[I:1][C:2]1[C:3]([C:7]2[S:8][CH:9]=[C:10]([Cl:12])[CH:11]=2)=[N:4][NH:5][CH:6]=1.[H-].[Na+].I[CH:16]([CH2:18][CH3:19])[CH3:17].C(N1C=C(I)C(C2SC=C(Cl)C=2)=N1)(CC)C>CN(C)C=O.CC(OC)(C)C.O>[CH:16]([N:4]1[C:3]([C:7]2[S:8][CH:9]=[C:10]([Cl:12])[CH:11]=2)=[C:2]([I:1])[CH:6]=[N:5]1)([CH2:18][CH3:19])[CH3:17]
To a solution of 4-iodo-3-(4-chloro-2-thienyl)-1H-pyrazole (3.3 mmol) in 10 mL dry N,N-dimethylformamide under argon atmosphere was added sodium hydride (3.9 mmol, 60% dispersion in mineral oil) in portions. The reaction mixture was stirred at room temperature for 15 min, then 2-iodobutane (4.9 mmol) was added dropwise. After 2 days at room temperature, water and MTBE were added to the reaction mixture. The phases were separated and the aqueous phase was extracted with MTBE. The combined organic extracts were successively washed with water and brine, dried over MgSO4, filtered and concentrated to afford 1.2 g of a mixture of 1-sec-butyl-3-(4-chloro-2-thienyl)-4-iodo-1H-pyrazole and 1-sec-butyl-5-(4-chloro-2-thienyl)-4-iodo-1H-pyrazole (88:12; 100% yield). The mixture was purified by chromatography on silica gel (toluene:ethyl acetate 100:0 to 0:100) to afford 923 mg 1-sec-butyl-3-(4-chloro-2-thienyl)-4-iodo-1H-pyrazole (74% yield) and 150 mg of 1-sec-butyl-5-(4-chloro-2-thienyl)-4-iodo-1H-pyrazole (11% yield).
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