Pericyclic assistance for SN-1 solvolysis
April 3rd, 2009
Click on diagram to see model.
A Disrotatory 4n+2 electron anti-aromatic Möbius transition state for a thermal electrocyclic reaction.
April 2nd, 2009Mauksch and Tsogoeva have recently published an article illustrating how a thermal electrocyclic reaction can proceed with distoratory ring closure, whilst simultaneously also exhibiting 4n electron Möbius-aromatic character[1]. Why is this remarkable? Because the simple Woodward-Hoffmann rules state that a disrotatory thermal electrocyclic reaction should proceed via a Hückel-aromatic 4n+2 electron transition state. Famously, Woodward and Hoffmann stated there were no exceptions to this rule. Yet here we apparently have one! So what is the more fundamental? The disrotatory character, or the 4n/Möbius character in the example above? Mauksch and Tsogoeva are in no doubt; it is the former that gives, and the latter is correct.
References
- M. Mauksch, and S. Tsogoeva, "A Preferred Disrotatory 4<i>n</i> Electron Möbius Aromatic Transition State for a Thermal Electrocyclic Reaction", Angewandte Chemie International Edition, vol. 48, pp. 2959-2963, 2009. https://doi.org/10.1002/anie.200806009
