Photo-Fries rearrangement zeolites

Figure 32 Phenyl phenylacetates examined for photo-Fries rearrangement within zeolites and Nafion membranes.

For samples photolyzed on ZSM-5 zeolite, the product distributions of 31 and 32 are dramatically different from those photolyzed in homogeneous solutions. First, the rearrangement products were totally suppressed. Second, diphenylethane 39 resulted from coupling of benzyl radical was not found. Only phenol 38 and toluene were detected. In contrast, photolyses of 33 and 34 on ZSM-5 follow strikingly different pathways. Both photo-Fries rearrangement 36 and 37 and decarbonylation products 35 and 39 were formed. These results can be understood from consideration of size- and shape-selective sorption combined with restriction on the mobility of the substrates and reaction intermediates imposed by the pentasil pore system. 

Ramamurthy and coworkers studied the photo-Fries rearrangement of phenyl acetate and phenyl benzoate and photo-Claisen rearrangement of allyl phenyl ether (Fig. 34) included in two types of zeolite (faujasites X and Y and pen-tasils ZSM-5 andZSM-11) [192], The photolysis was performed with the zeolite slurry in either hexane or iso-octane. One of the most remarkable observations is that the product distribution is altered within zeolites from that in isotropic solvent. Furthermore, while in solution, nearly a 1 1 mixture of ortho and para isomers 40 and 41 (Fig. 34) was obtained, within zeolites one is able to direct the photoreaction selectively toward either the ortho or the para products by conducting the reaction either within faujasites or pentasils, respectively (Fig. 34). 

Figure 34 Photo-Fries rearrangement of phenyl acetate and phenyl benzoate, and photo-Claisen reaction of allyl phenyl ether in solution and within zeolites.

Recently, Ramamurthy and Weiss and their coworkers reported the photo-Fries rearrangement of three 1-naphthyl phenylacelates (Fig. 36) in cation-ex-changed zeolite Y and high-density polyethylene films [193], When the substrates were irradiated in hexane to <30% conversion, the eight photoproducts in Fig. 36 were detected. The photoproduct distributions from polyethylene or a Y-zeolite are drastically different from those in solution. Cage-escape products (54 and 55) are absent in both constrained media, and in zeolite Y, only 49 was detected. The... 

Figure 36 Photo-Fries rearrangement of 1-naphthyl acetates within Y-zeolite and low-density polyethylene films.

Another example of the effect of confined medium is found during photo-Fries rearrangement of naphthyl esters in zeolites [103,104]. Upon photolysis in isotropic solution 1-naphthyl benzoate undergoes the photo-Fries rearrangement to yield both ortho (2-) and para (4-) phenolic ketones (Sch. 4). When this ester is included in NaY zeolite and irradiated the main product (96%) is the ortho isomer. This remarkable ortho-selectivity within zeolites has been rationalized on the basis of interactions of the reactant 1-naphthyl benzoate and intermediate radicals with the sodium ion. Due to restrictions imposed by the medium the benzoyl radical, once formed, is compelled to react only with the accessible ortho position. 

The original Fries procedure has been modified extensively to occur under either UV irradiation (Photo-Fries Rearrangement) or anionic lithiation or lithium-bromo exchange (anionic ortho-Fries rearrangement). Other modifications include the application of microwaves,electron beam, BF3-H20, Y zeolite,zinc powder, Bi(OTf)3, and solid acid catalyst as the promoters. 

Pitchumani, K., Warrier, M., and Ramamurthy. V. 1996. Remarkable product selectivity during photo-Fries and photo-Claisen rearrangements within zeolites /. Am. Chem. Soc. 118 9428-9429. 

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