Nonsolvent Application of Ionic Liquids: Organo-Catalysis by 1-Alkyl-3-methylimidazolium Cation Based Room-Temperature Ionic Liquids for Chemoselective N-tert-Butyloxycarbonylation of Am

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• 作者：Anirban Sarkar ; Sudipta Raha Roy ; Naisargee Parikh ; Asit K. Chakraborti
• 刊名：Journal of Organic Chemistry
• 出版年：2011
• 出版时间：September 2, 2011
• 年：2011
• 卷：76
• 期：17
• 页码：7132-7140
• 全文大小：961K
• 年卷期：v.76,no.17(September 2, 2011)
• ISSN：1520-6904

文摘

1-Alkyl-3-methylimidazolium cation based ionic liquids efficiently catalyze N-tert-butyloxycarbonylation of amines with excellent chemoselectivity. The catalytic role of the ionic liquid is envisaged as 鈥渆lectrophilic activation鈥?of di-tert-butyl dicarbonate (Boc₂O) through bifurcated hydrogen bond formation with the C-2 hydrogen of the 1-alkyl-3-methylimidazolium cation and has been supported by a downfield shift of the imidazolium C-2 hydrogen of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][NTf₂]) from 未 8.39 to 8.66 in the presence of Boc₂O in the ¹H NMR and a drastic reduction of the catalytic efficiency with 1-butyl-2,3-dimethylimidazolium ionic liquids that are devoid of the C-2 hydrogen. The differential time required for reaction with aromatic and aliphatic amines has offered means for selective N-t-Boc formation during inter and intramolecular competitions. Preferential N-t-Boc formation with secondary aliphatic amine has been achieved in the presence of primary aliphatic amine. Comparison of the catalytic efficiency for N-t-Boc formation with a common substrate revealed that [bmim][NTf₂] is superior to the reported Lewis acid catalysts.