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Nonsolvent Application of Ionic Liquids: Organo-Catalysis by 1-alkyl-3-methylimidazolium Cation Based Room-Temperature Ionic Liquids for Chemoselective N-tert-butyloxycarbonylation of Amines and the Influence of the C-2 Hydrogen on Catalytic Efficiency

Nonsolvent Application of Ionic Liquids: Organo-Catalysis by 1-alkyl-3-methylimidazolium Cation Based Room-Temperature Ionic Liquids for Chemoselective N-tert-butyloxycarbonylation of Amines and the Influence of the C-2 Hydrogen on Catalytic Efficiency

Anirban Sarkar, Sudipta Raha Roy, Naisargee Parikh, Asit K Chakraborti

J Org Chem. 2011 Sep 2;76(17):7132-40.

PMID: 21774556

Abstract:

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 "electrophilic activation" of di-tert-butyl dicarbonate (Boc(2)O) 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][NTf(2)]) from δ 8.39 to 8.66 in the presence of Boc(2)O in the (1)H 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][NTf(2)] is superior to the reported Lewis acid catalysts.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP350493082	1-Butyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide		350493-08-2	Price

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