Light photo-Fries rearrangement

The API fenoprofen calcium is a diaryl ether. Degradation of fenopro-fen under intense ultraviolet light in solution yields a mixture of isomeric biphenyls via a photo-Fries rearrangement mechanism (Fig. 76) (117). 

Polyurethanes.—The photo-oxidation of polyurethane elastomers based on aromatic isocyanate units has been studied and found to involve two principal reactions. The first is a photo-Fries rearrangement with light wavelengths <330 nm and the second is a photoinduced hydroperoxidation.Several hydroperoxide structures were identified [e.g., (5)—(8)] and their importance examined." " Type (5) hydroperoxides are the most photolabile and are... 

Research in the laboratory of P. Magnus showed that the macrocyclic skeleton of diazonamide could be synthesized with the use of macroiactonization followed by a photo-Fries rearrangement. First, the aromatic carboxylic acid and the phenol were coupled with EDCI to form the macrolactone (phenolic ester), which was then exposed to light at high-dilution to cleanly afford the macrocyclic ortho-acylated phenol skeleton of diazonamide. 

Fig. 1. Scheme for the SAM formation of MUAP, the photo-Fries rearrangement reaction upon irradiation with UV-light, and the post-modification reaction with perfluorobutyryl chloride. Below images of water droplets and CH2I2 droplets on each surface. 

It has been shown that the efficiency of esters of 4-hydroxy-3,5-di-f-butylbenzoic acid as light stabilizers for polyolefins is not related to the yield of the photo-Fries rearrangement [132]... 

The structure of XIV is difficult to elucidate but may be formed by the combination of the loss of the -COCHg moiety from and Photo-Fries rearrangement of III to yield most probably a semi-qulnone type of structure. If this is the case, then it appears that Photo-Fries rearrangements compete with photodegradation in these processes. Allen, et al. (15.16) have attributed the yellowing of BAE films under UV light to the formation of quinone structures, as shown below (XV), by photo-sensitized oxidation of the blsphenol A unit. 

In addition to the above, photo-Fries rearrangements occur in various aromatic polyester films upon ultraviolet light irradiation [560, 561]. Also, photo-Fries rearrangements are believed to occur in polycarbonate resins as well [562]. This can be illustrated as follows ... 

Furthermore, the use of light has also been used, wherein Magnus was able to effect the rearrangement and develop a photo-Fries rearrangement for the synthesis of the diazonamide macrocycle (160 161) [80]. Irradiation of 160 in benzene (0.001 M) with a medium pressure mercury vapor lamp at 23°C gave 161 (39%) along with about 20% of the para-isomer. 

The light-induced rearrangement of phenyl esters 36 into hydroxy aryl ketones 37 and 38 is called the photo- Fries rearrangement [41]. Because of low yields, this procedure has little commercial importance. The reaction is usually carried out in an aprotic solvent and involves a radical mechanism by the homolytic cleavage of the (9-acyl bond from its singlet excited state [41]. 

Phenyl-substituted p-hydroxybenzoates (Structure 4) have been used as light Stabilizers in polyolefins for some time. They were shown to operate through a photo-Fries rearrangement to give a more effective 2-hydroxy-benzophenone product by the following reaction sequence (Scheme 4) to give 2-hydroxybenzophenones as products [1,2]. Obviously for such a reaction to occur, the original stabilizer must absorb appreciably in... 

Norrish type 1 and Norrish type 2 reactions as well as the photo-Fries rearrangement are processes induced by photons. Light-induced transitions, such as the photo-Fries reaction. Figure 5.13, lead to changes in polymer structure and all related properties [38]. 

Also obtained by UV light irradiation of phenyl acetate (photo-Fries rearrangement),... 

Also obtained by UV light irradiation of o-tolyl acetate at 25° (photo-Fries rearrangement), in the presence of potassium carbonate in hexane (74%) [2015] or without potassium carbonate in hexane (32%) [2015] or in ethyl ether (16%) [2193],... 

Preparation by UV light irradiation of m-tolyl acetate, at r.t. (photo-Fries rearrangement) [2192], in ethanol (37%), with aqueous p-cyclodextrin solution (54%) or with p-cyclodextrin (soM) (95%). 

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