[NH:1]1[C:5]([C:6]([O:8][CH2:9][CH3:10])=[O:7])=[CH:4][C:3]([C:11]([O:13][CH2:14][CH3:15])=[O:12])=[N:2]1.C(=O)([O-])[O-].[Cs+].[Cs+].Br[CH2:23][C:24]([O:26][C:27]([CH3:30])([CH3:29])[CH3:28])=[O:25].C(OCC)(=O)C>CC(C)=O>[CH2:9]([O:8][C:6]([C:5]1[CH:4]=[C:3]([C:11]([O:13][CH2:14][CH3:15])=[O:12])[N:2]([CH2:23][C:24]([O:26][C:27]([CH3:30])([CH3:29])[CH3:28])=[O:25])[N:1]=1)=[O:7])[CH3:10]A solution of 6.25 g (29.5 mmol) of diethyl 3,5-pyrazoledicarboxylate (1) in 225 mL of acetone was added 11.7 g (36 mmol) of cesium carbonate, followed after 10 min by the addition of 5.3 mL (36 mmol) of t-butyl bromoacetate and the mixture was stirred overnight at room temperature. Since TLC analysis confirmed that the reaction was complete (Rf product=0.6 (7:3 hexanes:ethyl acetate)), the mixture was filtered and concentrated to give quantitatively 1-tert-butoxycarbonylmethyl-1H-pyrazole-3,5-dicarboxylic acid diethyl ester (2) as a clear oil as indicated by 1H NMR (containing a trace of t-butyl bromoacetate). (δ(300 MHz, CDCl3) 7.14 (s, 1H), 5.15 (s, 2H), 4.29 (q, J=7.1 Hz, 2H), 4.24 (q, J=7.1 Hz, 2H), 1.30 (s, 9 H), 1.27 (t, J=7.1 Hz, 3H), 1.25 (t, J=7.1 Hz, 3H)). This material was used without further purification in the next reaction.
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