One-pot synthesis of tryptophols with mesoporous MCM-41 silica catalyst functionalized with sulfonic acid groups

Mesoporous MCM-41 silica functionalized with sulfonic acid groups (SO3H-MCM-41) was prepared through the condensation of MCM-41 with benzyl alcohol followed with sulfonation, which was characterized by XRD, FT-IR and nitrogen adsorption analyses. One-pot Fischer indole synthesis of tryptophols under the catalysis of SO3H-MCM-41 was reported with phenylhydrazine hydrochlorides and 2,3-dihydrofuran. The acidity and amount of sulfur loading were surveyed and also were the catalytic performance of SO3H-MCM-41. The results showed that higher amount of sulfur loading leads to higher acidity and consequently better yields of tryptophols. Moreover, SO3H-MCM-41 displayed good shape-selectivity in Fischer indole synthesis and inhibited the production of bulky byproduct polyindoles which were generally found in traditional acid catalysis. A series of tryptophols were synthesized with SO3H-MCM-41 in better yields than those of conventional methods reported.

Graphical abstractOne-pot synthesis of tryptophols was reported with phenylhydrazine hydrochlorides and 2,3-dihydrofuran under the catalysis of mesoporous MCM-41 silica functionalized with sulfonic acid groups (SO3H-MCM-41) which was prepared through the condensation of MCM-41 with benzyl alcohol followed with sulfonation.Figure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights► MCM-41 functionalized with sulfonic acid groups (SO3H-MCM-41) was prepared. ► The acid amount of SO3H-MCM-41 increased with the reacting amount of ClSO3H. ► Tryptophols were synthesized in one-pot Fischer indole synthesis with SO3H-MCM-41. ► The yields of tryptophols improved with the increase of acid amount of SO3H-MCM-41.