2-Pyridineseleninic anhydride

Iodylbenzene with catalytic amounts of 2,2-dipyridyl diselenide converted alkenes into allylic ketones directly the actual oxygenating agent was 2-pyridineseleninic anhydride, formed in situ. 

More recently Barton and Crich reported the use of 2-pyridineseleninic anhydride in the allylic oxidation of alkenes. This reagent is prepared in situ by the oxidation of the corresponding diselenide by iodylbenzene. It effects oxidation to a, -unsaturated ketones with retention of the double bond regio-chemistry e.g. equation SO). 

Pyridineseleninic anhydride was also shown to be more reactive towards benzylic oxidation than the previously reported benzeneseleninic anhydride. This was rationalized as an effect of the greater electron-withdrawing properties of the pyridine nucleus in rendering the Se>> bond a better enophile. Alternatively, the 2-pyridineseleninic anhydride may exist in equilibrium with a pyridinium salt which is the effective oxidant (equation SI). 

Several catalytic oxidative systems using iodylbenzene as a stoichiometric co-oxidant have been developed. Barton and coworkers have developed an efficient allylic oxidation protocol with 2-pyridineseleninic anhydride 806 (R = 2-Py) as the principal oxidant, generated in situ by oxidation of the corresponding diselenide 807 with iodylbenzene or 3-iodylbenzoic acid (Scheme 3.318) [1111]. This reaction proceeds in chlorobenzene at 100 °C within 2.5-3 h. Most likely, the initial oxidation of alkenes 808 leads to the formation of allylic alcohols, which undergo further oxidation into a,(3-unsaturated ketones 809. In contrast with the... 

This may be attributed to the greater electron-withdrawing effect of the pyridine nucleus. Consequently, pentafluoroseleninic acid (95) and 2-(AT-oxi-do)pyridineseleninic anhydride (96) were introduced [47] as the most efficient reagents in the oxidation of alcohols and in the allylic oxidation of olefins. 

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