Oximes, photochemical rearrangement

The formation of the oxime (2) probably results from the presence of adventitious traces of hydroxylic material which catalyze the isomerization of the nitroso monomer, the primary product of the Barton reaction, to an oxime. More direct evidence for the formation of nitroso compounds in the photochemical rearrangement of nitrites is provided by the isolation of nitroso dimers. ... 

A transformation of this type also occurs in the photochemical rearrangement of the acyclic nitrone (177). to the amide (178) and an intermediate oxaziridine may. be, involved in the photochemical conversion149 of aryl oximes into the corresponding amides [Eq. (42)]. 

Aromatic y, y-unsaturated oximes, oxime esters, acyl hydrazones and semicar-bazones 46 undergo photochemical rearrangements into their cyclopropane derivatives 47. These rearrangements are known as the aza-di-ic-methane (ADPM) rearrangements [48]. 

A photochemical partial synthesis of aldosterone (19) made the hormone available on an industrial scale for the first time (114). Corticosterone acetate (51 acetate) is treated with nitrosyl chloride in pyridine at 20°C to yield the 11-nitrite (115). Irradiation of (115) leads to rearrangement with formation of the C g-oxime (116). Removal of the oxime residue with nitrous acid furnishes aldosterone (19) in excellent yield. 

Toray. The photonitrosation of cyclohexane or PNC process results in the direct conversion of cyclohexane to cyclohexanone oxime hydrochloride by reaction with nitrosyl chloride in the presence of uv light (15) (see Photochemical technology). Beckmann rearrangement of the cyclohexanone oxime hydrochloride in oleum results in the evolution of HCl, which is recycled to form NOCl by reaction with nitrosylsulfuric acid. The latter is produced by conventional absorption of NO from ammonia oxidation in oleum. Neutralization of the rearrangement mass with ammonia yields 1.7 kg ammonium sulfate per kilogram of caprolactam. Purification is by vacuum distillation. The novel chemistry is as follows ... 

The N-diazeniumdiolates are quite photosensitive. Studies of various 02-substi-tuted compounds, both alkyl and aryl, revealed a primary photochemical reaction involving cleavage of the N=N bond to yield a nitrosoamine and an O-substituted nitrene which rearranges to a C-nitroso compound (Scheme 3.31), the latter is often isolated as the oxime [224]. 

Photochemical Beckman rearrangement of oximes results in the formation of carboxamides as the major product151 (equation 92). 

Solid-state photochemistry of (—)-2-chloro-2-nitrosocamphane 275 was studied145 by irradiation of the blue-crystal with red light to invert the configuration at C(2) (equation 123). This also causes a photochemically initiated Beckmann rearrangement to form chloroxime 276 to give nitroxide radical 278 (equation 124). The intermediate chloro oxime 276 is proposed to arise from the njr excitation and is believed to be the common intermediate for the photo-epimerization and Beckmann rearrangement. Extended... 

The synthesis of compounds 39, 41, and 43 by the ODPM rearrangement opens a novel photochemical route to chrysanthemic acid and other cyclopropane carboxylic acids present in pyrethrins and pyrethroids [52]. In fact, aldehyde 43 can be transformed to tran -chrysanthemic acid by simple oxidation. This new synthetic route to ecologically benign insecticides competes with the one previously described by us using the 1-ADPM rearrangement of p,y-unsaturated oxime acetates [30,53]. 

In qualitative terms, the rearrangement reaction is considerably more efficient for the oxime acetate 107b than for the oxime ether 107a. As a result, the photochemical reactivity of the oxime acetates 109 and 110 was probed. Irradiation of 109 for 3 hr, under the same conditions used for 107, affords the cyclopropane 111 (25%) as a 1 2 mixture of Z.E isomers. Likewise, DCA-sensitized irradiation of 110 for 1 hr yields the cyclopropane derivative 112 (16%) and the dihydroisoxazole 113 (18%). It is unclear at this point how 113 arises in the SET-sensitized reaction of 110. However, this cyclization process is similar to that observed in our studies of the DCA-sensitized reaction of the 7,8-unsaturated oximes 114, which affords the 5,6-dihydro-4//-l,2-oxazines 115 [68]. A possible mechanism to justify the formation of 113 could involve intramolecular electrophilic addition to the alkene unit in 116 of the oxygen from the oxime localized radical-cation, followed by transfer of an acyl cation to any of the radical-anions present in the reaction medium. 

Another process utilizes a photochemical reaction in which cyclohexane is converted into cyclohexanone oxime hydrochloride (Fig. 2), from which cyclohexanone is produced. The yield of cyclohexanone is estimated at about 86 percent by weight. Then, in a rearrangement reaction, the cyclohexanone oxime hydrochloride is converted to e-caprolactam. 

Steric and electronic effects on the photochemical reactivity of oxime acetates of p/y-unsaturated aldehydes. Journal of the Chemical Society, Perkin Transactions 1, 163-169 (b) Armesto, D., Horspool, W.M., Mancheno, M.J., and Ortiz, M.J. (1990) The aza-di-jt-methane rearrangement of stable derivatives of 2,2-dimethyl-4,4-diphenylbut-3-enal. Journal of the Chemical Society, Perkin Transactions... 

There are a number of thermal and photochemical reactions for which oxaziridine intermediates have been proposed but never isolated. These include, among others, the photochemical Beckmann rearrangement of oximes, many photochemical reactions of aromatic A -oxides, and the thermal rearrangement of nitrones to amides. A brief discussion of the first two seems warranted in this review because they have been studied extensively and some strong inferential evidence for oxaziridine intermediates has been obtained. 

The first photochemical Beckmann rearrangement of aromatic aldoximes was reported in 1963. Subsequently, cyclohexanone oxime was shown to rearrange, upon photolysis, to caprolactam. Although the presence of oxaziridines in the solutions of photolyzed oximes was demonstrated, no oxaziridines have been isolated from these reaction mixtures presumably because of the general instability of oxaziridines that have no substituents on the ring nitrogen. The qualitative results are consistent with the intermediacy of oxaziridines in the photolysis of oximes to amides, yet the possibility of the reactions following other pathways cannot be ruled out. ... 

The photochemically induced oxidation of the isoxazolidines (220), (221), and (222) has been investigated.Typically, the major product from the photolysis of (220) in acetone was the nitro-compound (223), whereas in benzene it was the dimer (224). In an attempt to establish the general mechanism, photo-Beckmann rearrangements were studied for a series of oximes. In each case a pair of... 

Evidence that the photochemical Beckmann rearrangement of oximes proceeds through an oxaziridine intermediate ccmes fran the observation that the relative migratory tendencies of H and aryl groups in the rearrangement of RCH NCH (R=Ph, 4-MeOCgH, 4- 1 ) are similar to those of (352)25. ... 

Further study of the photo-Beckmann rearrangement of oximes suggests that the reaction occurs by way of a concerted pathway from an excited singlet oxaziridine intermediate.84 Thus, in the rearrangement of syn- or anti-5jS-cholestan-6-one oximes (107), which are photochemically interconvertible, the original configuration at C-5 is retained in both lactam products (108) and (109). 

Acetic acid irradiation Photochemical Beckmann rearrangement Lactams from cyclic oximes... 

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