Formaldehyde → Benzyl(2R,5S)-2-[bis(tert-butoxycarbonyl)amino]-5-(2,3-difluorophenyl)-7-hydroxy-6-nitroheptanoate

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Reaction Steps

To a solution of (5S)—N,N-bis(tert-butoxycarbonyl)-5-(2,3-difluorophenyl)-6-nitro-D-norleucinate (2.30 g, 3.975 mmol) and 1,1,3,3-tetramethylguanidine (46 mg, 0.40 mmol) in acetonitrile (20 mL) was added formaldehyde (0.15 mL, 37% aqueous solution). After stirring for 60 min, more formaldehyde (0.050 mL, 37% aqueous solution) was added. After stirring for an additional 60 min the mixture was diluted with saturated aqueous NaHCO3 and extracted with CH2Cl2 (3×). The combined organics were dried over magnesium sulfate, filtered and concentrated to give a residue that was purified by silica gel chromatography (25%→75% ethyl acetate/hexanes) to give the title compound (1.44 g,). MS 409.1 (M+1-2Boc).

Provenance & Evidence