Cobalt(II) chloride as a novel and efficient catalyst for the synthesis of 1,2,5‐trisubstituted pyrroles under solvent‐free conditions

Biomimetic Clauson‐Kass and Paal‐Knorr Pyrrole Synthesis Using β‐Cyclodextrin‐SO3H under Aqueous and Neat Conditions ‐ Application to Formal Synthesis of Polygonatine†

“…Amongst these, Clauson‐Kaas and Paal–Knorr are most commonly used reactions for the synthesis of pyrroles as they use simple and readily available precursors. These reactions were reported with several catalysts such as Ionic liquid, zeolite, Sc(OTf) 3 , Ti(OiPr) 4 , Al 2 O 3 , Bi(NO 3 ) 3 , Yb(OTf) 3 , CoCl 2 , InCl 3 , RuCl 3 , montmorillonite‐KSF, sulfamic acid, SnCl 2 ⋅2H 2 O, silica sulfuric acid, microwave, P 2 O 5 , CuCl 2 , FeCl 3 .7H 2 O, montmorillonite K‐10, CeCl 3 , Bi(NO 3 ) 3 .5H 2 O, MgI 2 Et 2 O, I 2 , Cyclodextrin, ultrasound irradiation, nano‐organocatalyst, Amberlite IR 120, Pr(OTf) 3 , and PEG‐SO 3 H . Despite the advances, many of them suffer from certain drawbacks such as harsh reaction conditions, use of expensive reagents, toxic solvents, strongly acidic conditions, costly catalysts, longer reaction times, non‐recyclability, involve tedious workup procedures and use extra energy sources such as microwaves or ultrasound.…”

Effect of Mn2+ dopants on the photocatalytic efficiency of MoS2

“…The Paal-Knorr reaction could be promoted via various acidity catalysts, including mineral acids [14], metal salts [15], metal oxides [16], zeolite [17], and montmorillonite [18]. In addition, this reaction was carried out in ion liquid media [7], or under assisting microwave [19] and ultrasonic [20].…”