Trifluoroacetic acid → trans-Methyl 2-(1-benzyl-4-cyanopyrrolidin-3-yl)benzoate

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In a 50 mL round bottom flask were combined methyl 2-(2-cyanovinyl)benzoate (Example 1A, 11.03 g, 58.9 mmol) trifluoroacetic acid (0.045 mL, 0.589 mmol) and dichloromethane (100 mL). N-Benzyl-1-methoxy-N-((trimethylsilyl)methyl)methanamine (64.8 mmol) was added as a solution in dichloromethane (100 mL) dropwise over 15 minutes while stirring under argon. The reaction was stirred at room temperature for 20 hours, then quenched with aqueous sodium bicarbonate and extracted with dichloromethane. The organic washes were combined and washed with brine, dried over Na2SO4, filtered, and the solvent was removed in vacuo to provide the crude product. The mixture of isomers was added to a silica gel column and was eluted with ethyl acetate/hexanes (gradient 0-20%, 40 minutes) to provide the title compound as the faster eluting (less polar) isomer. 1H NMR (500 MHz, CDCl3) δ ppm 2.82 (dd, 1H, J=9.09 Hz, J=7.81 Hz), 2.88 (dd, 1H, J=9.74 Hz, J=4.27 Hz), 2.99-3.03 (m, 1H), 3.05-3.09 (m, 1H), 3.29 (t, 1H, J=8.37 Hz), 3.71 (m, 2H), 3.94 (s, 3H), 4.51 (ddd, 1H, J=8.29 Hz, J=6.36 Hz, J=4.35 Hz), 7.25-7.40 (m, 6H), 7.50 (dt, 1H, J=7.65 Hz, J=1.45 Hz), 7.62 (d, 1H, J=7.24 Hz), 7.81 (dd, 1H, J=7.89 Hz, J=1.29 Hz); MS (DCI+) m/z 321.2 [M+H]+.

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