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Rearrangements of Spirocyclobutane‐Substituted 2‐Norbornyl Cations
Author(s) -
Kirmse Wolfgang,
Landscheidt Heinz,
Siegfried Rainer
Publication year - 1998
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/(sici)1099-0690(199802)1998:2<213::aid-ejoc213>3.0.co;2-u
Subject(s) - chemistry , cyclobutane , cyclopropane , 2 norbornyl cation , bicyclic molecule , heptane , dichlorocarbene , ring (chemistry) , stereochemistry , medicinal chemistry , solvolysis , cyclopentadiene , photochemistry , organic chemistry , hydrolysis , catalysis
2‐Norbornyl cations with spiroannellated cyclobutane rings were generated for comparison with the previously studied cyclopropane analogues. Starting with the Diels‐Alder reaction of cyclopentadiene with methylenecyclobutane, spiro‐ [bicyclo[2.2.1]heptane‐2,1′‐cyclobutan]‐6‐one ( 11 ) was prepared. The tosylhydrazone 12 of 11 was photolyzed in NaOD/D 2 O to give the analogous alcohol 13 with a ca. 1:1 distribution of deuterium. Ring expansion was not observed, in contrast to the cyclopropane analogue. − The tosylhydrazone 22 of spiro[bicyclo[2.2.1]heptane‐2,1′‐cyclobutan]‐3‐one ( 21 ) and the related tosylates ( 28 , 32 ) rearranged, in part, to afford derivatives of spiro[bicyclo[2.2.1]heptane‐7,1′‐cyclobutane] ( 29 , 33 , 34 ). In both series, ring expansion of the spiroannellated cyclobutane, by exo ‐3,2‐C shift, was the major reaction, giving rise to a uniquely endo ‐selective tertiary cation ( 36 ). Analogously positioned cyclopropane rings remain intact, due to stabilizing interactions with the neighboring positive charge which are lacking in the cyclobutane systems. − In CDCl 3 solution, the tosylate 32 produced mixtures of isomeric tosylates by way of ion pair recombination. We observed that exo → exo shifts of the counterion proceed with little scrambling of 18 O whereas complete equilibration of the tosylate oxygens is attained in exo → endo shifts.