7-Phenyl-2,4,6-heptatrienal

Prompted by W. M. Jones work on the formation of heptafulvene from phenyl-carbene in the gas phase,which implied a seven-membered ring intermediate, and by the implications of the possible reversibility of the process, Baron et al. rediscovered Vander Stouw s cryptic work and showed that all three possible tolyl-carbenes gave benzocyclobutene and styrene, albeit in different ratio from the ortho isomer than from the meta or para species.Baron et al. ° proposed a mechanism in which a methylcycloheptatrienylidene (CH3-7I) was the active seven-membered species, and which additionally feamred the intermediacy of methylbicyclo[4.1.0]-heptatrienes 73 and 73 (Scheme 7.35). 

Rate constants of thermolysis of 7-dimethylamino-l-phenyl-2,4,6-heptatrien-l-one6)... 

Mattox and Grosse262 report the formation of biphenyl, anthracene, and naphthalene from benzene, toluene, or butylbenzene in presence of a chromium-aluminum dehydrogenation catalyst and if 1 -phenyl-frws-l,cis-3, f/my-5-heptatriene is heated for 15 min with palladized charcoal in an evacuated tube at 180°, a very good yield of 2-methylbiphenyl is obtained 263... 

Phenylcyclopentadienes are formed by thermal rearrangement of spirocyclo-heptatrienes(265) radical and ionic mechanisms were proposed for rearrangements of phenyl- and chlorine-substituted cases, respectively. " Photolysis of the diphenyl-substituted spirocycloheptatriene (265 = Ph R = R = H) at 203 K... 

The effect of steric factors on the equilibrium between norcaradiene and cyclo-heptatriene has been further studied. The presence of an endo-7-phenyl substituent in (263) favours the norcaradiene form by ca. 2kcalmol compared with (263 R = COjMe), and the introduction of chloro substituents at C-2 and C-5 changes R. . PO(OMe>2... 

Few examples of 1,3-dipolar cycloadditions to highly fluorinated acetylenes are known, which enhances the significance of recent studies of the reactions between hexafluorobut-2-yne and a series of phenylated and annelated diazocyclopentadienes. For example, diazofluorene is converted into the spiro-adduct (165) which, although stable at -30 °C in the dark, is photo-lysed readily with loss of nitrogen, yielding the spiro[2,4]heptatriene (166). ... 

C-Labelling showed that the thermal conversion of the phenyl trimethylsilyl diazo-compound (168) into (169) involved isomerization of a phenyl carbene into a cycloheptatrienylidene, silacyclopropanes were not involved. It was shown that the P-naphthyl carbene obtained by rearrangement of 4,5-benzocycloheptatrienylidene enters the singlet-triplet manifold as a singlet. Evidence has been reported that aryl carbenes can show both electrophilic and nucleophilic properties in their intramolecular ring expansion. Low-temperature photolysis of the sodium salt of the toluene-p-sulphonyl hydrazone (170) gave, by intramolecular carbene addition, the dibenzobicyclo[4,l,0]heptatriene (171) which was trapped by buta-l,3-diene. ... 

---