Bicyclo nonatriene

The bicyclo[6.1.0]nonatriene 46 is transformed to the 8,8-dihydroindene on treatment with a catalytic amount of [Rh(CO)2Cl]2 [24], The stereoselectivity depends on the reaction temperature. [5 + 2]cycloaddition of vinylcyclo-propanes 47 with alkynes is catalyzed by RhCl(PPh3)3 in the presence of silver triflate to give seven-membered rings 48 [25]. (Scheme 17 and 18)... 

In summary, the parent 1,3-bishomotropylium ion [43] is produced upon protonation of the bicyclo[6.1.0]nonatriene [44] and its NMR spectrum was recorded under stable ion conditions. Two different bridged 1,4-bishomo-tropylium ion skeletons [45] and [46] have been prepared from a multitude of different precursors. However, no unbridged 1,4-system has yet been characterized. 

A diazide was obtained91 as the sole product also by addition of IN3 in acetonitrile to c -bicyclo[6.1.0]nonatriene. In this case, however, at variance with the medium-size ring unsaturated compounds, the reaction did not afford a normal vie-diazide. A mechanism involving a bishomotropylium or cyclopentadienyl cation has been proposed (equation 64). 

The bicyclo[4.2.1]nonatriene 323 was prepared by the [6+2] cycloaddition of internal alkyne with the complex 322 under irradiation [79]. Ligand exchange of 323 with toluene liberated 324. The complex 325 underwent the [6+2] cycloaddition with two moles of terminal alkyne to give the tetracyclic compound 327 via 326. The [6+2] cycloaddition of the complex 322 and 1,7-octadiyne (328) afforded 329 as a primary product, which was converted further to 330 in 56% yield by further intramolecular [6+2] cycloaddition [80]. The tropone complex 331 underwent intramolecular [6+2] cycloaddition under irradiation to give the strained tricyclic compound 332 in moderate yield [81]. 

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). 

We are, of course, aware of the strict Hiickel definition linking aromaticity to the presence of 4n + 2 rc-electrons, On the other hand, we note that the radical cations discussed below have SOMOs, which have one electron less than the Hiickel requirement and which show cyclic homoconjugation, even though the parent molecules assume alternative structures. In view of the precedence established for the radical anion (156) of bicyclo[6.1.0]nonatriene [416,417], in order to emphasize the dramatic difference between the structures of these radical cations and their precursors, and for reasons of convenience, we will refer to these species as homo- or bis-homoaromatic. The paradigm of these remarkable species is found in the barbaralane system. 

ESR cavity produces a signal (nonuplet, ajj = 3,23 G), which indicates eight equivalent protons. When bicyclo [6.1.0] nonatriene (196) was reduced in the ESR cavity the spectra of the cyclononatriene radical anion (197) and of the methyl-cyclooctatetraene radical anion (198 Eq. (251) ) were observed. 

Barborak and Schleyer (1970) also solvolyzed 4-deuterio-bicyclo[3.2.2]-nona-2,6,8-trien-4-yl-3,5-dinitrobenzoate [426] in 60% aqueous acetone. Two products were obtained in 1 1 ratio deuterated 9-barbaralyl dinitro-benzoate [427] formed by return and deuterated [425 X = OH]. No bicyclo-[3.2.2]nonatrien-2-ol product could be detected. The deuterium in [427] and... 

When bicyclo[3.2.2]nonatrien-2-ol [429] reacted with superacid at —135°C and was observed at the same temperature by H-nmr spectroscopy, a sharp singlet at S 6.59 was obtained (275). A rapidly rearranging carbocation was concluded to be responsible for the observed singlet since there is no regular... 

Trapping of less stable valence tautomers with benzylideneacetone(tricarbonyl)iron [BDA-Fe(CO)3] was applied to bicyclo[6.1.0]nonatriene (40a) and its i>> -9-methyl derivative (40b). Reaction with BDA-Fe(CO)3 gave three products, one of which was a complex of tricyclo[4.3.0.0 ]nona-2,4-diene 41. As the major product tricarbonyl(tricyclo[4.3.0.0 ]... 

Bishomotropylium ions are postulated as intermediates in the cycloadditions of TCNE and chlorosulfonyl isocyanate onto c -bicyclo[6.1.0]nonatrienes... 

The remarkable virtuosity of the bicyclo[6.1.0]nonatriene structure 1 is further exemplified by its rearrangement to cyclononatriene 2 on treatment with lithium, sodium or potassium metals in liquid ammonia, or in a mixed solvent consisting of hexamethylphosphoric triamide and tetrahydrofuran. 

It should be noted that, in contrast to well-known cA-bicyclo[6.1.0]nonatrienes, the thermal behavior of fraK5-bicyclo[6.1.0]nonatrienes has been insufficiently explored ... 

The comparison of the walk rearrangements in the vinylogous systems bi-cyclo[2.1.0] pentene, norcaradiene, and bicyclo[6.1.0] nonatriene is particularly instructive in the context of the borderline between concerted and nonconcerted processes. Each rearrangement turns out to occur with inversion at the migrating carbon atom. In the case of bicyclopentene and bicyclononatriene, the stereochemical course is in accord with the predictions of orbital symmetry (4), but this is not so for the norcaradiene. Obviously stereochemistry is no reliable criterion for the distinction between a concerted and nonconcerted process in these cases. 

In the case of the bicyclo[6.1.0] nonatriene system, substituents at C-9 also have an influence on the rate of the cleavage of the central cyclopropane bond between C-l and C-8 (91). fThe additional methyl group at C-l in the bicyclopentene systems should facilitate the opening of the bond between C-l and C-5 by about 2 kcal/mol (40). The homolytic cleavage of a cyclopropane bond is expected to have a smaller activation barrier in norcaradiene than in bicyclopentene (by about 5.3 kcal/mol) due to the different stabilization of the radical site at C-l, pentadienyl resonance vs. allyl resonance (92). The nonplanar geometry of the cyclooctatriene ring does not permit any prediction for the bicyclo[6.1.0) nonatriene system. 

Figure 10. Comparison of the stereochemical course and the Gibbs activation enthalpies of the walk rearrangements in bicyclo[2.1.0]pentene, bicyclo[4.1.0]heptadiene, and bicyclo-[6.1.0] nonatriene. AG values are in kcal/mol.

Dureh Bestrahlung bei 0° wcchselt bei endo-9-tert.-Butyl-cis-bicyclo[G. 1.0J nonatrien-(2,4,6) der Substituent seine raumliche Lagc6. 

Therefore, 8 r-heteronines 2 and 16 engage in pericyclic reactions observing the Woodward-Hoffmann rules photochemical j8o-isomerizations lead to bicyclo[6.1.0]nonatrienes 18, thermal 6cr isomerizations yield c/5-bicyclo[4.3.0]nonatrienes 19 ... 

Reaction with benzene follows a similar pathway, yielding a bicyclo[3.2.2]nonatriene structure. Vinylcarbenoids also react with pyrroles to give tropanes via a cyclopropanation-Cope rearrangement route. The direct addition of carbenes to acetylenes does not give satisfactory yields of cyclopropanes, but the rhodium carboxylate catalysed reaction of diazo compounds with acetylenes is a useful source of cyclopro-panes. Carbenoids can also attack a carbonyl oxygen atom, giving rise to a zwitterion (249). An excellent review of intramolecular carbenoid reactions has appeared. ... 

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