One‐Pot Synthesis of 4‐(Alkylamino)‐1‐(arylsulfonyl)‐3‐benzoyl‐1,5‐ dihydro‐5‐hydroxy‐5‐phenyl‐2 H ‐pyrrol‐2‐ones via a Multicomponent Reaction

An effective route to novel 4‐(alkylamino)‐1‐(arylsulfonyl)‐3‐benzoyl‐1,5‐dihydro‐5‐hydroxy‐5‐phenyl‐2 H ‐pyrrol‐2‐ones 10 is described ( Scheme 2 ). This involves the reaction of an enamine, derived from the addition of a primary amine 5 to 1,4‐diphenylbut‐2‐yne‐1,4‐dione, with an arenesulfonyl isocyanate 7 . Some of these pyrrolones 10 exhibit a dynamic NMR behavior in solution because of restricted rotation around the CN bond resulting from conjugation of the side‐chain N‐atom with the adjacent α , β ‐unsaturated ketone group, and two rotamers are in equilibrium with each other in solution ( 10  ⇌  11 ; Scheme 3 ). The structures of the highly functionalized compounds 10 were corroborated spectroscopically (IR, 1 H‐ and 13 C‐NMR, and EI‐MS), by elemental analyses, and, in the case of 10a , by X‐ray crystallography. A plausible mechanism for the reaction is proposed ( Scheme 4 ).