The stereochemistry of [1,7]-sigmatropic migrations of hydrogen atoms in hydrocarbons is known to be antarafacial. However, qualitative theories suggest that a pseudopericyclic 1,7-hydrogen migration would be allowed via a planar pathway. A computational survey of several 5-hydroxy-2,4-diene systems suggested thatbicyclo[3.3.0]octa-1-ene-2,8-dicarbaldehyde (1) had a suitable geometry to permit an in-plane arrangement of the 8 central atoms at the transition state. The optimized transition state geometry and activation energy for 1 were calculated at B3LYP/6 31G(d,p) and MP2/6-31G(d, p) levels of theory respectively. The barrier for hydrogen transfer was calculated to be 4.3 Kcal/mol.  To confirm this experimentally, 1 is currently being synthesized with the following scheme.   Observing the degenerate hydrogen migration in 1 would experimentally probe our prediction that the [1,7]-sigmatropic rearrangement can also take place through a pseudopericyclic planar transition state in contrast to the well known non-planar transition states of pericyclic reactions.

Search for the pseudopericyclic nature of [1,7]-sigmatropic rearrangements

242nd National Meeting (2011)

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