1.3.5- Cycloheptatriene, interconversion with

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... 

The reaction of cycloheptatriene with 2,S-dimethyl-3,4-diphenylcyclopentadienone is typical for this class of compounds, resulting in the formation of six distinct products. Equation (5) displays the major products of interest, which include a modest quantity of the exo [6 -i- 4] adduct (82). The mechanistic details of this process were gleaned from monitoring an equimolar mixture of the two reactants maintained at 120 C. This experiment revealed that both the [2 -I- 4] adduct (83) and the [6 + 4] adduct (82) were formed from the outset of the reaction. However, adduct (83) was subsequently converted quantitatively into the [4 -I- 2] cycloadduct (84) via a Cope rearrangement. This interconversion is reminiscent of a similar transformation in the tropone-diene series (see Section 5.2.2.1.1 and ref. 24). 

Cycloheptatriene, Norbomadiene, Methylenecyclohexadienes (Isotoluenes) and Bicy-clof3.2.0/heptadienes. The gas-phase ion chemistry of ionized 1,3,5-cycloheptatriene is closely related to that of ionized toluene, in particular, and to that of norbomadiene and other non-aromatic ( yllx isomers. This extensive body of work will not be discussed here since a detailed review on this topic has been published by one of these authors in the context of the gas-phase chemistry of the alkylbenzene radical cations This chemistry pertains also to the well-known isomerization of the even-electron CvHv ions and to their formation from the respective parents, e.g. CyHs" " . A related, albeit chemically different held concerns protonated cycloheptatriene, i.e. the even-electron C7H9+ ions , and alkylcycloheptatrienes, which are closely related to protonated toluene and higher alkylbenzenium ions. A parallel review by one of these authors on protonated alkylbenzenes has been pubUshed, and recent investigations on protonated alkylcycloheptatrienes have highUghtened the complexity of this gas-phase ion chemistry 42 jp a minor extent, ionized and protonated fulvenes have also been investigated with respect to their interconversion to their (mainly arene-derived) isomers. 

In order to answer the question posed in Scheme 8.8 as to whether or not external cyclopropane bond homolysis was reversible in norcaradiene, Willcott and Berson examined the pyrolysis of 3,7,7-trimethyl-cycloheptatriene. " Remarkably, the 2,7,7- and 1,7,7-isomers were formed in a 10 1 ratio, respectively, along with small amounts of m- and p-cymene. Importantly, substantial quantities of l-methyl-3-isopropenyl-1,4-cyclohexadiene and 2-methyl-3-isopropenyl-1,4-cyclohexadiene were also found, and these reverted to the cycloheptatrienes under the reaction conditions. Therefore, the interconversion could be the result of biradical formation or reversible homodieny 1-1,5-hydrogen shifts (Scheme 8.10). 

---