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Highly Efficient Chemoselective Deprotection of O,O-Acetals and O,O-Ketals Catalyzed by Molecular Iodine in Acetone

Jianwei Sun, Yanmei Dong, Liya Cao, Xinyan Wang, Shaozhong Wang and Yuefei Hu*

*Department of Chemistry, Tsinghua University, Beijing 100084, P. R. China, Email: yfhmail.tsinghua.edu.cn

J. Sun, Y. Dong, L. Cao, X. Wang, S. Wang, Y. Hu, J. Org. Chem., 2004, 69, 8932-8934.

DOI: 10.1021/jo0486239


Abstract

A convenient deprotection of acyclic and cyclic O,O-acetals and O,O-ketals is achieved in excellent yields within minutes under neutral conditions in the presence of a catalytic amount of iodine. Double bonds, hydroxyl groups, acetate groups, and highly acid-sensitive groups such as furyl, tert-butyl ethers, and ketoximes are tolerated.

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Details

The document reports a highly efficient method for the chemoselective deprotection of O,O-acetals and O,O-ketals using molecular iodine (10 mol %) in acetone. This protocol achieves excellent yields within minutes under neutral conditions, preserving sensitive functional groups such as double bonds, hydroxyl groups, acetate groups, furyl moieties, tert-butyl ethers, and ketone-oximes. Traditional methods for deprotection often involve aqueous acid hydrolysis, which can be incompatible with many functional groups. The new method leverages a substrate exchange mechanism rather than hydrolysis, making it mild and highly selective. The reaction is fast, with acyclic ketals deprotected in 5 minutes and cyclic ketals in 45 minutes at room temperature. The process is further accelerated at higher temperatures. The study demonstrates the method's broad applicability and chemoselectivity across various substrates, including dialkyl acetals and ketals. The experimental procedure involves stirring the acetal or ketal with iodine in acetone, followed by solvent removal and purification. This method is expected to be valuable in the manipulation of carbonyl groups in complex organic syntheses. The research was supported by the National Natural Science Foundation of China, and detailed NMR spectra are available online.


Key Words

Acetals, Dimethyl Acetales, Dioxolanes, Deprotection


ID: J42-Y2004-1050