To a solution of LDA (2M, 9.1 mL, 18.17 mmol) at −70° C. was added HMPA (10 mL) followed by the drop wise addition of a solution of the compound of example 27 (6.12 g, 15.14 mmol) in anhydrous THF (10 mL). The reaction mixture was allowed to warm up to −40° C. and was stirred for another 30 minutes, after which, a solution of tert-butyl bromoacetate (2.5 mL, 16.65 mmol) in anhydrous THF (10 mL) was added. The reaction mixture was stirred for 1 h at the same temperature and then allowed to warm up to room temperature followed by stirring for 24 h. The reaction mixture was portioned between ether and saturated ammonium chloride. The water phase was extracted several times with ether. The recombined organic layer was washed with brine, dried, filtered and evaporated. Silica gel chromatography using 5% ethyl acetate in hexanes provided the product as a light yellow oil. 1H-NMR(CDCl3, 400 MHz: 1.24(t, J=7.1 Hz, 3H); 1.43(s, 9H); 1.40-1.57(m, 4H); 2.15(m, 2H); 2.24(m, 1H); 2.58(m, 2H); 4.12(q, J=7.1 Hz, 2H), 7.19-7.23, 7.26-7.30, 7.41(m, 15H).
