Access to spiro(bicyc1o [ 2.2.1 ] heptane3,l '-cycloprop-6-yl) derivatives was gained from the alkene spiro(bicyclo [ 2.2.1 ] hept-Cene-2,l '-cyclopropane via separation of positional isomers. Spiro(bicyc1o 12.2.1 ] -2,l'cycloprop-exo-6-yl) p-toluenesulphonate (10) and spiro(bicyc1o [2.2.1] heptane-2,l'-cycloprop-exod-yl) trifluoroacetate were found to solvolyse faster than the analogous exo-2-norbornyl esters, as predicted by theory. Ion-pair recombination, with the formation of tricyclo [4.2.1.@*'] non-3-yl p-toluenesulphonate, accounts for previous failures to assess the true reactivity of 10. An intervening bridged carbocation (3), labelled with deuterium, was shown to achieve equivalence of C-1 and C-6 prior to ring expansion. The rate of the formal Wagner-Meerwein rearrangement is estimated to be of the order of molecular vibrations, thus supporting the symmetrical bridged structure of 3. Methyl substitution at C-6 was found to direct nucleophilic attack exclusively to the tertiary carbon, and ring expansion preferentially to the secondary carbon. An equilibrating pair of 6(1)methylspiro(bicyc1o [ 2.2.1 ] heptane3,l' -cycloprop-6-yl carbocations is thought to explain these observations most reasonably.

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/D2O 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 CDCl3 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 18O whereas complete equilibration of the tosylate oxygens is attained in exo → endo shifts.

Rearrangements of 1-and 2-Cyano-2-norbornyl CationsSulfonates 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[2.2.1.02~6]heptane-l-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-CzFS. Ring expansion of a spiroannelated cyclopropane, involving a 6,2 shift of carbon, was also observed (25, 26 -+ 21, 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.Destabilisierte Carbokationen, die elektronenziehende Substituenten am positiv geladenen C-Atom oder in dessen Nachbarschaft tragen, finden in neuerer Zeit starkes Interesse"]. Cyan-und Perfluoralkyl-Gruppen erweisen sich als besonders wirksam. In das umlagerungsfreudige und intensiv untersuchte Norbornyl-System wurde CN bereits in l -S t e l l~n g [ *~~~ und 6-Stell~ng[~.~' eingefiihrt. uber das Verhalten von 2-Cyan-2-norbornyl-Edukten war bisher nichts bekannt; diese Lucke wird nun geschlossen. Ferner berichten wir iiber 2,6-H-Verschiebungen in CN-substituierten Norbornyl-Kationen und uber analoge Kohlenstoff-Verschiebungen von Spiro(norbornan-2,1'-cyclopropyl-6-yl)-Kationen. Umlagerung und Solvolyse von Sulfonsaureestern des 2-Hydroxy-bicyclo[ 2.2.11 heptan-2-carbonitrilsDie Umsetzung von Norbornan-2-on (1) mit Cyanwasserstoff ist in der L i t e r a t~r~~, '~ erwahnt, ohne dal3 die epimeren Cyanhydrine 2a, 3a getrennt und charakterisiert wurden. Wie wir fanden, erhalt man aus 1 mit NaCN/H2S04 vorwiegend die exo-Verbindung 2 a (thermodynamische Kontrolle; 2a: 3a = 87: 13). Trimethylsilylcyanid/Zn12n liefert fast ausschlieBlich den endo-Silylether 3 b (kinetische Kontrolle; 3b:2b = 96:4), aus dem 3a durch saure Hydrolyse zuganglich ist. Die Stereoisomeren lieBen sich durch HPLC trennen bzw. reinigen. Die Konfigurationszuordnung beruht -neben der Darstellungsweise -auf den 'H-NMRSpektren. Die Signale von 3-H,,, und 3-Hend, (J3x,3n = 13.5 Hz) sind durch die Kopplungen J3xp bzw. J3n,7a leicht zu unterscheiden. Das Signal von 3-H,,, ist in 2a durch die vicinale OH-Gruppe hochfeldverschoben (6 = 1.77), in 3a durch die vicinale CN-Gruppe tieffeldverschoben (6 = 2.25).Die Signale von 3-Hend, verhalten sich umgekehrt (2a: 6 = 1.90; 3a: 6 = 1.35). 6 IAus 2 a...

Rearrangements of 1-and 2-Cyano-2-norbornyl Cations.-2-Carbonitriles of type (I) undergo Wagner-Meerwein rearrangement in dioxane/H2O to yield 1-carbonitriles like (II) and (III). Attempts to trap norbornyl cation intermediates fail, but degenerate 6,2-H shift in the labeled nitriles (IV) and (VII) as well as in optically active nitriles is good evidence for their generation. In spiroannelated cyclopropane analogues (cf. (VIII)), a 6,2-C shift can also be observed. -(GEIER, H.; KAUTZ, C. B.; KIRMSE, W.; LANDSCHEIDT, H.; SCHIMPF, I.; SIEGFRIED, R.; Chem.