Photolytic rearrangement

Perfluorotoluene (3) rearranges photolytically to give a 20% yield of positional isomers 4 and 5 in a ratio of ca. 2 1, a mixture which cannot be resolved by GC.19 21 These per-fluoro(methylbicyclo[2.2.0]hexadiene) isomers revert to toluene 3 when heated at 80 C for 4 hours in the vapor phase.19... 

In contrast, 826a rearranged photolytically to give 4,5-diphenyl-5-(2-propenyl)-2(5/f)-oxazolone 830. Unfortunately, no conditions for extruding carbon dioxide from 827a or 830 could be identified. 

Nitrile oxides have been long known to rearrange to isocyanates under the influence of heat or light now it is reported that carrying out the rearrangement photolytically in the presence of sulphur dioxide provides a mild high-yield synthetic... 

The most intriguing hydrocarbon of this molecular formula is named buUvalene, which is found in the mixture of products of the reaction given above. G. SchrOder (1963, 1964, 1967) synthesized it by a thermal dimerization presumably via diradicais of cyciooctatetraene and the photolytical cleavage of a benzene molecule from this dimer. The carbon-carbon bonds of buUvalene fluctuate extremely fast by thermal Cope rearrangements. 101/3 = 1,209,6(X) different combinations of the carbon atoms are possible. 

D. Cyclic a-Diazoketones Ring-Contraction in Photolytic Wolff Rearrangements... 

The photolytic decomposition of a-diazoketones, accompanied by rearrangement to ketene (photolytic Wolff rearrangement), has been used successfully in the preparation of A-nor- and C-norsteroids. The method is reviewed in chapter 15 by R. M. Scribner. ... 

Benzylenol ethers rearrange in an apparently similar fashion via photolytic fission of the benzyl-oxygen bond and subsequent recombination steps. Irradiation in quartz of a cyclohexane solution of 3-benzyloxycholesta-3,5-diene (250) leads to 23% (251), 13% (252) [presumably formed from (251) during workup] and 10% (253). ... 

Retropinacol rearrangement, 416 Ring contraction in photolytic cyclic a-diazoketones rearrangements, 316 12- p/-rockogenin mesylate, 400... 

In this review an attempt is made to discuss all the important interactions of highly reactive divalent carbon derivatives (carbenes, methylenes) and heterocyclic compounds and the accompanying molecular rearrangements. The most widely studied reactions have been those of dihalocarbenes, particularly dichlorocarbene, and the a-ketocarbenes obtained by photolytic or copper-catalyzed decomposition of diazo compounds such as diazoacetic ester or diazoacetone. The reactions of diazomethane with heterocyclic compounds have already been reviewed in this series. ... 

Acyl azides can undergo photolytic cleavage and rearrangement upon irradiation at room temperature or below. In that case acyl nitrenes 8 have been identified by trapping reactions and might be reactive intermediates in the photo Curtius rearrangement. However there is also evidence that the formation of isocyanates upon irradiation proceeds by a concerted reaction as in the case of the thermal procedure, and that the acyl nitrenes are formed by an alternative and competing pathway " ... 

In his investigations of strained bicycHc systems, Meinwald 4) has explored the photolytic rearrangement of a-diazoketones to carboxylic acids according to the reactions. The procedure given below is an example of this process, employing as the... 

Photolytic reactions of dienes frequently give complex mixtures of rearranged products. Described here, however, is a photolytic isomerization of 1,5-cyclooctadiene (present in solution, in part, as a complex with cuprous chloride) that affords a good yield of one product. 

In this section we first discuss photolytic reactions of arenediazonium salts and report on quinone diazides at the end of the section in the context of imaging technology. Diazoalkenes, non-quinonoid diazo ketones, and the Wolff rearrangement are treated in the book on aliphatic diazo compounds (Zollinger, 1995, Chap. 8). 

The photolysis of o-quinone diazides was carefully investigated by Stis in 1944, many years before the development of photoresists. Scheme 10-102 shows the photolysis sequence for the diazoquinone 10.75 formed in the diazotization of 2-amino-1-naphthol. The product of the photolytic step is a ketocarbene (10.76), which undergoes a Wolff rearrangement to a ketene (10.77). In the presence of water in-dene-3-carboxylic acid (10.78) is formed this compound is highly soluble in water and can be removed in the development step. The mechanism given in Scheme 10-102 was not postulated as such by Stis, because in 1944 ketocarbenes were unknown (for a mechanistic discussion of such Wolff rearrangements see review by Zollinger, 1995, Sec. 8.6, and Andraos et al., 1994). 

Arylsulphonylmethyl sulphonates as photolytic products 882 Sulphone-Fries rearrangement 171 Sulphone metabolites, mass spectra of 153, 154... 

Scheme 10.14 gives some other examples of Wolff rearrangement reactions. Entries 1 and 2 are reactions carried out under the classical silver ion catalysis conditions. Entry 3 is an example of a thermolysis. Entries 4 to 7 are ring contractions done under photolytic conditions. Entry 8, done using a silver catalyst, was a step in the synthesis of macbecin, an antitumor antibiotic. Entry 9, a step in the synthesis of a drug candidate, illustrates direct formation of an amide by trapping the ketene intermediate with an amine. 

The preparation of N-carbethoxy-8-azabicyclo [5.1.0] oct-3-ene (158) from ethyl azidoformate (157) and 1,4-cycloheptadiene through a photolytic reaction, and its palladium(II)-catalyzed multistep rearrangement to N-carbethoxynortropidine (159), has been presented by Wiger and Retting as a new route to the 8-azabicyclo[3.2.1]octene skeleton (87) (Scheme 8). 

The formal relationship between cyclopropenone and an a,a -biscarbene of a ketone (R—C—CO—C—R ) initiated investigations on photolytic and Ag-catalyzed decomposition of a, a -bisdiazo dibenzyl ketone (49) (Trost50 ). Indeed, diphenyl-cyclopropenone was formed in addition to other products (52 and tolane) derived from it furthermore, products resulting from solvent insertion and Wolff rearrangement of the monocarbene 50 were isolated (51) ... 

The irradiation of 3-( -aminophenyl)-l,2,4-oxadiazoles 65 allowed the process to be extended to the formation of an internal N-N bond (Scheme 4), leading either to the indazoles 68 directly from photolytic species 66, or to the formation of benzimidazoles 69, which were formed from the carbodiimide 67, the rearrangement product of photolytic species 66 <1996JOC8397>. 

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