Direct formation of 4- or 4,6-alkyl and aryl substituted diethyl 3-hydroxyphthalates from the correspondingly substituted Diels–Alder adducts of 2- or 2,5-substituted furans and diethyl acetylenedicarboxylate is promoted by AlCl3 in CH2Cl2 at room temperature. The first adduct of 2,5-diphenylfuran to be isolated has been obtained from the same reaction at −20°. The aromatic compounds can be obtained alternatively by treating the adducts with BF3 or H2SO4: where the adducts can be prepared by conventional means this two-step procedure has resulted in greatly improved yields. Adducts of furan and furfuryl alcohol are similarly converted to substituted phenols. HCl effected conversion only in the case of adducts carrying a bridgehead aryl substituent; in all other cases HCl added to the substituted double bond. The mechanism of the adduct rearrangement is discussed.
通过AlCl
3在室温下促进2-或2,5-取代
呋喃和乙二酰
乙烯二甲酯相应取代的Diels-Alder加合物直接形成4-或4,6-烷基和芳基取代的
乙酯基3-羟基
邻苯二甲酸酯。首次从相同反应在-20°下获得了
2,5-二苯基呋喃的第一个加合物。芳香化合物可以通过用BF
3或H
2SO
4处理加合物来替代获得:其中加合物可以通过传统方法制备,这种两步程序导致产率大大提高。
呋喃和
糠醇的加合物同样可以转化为取代
酚。HCl只在携带桥头芳基取代物的加合物的情况下发生转化;在所有其他情况下,HCl添加到取代双键上。讨论了加合物重排的机制。