A new one-pot and divergent synthesis of multisubstituted quinolin-2(1H)-ones and oxireno[2,3-c]quinolin-2(1aH,3H,7bH)-ones via sequential Ugi/Knoevenagel condensation/hydrolysis and Ugi/Corey–Chaykovsky epoxidation reactions was developed. The four-component reactions of 2-acylanilines, aldehydes, (carboxymethyl)(dimethyl)sulfonium bromides and isocyanides gave Ugi adducts, which were subsequently treated with DBU to produce polysubstituted quinolin-2(1H)-ones or oxireno[2,3-c]quinolin-2(1aH,3H,7bH)-ones in good overall yields by intramolecular Knoevenagel condensation/hydrolysis or intramolecular Corey–Chaykovsky epoxidation reactions.