Aqueous Media Deprotection of Ketoximes with Ammonium Persulfate

Abstract

Oximes are very useful for protecting groups in organic synthesis. These highly crystalline compounds can be prepared from carbonyl and non carbonyl compounds. The regeneration of carbonyl compound from oximes provides an alternative method for the preparation of these compounds. The classical method for regeneration of carbonyl compounds from oximes reqire strongly acidic conditions, which is not suitable for acid sensitive compounds. In order to avoid this, many oxidative deoximation methods have been developed in recent years. Ammonium persulfate is an inexpensive and readily accessible oxidizing agent. It is commonly used in industry for bleaching and for wastewater treatment. However, only sporadic literature is available that describes its applications in organic synthesis, the oxidations of alkenes, substituted aromatics, cyclization and deoximation under strenuous conditions using sulfuric acid. Synthetic chemists continue to explore new methods to carry out chemical transformations. One of these new methods is to run reactions in aqueous media. Organic reactions in water, without the use of any harmful organic solvents, are of great current interest, because water is an easily available, economical, safe and environmentally benign solvent. In continuation of our ongoing program to develop environmentally benign methods in the absence of organic solvent, we now wish to report that ammonium persulfate deoximates ketoximes to the parent ketones cleanly and in good yield in an aqueous media. This reagent oxidizes aldehydes to acids, so deoximation of aldoximes is unlikely to be useful. Dissolution of ammonium persulfate in water and subsequent reaction with ketoximes under stirring at room temperature or reflux gave the corresponding carbonyl compounds in good yields. Table 1 contains a summary of the results we have obtained for variety of ketoximes. The synthetic value of these results is apparent when it is noted that such reactions in the past have usually been achieved by the use of activated ammonium persulfate. Even the sterically hindered ketoximes were successfully deoximated in excellent yields (entries 1 and 9). This reaction does not require an activation procedure or the use of expensive equipment or materials.