1.3.5- Cycloheptatrien

One compound, either 7-bromo-1,3,5-cycloheptatriene or 5-bromo-1,3-cyclopentadiene, dissociates into ions when dissolved in water. Which molecule do you think displays this behavior How do you think the other molecule behaves when mixed with water ... 

Cycloheptatriene might be expected to be even more acidic, since seven resonance contributors can be drawn for its conjugate base. However, the fact that several resonance contributors can be drawn for a molecule does not necessarily guarantee that it will actually be resonance stabihzed (see also Chapter 12, Problem 9). 

Tropidene (Problem 24.58) can be converted by a series of steps into tropili-dene (1.3,5-cycloheptatriene). How would you accomplish this conversion ... 

The norcarane peroxides 18 are derived from 7-substituted 1,3,5-cycloheptatriene via the singlet oxygen-diimide route (equation 13)30). 

Cycloheptatriene, as an example of a conjugated triene, is mainly cyclopro-panated at an outer double bond (Scheme 6). This is true for Rh2(OAc)4, Cu(OTf)2 and Pd(OAc)2, but the highest yield is obtained again with the rhodium catalyst72>. Twofold cyclopropanation occurs to only a minor extent, as long as an excess of olefin is applied. With equal amounts of diazo ester and cycloheptatriene, double cyclopropanation increases and even traces of the triply cyelopropanated triene are found with Rh2(OAc)4 and Cu(OTf)2. This behavior essentially parallels the earlier... 

Finke, H.L., Scott, D.W., Gross, M.E., Messerly, J.F., Waddington, G. (1956) Cycloheptane, cyclooctane and 1,3,5-cycloheptatriene. Low temperature thermal properties, vapor pressure and derived chemical thermodynamic properties. J. Am. Chem. Soc. 78, 5469-5476. 

On the other hand, the anodic oxidation of 1,3,5-cycloheptatrienes is one of the most powerful key tools for the preparation of a variety of non-benzenoid aromatic compounds such as tropylium salts, tropones, tropolones, 2H -cyclohcpta h furan-2-oncs and azulenes14. 

In addition to 534, further [4+2]-cycloadducts of 5 were prepared by using 1,3-dienes, some of which are well known as trapping reagents of short-lived cyclic allenes and cycloalkynes. Further, cycloadditions could be achieved with tropone and several 2-substituted tropones, 8,8-dicyanoheptafulvene, 1,3,5-cycloheptatriene and a few of its 7-substituted derivatives. The products of these reactions are represented in Scheme 6.108. 

Scheme 6.108 Products ofthe interception of 1,2,4,6-cyclohepta-tetraene (5) with 1,3-diphenylisobenzofuran, anthracenes, 2,5-dimethyl-3,4-diphenylcyclopenta-2,4-dien-l-one, methyl 2-pyrone-5-carboxylate, tropones, 8,8-dicyanoheptafulvene and 1,3,5-cycloheptatrienes.

More recent work on the chemistry of gaseous 1,3,5-cycloheptatriene radical cations concerns the energetics and dynamics of the interconversion with ionized toluene and the competing losses of H from both isomers. Lifshitz and coworkers22,143 have reported on the details of the energy surface of the ions. Most importantly, the critical energies... 

Formation of dihydrotropylium ions is a key feature of the C H9+ hypersurface. Currently, efforts in our laboratory276 have concentrated on the presence of different C H9+ isomers by probing their bimolecular reactivity. Thus, gas-phase titration in the FT-ICR mass spectrometer has revealed that mixtures of C7H9+ ions are formed by protonation of 1,3,5-cycloheptatriene, 6-methylfulvene and norbomadiene as the neutral precursors but that, in contrast to the results obtained by CS mass spectrometry, fragmentation of the radical cations of limonene yields almost exclusively toluenium ions275. 

In the case of 1,3-butadiene, the chemical shifts of inner (H2, H3) protons and outer (HI, H4) is large, while in the case of cycloalkadienes (e.g. 1,3-cyclopentadiene and 1,3-cyclohexadiene), the difference is very small. It is interesting to note that in 1,3,5-cycloheptatriene, the chemical shifts of three kinds of olefinic protons are very diverse. The effect of the ring size and in the chemical shifts of radialenes was also included. 

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