F. Haeffner et al., Mechanistic variations and rate effects of alkoxy and thioalkoxy substituents on anionic oxy-cope rearrangements, J AM CHEM S, 121(50), 1999, pp. 11880-11884
The effects of thiomethoxy and methoxy substituents on the rates and the me
chanisms of anionic oxy-Cope rearrangements were investigated with density
functional theory (B3LYP/6-31+G*), Thiomethoxy substituents at positions C4
or C6 of 3-oxido-1,5-hexadienes cause acceleration and promote heterolytic
cleavage rather than concerted rearrangement, and the Cope product is form
ed via a stepwise pathway. The corresponding methoxy substituents impede he
terolytic cleavage and slow the concerted rearrangement.