Byproduct-Free, One-Pot Synthesis of Ortho Hydroxy Aryl Assimilated Dihydropyrimidones Over-Engineered Sulfonated Graphene Oxide at Room Temperature

Dihydropyrimidinones (DHPMs) are an important class of heterocyclic compounds that exhibit a wide range of biological activities. They serve as a key structural motif in pharmaceuticals and agrochemicals, making their efficient and sustainable synthesis highly desirable. The nucleophilic nature of hydroxy groups often alters the reaction pathway towards the formation of oxygen-bonded tetracyclic derivatives and lactonization by-products, which is a significant challenge for the synthesis of dihydropyrimidinone derivatives (DHPM) with ortho-hydroxy groups. In the present study, a highly promising and environmentally friendly protocol has been developed for the synthesis of DHPM derivatives using sulfonated graphene oxide (GO-HSO₃) as a metal-free heterogeneous catalyst. The reaction proceeded in ethanol at room temperature, rendering a sustainable and greener approach. The catalytic system efficiently facilitated the Biginelli reactions between ethyl acetoacetate, urea, and azo salicylaldehyde or salicylaldehyde, leading to the selective transformation of DHPMs with excellent yields (84–94%) and minimal byproducts. The superior catalytic activity of GO-HSO₃ is attributed to its abundant –SO₃H functional groups, which enhance the proton donation and reaction kinetics. This approach is a sustainable and practical method for DHPM synthesis due to its excellent yield, ease of execution, reusability of the catalyst, and adherence to green chemistry principles. Compared to conventional methods that yield an undesired side product, this approach ensures high selectivity and cleaner synthesis. The developed strategy not only aligns with the principle but also demonstrates the potential of sulfonated graphene oxides as a sustainable catalyst for organic transformations.