Facile and Chemically Sustainable One‐Pot Synthesis of a Wide Array of Fused <i>O</i>‐ and <i>N</i>‐Heterocycles Catalyzed by Trisodium Citrate Dihydrate under Ambient Conditions

Abstract

Abstract A simple, straightforward, and highly efficient multicomponent one‐pot synthesis of pharmaceutically interesting diverse functionalized O ‐ and N ‐heterocyclic scaffolds, such as spiro[indolin‐2‐one‐3,4′‐pyrans] ( 4 aa – 4 ah ), spiro[indolin‐2‐one‐3,4′‐pyran]‐annulated ( 4 ba – 4 bd , 4 b′a – 4 b′b , 4 ca – 4 cf , 4 da – 4 dd , 4 ea – 4 ee ), and spiro[acenaphthylen‐1‐one‐3,4′‐pyran]‐annulated ( 7 ba , 7 b′a , 7 ca , 7 da , 7 ea ) derivatives, pyrano[2,3‐ c ]pyrazoles ( 4 fa – 4 fz , 4 ha – 4 hf ), spiro[indolin‐2‐one‐3,4′‐pyrano[2,3‐ c ]pyrazoles] ( 4 ga – 4 gh , 4 ia – 4 ic ), and spiro[acenaphthylen‐1‐one‐3,4′‐pyrano[2,3‐ c ]pyrazoles] ( 7 fa – 7 fd ), has been developed based on commercially available trisodium citrate dihydrate as an inexpensive and eco‐friendly catalyst for the tandem Knoevenagel–cyclocondensation of isatin/aldehyde/acenaphthylene‐1,2‐dione, malononitrile, and various C−H activated acids in aqueous ethanol at room temperature. The salient features of this protocol are mild reaction conditions, excellent yields, applicability for the synthesis of a large number of diverse heterocycles, high atom economy, eco‐friendliness, easy isolation of products, no column chromatographic separation, and the reusability of reaction media. It is noteworthy to mention that the present method offers a general way to synthesize various O ‐ and N ‐heterocyclic scaffolds following a unified approach, which could replace a huge number of alternative methods reported so far.