Syntheses and Dynamic Behavior of Chiral Heptalenes

Cycloaddition reactions of azulenes with dimethyl acetylenedicarboxylate afford an excellent access to a large variety of substituted dimethyl 1,2-heptalenedicarboxylates. These can be converted into various methylheptalenes, which proved to be remarkably stable. This allowed for the first time a separation of the bond shift isomers as well as an optical resolution of derivatives of this axial chiral 12π-electron system. Kinetic studies of bond shifting and ring inversion provide information on the transition states of these dynamic processes.