The solution of d (1 eq) in THF was added TBAF•3H2O (2 eq) at 0 °C and stirred overnight at r. t. At the conclusion of the reaction, the reaction was dried over anhydrous Na2SO4. After removal of the solvent, the crude residue was purified by flash column chromatography on silica gel with hexanes/EtOAc (5: 1) as the eluent to afford e as colorless oil (82% yield).