In this study, the mechanism of the replacement reaction of an aluminum atom by a boron atom in the 1-ethyl-3-substituted alumolanes with boron halides is proposed. Theoretical and experimental justifications based on the DFT quantum chemical calculations of the energy parameters of possible reaction routes coupled with monitoring of the reaction between 1-ethyl-3-butylalumolane and BF3·Et2O, BCl3 and BBr3 using 1H, 13C, 11B and 27Al NMR spectroscopy are provided.