| Abstract
| - A comprehensive theoretical and experimental investigation of dehydro Diels−Alder reactionsexamining the evolution of the cyclic allene intermediates under conditions for intramolecular andionic and radical intermolecular cycloaromatization processes is reported. Theoretical calculationsshowed that the most favored intramolecular path for cycloaromatization of 1,2,4-cyclohexatriene4 and its benzoannulated derivative 14, strained cyclic allenes, consists of a pair of successive [1,2]H shifts rather than a [1,5] shift. Cycloaromatization of cyclic allenes may follow both inter- andintramolecular pathways, depending on the experimental conditions (use of protic or aproticsolvents). For synthetic purposes, the best procedure is to use a protic solvent to promote the ionicintermolecular route, the fastest and highest yielding. When the reaction is carried out in CCl4,intermolecular radical addition of chlorine to the cyclic allene competes with intramoleculararomatization paths. Theoretical calculations predict a low barrier for the reaction of cyclic alleneswith carbon tetrachloride, and that the cyclic allenes act as nucleophiles in this reaction.
|
