Industrial preparation process of linagliptin

The invention relates to the technical field of medicines and particularly relates to an industrial preparation process of linagliptin. The industrial preparation process comprises the steps of adding a reactant a (2-chloromethyl-4-methyl-quinazoline), an equal molar ratio of reactant b (8-bromo-7-(2-butynyl)-3-methylxanthine), an acid-binding agent and a proper amount of solvent into a reaction kettle to react at 0-140 DEG C for 3-8 hours, after TLC detection reaction is finished, directly adding a reactant c ((R)-3-phthalimide piperidine-tartaric acid) and an acid-binding agent, namely N,N-diisopropylethylamine without processing a reaction mother liquid to react at 0-125 DEG C for 3-10 hours, after the TLC detection reaction is finished, adding ethanolamine without processing the reaction mother liquid to react for 2-10 hours, after the TLC detection reaction is finished, dropwise adding purified water, carrying out suction filtration to obtain a linagliptin rough product, and refining by virtue of a refining method disclosed in a patent CN101437823A, so as to obtain a linagliptin refined product. According to the industrial preparation process, linagliptin is synthesized by virtue of a one-pot continuous feeding method, the consumption of the solvent is low, and the operation is easy; and the industrial preparation process is suitable for industrial production.