Angewandte Chemie International Edition
© WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Cover Picture: Breaking Down Barriers: The Liaison Between Sigmatropic Shifts, Electrocyclic Reactions, and Three-Center Cations (Angew. Chem. Int. Ed. 47/2003)
Orbital-symmetry control was initially explored almost 40 years ago. However, new principles can still be discovered: There is a striking congruence in the geometries of the transition states (not reactants and products) of electrocyclic reactions and sigmatropic shifts related by a proton. A link between these reactions and three-center hydride transfers in a cation is forged, and the idea of a transition-state proton affinity is reintroduced by R. Hoffmann and D. J. Tantillo in their Communication on page 5877 ff.