The tert-butyl 2- (4-(2,6-dioxopiperidin-3-yl)phenoxy)acetate (compound 13, 2.00 g) was synthesized following a previously reported method . To a solution of compound 13 (0.490 g, 1.53 mmol, 1 eq.) in DCM (15 mL) TFA (3 mL) was added, the mixture was stirred at room temperature for 2 h. The complete removal of tert-butyl group was monitored by TLC. Afterwards, the mixture was dried in vacuo to provide the crude product for the next step. To a solution of the resulting crude in anhydrous DMF (15 mL) HATU (1.17 g, 3.07 mmol, 2 eq.) and DIPEA (0.595 g, 4.60 mmol, 3 eq.) were added. The mixture was stirred for 30 min at room temperature. Next, hex-5-yn-1-ol (0.301 g, 3.07 mmol, 2 eq.) was added to the reaction mixture and stirred for 15 h. The completion of the reaction was monitored by HPLC. The mixture was poured into water (100 mL) and extracted with ethyl acetate (3 x 30 mL). The combined organic layer was then washed with water (3 x 50 mL) and followed by brine (50 mL), dried over anhydrous Na2SO4, filtered, and concentrated in vacuo to offer the crude product, which was then