Triphenylphosphine → tert-Butyl 4-(2-methoxy-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenoxy)piperidine-1-carboxylate

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Reaction Steps

To a solution of 2-methoxy-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenol (0.8 g, 3.2 mmol, 1 eq), 1-boc-4-hydroxypiperidine (0.97 g, 4.8 mmol, 1.5 eq) and triphenylphosphine (1.26 g, 4.8 mmol, 1.5 eq) in anhydrous THF (8 mL) was added DIAD (0.94 mL, 4.8 mmol, 1.5 eq) dropwise at 0° C. The solution was stirred at RT for 45 h. The solvent was removed, and the resulting light orange oily residue was treated with 20% AcOEt/c-hexane to give white crystals (PPh3O) which were filtered off and washed with the same mixture. The filtrate was evaporated to give an oily residue which was treated with c-hexane and a few drops of AcOEt to give a white precipitate that was removed by filtration and an oily residue that solidified upon standing. The crude product (1.93 g containing some c-hexane) was used as it was in the subsequent step. The remainder was purified by column chromatography (Isolute Flash Si II column, 25 g silica gel, 0-8% AcOEt in c-hexane) to give the pure desired product (0.991 g). HPLC-MS (10-95% B in 4 min at 0.5 mL+2 min 100% B, flow 0.8 mL/min, 50° C.): tR=5.10 min, [M+H]+ m/z 334.3.

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