Sodium Hydroxide → (4AS,5aS)-1-(pyrazin-2-yl)-4,4a,5,5a-tetrahydro-1H-cyclopropa[4,5]cyclopenta[1,2-c]pyrazole-3-carboxylic acid

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To a suspension of (1aS,5aS)-2-(pyrazin-2-yl)-1a,2,5,5a-tetrahydro-1H-2,3-diaza-cyclopropa[a]pentalene-4-carboxylic acid ethyl ester (106 g, 392 mmol) in MeOH (300 mL) and THF (300 mL) was added a 2.0 M aqueous solution of NaOH (235 mL, 471 mmol). The reaction was stirred at 23° C. for 20 h. The organic solvents were removed on rotovap. The remaining aqueous solution was diluted to −1.5 L with H2O then acidified to pH ˜2 with 6 M HCl (ca. 95 mL). The resulting fine precipitate was collected by filtration, rinsed with water, and dried to give the title compound (95 g) as a white solid. LCMS m/z=243.1 [M+H]+; 1H NMR (400 MHz, DMSO-d6) δ 0.43 (td, J=4.6, 3.2 Hz, 1H), 1.26 (td, J=8.0, 4.4 Hz, 1H), 2.27-2.33 (m, 1H), 2.71-2.75 (m, 1H), 2.76 (d, J=16.8 Hz, 1H), 2.89 (dd, J=16.4, 6.4 Hz, 1H), 8.61 (dd, J=2.7, 1.5 Hz, 1H), 8.67 (d, J=2.5 Hz, 1H), 9.17 (d, J=1.5 Hz, 1H), 13.02 (s, 1H).

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