A novel catalyst- and solvent-controlled dimerization of aliphatic alkynones through tandem Michael addition/rearrangement/cyclization sequence has been developed. The elaborated protocol provides a convenient chemo-, regio- and stereoselective access to rare 3(2H)-furanones decorated with 2-exo-methylene and 4-ethenyl functionalities. A comprehensive density functional theory (DFT) study of possible reaction mechanism including ab initio molecular dynamics (AIMD) simulations and quantum theory of atoms in molecules (QTAIM) analysis of various substrate/catalyst/solvent complexes has revealed the Janus-like behavior of the employed sodium tert-butoxide/toluene system that is responsible both for the chemoselectivity of the initial addition step and the inhibition of the final cyclization step.