Synthesis Of N-protected Functionalized Pyrroles Via One-pot Multi-component Reaction

Pyrrole is one of the most important simple heterocycles owing to its antitumor,anti-inflammatory, antibacterial, antioxidant, and antifungal properties. Furthermore, thepyrrole ring has been frequently found in a broad range of natural products and biologicallyactive compounds. In addition, pyrrole derivatives are also particularly important in materialsscience. These utilities continue to drive the interest in the development of new syntheticmethods for pyrroles. Very recently, multicomponent coupling reactions (MCRs) which leadto the connection of three or more starting materials in a single synthetic operation with highatom economy and bond-forming efficiency offer significant advantages over classicalstepwise methods.In view of green and sustainable chemistry, magnetic supported nanocatalysts have beenapplied to a wide range of catalytic reactions because of the advantage of a larger surface areato volume ratio which enhanced the contact between reactions and catalyst, as well as easyand efficient isolation and recovery. Magnetic supported nanocatalysts have been applied to awide range of catalytic reactions, including oxidations, hydrogenations, photocatalysis, andC-C bond formation, as well as in novel applications in asymmetric synthesis, hydration, andKnoevenagel condensations reactions. Among various magnetic nanoparticles, cobalt ferrite(CoFe2O4) is a well-known magnetic material with the properties of high magnetocrystallineanisotropy, moderate saturation magnetization, excellent chemical stability, low toxicity,readily accessibility and inexpensiveness which make it a promising material as catalystsupport.Combining both advantages of multicomponent reaction and the magnetic supportednanocatalysts, the development of a new atom-efficient and environmentally friendlysynthetic procedure for the efficient preparation of multisubstituted pyrroles is therefore aninteresting challenge. We have designed a novel magnetic nanoparticle CoFe2O4supportedmolybdenum catalyst [CoFe2O4@SiO2-NH2-Mo(acac)2] and successfully used it in a one-potfour-component coupling reaction of amines, aldehydes,1,3-dicarbonyl compounds andnitromethane. Structural diversity of pyrroles can be produced in a single step by use of various kinds of amines, aldehydes and1,3-dicarbonyl compounds with good to excellentyields. The easy recovery of the catalyst and its reusability, broad substrate scope, shortreaction time, high yield of products and solvent-free conditions make this protocol practical,environmentally friendly and economically attractive.In addition, a novel magnetical nano-CoFe2O4supported Sb ([CoFe2O4@SiO2-DABCO-Sb]) was successfully constructed, which exhibited high catalytic activity for one-potthree-component synthesis of multisubstituted pyrroles in the reaction of amines, nitroolefinand1,3-dicarbonyl compounds. The magnetic heterogeneous catalyst could be easilyrecovered using an external magnet and reused many times without significant loss ofcatalytic activity.