Acetic acid mediated Michael-addition/cyclization cascade sequence of cyclic diones and enones; A convenient, proficient, and eco-friendly access to the fused dihydropyrans

An acetic acid-mediated Michael addition-cyclization cascade sequence of cyclic diones and enones is developed to afford fused dihydropyrans. A broad range of structurally diverse aliphatic, aromatic, and functionalized enones are successfully employed under the optimized reaction conditions. The current strategy takes advantage of using easily accessible and environmentally benign conditions to access the synthetically challenging 3,4-dihydropyran in high yields (up to 90%) and selectivity (up to 20:1). The applicability of these reaction conditions is underscored by successfully isolating the desired dihydropyrans from the Michael adduct, for the first time. Moreover, Density Functional Theory (DFT) provided a comprehensive analysis involving Frontier Molecular Orbital (FMO), Mulliken population, and Molecular Electrostatic Potential (MEP) investigations to gain deeper insights into the underlying reaction sequence