In a specific embodiment, in step (1), a mixed solution of ethyl acetate and petroleum ether with a weight ratio of 1: (4-8) is used as a developing agent to monitor the reaction.
In a specific embodiment, in step (1), a mixed solution of ethyl acetate and petroleum ether in a weight ratio of 1: (4-8) is used as the developing agent to monitor the reaction on a dot plate.
In a specific embodiment, in step (1), a mixed solution of ethyl acetate and petroleum ether with a weight ratio of 1: (4-8) is used as a developing agent to monitor the reaction.