To 5-(2,6-dimethyl-4-triisopropylsilanyloxybenzyl)-2-methoxymethoxy-benzaldehyde (compound 15, step e; 0.460 g, 1.01 mmol) in dichloromethane 30 mL was add mCPBA (0.870 g, 2.52 mmol) and saturated sodium bicarbonate solution (2 mL). After stirring at rt overnight, the reaction mixture was poured into dichloromethane 50 mL and washed 3× with 10 mL of saturated aqueous sodium bicarbonate. The dichloromethane was dried over sodium sulfate, filtered and concentrated under reduced pressure. The resulting residue was combined with methanol (10 mL) and 2 mL of 1 N NaOH and stirred for 1.5 hours at room temperature. The reaction was acidified with 12 N HCl (pH<3) and poured into 50 mL ethyl acetate. The layers were separated and the organics were dried over sodium sulfate, filtered and concentrated. Flash column chromatography using silica and a step gradient of hexane/ethyl acetate [20:1], hexane/ethyl acetate [9:1] provided 5-(2,6-dimethyl-4-triisopropylsilanyloxybenzyl)-2-methoxymethoxy-phenol (0.189 g, 42%): 1H NMR (300 MHz, DMSO-d6): δ 8.95 (s, 1H), 6.86 (d, 1H, J=8.1 Hz), 6.56 (s, 2H), 6.41 (d, 1H, J=2.1 Hz), 6.34 (dd, 1H, J=2.1 Hz and J=8.7 Hz), 5.05 (s, 2H), 3.78 (s, 2H), 3.38 (s, 3H), 2.13 (s, 6H), 1.11 (m, 3H), 1.00 (m, 18H); Uniplate silica gel, 250 microns; Mobile phase=10% ethyl acetate in hexane: Rf=0.15
