To a solution of Intermediate 8B (717 mg, 2.184 mmol) and (S)-2-methylpropane-2-sulfinamide (529 mg, 4.37 mmol) in THF (10 mL) was added tetraethoxytitanium (1993 mg, 8.74 mmol) in THF (20 mL). The resulting mixture was reflux for 5 h. TLC (20% EtOAc in hexane) indicated the starting ketone was completely consumed. The solvent was evaporated to afford a yellow oil. This yellow oil was dissolved in EtOAc and then washed with saturated NaHCO3 (25 mL) and a large amount of white precipitation formed which was removed by filtering through a bed of Celite®. The white precipitation was rinsed with EtOAc. The combined EtOAc solution was washed again with saturated NaHCO3, dried (MgSO4) and concentrated. The crude product was purified by silica gel chromatography (40 g silica gel, eluted with EtOAc in hexanes) to afford Intermediate 8C (620 mg, 66%).
