p-Toluenesulfonic acid → 4-methoxybenzyl (2RS)-2-hydroxy-2-[(3R,4R)-4-mercapto-3-phenylacetamidoazetidin-2-on-1-yl]acetate

Participants

Reaction Steps

Toluene-4-sulphonic acid (3.42g, 17.98mmol) in water (8ml) was added to a solution of 4-methoxybenzyl (2RS)-2-hydroxy-2-[(1R,5R)-3-benzyl-4-thia-2,6-diazabicyclo[3.2.0]hept-2-en-7-on-6-yl]acetate (4.12g, 10.0mmol) in dichloromethane (20ml) and acetone (20ml). After stirring for 2.5h at room temperature, the reaction mixture was diluted with dichloromethane, washed with water (x2), dried and concentrated in vacuo to yield crude 4-methoxybenzyl (2RS)-2-hydroxy-2-[(3R,4R)-4-mercapto-3-phenylacetamidoazetidin-2-on-1-yl]acetate as a colourless foam. The crude thiol was dissolved in acetone (50ml) and treated with a solution of 2-bromoacetyl-5-methyltetrahydrofuran (1.67g, 8.1mmol) in acetone (5ml). After 10 min., potassium carbonate (687mg, 5.0mmol) was added, and the mixture stirred for a further 30 min. The reaction mixture was diluted with ethyl acetate, washed successively with water (x2) and brine, dried and concentrated. The residue was purified by chromatography on silica gel eluting with 50, 70 and 80% ethyl acetate in hexane to yield the title compound as a colourless foam (2.68g, 60%); vmax (CH2Cl2) 3412, 1781, 1744, 1685 and 1515cm-1. (Mass spectrum: +ve ion (3-nitrobenzyl alcohol, sodium acetate) MNa+ (579)].

Provenance & Evidence