Orbital unsymmetrization of olefins arising from non-equivalent orbital interactions. σ-π Coupling in bicyclo[2.2.2]octenes

Article abstract of DOI:10.1248/cpb.44.296

We characterized experimentally the substituent effect of a 5-exo substituent on the π facial selectivities of bicyclo[2.2.2]octenes toward electrophilic oxidative reactions such as epoxidation and dihydroxylation, and we discuss the underlying orbital interactions of vicinal σ orbitals and the olefinic π orbital involved in bicyclo[2.2.2]octenes, and commonly in methylenenorbornanes. Of significance is the out-of-phase motif of these σ- π couplings. Electron-withdrawing substituents such as cyano and carboxylic acid groups unequalize the relevant σ-π coupling, leading to the observed syn-facial preference. Alkyl substituents exhibit an electron-donative perturbing effect, depending on the bicyclic ring system.

Full text of DOI:10.1248/cpb.44.296

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