The pyrano[3,4-b] indol-3-ones (13a,b), stable synthetic analogues of indole-2,3-quinodimethanes, undergo Diels–Alder reactions with acetylenes to give, with concomitant loss of carbon dioxide, carbazoles. Thus, reaction with dimethyl acetylenedicarboxylate and dibenzoylacetylene gives the carbazole diesters (15a,c) and dibenzoylcarbazoles (15b,d) respectively. The dibenzoylcarbazoles (15b,d) react with hydrazine to give pyridazo[4,5-b]carbazoles (16). The pyranoindolones (13) also react with benzyne to give the benzo[b]carbazoles (18).

中文翻译：

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吡喃并[3,4- b ]吲哚-3-酮（吲哚-2,3-喹二甲烷的稳定类似物）的Diels-Alder反应性

吡喃并[3,4- b ]吲哚-3-酮（13a，b）是吲哚-2,3-喹二甲烷的稳定合成类似物，与乙炔进行狄尔斯-阿尔德反应，生成二氧化碳，同时损失了咔唑。因此，与乙炔基二羧酸二甲酯和二苯甲酰基乙炔反应，分别得到咔唑二酯（15a，c）和二苯甲酰基咔唑（15b，d）。二苯甲酰咔唑（15b，d）与肼反应，得到吡啶并[4，5- b ]咔唑（16）。吡喃并吲哚酮（13）也与苯炔反应，得到苯并[ b ]咔唑（18）。