An unprecedented and challenging simultaneous carboxylation/halogenation, and next lactonization of γ,γ-dicarbonyl-substituted aldehydes has been realized using an eco-friendly, safe and inexpensive solid sodium chlorite (NaClO₂)/1,3-dibromo-5,5-dimethyl-hydantoin (DBDMH) combination. This new reaction is amenable to a multi-gram scale-up with high yield.