Perfluoro-Dewar benzene

Trifluorodiazoethane has featured in investigations of perfluorobicyclo-[2,2,0]hexa-2,5-diene (perfluoro- Dewar -benzene) as a dipolarophile [- the 7If-tautomer (71) (75%) at 0— 20 C during 4 weeks]. Bis(trifluoromethyl)diazo-... 

UV irradiafion of perfluoro o, m-, and p-xylenes in the gas phase gives a mixture of all possible Dewar benzene isomers Prismane valence bond isomers are proposed to be intermediates [148]... 

Perfluoro(l,3,5- and perfluoro(l,2,4-trimethylbenzene) (15 and 16, respectively) are inter-converted photolytically via the perfluorinated Dewar benzenes 17 and 18, and the unstable prismane isomer 19.22... 

Perfluoro(hexamethylbenzene) (20) rearranges to the three valence isomers, benzvalene 21, Dewar benzene 22, and prismane 23, when photolyzed in perfluoropentane23,24 or in the vapor... 

Perfluoro(hexaethylbenzene) (24), which has low solubility in all common solvents, has been irradiated as a suspension in perfluoropentane.23,24 After irradiation for 15 days, much of the material had gone into solution. The product mixture contained starting benzene 24 (33%), prismane 26 (64%), and Dewar benzene 25 (3%).24 Irradiation of 24 for 69 days using a Pyrex filter (light at > 270 nm) resulted in 4% recovery of benzene 24 and 96% of Dewar benzene 25.24 None of the corresponding benzvalene isomer was detected after irradiation with either filtered or unfiltered light. 

Perfluoro(3,5-dialkvlpyridazines) 35 rearrange photolytieally to the 2,6-disubstituted pyra/ines 36.40 The mechanism that best explains these results involves rearrangement of an intermediate Dewar benzene structure 37 to 38, followed by rearrangement to the pyrazine structure (Scheme 12).40... 

The strained double bonds in Dewar benzene and thiophene make them good dipolarophiles in 1,3-cycloadditions. The hexamethyl,148 1,3,5-trimethyl, and perfluoro-1,3-dimethyl122 Dewar benzenes all yield a monoadduct by reaction with phenyl azide. The hexafluoro derivative, however, gives, depending on the conditions, either a monoadduct (19) or a mixture of mono-and bisadducts accompanied by an aziridine resulting from thermolysis of the triazoline ring system (Scheme 19).146... 

The photolysis of perfluoro(l,3,5-trimethyl)benzene yields perfluorotrimethyl-prismane 19 The latter was considered to be formed via a Dewar benzene. The prismane was isomerized to another Dewar compound which is an intermediate of perfluoro(l,2,4-trimethylbenzene) (see Eq. 16). There are many reactions where prismanes are postulated as intermediates. Some of them are described in the review of Bryce-Smith and Gilbert 29). 

The photolysis of hexafluorobenzene in the presence of oxygen yields the corresponding Dewar benzene and its epoxide the latter may act as a dienophile and thermally rearrange to a perfluoro-l,3-cyclohexadienone (67)66). This reaction is in marked contrast to the reaction of hexamethyl Dewar benzene (see Eq. 56). 

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