Bromide 11d was synthesized from (−)-nopol via reaction with NBS–PPh3, as described in [32 (link)].
Triphenylphosphine (2.0 equiv., 6.1 g, 23 mmol) was dissolved in dry DCM (23 mL) under argon. N-bromosuccinimide (NBS) (2.0 equiv., 4.2 g, 23 mmol) was added to this solution in small portions over 5 min in an ice-water bath. Subsequently, the resulting deep red mixture was stirred at room temperature for 30 min. Then, pyridine (1 mL) was added, and the color turned reddish-brown. (–)-Nopol (1.0 equiv., 2.0 mL, 12 mmol) was added to the mixture dropwise over 10 min. The reaction mixture was stirred overnight at room temperature. Later, the mixture was diluted with hexane (40 mL) and filtered through a silica gel plug. Then, the reaction flask was stirred with EtOAc–hexane (1:1, 40 mL) and filtered through the silica gel plug. Later, it was concentrated in vacuo and the crude residue was purified by chromatography on SiO2 (hexane) to obtain bromide11d (2.3 g, 70% yield).
Triphenylphosphine (2.0 equiv., 6.1 g, 23 mmol) was dissolved in dry DCM (23 mL) under argon. N-bromosuccinimide (NBS) (2.0 equiv., 4.2 g, 23 mmol) was added to this solution in small portions over 5 min in an ice-water bath. Subsequently, the resulting deep red mixture was stirred at room temperature for 30 min. Then, pyridine (1 mL) was added, and the color turned reddish-brown. (–)-Nopol (1.0 equiv., 2.0 mL, 12 mmol) was added to the mixture dropwise over 10 min. The reaction mixture was stirred overnight at room temperature. Later, the mixture was diluted with hexane (40 mL) and filtered through a silica gel plug. Then, the reaction flask was stirred with EtOAc–hexane (1:1, 40 mL) and filtered through the silica gel plug. Later, it was concentrated in vacuo and the crude residue was purified by chromatography on SiO2 (hexane) to obtain bromide
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