The pyrano[4,3-b]indol-3-ones (7) are stable indole-2,3-quinodimethane type dienes, which undergo Diels–Alder reaction with alkynes to give, after loss of carbon dioxide, carbazoles. The reactivity of the diene is increased by the presence of the electron-withdrawing t-butoxycarbonyl group on the indole nitrogen. The pyranoindolones (7) are less reactive, and exhibit the opposite regiochemistry in their Diels–Alder reactions than the isomeric pyrano[3,4-b]indol-3-ones (1). Factors which affect the regiochemistry of the Diels–Alder reaction are discussed.

中文翻译：

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吡喃并[4,3 - b ]吲哚-3-酮，吲哚2,3-喹二甲烷类似物的Diels-Alder反应性

吡喃并[4,3 - b ]吲哚-3-酮（7）是稳定的吲哚-2,3-喹二甲烷型二烯，与炔烃进行狄尔斯-阿尔德反应，在失去二氧化碳后产生咔唑。通过在吲哚氮上存在吸电子的叔丁氧羰基，可以提高二烯的反应性。吡喃并吲哚并酮（7）的反应性较低，并且在Diels-Alder反应中表现出与异构吡喃并[3,4- b ]吲哚-3-酮（1）相反的区域化学反应。讨论了影响狄尔斯-阿尔德反应的区域化学的因素。