TEMPO氧化醇到醛酮

  • 1533
  • A+


Anelli在1987年报道了在二氯甲烷-水两相溶剂中使用TEMPO( ca. 1% mol), NaOCl,KBr 和NaHCO3将醇氧化为醛酮的反响。

TEMPO = 四甲基哌啶氧化物。2,2,6,6-四甲基哌啶氧自在基是一种市售的很波动的氮氧自在基化合物,在此反响中充任催化剂。

反响中参加碳酸氢钠的作用是坚持系统中的pH 在 8.6–9.5 ,由于市售的次氯酸钠的pH=12.7,碱性太强影响反响举行,当反响底物对碱敏感时可以用0.1 M HCl调治pH到6.5-7.5。

反响中参加KBr的作用大概是会发生一些HOBr,减速反响。反响一样平常在0℃到室温反响,反响速率很快(氧化到醛一样平常3min,氧化为酮7-10min)。

仲醇氧化到酮就会中止,但醛大概会持续氧化天生羧酸,但反响速率很慢,别的必需参加过量的次氯酸钠才可以持续氧化。详细内容参考往期公布的:TEMPO氧化。



关于一些位阻较大的醇,反响中参加季铵盐作为相转移催化剂,可以减速反响。但也会加速过氧化历程天生羧酸。

次氯酸钠会发生HOCl,可以和烯烃等一些富电子的底物反响。此历程可以经过TEMPO-PhI(OAc)2 (Protocol of Piancatelli and Margarita)法办理。


 【Jauch, J. Angew. Chem., Int. Ed. 200039, 2764.】


操纵步调

General Procedure for Oxidation of Alcohols with TEMPO-NaOCl (Anelli’s Protocol)


A two phase system consisting of a ca. 0.2–2.9 M solution of 1 equiv. of the alcohol in DCM, containing ca. 0.2–5% mol, typically 1–2% mol—of TEMPO and a ca. 0.02–2.6 M solution of ca. 0.02–0.5 equiv., typically 0.1 equiv. of KBr or NaBr in water, is vigorously stirred over a water ice bath (0C) or an ice-salt bath (-10C).

Over this two phase system, ca. 1.09–1.4 equiv. of NaOCl in a fresh solution, prepared by adjusting a ca. 5–13% aqueous solution of NaOCl to a pH of 8.6–9.5 by addition of an aqueous solution of NaHCO3, are slowly added. When starting compound is consumed, the organic phase is separated and the aqueous phase is washed with DCM. The collected organic phases are washed with a Na2S2O3 aqueous solution and water or brine.



后处置

Optionally, the collected organic phases may be washed with a solution of ca. 0.2–2.5 equivalents of KI in 10–20% hydrochloric acid, before washing with the sodium thiosulfate solution. Finally, the organic solution is dried (Na2SO4 or MgSO4) and concentrated, giving a residue that may need further purification.


ØGeneral Procedure for Oxidation of Alcohols TEMPO-PhI(OAc)2 (Protocol of Piancatelli and Margarita)


A ca. 0.04–1 M solution of the alcohol in DCM, containing 0.09–0.2 equiv., typically 0.1 equiv. of TEMPO and 1.1–5 equiv., typically 1.1 equiv. of PhI(OAc) 2 (BAIB), is stirred at room temperature till most of the starting alcohol is consumed. Then, some DCM may be optionally added in order to facilitate subsequent washings. The reaction mixture is washed with an aqueous Na2S2O3 solution. Optionally, the organic phase can be washed with aqueous NaHCO3 and brine. Finally, the organic solution is dried (Na2SO4) and concentrated, giving a residue that may need further purification.

此条件下反响不要求无水,反响工夫2-12h。



反响机理



反响实例





J. Org. Chem. 199661, 7452】



Org. Synth. 200683, 18】





weinxin
我的微信
存眷我理解更多内容

宣布批评

现在批评: