(Dimethyl sulfide)trihydroboron → (4R,9aR)-6-(1-(S)-Hydroxy-ethyl)-4-methyl-3,4,9,9a-tetrahydro-1H-2,4a,5-triaza-fluorene-2-carboxylic acid tert-butyl ester

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Reaction Steps

To a stirred solution of (R)-Me-CBS-oxazaborolidine (770 μl, 1M in toluene) in THF (3 ml) was added borane-dimethylsulfide (770 μl, 2M in THF) at 0° C. under nitrogen. A solution was stirred for 5 mins, then 6-acetyl-4-methyl-3,4,9,9a-tetrahydro-1H-2,4a,5-triaza-fluorene-2-carboxylic acid tert-butyl ester (Example 34, intermediate b) (255 mg) in THF (2.5 ml) was added dropwise over 45 mins. A solution was stirred at 0° C. for 3 hours, quenched with methanol and partitioned between aqueous ammonium chloride and EtOAc. The phases were separated and the organic layer was washed with brine, dried (MgSO4) and concentrated in vacuo. The residue was purified by column chromatography [SiO2; isohexane-ethyl acetate (1:1)] to afford 6-((1S)-1-hydroxy-ethyl)-(4R,9aR)-4-methyl-3,4,9,9a-tetrahydro-1H-2,4a,5-triaza-fluorene-2-carboxylic acid tert-butyl ester (185 mg) as a colorless oil: 1H NMR (400 MHz, CDCl3): 7.16 (1H, d, J 7 Hz), 6.35 (1H, d, J 7 Hz), 4.37–4.31 (1H, br s), 4.31–4.19 (1H, br s), 4.09–3.95 (1H, m), 3.95–3.85 (1H, m), 3.13–2.94 (2H, m), 2.79–2.55 (1H, br s), 2.54 (1H, dd, J 6 and 16 Hz), 1.48 (9H, s), 1.44 (3H, d, J 6.5 Hz) and 1.24 (3H, d, J 6.5 HZ); MS (ES) 334.3 (MH+).

Provenance & Evidence