Thermal concerted reactions Cope rearrangement

Although thermal [2 + 2] cycloadditions are forbidden as concerted reactions by the orbital symmetry conservation rules the same structural features which promote intermolecular cy-cioadditions will also promote intramolecular reactions. In addition, the proximity between two alkene moieties dictated by the tether length and rigidity would make these processes entropically favorable. A few reports have documented thermal intramolecular cycloadditions to cyclopropenes and activated alkenes. The thermal Cope rearrangement of allylcyclopropenes apparently proceeds by a two-step mechanism in which intramolecular [2 + 2] adducts have been observed.72-73... 

The oxy-Cope rearrangement can be thermally induced (equation 223, path a) but this process competes with an other well-established, concerted pericyclic reaction, i.e. the /1-hydroxyolefin retro-ene cleavage (path h)-- -. However, it was found that the oxy-Cope rearrangement can be accelerated under base-catalysis conditions (e.g. in the presence of potassium alkoxides) by a factor of I O - (the so-called anionic oxy-Cope rearrangement , path This base-induced acceleration is attributable to a dramatic decrease in the... 

A number of interesting and useful organic reactions involve isomerizations of substances having one or more carbon-carbon double bonds. This chapter deals with the kinetics of reactions of alkenes, cycloalkenes and substituted alkenes which involve migration of carbon-carbon double bonds, with or without structural alteration of the carbon skeleton of the starting materials. These reactions include prototropic and anionotropic rearrangements, several concerted unimolecular isomerizations such as the Cope and Claisen rearrangements, and a number of non-concerted thermal isomerization reactions. 

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