Lateral Nuclear Rearrangements

The archetypal photochemical lateral-nuclear rearrangement in aromatic compounds is the photo-Fries rearrangement, and a relatively simple example is reported in which /Mjhlorophenyl salicylate (189) gives 5-chloro-2,2 -dihydroxybenzophenone. Use is made of the photo-Fries rearrangertient of 1-naphthyl esters (190) in the regioselective synthesis of tricyclic analogues of 

Yamashita, T. Kaneda, T. Otsubo, and S. Misumi, Koen Yoshishu-Hibenzenkei Hokozoku Kagaku Toronkai (oyobi) Kozo Yuki Kagaku Toronkai, 12th, 1979, 181 (Chem. Abstr., 1980, 92, 181 150). I. Yamashita, M. Fujii, T. Kaneda, T. Otsubo, Y. Sakata, and S. Misumi, Kokagaku Toronkai Koen Yoshishu, 1979, 64 (Chem. Abstr., 1980, 93, 70447). 

Murato, T, Yatsunami, and S. Iwasaki, Helv. Chim. Acta, 1980, 63, 588. 

Yoshida, K. Kobayashi, J. Goto, E. Ishigamori, and T. Oishi, Koen Yoshishu-Tennen Yuki Kagobutsu Toronkai, 22nd, 1979, 548 Chem. Abstr., 1980, 92, 198606 1981, 93, 168461). 

The photorearrangement of sulphur, selenium, and tellurium analogues of phenyl carboxylates has been reported in a series of papers over the past few years. Some of the reactions are reviewed in a more general account of the photochemistry of organic selenium and tellurium compounds. Typical examples of the process are seen in the reactions of thiol esters (194) and (195), and those 

Arenes of the type Ar-X-Y in vbich the X-Y bond is readily cleaved homolytically undergo facile lateral-nuclear rearrangement. The archetypal example of this process is the photo-Fries rearrangement which occurs with aryl esters and anilides and several reports of these reactions have appeared within the review period. Several 

The yield of 2-acetyl-l-naphthol, the in-cage product from 1- 

C ester. This feature is explained in terms of a radical pair 

2 -hydroxy chalcones (290). The 4 -isomer (291) is also formed and although the ratio of the two products depends on the aryl substituents, the total yields of rearrangement are between 70 and 90%. The other study of the photochemistry of cinnamates 

Acetanilides have been known for many years to undergo photo-182 

The photo-Fries reaction of N-acylindoies favours the formation of 

N-acetyl derivatives of these products along with unspecified amounts of Indole were also formed. Further irradiation of the products converted them in high yield into the corresponding indoles. Photo-Fries rearrangement of 

N-aroylcarbazoles has also been reported it is stated that irradiation with 

Systems in which carbon-carbon bond cleavage in an aryl substituent leads to products In which the cleaved substituent Is bonded to the arene ring include the alkylated dibenzyl ketones (234). 51 Ramamurthy has compared the photochemistry of these compounds when Irradiated In solution with that obtained when they are irradiated in the presence of 9-cyclodextrin. In the absence of 

N-dimethylamino)-2.2-dlphenylethane also leads to products of photo-Fries rearrangement as minor components of the reaction mixture. 52 

The photo-Fries rearrangement of phenyl acetate in aqueous solution in the presence and absence of B-cyclodextrin has been reexamined. In aqueous solution a mixture of phenol and the ortho and para isomers of hydroxyacetophenone is produced. When 3-cyclodextrin is present the quantum efficiency of formation of phenol and of the ortho product is increased. It is suggested that the enhanced photochemical yield of the ortho product reflects the less polar environment of the cyclodextrin cavity while the increased quantum yield of phenol formation reflects the availability of abstractable hydrogen within the cyclodextrin cavity. 

The suitability of the photo-Fries reaction for the conversion of phenyl succinates (278)-(283) to the phenols (284)-(289), respectively, has been examined and compared with the corresponding thermal reaction catalysed by aluminium trichloride. Photochemists will be pleased to read that the authors conclude that the photochemical route is more general than the ground state procedure 

Products resulting from intramolecular photo-Fries reaction of an anilide have been observed during the u.v. light irradiation of the azacholestenones (308) the rearranged compounds have structure 

Photo-Fries reactivity has also been found for N-aroyl- 

A full paper has appeared expanding on the previous report concerning the photo-Fries rearrangements of N-aroylcarbazoles. In polar solvents mixtures of carbazole and both (311) and (312) are obtained, while in non-polar solvents carbazole and low yields of (311) only are isolated instead. An intramolecular cyclisation reaction competed successfully with rearrangement in the case of N-(ortho-chlorobenzoyl)carbazole to yield (313) as the major product. In a report from a different laboratory the photo-Fries rearrangement of N-sulphonylcarbazole is described and the products identified as (314) and (315) in contrast to the results described above, these authors report that N-benzoylcarbazole is photochemically inert. 

The mechanism of the photo-Fries reaction, both in the vapour and condensed phases, has been thoroughly established, and the many reported examples of the process with a wide variety of systems indicate the generality of the reaction.10 Although o- and p-migration products normally result from irradiation of aryl esters, structural constraints can lead to meto-rearrangement products, and the first useful meta-Fries reaction has now been described.188 Thus irradiation of the amino-lactone (147) in THF leads to 57% of the red crystalline isomer (148) via, 

The migration reaction has been reported for both heteroaromatic acid phenyl esters154 184 and hydroxypyridine esters.185 The former report describes the process for both 3- and 4-isomers of (150) and for the 5-ring heteroaromatic compounds 

Itoh and Y. Kanaoka, Chem. andPharm. Bull. (Japan), 1974, 22, 1431. 

Irradiation of 3,5-dimethoxybenzyl acetate in hexane leads to l,3-dimethoxy-5-methylene-6-acetoxycyclohexa-l,3-diene (157) as one of the major products.192 Compound (157) may be regarded as a precursor of the rearrangement product (158) and indeed is readily converted into this. Other reaction products are 

5-dimethoxy toluene, 3,5-dimethoxyethylbenzene, 3,5-dimethoxy heptylbenzene, and 3,5,3, 5 -tetramethoxybibenzyl. The first step in the reaction which leads to all these products is reasonably considered to be benzyl—OCOMe bond fission. Irradiation of the labelled compound (159) leads to carboxyl oxygen equilibration. The absence of the crossed product from irradiation of (159) in the presence of 3,5-dimethoxy[l,l-2H2]benzyl acetate clearly indicates that the equilibration reaction is intramolecular.193 

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Two examples of ring expansion by lateral-nuclear rearrangement have been reported within the year. Japanese workers have given a fuller account of their earlier reported observations concerning the photorearrangement of 2-aryl-1,2-benzisothiazolin-ones (299) which with 340 nm radiation in benzene solution give... 

Irradiation of sulphonium salts (308) in acetonitrile solution has been shown to lead to lateral-nuclear rearrangement and the gg formation of l-(methylthio)-2-substituted alkylnaphthalenes (309). The quantum yield of product formation varies between 0.24 and 0.1 but bond cleavage to yield 1-naphthyl methyl sulphide also occurs and MeCONH-CHg-R is a by-product of the migrating group and the solvent. The steric crowding in r.tris(trimethylsilyl )methyl] benzene (310) is considered to be the origin of its photolability and on irradiation it efficiently yields (311), (312), and five... 

The lateral-nuclear rearrangement of aryloxy-l,3,5-triazines had previously received the attention of Shizuka and co-workers.194 The same research school now reports the effect of irradiation on a large number of aryloxy-sym-triazines (160).195 In general o- and/or p-hydroxy-derivatives of aryl-sym-triazines (161)... 

Lateral-nuclear migrations also occur with heteroarenes, and it is reported that all three isomeric nitraminopyridines (300) irradiated at 254 nm in methanol solution undergo this type of rearrangement. Thus the 2-isomer yields both 3-nitro- and 5-nitro-2-aminopyridines in a respective ratio of 6.25 1, 3-nitraminopyridine gives the 4-nitro- and 2-nitro-3-aminopyridines (1.28 1 ratio respectively), while the 4-nitramine isomer produces only 3-nitro-4-aminopyridine. Under similar conditions, l-methyl-4-nitraminopyridine... 

Lateral nuclear shifts have been found to contribute to the photochemistry of spiro[cycloalkyIphenalenes] (334) The cyclopropyl and cyclopentyl derivatives of (334), i.e. n=0 or 2, appear to react by cleavage to biradicals (335) which recombine to produce the isolated products (336) and (337). The cyclohexyl homologue (334), n=3, yields (338) which may be a di-m-methane rearrangement product. 

Silicon-silicon bond homolysis and migration/recombination account for the photochemically induced rearrangement of the bis-(disilanyl)naphthalene (339) to (340). However, analogous products from a photochemical lateral nuclear shift are not seen for the digermane (341) even though germanium-germanium bond homolysis does occur upon excitation. 

Why are these isotopes important in biochemistry and medicine The isotopes we have mentioned occur at very low natural abundance , e.g. in the world around us only about 1 carbon atom in 10 (a million million) is C. However, with the advent of nuclear physics and specifically the Manhattan Project, the atomic bomb project in World War 11, radioactive isotopes started to be produced artificially, and this meant that chemical compounds could be radioactively labelled , either uniformly (e.g. in every carbon position) or selectively (i.e. with radioactive enrichment in particular positions). In the case of carbohydrate metabolism, it was possible to study the relative importance of glycolysis and PPP by comparing the release of radioactivity from glucose, specifically labelled either in carbon 1 or in carbon 6. If you look at Topic 28, you will see that in the initial reactions of the PPP the CO2 that is produced comes entirely from the Cl position. Over time, as the later molecular rearrangements come into play, C6 atoms could also eventually be released but not initially. On the other hand, if you revisit Topics 13 and 14, you will see that, because the sugar phosphate is split down the middle into two triose phosphate halves that are then handled identically, CO2 released in the oxidation of pyruvate to acetyl CoA will be derived equally from Cl and C6. This allows biochemists to assess the relative activities of PPP and glycolysis in different tissues or in the same tissue over time. This is how it was possible to estimate (Topic 28) that 30% of glucose breakdown in liver is via PPP. 

Gallina et al. [20] introduced the hyperspherical symmetrical parametrization in a particle-physics context, as did Zickendraht later [21, 22], At the same time, F.T. Smith [23] gave the definitions of internal coordinates following Fock s work already mentioned [16], Clapp [24, 25] and others and established, for the symmetrical and asymmetrical parametrization, the basic properties and the notation we follow. Since then, applications have been extensive, especially for bound states. For example, the symmetrical coordinates have often been used in atomic [26], nuclear [27] and molecular [28-31] physics. This paper accounts for modem applications, with particular reference to the field of reaction dynamics, in view of the prominent role played by these coordinates for dealing with rearrangement problems. 

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