[C:1]([O:5][C:6]([CH3:9])([CH3:8])[CH3:7])(=[O:4])[CH:2]=[CH2:3].[Si]([CH:14]=[N+:15]=[N-:16])(C)(C)C.C(O)(C(F)(F)F)=O>C1(C)C=CC=CC=1.C(Cl)Cl>[NH:16]1[CH:2]([C:1]([O:5][C:6]([CH3:9])([CH3:8])[CH3:7])=[O:4])[CH2:3][CH:14]=[N:15]1To a solution of t-butyl acrylate (17 g, 133 mmol) dissolved in toluene (200 mL) and n-hexanes (200 mL) was added TMS-diazomethane (99 mL, 199 mmol) over 10 minutes. After 1 h the reaction mixture was concentrated and the residue diluted with DCM (300 mL) and TFA (20.44 mL, 265 mmol) was added slowly over 15 minutes. After 30 minutes the reaction mixture was concentrated, basified with 1N NaOH and extracted into DCM (400 mL). The organic layer was dried over anhydrous sodium sulfate, filtered, concentrated, and purified by filtration through a pad of silica gel eluting the product with 50% ethyl acetate/hexanes to afford 10 g (54.6 mmol) of 1,1-dimethylethyl 4,5-dihydro-1H-pyrazole-5-carboxylate as a yellow oil. LC-MS (ES) m/e 170.91 (M+H)+.
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