Ultrasound-Assisted Green Synthesis of Diversely Functionalized Pyrido[2,3-c]coumarins Catalyzed by Graphene Oxide Nanosheets under Solvent-Free Ambient Conditions

Graphene oxide nanosheet-catalyzed and ultrasound-assisted expedient synthesis of diversely functionalized pyrido[2,3-c]coumarins is reported based on a one-pot three-component reaction between 3-aminocoumarins, aromatic aldehydes, and phenylacetylene under solvent-free ambient conditions (room temperature and pressure). This synthetic protocol does not require tedious column chromatographic separation. Graphene oxide, being heterogeneous in nature, works efficiently under solvent-free conditions, providing the desired products in excellent yields (up to 97%). A metal-free synthetic protocol, faster reaction conditions (15–40 min), energy efficiency, operational simplicity, easily available cost-effective starting materials, the use of an eco-friendly carbocatalyst, low catalyst loading (8 mg), and the reusability of the catalyst are some of the salient features of the reported method. Moreover, this method demonstrates its capacity for gram-scale reactions (up to 10 g), and the recovered catalyst can be recycled without drastic changes for up to 5 cycles. This methodology for the synthesis of pharmaceutically interesting pyrido[2,3-c]coumarins is endowed with a very low E factor (up to 0.08), high atom economy, and high atom efficiency.