A yellow solution of VII (159.9 mg, 0.468 mmol), di-n-butylamine (64 mg, 83 μL, 1.05×0.468 mmol) and triethylamine (47 mg, 65 μL, 0.468 mmol) in 2.5 mL of dry THF was stirred at room temperature overnight. One equivalent of diisopropylethylamine and 0.5 equivalent of dibutylamine were added, and stirring continued for three days. The solution was diluted with dichloromethane and extracted with 1N HCl and then saturated NaCl. The organic layer was dried over MgSO4, filtered and concentrated. The crude material was covered with 5 mL of 7:3 hexanes/ethyl acetate solution and a few drops of ethyl acetate to render a solution. Upon standing overnight, much of the mercaptothiazoline crystallized out. The supernatant was withdrawn, and the crystals were rinsed with a small portion of 7:3 hexanes/ethyl acetate. The combined organic layer was concentrated and redissolved in dichloromethane/diisopropyl ether (86:14, v/v). Column chromatography on silica gel eluting with dichloromethane/diisopropyl ether (86:14, v/v) gave 113.9 mg (69%) of 7 as a clear oil: Rf=0.72 (dichloromethane/diisopropyl ether, 86:14, v/v); 1HNMR (CDCl3) δ 6.98 (d, 3J=8.0 Hz, 1H), 6.95 (d, 4J=1.65 Hz, 1H), 6.90 (dd, 3J=8.0 Hz, 4J=1.75 Hz, 1H), 5.07 (s, 2H), 3.80 (s, 3H), 3.24-3.18 (m, 4H), 2.29 (s, 3H), 1.53-1.43 (m, 4H), 1.32-1.21 (m, 4H) and 0.92-0.85 (m, 6H). Exact mass (FAB+) calculated for C19H30NO5 [M+H] 352.2118. found 352.2115.
