Issue in Honor of Prof. James Bull ARKIVOC 2002 (ix) 28-36
Ceric ammonium nitrate impregnated on silica gel in the removal of the tert-butoxycarbonyl group
Jih Ru Hwu,*a, b Moti L. Jain,a, b Fu-Yuan Tsai,a, b A. Balakumar,b
G. H. Hakimelahi,b and Shwu-Chen Tsay c a Organosilicon and Synthesis Laboratory, Department of Chemistry, National Tsing Hua University, Hsinchu, Taiwan 300, b Institute of Chemistry, Academia Sinica, Nankang, Taipei, Taiwan 115, and c Well-being Biochemical Corporation, Neihu Chiu, Taipei, Taiwan 114, Republic of China
E-mail: jrhwu@mx.nthu.edu.tw
Dedicated to Professor James R. Bull for his contributions to Chemistry and on his retirement from the University of Cape Town
Abstract
The tert-butoxycarbonyl group was efficiently (80–99% yields) removed from an amino, hydroxy, or mercapto functionality in organic compounds by use of 0.20 equiv of Ce(NH4)2(NO3)6 in acetonitrile at reflux. Application of the solid-supported reagent involving the use of 0.20 equiv of Ce(NH4)2(NO3)6 impregnated on silica gel in toluene at reflux gave the deprotected products in 90–99% yields. These reactions likely proceed through an electron transfer process.
Keywords: Ceric ammonium nitrate, silica gel, tert-butoxycarbonyl, deprotection, amino ester
Introduction
The tert-butoxycabonyl (t-BOC) group is often used for the protection of amino acids in peptide synthesis.1 Reagents used to cleave the t-BOC group include boron trifluoride,2 hydrogen chloride,3 hydrogen fluoride,4 sulfuric acid,5 trifluoroacetic acid,6 trimethylsilyl triflate,7–9 trimethylsilyl perchlorate,8 etc. Each of these methods, however, has its own limitations.1–9 Therefore it is desirable to develop a new and efficient method for deprotection of the t-BOC group.
Ceric ammonium nitrate (Ce(NH4)2(NO3)6, CAN) can function as a one-electron transfer catalyst in various organic reactions.10–12 Recently we have reported the use of a catalytic
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