Biradicals spin center shift

Another example of the application of the spin-center-shift concept is depicted in Scheme 8b. On irradiation of /3-ketoamides 43, hydrogen abstraction occurs from the d-position, followed by smooth elimination of methanesulfonic acid. In contrast with the applications of spin-center-shift mentioned above, the enolate radical moiety of biradicals 44 reacts solely as oxygen radicals 44b to give the oxa-zinones 45 [20],... 

The idea of a spin center shift as an extension of the synthetic scope of the Norrish-Yang reaction was already discussed twice in this chapter. A third example applies to the preparation of six-membered rings. Thus, by treating (3-ketoamides 42 (Sec. 3.4.2.1, Ih) with hypervalent iodine(III) reagents the oc-methanesulfonyloxy-(3-ketoamides 59 are obtained in excellent yields. On irradiation, the 1,5-biradicals 60 are formed, which are converted into the biradicals 61 by elimination of methanesulfonic acid. 

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