Reactions of 5‐R‐1‐indanones (R = Me, t‐Bu, Cl, F) in ionic liquids in the presence of Brønsted acid afforded substituted truxenes as aldol cyclotrimerization products, whose yields were found to be better in [BMIM][Tf₂N] than in [BMIM][BF₄]. Their cyclotrimerizations were slower and gave lower yields than that of the parent 1‐indanone. Furthermore, the reaction mixtures contained some amounts of intermediate products, 5‐R‐2‐(5‐R‐1‐indanylidene)‐1‐indanone, formed by the initial aldol condensation. These results suggested that both the electron‐donating and the electron‐withdrawing substituents at the C(5) position reduced the rate of cyclotrimerization. This rate retardation was supported by DFT/B3LYP calculations with the PCM solvation model. The activation energies of the reaction of the protonated indanones and the indenols in the initial aldol condensation were increased by both the electron‐donating group (EDG) and the electron‐withdrawing group (EWG). The transition states in the second aldol condensation and in the electron‐cyclization were also destabilized by both the EDG and the EWG.

中文翻译：

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离子液体中布朗斯台德酸催化的1-茚满酮的醛醇醛环三聚：取代基效应的实验和DFT研究

在布朗斯台德酸存在下，离子液体中的5‐R‐1‐茚满酮（R = Me，t‐ Bu，Cl，F）反应提供了取代的丁烯作为羟醛环三聚产物，在[BMIM]中发现其收率更高[Tf ₂ N]比[BMIM] [BF ₄]。与母体1-茚满酮相比，它们的环三聚反应速度较慢，且产率较低。此外，反应混合物还包含一些中间产物，即最初的醛醇缩合形成的5‐R‐2‐（5‐R‐1‐茚二烯基）-1-茚满酮。这些结果表明，C（5）位置上的给电子取代基和吸电子取代基都降低了环三聚反应的速率。使用PCM溶剂化模型进行DFT / B3LYP计算可以支持这种速率延迟。给电子基团（EDG）和吸电子基团（EWG）都增加了质子化的茚满酮与吲哚在最初的醛醇缩合反应中的活化能。