1,1'-Carbonyldiimidazole → cis-Methyl 2-(3,3-dimethylbutyl)-4-(3-ethoxy-3-oxopropanoyl)piperidine-1-carboxylate

Participants

Reaction Conditions

Reaction Steps

A suspension of magnesium chloride (0.852 g, 8.94 mmol) and ethyl potassium malonate (2.283 g, 13.42 mmol) in dry THF (40 mL) was stirred under nitrogen atmosphere at 50° C. for 3.5 h (flask 1). In another flask was added carbonyldiimidazole (1.740 g, 10.73 mmol) portionwise to a solution of 2-(3,3-dimethylbutyl)-1-(methoxycarbonyl)piperidine-4-carboxylic acid (2.427 g, 8.94 mmol) (reference compound 42) in dry THF (40 mL) at 0° C. under nitrogen atmosphere. This solution was stirred for 1.5 h (flask 2). The contents of flask 1 was added over 10 min to flask 2 and the resulting mixture was stirred at room temperature for 20 h. The reaction mixture was concentrated and the residue was taken up in EtOAc and H2O. The aqueous phase was extracted once with EtOAc and the combined organic phase was washed with H2O, satd NaHCO3 and then dried over Na2SO4, filtered and evaporated to give a black oil. Separation using Biotage (340 g column, grad 20-30% EtOAc in heptane 7 CV) yielded trans-methyl 2-(3,3-dimethylbutyl)-4-(3-ethoxy-3-oxopropanoyl)piperidine-1-carboxylate (574 mg, 24%) and cis-methyl 2-(3,3-dimethylbutyl)-4-(3-ethoxy-3-oxopropanoyl)piperidine-1-carboxylate (1.74 g, 72%) as yellow oils. Cis-isomer: 1H NMR (400 MHz, cdcl3) δ 0.85 (s, 9H), 1.03-1.95 (m, 10H), 2.01-2.10 (m, 1H), 2.65-2.75 (m, 1H), 2.98-3.08 (m, 1H), 3.51 (s, 2H), 3.69 (s, 3H), 3.83-4.02 (m, 2H), 4.19 (q, 2H). MS m/z 342 (M+H)+. Trans-isomer: MS m/z 342 (M+H)+

Provenance & Evidence