Inner-phase stabilization cyclobutadiene

The taming of cyclobutadiene inside 15 is the first example of an inner phase stabilization of a reactive intermediate and nicely demonstrates the power of this approach (Figure 9.17). Cyclobutadiene 52 is the prototypical example to verify theory of aromaticity. ... 

The successful inner phase stabilization of cyclobutadiene suggests that this approach may allow stabilization of other molecules with highly strained multiple bonds. An interesting class of hydrocarbons with twisted C=C bonds are anti-Bredt bridgehead olefins. These bicycloalkenes have a trani-cycloalkene and are unstable if their olefinic strain (OS) is OS > 21kcalmor. Bicyclo[2.2.2]oct-l-ene 60 and (Z)-bicyclo[3.2.1]oct-l-ene... 

Shielding and Stabilization. Inclusion compounds may be used as sources and reservoirs of unstable species. The inner phases of inclusion compounds uniquely constrain guest movements, provide a medium for reactions, and shelter molecules that self-destmct in the bulk phase or transform and react under atmospheric conditions. Clathrate hosts have been shown to stabiLhe molecules in unusual conformations that can only be obtained in the host lattice (138) and to stabiLhe free radicals (139) and other reactive species (1) similar to the use of matrix isolation techniques. Inclusion compounds do, however, have the great advantage that they can be used over a relatively wide temperature range. Cyclobutadiene, pursued for over a century has been generated photochemicaHy inside a carcerand container (see (17) Fig. 5) where it is protected from dimerization and from reactants by its surrounding shell (140). 

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