Here, we disclose an iron(ii)-catalyzed I-O bond cleavage of Koser's hypervalent iodine reagents (HIRs) that initiated the radical cyclization of unsaturated oximes at room temperature. This strategy is successfully applied for the construction of the isoxazoline backbone in an efficient manner. In particular, the direct introduction of a TsO group into products facilitates their late-stage transformations in organic synthesis.