An unexpected iodine(III)-mediated C(sp3)-C(sp2) bond cleavage of 3-(methylamino)-2-(2-substitutedbenzoyl)acrylates for efficient synthesis of privileged scaffold 4-quinolones was described. Notably, a wide range of alkyl groups (e.g. methyl, tert-butyl or alkyl chain) can be conveniently cleaved in this system. The detailed mechanism studies revealed that the transformation proceeded through cascade ipso-cyclization and 1,2-carbonyl migration, the smaller bond energy determined ortho C-C bond cleavage rather than C-H bond cleavage, via an enamine radical intermediate.