Abstract: The reaction mechanism of Rh(Ⅱ)-mediated carbenoid intramolecular C-H insertion have been intensively investigated. The reaction has been observed to be affected by the electrophilicity of the Rh(Ⅱ)-carbene intermediate, the substituents on the carbon at which the C-H insertion occurs, and steric and conformational factors.¹ It has been well documented that the electronic property of the ligands of the Rh(Ⅱ) catalyst has marked influence over the electrophylicity of Rh(Ⅱ)-carbene intermediate. In addition, the α-substituent on the carbenoid carbon are expected to exert similar affect on the reactivity of Rh(Ⅱ)-carbene. According to the reaction mechanism proposed by Doyle, an electron-donating α-substituent decreases the electrophilicity of the Rh(Ⅱ)-carbene complex and causes the C-H insertion to occur with a later transition state,while an electron withdrawing α-substituent operates in the opposite way. However, this prediction is still lack of solid support by experimental data. Most of the studies on the electronic effects have so far been concentrated on electron-withdrawing α-substituent, such as ester or acetyl group. The α-substituent effect, although important, is generally subtle and may be readily overridden by other effects, such as steric and conformational effects. This makes it difficult to accurately evaluate the α-substituenteffect.