Vinyl chloroformate → 4-(4-Nitro-phenyl)-pyrrolidine-1,3-dicarboxylic acid 3-ethyl ester 1-vinyl ester

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Reaction Steps

A stirred solution of 1-benzyl-4-(4-nitro-phenyl)-pyrrolidine-3-carboxylic acid ethyl ester (9.56 g, Reference Example 6) in 1,2-dichloroethane (25 ml), at 25° C. and under an atmosphere of argon, was treated dropwise with vinyl chloroformate (2.5 ml). The resulting mixture was heated at reflux for 20 hours then evaporated (40° C. and 2.7 kPa). The residue was subjected to flash chromatography on silica (0.045-0.020 mm particle size) eluting with a mixture of cyclohexane and ethyl acetate (50:50, v/v) affording the title compound (8.38 g) as a white solid. 1H-NMR [500 MHz, (CD3)2SO]: δ 1.07 (m, 3H); 3.35 to 3.70 and 3.70 to 4.00 (2 m, 6H); 4.03 (m, 2H); 4.54 and 4.56 (2 d, J=6 Hz, 1H); 4.79 and 4.85 (2 d, J=14 Hz, 1H); 7.16 (dd, J=14 and 6 Hz, 1H); 7.69 (d, J=8 Hz, 2H); 8.23 (d, J=8 Hz, 2H). MS (EI): 334 [M]+.

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