Stereochemical Evidence for the Formation of Intermediates in the Ene Reaction of Singlet Oxygen with Tetraalkyl-Substituted Alkenes

Article abstract of DOI:10.1021/jo00346a021

The tetrasubstituted alkenes syn- and anti-1-(4-tert-butylcyclohexylidene)-4-tert-butylcyclohexane (6 and 7, respectively), both of which have been shown to be conformationally fixed, undergo the ene reaction with singlet oxygen to afford the allylic hydroperoxides 8a and 9a, the stereochemistries of which have been assigned.The reactions are not stereospecific in the fashion anticipated for a concerted reaction of singlet oxygen with 6 and 7.Rather, the results are better explained by assuming the formation of an intermediate during photooxygenation; this intermediate must be long-lived relative to conformational changes.The distribution of allylic hydroperoxides from 6 and 7 is mildly temperature dependent; a possible explanation for this observation is given.The results of the photooxygenation of some other new tetrasubstituted conformationally fixed alkenes are also reported.