Stabilization of an adjacent carbocation centre by cycloalkyl groups. The uniqueness of cyclopropyl

Sørensen, Thomas Sangild; Miller, IJ; Ranganayakulu, K.

doi:10.1071/ch9730311

Cited by 4 publications

(4 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The triplet excited state of a-pinene (€9, generated by triplet energy transfer using acetophenone as a photosensitizer (triplet energy transfer), gives cis-and trans-ocimene (28) as the major rearrangement products; limonene (13) was a minor product (reaction [7]) (25a). Limonene (13) is also a minor product Reactions [2] and [3] are regioselective; cleavage of the Reaction 171 cyclobutane ring (step 3a) affords a distonic radical cation, which reacts as a radical at the allylic moiety and as a carbocation at the tertiary alkyl moiety (step 3b).…”

Section: Discussionmentioning

confidence: 99%

“…In the context of the present study, the reactivity of the intermediate carbocation and radical, formed as a result of electrophilic or radical addition to a -and P-pinene (8 and 9), has been determined (5,6) and, in fact, could now be predicted. The cyclobutylcarbinyl cation and radical have been studied; both undergo rapid cyclobutane ring cleavage (7,8). The reactivity of the radical cations of a -and P-pinene (8" and 9") is less well understood (9).…”

Section: Introductionmentioning

confidence: 99%

“…The proposed mechanism is summarized in scheme 1 (4). 1,4-dicyanobenzene (1) and biphenyl (3) yields the photo-NOCAS adducts [4][5][6][7] Step 3 0…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

The photochemical nucleophile–olefin combination, aromatic substitution (photo-NOCAS) reaction. Part 5: methanol–monoterpenes (α- and β-pinene, tricyclene, and nopol), 1,4-dicyanobenzene

Arnold¹,

Du²

1994

Can. J. Chem.

View full text Add to dashboard Cite

. Can. J. Chem. 72,403 (1994).The reactivity of the radical cations of a-and P-pinene (8 and 9), tricyclene (la), and nopol (23) has been studied. The radical ions were generated, in acetonitrile-methanol (3:1), by single electron transfer (set) to the singlet excited state of 1,4-dicyanobenzene (1). Biphenyl (3) was used as a codonor. The cyclobutane rings of the initially formed radical cations of a-and P-pinene (8' ' and 9") cleave to distonic radical cations that react as tertiary alkyl cations and allylic radicals. The results of a b initio molecular orbital calculations (STO-3G) are consistent with the observation that the positive charge is largely associated with the tertiary alkyl moiety while the spin density is largely distributed over the allylic radical. There was no evidence, experimental or theoretical, indicative of a bonding interaction between the cationic and allylic moieties of these distonic radical cations. The cyclobutane ring cleavage is irreversible. The radical cation of tricyclene (18) also gives 1 : 1: 1 (nucleophile:cyclopropy1:aromatic) adducts. The regio-and stereochemistry of the adducts, and the nucleophile selectivity, are all indicative of nucleophile-assisted cleavage of the radical cation (18"). The radical cation of nopol (23") also cleaves to the distonic radical cation. The cyclobutane ring cleavage must be rapid; intramolecular 1,5-endo cyclization of the hydroxyl group cannot compete. DONALD R. ARNOLD et XINYAO Du. Can. J. Chem. 72,403 (1994).On a CtudiC la rCactivitt des cations radicalaires des a-et P-pinbnes (8 et 9), du tricyclbne (18) et du nopol (23). On a gtntrts les ions radicalaires dans un mtlange acttonitrile-mtthanol(3 : 1) par un transfert d'un seul tlectron (set) 2i l'ttat excitt singulet du 1,4-dicyanobenzbne (1). On a utilist le biphtnyle (3) comme codonneur. Les noyaux cyclobutane des cations radicalaires qui se foment initialement B partir des a-et P-pinbnes (8'' et 9") se clivent en cations radicalaires distoniques qui rtagissent comme cations alkyles tertiaires et radicaux allyliques. Les rtsultats de calculs d'orbitales molCculaires a b initio (STO-3G) sont en accord avec l'observation que la charge positive est associte largement avec la portion alkyle tertiaire alors que la densitt de spin est largement distribuke sur le radical allylique. 11 n'y a pas d'indications, soit exptrimentale ou thtorique, pour suggtrer l'existence d'une interaction de liaison entre les portions cationiques et allyliques de ces cations radicalaires distoniques. Le clivage du noyau cyclobutane est irrtversible. Le cation radicalaire du tricyclbne (18) donne aussi des adduits 1 : 1 : 1 (nuclCophile : cyclopropyle : aromatique). La rtgio-et la sttrtochimie des adduits et la stlectivitt du nucltophile indiquent toutes que le clivage du cation radicalaire (18") est assist6 par le nucltophile. Le cation radicalaire du nopol (23") se clive aussi en cation radicalaire distonique. Le clivage du noyau cyclobutane doit Etre rapide car la cyclisation intramoltculaire 1,5-endo du grou...

show abstract

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

The photochemical nucleophile–olefin combination, aromatic substitution (photo-NOCAS) reaction. Part 5: methanol–monoterpenes (α- and β-pinene, tricyclene, and nopol), 1,4-dicyanobenzene

Arnold¹,

Du²

1994

Can. J. Chem.

View full text Add to dashboard Cite

show abstract

“…Thus, the solvolysis rates of 1 are but slightly enhanced over those of 2 [3] [4] [5] . The effect of R ϭ cyclobutyl on the equilibrium 3 o 4 does not differ significantly from that of R ϭ cyclopentyl [6] . On the other hand, the technique of increasing the electron demand (by variation of Ar) was able to detect a small amount of conjugative stabilization in the cyclobutylcarbinyl system 6…”

mentioning

confidence: 49%

Rearrangements of Spirocyclobutane-Substituted 2-Norbornyl Cations

Kirmse¹,

Landscheidt²,

Siegfried³

1998

Eur. J. Org. Chem.

View full text Add to dashboard Cite

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.

show abstract

Formation, characterization, and some reactions of spiro[cyclobutane-1,1′-1′H-azulenium] ion

et al. 1999

View full text Add to dashboard Cite

Stabilization of an adjacent carbocation centre by cycloalkyl groups. The uniqueness of cyclopropyl

Abstract: In the ability of cycloalkyl groups to stabilize an adjacent carbocation centre, a cyclopropyl group is uniquely effective. Cyclobutyl, cyclopentyl, and cyclohexyl groups are about as effective as paraffinic substituents.

Cited by 4 publications

References 0 publications

The photochemical nucleophile–olefin combination, aromatic substitution (photo-NOCAS) reaction. Part 5: methanol–monoterpenes (α- and β-pinene, tricyclene, and nopol), 1,4-dicyanobenzene

The photochemical nucleophile–olefin combination, aromatic substitution (photo-NOCAS) reaction. Part 5: methanol–monoterpenes (α- and β-pinene, tricyclene, and nopol), 1,4-dicyanobenzene

Rearrangements of Spirocyclobutane-Substituted 2-Norbornyl Cations

Formation, characterization, and some reactions of spiro[cyclobutane-1,1′-1′H-azulenium] ion

Contact Info

Product

Resources

About