Mild, Efficient, and Greener Dethioacetalization Protocol Using 30% Hydrogen Peroxide in Catalytic Combination with Ammonium Iodide

Abstract

A simple, mild, efficient, and expedient greener dethioacetalization protocol employing a catalytic amount of nontoxic ammonium iodide (10 mol%) in combination with 30% hydrogen peroxide as terminal oxidizer is revealed. The reagent accomplished facile deprotection of 1,3-dithianes and dithiolanes of activated aromatic substrates in an aqueous medium in the presence of sodium dodecylsulfate (SDS) at room temperature under virtually neutral conditions. Deactivated and sterically encumbered substrates, which are otherwise reluctant to cleave under aqueous micellar conditions, were expeditiously cleaved in good to excellent yields in acetic acid. The method is tolerant, with several acid-sensitive protecting groups, such as tert-butyldiphenylsilyl (TBDPS) ether, aryl acetate, NHBoc, and NHBn, and with further oxidation of oxidation-prone activated benzaldehydes and furyl aldehydes. A tentative mechanism of hypoiodous acid–mediated catalytic cleavage is proposed.

Keywords:

• Ammonium iodide
• dethioacetalization
• 1,3-dithianes
• 30% hydrogen peroxide
• sodium dodecylsulfate (SDS)

ACKNOWLEDGMENTS

One of the authors (P. M.) is thankful to the Council of Scientific and Industrial Research, India, for financial assistance by way of a research fellowship. We thankfully acknowledge the facilities provided by the Department of Science and Technology–Funding for Infrastructure in Science and Technology and the University Grants Commission, SAP programs, government of India, to the Department of Chemistry, University of Kalyani.

Notes

^a Deprotections were carried out on a 1-millimolar scale at room temperature; amount of reagents/solvents refer to per mmol of substrate.

^b Refers to isolated yield upon chromatography.

^a Reaction conditions: NH₄I (10 mol%), 30% H₂O₂ (0.5 mL), H₂O (5 mL), SDS (0.2 mmol) per mmol of substrate, rt.

^b Refers to isolated yield after chromatographic purification; the carbonyl products are known compounds that showed physical and spectral features in good agreement with those reported in the literature.^{[ 18a ]}

^c Reaction conditions: NH₄I (10 mol%) in H₂O (0.5 mL), CH₃COOH (1.5 mL), 30% H₂O₂ (0.5 mL) per mmol of substrate, rt.

^d Yield was assessed from 2,4-dinitrophenylhydrazone derivative.