Propionic Acid → Acetate

Participants

Reaction Conditions

Reaction Steps

A solution of 4.4 g (14.53 mmol) of 5(S)-[1(S)-(Boc-amino)-2-phenylethyl]dihydrofuran-2-(3H)-one [preparation, see Example 2b)] in 21.4 ml of abs. THF and 2.4 ml of DMPU is treated, at -75° C. and under an N2 atmosphere, with 28 ml of a 1M solution of lithium bis(trimethylsilyl)amide in THF (Aldrich, Steinheim, FRG), and the mixture is subsequently stirred at this temperature for 15 min. A solution of 6.0 g (approximately 80%, 17.5 mmol) of p-(2-phenylethyl)benzyl bromide in 5.4 ml of abs. THF is then added dropwise, and this mixture is thoroughly stirred at -70° C. for 30 min. 5.4 ml of propionic acid are then added at -75° C., followed by 5.4 ml of water. The mixture is warmed to 0° C. and diluted with 150 ml of ethyl acetate; this mixture is then washed with 80 ml of a 10% solution of citric acid, with sat. sodium bicarbonate solution and with saline. The aqueous phases are reextracted 2× with ethyl acetate, and the organic phases are dried over sodium sulfate and evaporated. Column chromatography (SiO2, hexanelethyl acetate, 3:1) yields the pure title compound: TLC Rf (E)=0.27; tRet (II)=20.8 min; FAB-MS (M-Buten+H)+ =444.

Provenance & Evidence