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KHMDS (4.40 mL, 0.5 M in toluene, 2.18 mmol) and CS2 (164 mg, 130 L, 2.15 mmol)  were added to solution of secondary alcohol 11 (240 mg, 0.436 mmol) in THF (15 mL) at -78 °C. After stirring for one hour at -78 °C, MeI (319 mg, 140 L, 2.25 mmol) was added. The reaction mixture was allowed to warm to 22 °C. The mixture was then quenched with saturated aq. NaHCO3 solution (20 mL). The resulting mixture was extracted with EtOAc (3 x 20 mL), and the combined organic phase was washed with brine (10 mL) and dried over anhydrous Na2SO4. The solvent was filtered and allowed to evaporate, and the residue was purified by flash column chromatography with EtOAc/petroleum ether (1:10). This gave the corresponding xanthate as a yellow foam.

 

The xanthate was dissolved in degassed toluene (20 mL). AIBN (36.0 mg, 0.219 mmol) and n-Bu3SnH (260 mg, 240 L, 0.892 mmol) were sequentially added to this solution. The resulting mixture was heated at 110 °C for 2 h and then allowed to cool to 22 °C. The solvent was removed, and the residue was purified by flash column chromatography with EtOAc/petroleum ether (1:20 → 1:5). This gave the desired N-benzenesulfonyl anominine core as a pale yellow foam (168 mg, 72% over 2 steps).

The N-benzenesulfonyl anominine core (168 mg, 0.315 mmol) was then dissolved in toluene (5 mL). TBAF (0.96 mL, 1.0 M in THF, 0.96 mmol) was added to the solution at 22 °C. The resulting mixture was heated for 2 hours at 110 °C, then cooled to 22 °C and quenched with saturated aq. NaHCO3 solution (10 mL). After extraction with EtOAc (3 x 20 mL), the combined organic phase was dried over anhydrous Na2SO4, filtered, and concentrated under vacuum. The resulting residue was subjected to flash column chromatography using EtOAc/petroleum ether (1:5) as eluent to give anominine core 22 (107 mg, 86%) as a pale yellow oil.