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Rearrangements of 1‐ and 2‐Cyano‐2‐norbornyl Cations
Author(s) -
Geier Holger,
Kautz Cornelia Brigitte,
Kirmse Wolfgang,
Landscheidt Heinz,
Schimpf Iris,
Siegfried Rainer
Publication year - 1993
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.19931260326
Subject(s) - 2 norbornyl cation , chemistry , carbocation , nucleophile , solvolysis , medicinal chemistry , substituent , ring (chemistry) , cyclopropane , stereochemistry , lone pair , computational chemistry , organic chemistry , molecule , catalysis , hydrolysis
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 tricyclo[2.2.1.0 2,6 ]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‐C 2 F 5 . Ring expansion of a spiroannelated cyclopropane, involving a 6,2 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.