We achieved a palladium-catalyzed C-H activation/C-C coupling reaction between arenes with a pyridyl, aminoquinolinyl, imino, or amide directing group) and oxiranes. The reaction proceeded at room temperature without any additives and tolerated a wide variety of functional groups, and the products were obtained in good to excellent yields, even on grain scale. This is the first example of a transition-metal-catalyzed intermolecular direct coupling reaction between a C-H bond of aromatic compounds and a carbon atom Of oxiranes via C-H bond activation. By using N-methoxybenzamide as a substrate, we obtained 3-substituted isochroman-l-ones in One pot. The coupling reaction proceeded with stereoretention. Kinetic isotope effect experiments suggested that C-H bond activation is the rate-determining step.