UNUSUAL FACIAL SELECTIVITY IN THE CYCLOADDITION OF SINGLET OXYGEN TO A SIMPLE CYCLIC DIENE

Syntheses of 5-isopropyl-1,3-cyclohexadiene and syn-5-isopropyl-2,3-di oxabicyclo[2.2.2]octane, by routes that would allow completely diaster eoselective introduction of deuterium labels, are described. The react ion of the isopropyl cyclohexadiene with singlet oxygen is shown to gi ve an endoperoxide that is derived by preferential attack on the more sterically hindered face of the diene, A possible mechanistic explanat ion of this result is that the attack from the less hindered face lead s to ''ene'' reaction rather than endoperoxide formation, However, thi s mechanism would require that the ''ene'' reaction and cycloaddition proceed via a common intermediate-presumably a perepoxide.