148638-06-6Relevant articles and documents
Rearrangements of 1- and 2-Cyano-2-norbornyl Cations
Geier, Holger,Kautz, Cornelia Brigitte,Kirmse, Wolfgang,Landscheidt, Heinz,Schimpf, Iris,Siegfried, Rainer
, p. 739 - 746 (2007/10/02)
Sulfonates of exo-2-hydroxynorbornane-endo-2-carbonitrile (2c-e) were found to rearrange exothermally to give sulfonates of exo-2-hydroxynorbornane-1-carbonitrile (6c-e), solvolysis being a minor side reaction.In contrast, the analogous endo substrates (3c-e) afforded the rearranged alcohol 6a and tricyclo2,6>heptane-1-carbonitrile (4) as the major products.We have not been able to trap 2-cyano-2-norbornyl cations by external nucleophiles or by internal 6,2-shifts of hydrogen or carbon.On the other hand, there is good evidence for the generation of 1-cyano-2-norbornyl cations from both 3d, e and 6e.The degenerate 6,2-H shift in these species has been uncovered by means of labeled or optically active precursors.The 1-CN substituent clearly promotes the 6,2-H shift relative to the parent 2-norbornyl cation, but is inferior to 1-C2F5.Ring expansion of a spiroannelated cyclopropane, involving a 6,2-H shift of carbon, was also observed (25, 26 -> 27, 28).Our data strongly suggest that 2-cyano-2-norbornyl cations are less stable than 1-cyano-2-norbornyl cations.The reaction rates of 2c versus 6c do not reflect the stability of the incipient carbocations, owing to the large difference in ground state energy.Key Words: Carbocations, destabilized / Solvolysis / Wagner-Meerwein rearrangement / 6,2-H Shifts / Ring Expansion
