Introduction of the halogen atom or the acyl group at the C-ring of fraxinellone was investigated. Some unexpected halogenation products were obtained with the different chlorination/bromination reagents, and their possible reaction mechanisms were also proposed. Seven key steric structures of 2a', 2b, 2b', 2c', 3a, 3b, and one isomer (5'α-Cl) of 2a were further confirmed by single-crystal X-ray diffraction. Especially compounds 2a, 2a', 3a and 3c exhibited more potent insecticidal activity than toosendanin. Some structure-activity relationships of tested compounds were also described.