Influence of hydrogen bonding in the activation of nucleophiles: PhSH-(catalytic) KF in N-methyl-2-pyrrolidone as an efficient protocol for selective cleavage of alkyl/aryl esters and aryl alkyl ethers under nonhydrolytic and neutral conditions.
The nucleophilicity of arenethiols can be augmented via hydrogen bonding with "naked" halide anion. The activity of the halide anions follow the order F(-) >> Cl(-) approximately Br(-) approximately I(-) and is dependent on the countercation (Bu(4)N approximately Cs approximately K > Na >> Li). The solvent plays an important role in nucleophilic activation as well as regeneration of the effective nucleophile (e.g. ArS(-)) and those with high dielectric constant, high molecular polarizability, high donor number (DN), and low acceptor number (AN) are the most effective. Selective deprotection of alkyl/aryl esters and aryl alkyl ethers can be achieved under nonhydrolytic and neutral conditions by the treatment with thiophenol in 1-methyl-2-pyrrolidone (NMP) in the presence of a catalytic amount of KF. Aryl esters are selectively deprotected in the presence of alkyl esters and alkyl methyl ethers during intramolecular competitions.
Chakraborti
Asit K
AK
Department of Medicinal Chemistry, National Institute of Pharmaceutical Education and Research (NIPER), Sector 67, S. A. S. Nagar 160 062, India. achakraborti@niper.ac.in
Sharma
Lalima
L
Nayak
Mrinal K
MK