Photo-Fries carbamates

Arylamine Photodecomposition. A number of researchers have alluded to the fact that the products produced from photolysis of aromatic carbamates (i.e., la) also degrade upon irradiation (10), 17). Indeed, we found that the aryl amine 2b and the photo-Fries products 2c and 2d (resulting from photolysis of 2a) decomposed with respective disappearance quantum yields of 0.035, 0.004, and 0.003 when irradiated at 280 nm. These latter results agree with those of Schwetlick et al. (17), who found the rates of disappearance of lc and Id to be quite small. 

In order to characterize the intermediates leading to the photo-Fries/cleavage and hydroperoxide products shown in Schemes I and II, laser flash photolysis measurements of solutions of both MDI and TDI based polyurethanes were conducted. The results from this study are interpreted by comparison with transient spectra of an aryl monocarbamate and the bispropyl carbamate of MDI. In addition, a dimethylsilicon analog of the MDI bispropyl carbamate is used to... 

The photo-Fries rearrangement of heterocyclic carbamates has also been observed [144]. 

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]. 

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