Cope rearrangement fluxional molecule

The successful quest for bullvalene led to the investigation of a number of similar molecules. The fluxional behaviour of dihydrobullvalene (295) was apparent from its H-NMR spectrum at room temperature . This showed two type A protons which remain vinylic after Cope rearrangement, d 5.63 for type B S 3.68. The type C protons absorb at ca. d 1.87 and overlap with the methylene protons. The observed coupling... 

Electrocyclization in Cancer Therapeutics 910 Fluxional Molecules 913 A Remarkable Substituent Effect The Oxy-Cope Rearrangement 921... 

In his efforts to lower the activation energy for the Cope rearrangement, Doerlng designed the first fluxional molecule homotropUldine (79). Barbaralane (80), bullvalene (81), and semibullvalene (68) are each related to 79 as homotropilidines locked in the appropriate Cope conformation (79b). As a conse-... 

There are other types of proton shift tautomers, such as phenol/dienone, nitroso/oxime and imine/enamine, but these are less often encountered. There are also valence tautomers that exhibit fluxional structures, which undergo rapid sigmatropic rearrangements. Molecules that exhibit this type of isomerism are very interesting, but are not often encountered in undergraduate courses. An example of a valence tautomer is illustrated by the Cope system. 

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