Barton D, Ley S V
Ciba Found Symp. 1978(53):53-66. doi: 10.1002/9780470720349.ch5.
Selective ortho-substitution of phenols can be secured, in principle, by attachment of the substituting reagent to the phenolic hydroxy group and subsequent rearrangement of this derivative by a cyclic mechanism into the orthoposition. So far, only one example of this principle (the Claisen rearrangement) is well established. For ortho-hydroxylation, a phenolic ester of selenium(IV) should have the desired properties. Diphenylseleninic anhydride, PhSE(=0)0.Sec(=0)Ph, has proved has proved to be the new reagent for the application of this mechanism. Several phenols, including models of the phenolic ring A of tetracycline, gave o-hydroxydienones, with quinones and phenylselenated species as by-products, when treated with diphenylseleninic anhydride. When the phenols were converted into their corresponding anions before treatment with the anhydridide, the o-hydroxydienones were obtained in good yield free from other products arising from reaction at the para position. When phenols were added to a warm solution of diphenylseleninic anhydride, they were oxidized to the o-quinones even when the phenols were not substituted in para position.
原则上，酚类的选择性邻位取代可以通过将取代试剂连接到酚羟基上，并随后通过环状机理将该衍生物重排到邻位来实现。到目前为止，该原理的仅有一个例子（克莱森重排）已得到充分证实。对于邻位羟基化反应，四价硒的酚酯应具有所需的性质。二苯基亚硒酸酐，PhSe(=O)O.Se(=O)Ph，已被证明是应用该机理的新试剂。几种酚类，包括四环素酚环A的模型，在用二苯基亚硒酸酐处理时，生成了邻羟基二烯酮，并伴有醌和苯基硒化产物作为副产物。当酚类在与酸酐反应前转化为相应的阴离子时，可高产率地获得邻羟基二烯酮，且无对位反应产生的其他产物。当酚类加入到温热的二苯基亚硒酸酐溶液中时，即使酚类在对位未被取代，它们也会被氧化为邻醌。
