MIL-101(Fe) as an active heterogeneous solid acid catalyst for the regioselective ring opening of epoxides by indoles

Abstract

Ring opening of an epoxide by a nucleophile is considered as one of the viable strategies to prepare biologically active molecules using homogeneous or heterogeneous Lewis acid catalysts. Very often, the ring opening of epoxide was performed with oxygen, sulfur and nitrogen based nucleophiles. Recently, metal organic frameworks (MOFs) were identified as one of the promising solid heterogeneous catalysts for ring opening of epoxide with oxygen and nitrogen based nucleophiles, but however, use of carbon nucleophile like indole is limited. Hence, the present work reports the catalytic performance of MIL-101(Fe) as a highly active regioselective heterogeneous solid Lewis acid catalyst in promoting the ring opening of styrene oxide by indole. Among the various catalysts employed for this reaction, MIL-101(Fe) exhibited the highest catalytic activity. A series of control experiments indicated the pivotal role played by Lewis acids within the frameworks of MIL-101(Fe) and further, the catalytic reaction was found to be heterogeneous in nature as evidenced by leaching test. Further, MIL-101(Fe) was reused four cycles with no decay in its activity. Also, MIL-101(Fe) exhibited wide substrate scope in providing series of heterocyclic compounds in moderate to higher yields. A suitable mechanism was also proposed considering the present results and the knowledge from the literature.