The product from Example 26D (87.5 mg, 0.155 mmol) in 1,2-dichloroethane (3.0 mL) was treated with trimethylacetaldehyde (21 μL, 0.186 mmol) at ambient temperature. After stirring for 15 minutes, the mixture was treated with acetic acid (11 μL, 0.181 mmol) followed by sodium triacetoxyborohydride (53 mg, 0.248 mmol). After stirring at ambient temperature for 24 hours, the mixture was treated with aqueous 10% NaHCO3 (5.0 mL) and extract with ethyl acetate (3×10 mL). The ethyl acetate extracts were combined, wash with brine (20 mL), dried over sodium sulfate, filtered, and the filtrate was concentrated. The residue was purified on a silica gel cartridge eluting with chloroform to provide the title compound (12.5 mg, 13%). 1H NMR (CDCl3) δ 8.73 (s, 2H), 7.79 (s, 2H), 7.28-7.05 (m, 10H), 5.20 (s, 4H), 4.88-4.76 (br s, 2H), 3.90-3.66 (m, 2H), 2.87 (dd, 2H), 2.75-2.60 (m, 2H), 2.47 (d, 4H), 2.17 (s, 2H), 0.78 (s, 9H); MS (ESI+) m/z 636 (M+H)+.
