1,3,5,7-Cyclononatetraene

9-Chloro-9-deuterio-cis-4-cyclononatetraene dissolves in liquid SO2 at — 66 °C to give (after replacement of the solvent by methylene chloride and trapping of the intermediate with 4-phenyl-1,2,4-triazoline-3,5-dione) compound (309) in which the D-label is completely scrambled this is interpreted in terms of the formation of cyclononatetraenyl cation. If (310) is dissolved in liquid SO2 at — 66 to — 20 C, the D-label is found exclusively at C-1 and C-3 in (309), whereas the 9-chloro-9-deuterio-compound rearranges in CDCI3 to (310) with no scrambling of the label. 

Low-temperature reaction of cyclononatetraenide ion and tropylium ion gives (311), which rearranges photochemically to (312) both (311) and (312) give (313) on heating.  

The effect of cyclononatetraene on the H chemical shift of acetonitrile indicates a weak ring paramagnetism.  

7-Diphenyl-3,4 5,6-dibenzocyclononatetraene gives the corresponding anion on reaction with n-butyl-lithium.  

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Evaluate each of the following processes applied to cyclononatetraene and decide whether the species formed is aromatic or not... 

All-ci5-cyclononatetraene undergoes a spontaneous electrocyclic ring closure at 25°C to afford a single product. Suggest a structure for this product. Also, describe an alternative symmetry-allowed electrocyclic reaction that would lead to an isomeric bicyclononatriene. Explain why the product of this alternative reaction pathway is not formed. 

Compounds in which the RsSn group is attached to a 2,4-dienyl group, such as cyclopentadiene, cycloheptadiene, cycloheptatriene, and cyclononatetraene, whose formulas are shown, are fluxional. 

Cyclononatetraene can theoretically undergo three different electrocyclic ring closures. 

Aza analogs of cyclopentadiene and cyclononatetraene rings could act as acceptor parts in push-pull systems, and possibly be more powerful than their carbocyclic analogs, but no stereochemical studies of such systems seem to have been reported. The remaining group of systems with potentially aromatic acceptors, the quinone methides, have a number of counterparts in heterocyclic chemistry. 

The reader may gain better appreciation of the many basic differences responsible for the division into different classes of heteronin by comparing certain representative members, directly or through appropriate models, in terms of the information presented in Table II. First, one notes that the classification of oxonin (24a) as atropic, jV-methylazonine (27a) as nondescript, and 1 //-azonine or its anion as diatropic, originally proposed on the basis of NMR chemical shifts (data shown in first three rows), was confirmed by the determination of solvent shift character (S values)38 39 that revealed 1//-azonine to possess significant diatropic influence (comparable to that of naphthalene +1.3538), the V-methyl counterpart to exhibit a far weaker effect in the same direction, and oxonin to be atropic or mildly paratropic under this criterion, its S value being closely similar to that of the family s 8 --electron polyenic model, all-cis-cyclononatetraene (24 X = CH2). Major differences between oxonin and parent azonine are also seen to exist in terms of thermal stability and 13C NMR and UV spectroscopy, all of which serve further to emphasize the close structural similarity of oxonin with n-... 

The temperature dependence for this type of mechanism is quite different from the dependence discussed above. Here, the key step for the isomerization is a decay process, which should be temperature independent, at least over an appropriate temperature range. We have found CIDNP evidence for this behavior in several systems, including the rearrangement of bicyclo[6.1.0]nonatriene to cyclononatetraene (vide infra). 

Compared to the cyclooctatetraenyl dianion 19, other cyclic anions (besides cyclopentadienyl anions discussed in Sect. 1.5) have received considerably less attention. Of those that have been studied, not all of them display electron photoejection as a reaction pathway. For example, the 8,8-dimethyl-2,4,6-cyclooctatrienyl anion 22 undergoes cyclization to give 8,8-dimethylbicy-clo[5.1.0]octa-3,4-dienyl anion 23 on photolysis as the exclusive photochemical pathway [42] (Eq. 6). Photolysis of the cyclononatetraenyl anion 24 results in protonation of the more basic excited state anion, to give transient cis, cis, cis, cis-1,3,5,7-cyclononatetraene 25 (Eq. 7), which subsequently undergoes intramole-... 

Treat 1,3,5,7-cyclononatetraene with a strong base to remove a proton. 

Borylated derivatives of the larger cycles cycloheptatriene, cyclooctatetraene, and cyclononatetraene have been studied with regard to their interesting fluxional behavior and tendency to rearrange to a variety of other cychc species. For instance, cyclononatetraenylborane (100) was obtained through reaction of cyclononatetraenyl lithinm with Pr2BCl at —35°C. A combination of dynamic NMR techniqnes and ab initio calcnlations showed that... 

E14b, 246 [Keton + R-N(A1C12)2] Cyclohexen 3-Anilino- E21e, 5426 (En + Ar —N3/AICI3) Cyclononatetraen 9-(Dimethyl-amino-methylen)- V/2c, 788 Ethen 1 -Phenyl- 1-pyrrolidino-E15/1, 617 (Keton + Amin), 618 (Keton + Amino-brom), 688 (Lactam-Red.)... 

Use the inscribed polygon method to show the pattern of molecular orbitals in 1,3,5,7-cyclononatetraene and use it to label its cation, radical, and anion as aromatic, antiaromatic, or not aromatic. 

A scheme that would seem to be consistent with all of the facts is shown in Figure 43. Alternative routes to the all-cis-cyclonona-l,3,5,7-tetraene are possible but seem implausible. Thus competitive disrotatory ring-opening of either 13 or the bicyclo[5.2.0]nona-2,5,8-triene would provide pathways to the all-cis-cyclononatetraene but the activation parameters for these processes would have to be very unusual since it would be necessary to explain how they occur at negligible rates relative to the pathway shown in Figure 43 when the temperature is 31°C (where C(9) epimerization and trapping... 

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