Photo-Fries rearrangement amides

When the crystal of 59c was irradiated at 0°C, a single regioisomer of 60c was obtained quantitatively. The photoproduct 60c showed an ee of 42%. Furthermore, a higher ee value of 60c (87% ee) was obtained in the reaction at -50°C. The radical mechanism has been confirmed in the photo-Fries rearrangement of aromatic amides. 

More than half a century ago, Anderson and Reese reported the first example of a photo-Fries rearrangement (PFR), where 2-hydroxyphenylacetate was converted into 2,3- and 3,4-dihydroxy acetophenone upon UV irradiation [1]. Since then, hundreds of articles have appeared on this reaction, which has been extended from the initial aryl esters to amides, carbonates, carbamates, thioesters, sulfonates, etc. [2-4]. 

Finally, a rearrangement of aryl esters and amides known as the photo-Fries rearrangement has occasionally found synthetic utility (Eq. 16.63). Although these reactions are superficially diverse, they all are initiated by a cleavage at the carbonyl, followed by conventional radical chemistry. 

One special type of light-induced alterations concerns the rearrangement of constituent groups in either the main chain or the pendant groups of linear polymers. Typical processes that have gained importance are the photo-Fries rearrangement of aromatic esters, amides, and urethanes, and the o-nitrobenzyl ester rearrangement. Some typical examples are illustrated in Schemes 3.22 and 3.23. 

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