Synthesis of N-Substituted Pyrroles Catalyzed by Low-Cost and Commercially Available Aluminas

The Paal-Knorr reaction of acetonylacetone with primary amines catalyzed by CATAPAL 200 under conventional heating at 60 degrees C for 45 min afforded N-substituted pyrroles in 68-97% yields. The pyrrole 3g was studied by single-crystal and powder X-ray diffraction. The high percentage of Bronsted-Lewis acid sites (23%) and pore diameter (37.8 nm) of CATAPAL 200 favor the formation of the pyrrole ring because an increase in Bronsted acid sites efficiently catalyzes condensation and dehydration processes. This protocol is distinguished by its operational simplicity, high yields, reduced reaction time, no solvent required, stoichiometric amounts of reactants, low catalyst loading, and clean reaction profile. In addition, the CATAPAL 200 is cheap and commercially available leading to an efficient and lower-cost chemical transformation. The reusability of the catalyst for up to five cycles without appreciable loss of its catalytic activity makes the present protocol sustainable and advantageous compared to conventional methods.

Automated summary

The Paal-Knorr reaction of acetonylacetone with primary amines catalyzed by CATAPAL 200 under conventional heating at 60 degrees C for 45 min resulted in N-substituted pyrroles in yields of 68-97%. CATAPAL 200, with its high percentage of Bronsted-Lewis acid sites (23%) and pore diameter (37.8 nm), promotes the formation of pyrrole ring by facilitating condensation and dehydration processes. This protocol offers simplicity, high yields, reduced reaction time, solvent-free conditions, stoichiometric amounts of reactants, low catalyst loading, and clean reaction profile. Furthermore, CATAPAL 200 is inexpensive and readily available, making it a cost-effective option for chemical transformations. The catalyst can be reused for up to five cycles without significant loss of catalytic activity, making this protocol sustainable and advantageous compared to conventional methods.