Carbon Dioxide → (R)-3-(N-tert-Butyl-N-n-propylamino)-8-fluoro-5-hydroxy-3,4-dihydro-2H-1-benzopyran

Participants

Reaction Steps

(R)-3-(N-tert-Butyl-N-n-propylamino)-8-fluoro-5-methoxy-3,4-dihydro-2H-1-benzopyran hydrochloride (1.3 g, 3.9 mmol) in dry methylene chloride (40 mL) under nitrogen was cooled on a dry ice-EtOH bath to -50° C. Boron tribromide (0.75 mL, 7.8 mmol) was added dropwise (in 1 min) to the stirred solution above. Five minutes after the addition of boron tribromide was complete, the dry-ice bath was changed to an ice bath (+4° C). After stirring for 4 h at the same temperature the solution was poured on ice (100 g) and solid NaHCO3 was added to adjust pH to 8-9. When the ice had melted the mixture was extracted with ether (4×75 mL). The ether extracts were combined, washed with brine, dried (Na2SO4), filtered and concentrated in vacuo to afford 1.1 g (96% yield) of the title compound as a pale yellow oil. [α]21D =-91.7° (C=10; CHCl3) GC-MS (70 eV) M=281 (6%).

Provenance & Evidence