Preparation method of 2-(2-(tert-butyloxycarbonyl)-2-azaspiro [3.4] octane-5-yl) acetic acid

The invention discloses a preparation method of 2-(2-(tert-butyloxycarbonyl)-2-azaspiro [3.4] octane-5-yl) acetic acid. The preparation method comprises the following steps: dissolving a compound 1 and a compound 2 in 2-methyl tetrahydrofuran, dropwise adding lithium bis (trimethylsilyl) amide, and reacting to obtain a compound 3; dissolving the compound 3 into acetone, and reacting with sodium iodide to obtain a compound 4; dissolving the compound 4 in 2-methyl tetrahydrofuran, dropwise adding n-butyllithium, and reacting to obtain a compound 5; dissolving the compound 5 into 2-methyl tetrahydrofuran, then adding a compound 6, alkali and 1, 8-diazabicyclo undecene-7-ene, and reacting at room temperature to obtain a compound 7; dissolving the compound 7 into ethyl acetate, adding a catalyst, and reacting in hydrogen to obtain a compound 8; dissolving the compound 8 into tetrahydrofuran and water, adding alkali for hydrolysis to obtain a final compound 9, and continuously optimizing thestructure of a spiro com