Raviola Carlotta, Fagnoni Maurizio
PhotoGreen Lab, Department of Chemistry, V. Le Taramelli 12, 27100 Pavia, Italy.
Photochem Photobiol Sci. 2018 Jan 17;17(1):107-117. doi: 10.1039/c7pp00372b.
The site-selective cleavage of an Ar-X bond in polyhalogenated aromatics is an important tool in synthetic planning especially when more than one identical halogen atom is present. An alternative to the usual metal-catalyzed cleavage is represented by photochemistry although only a few examples have been reported. We then investigated the feasibility of the site-selective photodechlorination of some dichloroanisoles through a combined experimental and computational study. In the case of 2,4-dichloroanisole, selective detachment of the chlorine atom at the ortho position with respect to the OMe group was observed upon photohomolysis (in cyclohexane) or photoheterolysis (in MeOH) of the Ar-Cl bond. In the latter case, 5-chloro-2-methoxy-1,1'-biphenyl was exclusively formed upon reaction of the resulting phenyl cation with benzene. The substitution of an OH group for a OMe group was detrimental since a lower photoreactivity resulted with no improvement in the selectivity.
在多卤代芳烃中，芳基 - 卤键的位点选择性裂解是合成规划中的重要工具，特别是当存在多个相同卤原子时。光化学是通常金属催化裂解的一种替代方法，尽管仅报道了少数实例。然后，我们通过实验和计算相结合的研究，研究了一些二氯苯甲醚进行位点选择性光脱氯的可行性。对于2,4 - 二氯苯甲醚，在Ar - Cl键发生光均裂（在环己烷中）或光异裂（在甲醇中）时，观察到相对于甲氧基在邻位的氯原子选择性脱离。在后一种情况下，所得苯基阳离子与苯反应时仅生成5 - 氯 - 2 - 甲氧基 - 1,1'- 联苯。用羟基取代甲氧基是有害的，因为光反应性降低且选择性没有提高。
