Additions of Singlet Oxygen to Alkoxy-Substituted Butadienes. An Unexpectedly Large s-Cis/s-Trans Ratio in an (E, Z)-Diene or a Kinetic Anomeric Effect?

Article abstract of DOI:10.1021/jo00359a012

A study of the rates of reaction of (E,E)-, (E,Z)-, and (Z,Z)-1,4-di-tert-butoxy-1,3-butadiene with singlet oxygen demonstrated that rapid physical quenching and /or dioxetane formation do not competitively inhibit endoperoxide formation in the (E,E)-diene.Instead we suggest that an abnormally large s-cis/s-trans equilibrium constant for the (E,Z)-diene is the reason for the larger observed rate constant (k_obsd = K_eqk) for endoperoxide formation in the (E,Z)-diene in comparison to its E,E isomer.The possibility that anomeric interactions in the transition state for the reaction of the (E,Z)-diene contribute to the large rate of endoperoxide formation cannot be unequivocally ruled out.