Boron trifluoride ethyl acetate complex is an organic compound with the chemical formula BF3 · Et2O, where BF3 represents boron trifluoride and Et2O represents ethyl acetate (diethyl ether). This complex is a colorless liquid commonly used as a Lewis acid catalyst in organic synthesis. It has high reactivity and selectivity, and is widely used in the synthesis of organic molecules and polymers.