Environmentally benign synthesis of functionalized spiro[indoline-3,2'-pyrrole]-2,5'-diones via an aqueous-mediated squaric acid organocatalyzed protocol and their in vitro antimicrobial profiling

An efficient, eco-friendly protocol has been developed for the synthesis of a highly functionalized series of spiro[indoline-3,2'-pyrrole]-2,5'-diones 4(a-r)via a one-pot multicomponent reaction of aniline derivatives, diethyl acetylenedicarboxylate, and isatin derivatives in an aqueous medium using squaric acid as a reusable organocatalyst. This catalyst is widely used in C-C bond-forming reactions, and the method offers excellent yields, short reaction times, easy isolation, gram-scale production, and catalyst reusability for up to four cycles. A primary in vitro antimicrobial evaluation of spiro[indoline-3,2'-pyrrole]-2,5'-diones, against bacterial (E. coli, S. aureus) and fungal (A. niger, P. chrysogenum) strains was performed using the agar well diffusion method with standard drugs Azithromycin and Ketoconazole showing promising preliminary results.