A mixture of (+)-camphoric acid (Aldrich, 2.00 g, 10.0 mmol) and phosphorus pentachloride (Aldrich, 4.16 g, 20.0 mmol) in hexane (75 mL) was heated to reflux and stirred for 24 hours. After cooling to ambient temperature, the reaction mixture was concentrated by rotary evaporator to give a pale yellow oil. The crude bis acid chloride (474 mg, 2.00 mmol) was added to a mixture of the product from Example 92B (425 mg, 2.00 mmol) and triethylamine (1.01 g, 10.0 mmol) in anhydrous tetrahydrofuran (12 mL). The mixture was stirred for 2 hours Anhydrous methanol (10 mL) was added and the resulting mixture was stirred overnight. The mixture was concentrated by rotary evaporator to give a brown oil. Flash chromatography (silica gel, 5-25% ethylacetate in hexanes) afforded 343 mg (42%) of the title compound. 1H NMR (DMSO-d6) δ 0.53 (s, 3H), 0.90 (t, J=7.3 Hz, 3H), 1.20 (s, 3H), 1.23 (s, 3H), 1.23-1.40 (m, 2H), 1.41-1.50 (m, 1H), 1.57 (s, 9H), 1.57-1.67 (m, 2H), 1.71-1.84 (m, 1H), 2.24-2.36 (m, 1H), 2.41-2.48 (m, 1H), 2.61-2.67 (m, 2H), 3.00-3.06 (m, 1H), 3.59 (s, 3H), 8.52 (s, 1H). MS (ESI+) m/z 409 (M+H)+. Anal. calcd. for C22H36N2O3S: C, 64.67; H, 8.88; N, 6.86. Found: C, 64.52; H, 8.76; N, 6.84.
