Bullvalene, structure

Unexpectedly, the reaction of 284 toward tetracyanoethylene at room temperature resulted neither in the formation of the [4 + 2] adduct 299 nor in the formation of its azepine derivative, but the novel 4,6-diazasemi-bullvalene structure 300 was isolated as colorless crystals in 70-85% yield (90CC1057) (Scheme 66). Although mechanistic rationalization of this process is not a simple matter, a possible reaction course would involve the formation of Michael adduct 301, which would undergo intramolecular... 

Schroder and Witt ° have reported the synthesis of crown ethers having fluctuating ring sizes which they have termed breathing crown ethers . The structures are based on the bullvalene subunit and, as the tetracyclic subunit undergoes Cope rearrangement, the size of the macroring likewise varies. The synthetic steps follow the conventional routes used for the preparation of crown ethers and are illustrated in Eq. (3.44). 

A number of azabullvalenes (106 containing heterocyclic nitrogen) have been synthesized. They also have fluxional structures when heated, though with fewer tautomeric forms than bullvalene itself Paquette, L.A. Malpass, J.R. Krow, G.R. Barton, T.J. J. Am. Chem. Soc., 1969, 91, 5296. 

In principle, the divinylcyclopropane structure discussed here is incorporated into very well known systems such as bullvalene 547, barbaralane 548 and semibullvalene 549, which very easily undergo a Cope rearrangement. 

If the two methylenes of 9 are bridged with two double-bonded carbons, we get the remarkable structure 10, called bullvalene, which rapidly interconverts amongst equivalent structures ... 

Doering and Roth, at the time of their first investigations of 86 in 1963, proposed that the structure 90, which they named bullvalene, should undergo degenerate Cope rearrangements that would make each of the ten CH groups equivalent.179 Equation 12.109 illustrates just a few of these transformations.180... 

If each of the ten CH groups were individually labeled, there would be 101/3, or 1,209,600, different ways of arranging them in the Structure 90.181 Doering and Roth pointed out that observation of a single line in the proton magnetic resonance spectrum would mean that all of these structures were simultaneously present and rapidly interconverting.182 Later in the same year Schroder announced the synthesis of bullvalene and reported that the proton magnetic... 

Particularly interesting is the dimer formed from didehydrobullvalene (51) in which the two fluctuating bullvalene systems are fused to each other by a four-membered ring. According to H-NMR data (52), with the three-membered rings in the anticonfiguration, is the thermodynamically most stable of the 17 possible valence isomers, whereas the cyclobutadiene structure (55) is not present in the equilibrium mixture 200) in addition to these dimers, a trimer is also obtained 200). 

Gas-Phase NMR Studies of Structural Exchange in Sulfur Tetrafluoride and Bullvalene... 

The only complex having olefinic double bonds alone in the coordination sphere of the silver ion which has been subjected to a complete structural analyses (404) is the bullvalene (532) complex (CioHjo)sAgBF4. The structure consists of discrete (CioHio)3Ag+ cations and BF4 anions (Fig. 12). The three bullvalene molecules in the complex cation are... 

The extent of the restraints imposed on structure III by orbital symmetry conservation is brought into sharper perspective when its rigidity is contrasted to the fluxional behavior of von Doering s interesting invention (11), bullvalene (VI) (12). 

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