Cu(3)(BTC)(2) as a viable heterogeneous solid catalyst for Friedel-Crafts alkylation of indoles with nitroalkenes

Abstract

In the present work, Friedel-Crafts alkylation reaction of indole with β-nitrostyrene is examined using a readily available copper based metal-organic frameworks (MOFs) namely, Cu₃(BTC)₂ (BTC: 1,3,5-benzenetricarboxylic acid) as solid catalyst under mild reaction conditions. Among the various catalysts screened for this reaction, Cu₃(BTC)₂ exhibits higher activity under the optimized reaction conditions. Besides the absence of leaching of active sites, it is also observed that the catalyst can be reused for four cycles with a minimal decrease in its activity. Cu₃(BTC)₂ is used as a catalyst to synthesise a series of heterocyclic compounds with different indole and β-nitrostyrene derivatives in moderate to high yields. The present catalytic system shows comparable activity against to recent reports but the advantage of Cu₃(BTC)₂ is that it does not require any post-functionalization and above all it can be readily synthesised, thus contributing to the synthesis of heterocyclic compounds with high biological interest.

Keywords: Friedel-Crafts alkylation; Green chemistry; HKUST-1; Heterogeneous catalysis; Metal organic frameworks.