A study of Diels–Alder reactions of tetraphenylcyclopentadienone (II) coupled with development of two improved procedures for the generation of benzyne, one of which affords a practical route to the reactive dienophile 1,4-dihydronaphthalene-1,4-endo-oxide (Ia), led to an investigation of the reaction of Ia and II. At 80° these reactants combine readily to give the adduct IIIa, which is cleaved on pyrolysis to isobenzofurane VIIIa and 1,2,3,4-tetraphenylbenzene (IX). The transient existence of isobenzofurane (VIIIa) was established by trapping it with the 1,4-endo-oxide Ia and isolation of the adducts X and XI. In confirmation of the interpretation, X and XI were obtained by independent synthesis from the adduct Va from Ia and α-pyrone and thermal decomposition of Va in the presence of Ia as trapping agent. Parallel experiments with 1,4-dimethyl-1,4-dihydronaphthalene-1,4-endo-oxide, as well as mixed additions, supported the interpretations advanced. Evidence is presented to show that isobenzofurane (VIIIa) invariably adds exo to the bicyclic dienophile.
一项关于四苯基环戊二烯酮(II)的Diels-Alder反应研究,结合了两种改进的苯基生成方法,其中一种提供了一条实用的途径到反应性双烯丙烯1,4-二氢萘-1,4-内氧化物(Ia),导致对Ia和II的反应进行研究。在80°C下,这些反应物很容易结合形成加合物IIIa,经热解裂解为异苯并呋喃醚VIIIa和1,2,3,4-四苯基苯(IX)。通过与1,4-内氧化物Ia的捕获和加合物X和XI的分离,已经确定了异苯并呋喃醚(VIIIa)的短暂存在。通过与1,4-二甲基-1,4-二氢萘-1,4-内氧化物以及混合加成的平行实验,支持了提出的解释。提供了证据表明异苯并呋喃醚(VIIIa)总是朝向双环双烯丙烯的exo位置进行加成。