Participation of Non‐Conjugated Double Bonds in Diels‐Alder Reactions. A kinetic study of the addition of tropone to norbornens

Abstract

AbstractA kinetic study of Diels‐Alder additions between norbornene derivatives acting as dienophiles and the dienes tropone, perchlorocyclopentadiene and 9,10‐dimethylanthracene is presented. The results suggest that tropone thereby acts as an electron acceptor, classifying these reactions then as Diels‐Alder additions with ‘inverse electron demand’.The role of non‐reacting double bonds was investigated using 7‐alkylidenorbornene derivatives as dienophiles. These show comparable reactivity in ‘normal’ but enhanced reactivity in ‘inverse electron demand’ Diels‐Alder additions. This outcome is interpreted in terms of frontier orbital interactions between the reactants using photoelectron spectroscopical results as a basis for the qualitative perturbation treatment. It is suggested that the enhanced reactivity in the case of the 7‐alkylidene derivatives does not necessitate the consideration of a direct (‘through‐space’) participation of the non‐reacting double bond.