Importance of steric factors in face-selective cycloadditions: 1,6-annulated cyclohexa-1,3-dienes

Diastereotopically nonequivalent π-facial 1,6-annulated-1,3-cyclohexadienes have been explored as probe molecules to assess the face-selectivities in cycloadditions. Steric factors have been found to be important in controlling the face-selectivities with these dienes. Studies with the hitherto unexplored diene 5 were also consistent with the order C-H > C-C for hyperconjugative stabilization of the transition state.