带 来检验这些反应会产生个体的假设 2-和4-甲基菲的样品。 2-苯乙烯基萘的氧化光环化反应表现出很高的 区域选择性，几乎只得到苯并[c]菲; 区域异构的苯并[a]蒽仅以痕量形成。 为 类似的原因，二苯并[a，j]蒽和二苯并[a，h]蒽 系统也不能通过氧化光环化获得。 是 试图提供合成苯并[a]蒽的途径， 二苯并[a，j]-蒽和二苯并[a，h]蒽体系， 3-甲氧基-2-苯乙烯基萘的消除性光环化， 2，4-二甲氧基-1，5-二苯乙烯基苯和2，5-二甲氧基-1，4-二苯乙烯基苯， 分别 这些建议的实验尝试，以开发的合成效用， 消除式光环化法主要针对最简单分子 示例，但最终目的是将这些示例视为原型 用于将来将该方法应用于多替代系统。 的 扩大合成多核芳族体系的能力 这里所考虑的类型应该具有未来的重要性， 由于广泛发生的健康相关研究 与菲有关的生理活性天然产物， 苯并蒽的致癌性。

The objective of this proposal is to develop the synthetic potential of the photocyclization reaction in which the ultraviolet irradiation of o-methoxystilbenes in the absence of dissolved oxygen gives 4a-methoxy-4a, 4b-dihydrophenanthrenes as transient intermediates that subsequently can undergo elimination of methanol to give phenanthrenes. Except for a few examples of this eliminative photocyclization that were reported by other workers in 1974, this reaction has remained largely overlooked. Studies will be carried out with the parent o-methoxystilbene to establish optimum reaction conditions; in particular, the hypothesis will be tested that this eliminative photocyclization will proceed better in acidified methanol than it has in cyclohexane. Studies will be undertaken of the viability of this reaction as a method to overcome the regiochemical problems that sometimes limit the synthetic value of the well-known oxidative photocyclization method. For example, oxidative photocyclizations of meta-substituted stilbenes give mixtures of 2- and 4-substituted phenanthrenes, often with almost no regioselectivity. The eliminative photocyclizations of 2-methoxy-5-methylstilbene and 2-methoxy-3-methylstilbene will be carried out to test the hypothesis that these reactions will produce individual samples of 2- and 4-methylphenanthrene, respectively. Oxidative photocyclizations of 2-styrylnaphthalenes exhibit high regioselectivity, giving almost exclusively benzo[c]phenanthrenes; the regioisomeric benz[a]anthracenes are formed only in trace amounts. For similar reasons, the dibenz[a,j]anthracene and dibenz[a,h]anthracene systems also are not available by oxidative photocyclization. It is proposed to try to provide synthetic access to the benz[a]anthracene, dibenz[a,j]-anthracene, and dibenz[a,h]anthracene systems by carrying out eliminative photocyclizations of 3-methoxy-2-styrylnaphthalene, 2,4-dimethoxy-1,5-distyrylbenzene, and 2,5-dimethoxy-1,4-distyrylbenzene, respectively. These proposed experimental attempts to develop the synthetic utility of the eliminative photocyclization method focus on the simplest molecular examples, but the ultimate aim is to consider these examples as prototypes for future applications of the method to multi-substituted systems. The expansion of the capabilities for synthesizing polynuclear aromatic systems of the type considered here should have future importance for health-related studies because of the widespread occurrence of physiologically active natural products related to phenanthrenes, and the carcinogenicity of benzanthracenes.