The formation of P-lactone from epoxide and CO catalyzed by COCO4- has been studied using a novel ab initio molecular dynamics approach. Employing the so-called metadynamics methodology, we show that it is possible to unravel the reaction mechanism of the catalyzed lactone formation in a fairly unbiased way. We were able to reproduce all the elementary steps within relatively short simulation time: the epoxide opening, the CO insertion, the CO addition to the Co site, the lactone ring formation, and the product dissociation, as obtained in previous static calculations. In addition, the simulations revealed that the lowest energy path goes through a stable intermediate featuring a metalla-oxo-furanyl ring. The simulations also indicated a new, higher energy path, in which the lactone ring formation precedes the CO uptake of the Co center. We show that this route becomes competitive when the Lewis acid attached to the lactone oxygen is softer.