卡賓引發(fā)劑
氮雜環(huán)卡賓(NHC)在過(guò)去的幾十年里得到了相當(dāng)?shù)闹匾?。它作為配體和催化劑廣泛的應(yīng)用在有機(jī)轉(zhuǎn)換中。在市售催化量的NHC存在的溫和條件下，烯醇化以及非烯醇化的醛，羰基酯與Ruppert-Prakash試劑作用生成三氟甲基化產(chǎn)物。但是低活性的酮并不發(fā)生反應(yīng)，所以該方法可用于醛和酮的選擇性三氟甲基化1。
示例：
To 2,2-dimethyl-4-pentenal(1.36 mL, 10.0 mmol) in a dry flask under N2 were added DMF(anhydrous, 10 mL), TMSCF3 (4.2 g, 30 mmol), and carbine 9 (34 mg, 0.10 mmol).The mixture was stirred at room temperature for 4 h. HCl solution (2 N, 12 mL) was added and the solution was stirred at room temperature until all TMS protected intermediate converted to product. Water (60 mL) was added and the aqueous layer was extracted with ether (3×40 mL). Organic layers were combined and washed with saturated NaHCO3 aqueous solution (30 mL), brine (30mL), dried over MgSO4. Solvents were removed under vacuum to give the crude residue, which was purified by silica flash chromatography (10% Et2O/pentane) to give 1.29 g product (71% yield).
三苯基膦引發(fā)
三苯基膦是一種廣泛與Me3SiCF3使用的三氟甲基化反應(yīng)的催化劑。但是一般產(chǎn)率偏低并且反應(yīng)時(shí)間較長(zhǎng)，這可能歸因于三苯基膦較弱的親核性2。最近，Shibata研究出在DMF中使用催化量的三叔丁基膦可以適用于高效的路易斯堿催化的多種醛和酮的親核三氟甲基化3。
反應(yīng)實(shí)例：
Typical Experimental Procedure.
Tri-tert-butylphosphine [P(t-Bu)3,3.9 mg, 0.019 mmol]) was placed in a round-bottomed flask under N2. Dry DMF (0.25 mL) and aldehyde (0.19 mmol) were added. To the stirred solution, Me3SiCF3 (57 μL, 0.38 mmol) was added at r.t. The mixture was stirred at r.t. for 0.5 h; the reaction was concentrated under reduced pressure. The residue was chromatographed on silica gel using hexane to afford product.
【參考文獻(xiàn)】
1.Song, J. J.; Tan, Z.; Reeves, J. T.; Gallou, F.; Yee, N. K.; Senanayake, C.H. Org. Lett. 2005, 7, 2193-2196.
2.(a) Kim, J.; Shreeve, J. M. Org. Biomol. Chem. 2004, 2,2728-2734.
(b) Hagiwara, T.; Kobayashi, T.; Fuchikami,T. Main Group Chem. 1997, 2, 13-15.
3. Mizuta, S.; Shibata, N.; Sato, T.; Fujimoto, H.; Nakamura, S.; Toru, T. Synlett 2006, 2, 267-270.
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