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Please login to access the full content or check if you have access via Variation 2: Hydrolysis of α-Oxo Thioketals

DOI: 10.1055/sos-SD-026-00532

Landais, Y.; Vincent, J. M.Science of Synthesis, (200526668.

The hydrolysis of α-oxo thioketals is generally more difficult than the hydrolysis of α-oxo ketals. However, two mild protocols are available and these are widely used. The first relies on the well-known reactivity of the soft sulfur center with heavy metals such as mercury.[‌69‌,‌70‌] The second is an oxidation of the thioketal using N-chlorosuccinimide, N-bromosuccinimide, or bromine.[‌71‌,‌72‌] Both methods are widely employed and selection of the appropriate reagent depends on the nature of the substrates to be hydrolyzed. For example, mercury(II) perchlorate is used to deprotect thioketal 100 and provides the 1,2-diketone 101 in modest yield (Scheme 27).[‌69‌] This approach is unsuitable for the unmasking of the ketone functionality in sensitive systems such as that of pyrrole 102.[‌71‌] Similarly, electrophilic reagents such as bromine and N-bromosuccinimide react with the electron-rich pyrrole nucleus of 102. However, combining N-chlorosuccinimide with silver nitrate results in a very mild oxidation of 102, providing the required 1,2-diketone 103 in high yield in a few minutes. For less sensitive substrates,[‌72‌] N-bromosuccinimide in a mixture of acetonitrile and water at room temperature (Corey's method[‌73‌]) affords moderate to excellent yields of 1,2-diketones, e.g. oxidation of 104 to give 105.[‌72‌] This method is also suitable for 1,3-dithiane oxides, which are converted into the desired 1,2-diketones in high yield with negligible epimerization, e.g. 106 is converted into 107 in 7285% yield.[‌74‌,‌75‌] Finally, it is noteworthy that acyclic 1,3-dithiane oxides 108 are transformed into the 1,2-diketones 109 by a simple acidic treatment, albeit in moderate yield.[‌76‌] Alternative methods also employed use anodic oxidation on a platinum anode,[‌77‌] bismuth nitrate,[‌78‌] and bismuth oxide.[‌79‌]

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