(R)-3-(N-Cyclobutyl-N-isopropylamino)-8-fluoro-5-trifluoromethylsulfonyloxy-3,4-dihydro-2H-1-benzopyran (1.65 g, 4.01 mmol) was dissolved in a solution of DMF/methanol (6:2, 30 mL) and then degassed followed by the inlet of carbon monoxide (×3). With a slight positive pressure of carbon monoxide, palladium(II)-acetate (30 mg), 1,3-bis(diphenylphosphino)propane (55 mg) and triethylamine (1.25 mL, 8.8 mmol) were added and the reaction mixture was degassed and subjected to carbon monoxide once again. The reaction was heated to 70° C. under carbon monoxide atmosphere with vigorous stirring for 6 h. The reaction was allowed to cool and the solvent was removed in vacuo. The remains were taken into a 2M solution of NH3 and then extracted, twice, with diethyl ether. The combined ether portions were dried (MgSO4), filtered, and the solvent removed in vacuo to give the crude residue. Chromatography on silica (eluent: 8% ethyl acetate/hexane) gave 1.18 mg (92% yield) of the title compound as a clear oil. [α]21D =-139.1° (C=0.1; CHCl3). GC-MS (70 eV) M=321 (3%).
