Triphenylphosphine → bis[(4-nitrophenyl)methyl] (2S,4S)-4-[(Z)-[1-[(2-methylpropan-2-yl)oxy]-1,3-dioxobutan-2-ylidene]amino]oxypyrrolidine-1,2-dicarboxylate

Participants

Reaction Steps

4-Nitrobenzyl (2S,4R)-4-hydroxy-1-(4-nitrobenzyloxycarbonyl)pyrrolidine-2-carboxylate (3.24 g, 7.28 mmol) and triphenylphosphine (2.29 g, 8.7 mmol) in dry tetrahydrofuran (60 ml) under argon were treated with dimethyl azodicarboxylate (1.28 g, 8.7 mmol) in dry tetrahydrofuran (5 ml). After 5 min tert-butyl (Z)-2-hydroxyimino-3-oxobutyrate (2.59 g, 8.7 mmol) in dry tetrahydrofuran (10 ml) was added and the mixture was stirred under an argon atmosphere for 18 h. The tetrahydrofuran was removed and the residue taken up in ethyl acetate (150 ml) and washed with water containing a trace of acetone (100 ml,×6). The ethyl acetate layer was dried (MgSO4) and evaporated under reduced pressure. The residue was chromatographed on silica gel, eluting with ethyl acetate/hexane mixture to give the title compound (2.49 g, 55%) as a mixture of two conformers/rotamers; νmax (CH2Cl2) 1735, 1710, 1605, 1525, and 1350 cm-1 ; δH (250 MHz, CDCl3) 1.52 (9H, s), 2.31 (3H, s), 2.40-2.80 (2H, m), 3.75-4.0 (2H, m), 4.66 (1H, approx dt, J ca 9.3, 1.5 Hz), 4.94-5.05 (1H, m), 5.1-5.4 (4H, m), 7.35-7.55 (4H, m), and 8.05-8.25 (4H, m).

Provenance & Evidence