胺基N-O化合物引發(fā)
由于氟離子和金屬烷氧化合物的強(qiáng)堿性，這些引發(fā)劑不適用于對(duì)堿敏感的底物，并且它們對(duì)濕氣非常敏感。而三乙基胺N-O化合物可作為活化TMSCF3的親核性的催化劑，該引發(fā)劑適用于對(duì)堿敏感的底物。多種芳香族，脂肪族以及α,β-不飽和醛在三乙基胺N-O化合物引發(fā)下都能以中等到良好的收率生成相應(yīng)的三氟甲基化產(chǎn)物1。
示例：
General Procedure for the Addition of TMSCF3 to Aldehyde/Ketone under Me3N+-O-in DMF.
Aldehyde/ketone(1 mmol) and TMSCF3 (neat) in dry DMF (3 mL) were placed in a 25 mL round-bottom flask (or a 30 mL vial). To this solution was added Me3N+-O-(0.05 eq.), and the mixture was stirred vigorously at room temperature. Completion of the reaction was monitored by TLC and GCMS. The reaction mixture was then poured in brine solution (15 mL) and extracted with diethyl ether (3×30 mL). Combined organic layers were finally washed with brine solution, dried over anhydrous Na2SO4, and then solvent was removed under reduced pressure. The crude product was further purified by chromatography to afford pure TMS-protected alcohols.
醋酸鹽引發(fā)
醋酸鋰通過活化Me3SiCF3的C-Si鍵催化三氟甲基化反應(yīng)。多種醛，酮以及酰亞胺化合物在催化量醋酸鋰的存在下與Ruppert-Prakash試劑作用以高收率生成相應(yīng)的三氟甲基化的產(chǎn)物。另外，使用苯甲酸鋰，三甲基乙酸鋰以及醋酸鈉，醋酸鉀，醋酸銨都能有效的高產(chǎn)率的得到三氟甲基化產(chǎn)物。該方法非常實(shí)用，因?yàn)樗鼉H需要溫和并且價(jià)廉易得的路易斯堿催化劑2。
示例：
Typical Experimental Procedure for Tri?uoromethylation of Carbonyl Compounds.
To a stirred solution of AcOLi(1.3mg, 0.02mmol) in DMF(0.6mL) were added successively a solution of aldehyde (0.4 mmol) in DMF(0.6 mL) and TMSCF3 (74.8μL, 0.48mmol, 95% content) at 0 oC. The mixture was stirred for 10min at the same temperature, and then quenched with saturated aqueous NH4Cl. The mixture was extracted with Et2O and the organic layer was washed with brine and dried over anhydrous Na2SO4. After ?ltration and evaporation of the solvent, the crude product was puri?ed by preparative TLC to a?ord the corresponding adduct(80%).
【參考文獻(xiàn)】
1.Surya Prakash, G. K.; Mandal, M.; Panja, C.; Mathew, T.; Olah, G. A. J.Fluo. Chem. 2003, 123, 61-63.
2.Kawano, Y.; Kaneko, N.; Mukaiyama, T. Bull. Chem. Soc. Jpn. 2006,79, 1133-1145.
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