Hydrochloric Acid → 2-(2-Oxo-3-benzyl-5-methyl-cyclohept-4-en-1-yl)-1-oxo-ethyl-valinyl valine methyl ester

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Reaction Steps

To the above keto ester (23) (0.51 g) in 4:1 dioxane, water (10 mL) was added LiOH.H2O (82 mg). The reaction was stirred overnight at room temperature, evaporated, taken up in ethyl acetate washed with aqueous 1N HCl, saturated NaCl, dried over MgSO4 and evaporated to give the crude keto acid. The acid was dissolved in DMF (10 mL) to which was added HCl.Val-Val-OMe (0.51 g), triethylamine (1.5 mL), hydroxybenzotriazole (0.48 g) followed by Bop reagent (1.57 g). The reaction was stirred overnight at room temperature and evaporated to dryness. The product (24) was obtained as a mixture of diastereomers by flash chromatography on silica gel eluted with 50% ethyl acetate in n-hexane. (0.44 g, 51%) (24); TLC Rf 0.24 and 0.26 (40% ethyl acetate, n-hexane); 1H NMR (CDCl3) δ0.8-1.0(12H, m) Val γ(CH3)2's, 1.7(3H, s) allylic CH3, 3.7(3H, s) CO2CH3, 3.8 (1H, br s) allylic CH, 4.55 (2H, dd), 5.15 (1H, m) vinylic CH, 7.25 (5H, s) phenyl.

Provenance & Evidence