Acetic Anhydride → 4-nitrobenzyl (5R)-6-[(acetyloxy)(6,7-dihydro-4H-pyrazolo[5,1-c][1,4]oxazin-2-yl)methyl]-6-bromo-7-oxo-4-thia-1-azabicyclo[3.2.0]hept-2-ene-2-carboxylate

Participants

Reaction Conditions

Reaction Steps

To a solution of MgBr2 (0.94 g, 5.1 mmol) in acetonitrile (25 ml) under nitrogen was added 6,7-dihydro-4H-pyrazolo[5,1-c][1,4]oxazine-2-carbaldehyde (0.26 g, 1.7 mmol) at room temperature with stirring. A solution of (5R,6S)-6-bromo-7-oxo-4-thia-1-azabicyclo[3.2.0]hept-2-ene-2-carboxylic acid 4-nitrobenzyl ester (0.58 g, 1.5 mmol) in THF (25 ml) was then added, and the mixture was cooled to −20° C. Triethylamine (0.71 ml, 5.1 mmol) was introduced, and the mixture was stirred at −20° C. in the dark for 5 hr. It was then treated with acetic anhydride (0.6 ml, 6.0 mmol), and 4-N,N-dimethylaminopyridine (24 mg, 0.2 mmol), and kept at 0° C. for 18 hr. The mixture was concentrated and the residue was dissolved in ethyl acetate. The ethyl acetate solution was washed with 5% citric acid, saturated sodium bicarbonate solution, and brine, dried over anhydrous sodium sulfate, and evaporated. The crude material was chromatographed with silica gel (EtOAc-CH2Cl2/1:5) to give 0.77 g of a white foam; MS (ESI) m/z 578.9 (M+H).

Provenance & Evidence