Unless the MnIII‐produced carbon‐radical from β‐ketocarbonyl compounds undergoes smooth intramolecular addition to alkenes, it traps molecular oxygen in the reaction medium to produce a peroxy radical, which reacts with the neighbouring carbonyl group to form 1,2‐dioxetane. Thermal decomposition of 1,2‐dioxetane completes the oxidation to produce α‐oxo ester. This oxidation seems to be general at 50 °C under aerobic conditions, and can be catalytic for MnIII in AcOH with ultrasonic irradiation. Thus, the development of a new synthetic method for diversely substituted furans has been accomplished based on a couple of the MnIII‐initiated domino oxidation of β‐ketocarbonyl compounds with a suitable α‐allylic substitution.