Pyramidalization alkene distortion

Bicyclo[3.3.0]oct-l(5)-ene 178 (Scheme 4.55) is a stable compound with a flattened alkene fragment and exhibits a regular pattern of reactivity. Computational studies revealed, however, that installation of a short 3,7-bridge should lead to noticeable pyramidalization of the double bond. Compounds like 179-181 were synthesized to check this prediction. Tricyclic hydrocarbon 179, with the smallest possible bridge, was generated as a transient species from diiodide 182. The formation of 179 is implicated by the isolation of its cyclodimer 183 (or respective Diels-Alder adduct if the reaction is carried out in the presence of a 1,3-diene). The next member of this series, 180, is more stable. In fact, the formation of 180 was ascertained not only from the structure of the final products (as was done for 179), but also by its matrix isolation and analysis of spectral data. The selenium derivative 181 was found to be stable at ambient temperature in the absence of oxygen. X-ray data confirmed a noticeable pyramidalization of the double bond in 181 but the distortion was different [Pg.372]

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