Novel aromatic systems. II. Cyclobutenyl cations and the question of their homoaromaticity. Preparation and study of the homocyclopropenium ion, the simplest homoaromatic system

Oláh, George A.; Staral, John S.; Spear, Robert J.; Liang, Gao

doi:10.1021/ja00852a029

Cited by 99 publications

(38 citation statements)

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“…increase of the reaction rate of compounds VII-IX with nucleophiles, VII < VIII < IX [7]). The possibility for homoaromatic stabilization was considered for polymethylsubstituted benzocyclobutenyl cations [8], cyclobutenyl cation [9] and its perfluorinated analog [10], and 2-methoxytetrafluorocyclobutenyl cation [11].…”

Section: Xiii-xvmentioning

confidence: 99%

Generation of perfluoro- and 1-chloropolyfluorobenzocycloalken-1-yl cations and their relative stability

et al. 2012

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Treatment of perfluorinated benzocyclobutene, indan, and tetralin with SbF 5 -SO 2 Cl 2 , as well as of their 1,1-dichloro analogs with SbF 5 , gave 1-chloropolyfluorobenzocycloalken-1-yl cations whose structure was studied by 19 F and 13 C NMR and confirmed by their transformations into perfluorinated ketones upon hydrolysis. Dissolution of perfluorinated benzocyclobutene, indan, and tetralin in excess SbF 5 generated perfluorobenzocycloalken-1-yl cations in equilibrium with their precursors. The relative stability of perfluoroand 1-chloropolyfluorobenzocycloalken-1-yl cations decreases as the size of the alicyclic fragment increases.Polyfluorinated benzocycloalkenes such as benzocyclobutene, indan, and tetralin in the presence of antimony(V) fluoride are capable of acting as electrophilic reagents, e.g., in the alkylation of pentafluorobenzene [1] and polyfluoroolefins [2]. The formation of perfluorobenzocyclobutenyl cation I was confirmed by 19 F NMR data [2]. Perfluoroindan-1-yl (II) and perfluoro(1,2,3,4-tetrahydronaphthalen-1-yl) (III) cations were not detected by 19 F NMR spectroscopy [2]. On the other hand, 1-chlorooctafluoroindan-1-yl cation was generated, and its structure was confirmed by 19 F and 13 C NMR spectra [3]. With a view to compare the properties of polyfluorinated benzocycloalkenyl cations having four-, five-, and six-membered alicyclic fragments, in the present work we generated under comparable conditions 1-chlorohexafluoro-1,2-dihydrocyclobutabenzene-1-yl (IV), 1-chlorooctafluoroindan-1-yl (V), and 1-chlorodecafluoro-1,2,3,4-tetrahydronaphthalen-1-yl (VI) cations and examined their structure by 19 F and 13 C NMR spectroscopy. In addition, the 13 C chemical shifts of cation I and 19 F chemical shifts of cations II and III were measured.Dissolution of perfluorinated benzocyclobutene (VII), indan (VIII), and tetralin (IX) in excess SbF 5 (20 mol per mole of the substrate) containing SO 2 ClF gave cations I-III as equilibrium mixtures with their precursors. In the first case, the equilibrium was displaced toward cation I, and in the second case, toward precursor VIII; cation III was detected in a very small amount (≤3%, 19 F NMR). This means that the relative stability of the above cations decreases in the series I > II > III. Signals of cationic species in the NMR spectra were poorly resolved, presumably as a result of exchange processes involving their precursors (Scheme 1).As shown in [3], dissolution of perfluoroindan (VIII) in SbF 5 with addition of SbCl 5 is accompanied by generation of chlorine-containing cation V. In the present work, instead of SbCl 5 as source of chloride ions, we used SO 2 Cl 2 which is known to react with SbF 5 to give SO 2 ClF. Dissolution of benzocycloalkenes VII-IX in SbF 5 -SO 2 Cl 2 generated chlorine-containing cations IV-VI, the conversion of VII and VIII being complete, whereas fluorotetralin IX remained almost unchanged. On the other hand, 1,1-dichlorohexafluoro-1,2-dihydrocyclobutabenzene (X) and analogous indan and tetralin derivatives XI and XII in SbF...

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Section: Xiii-xvmentioning

confidence: 99%

Generation of perfluoro- and 1-chloropolyfluorobenzocycloalken-1-yl cations and their relative stability

et al. 2012

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“…228 Deno 229 has reviewed the chemistry of these ions. Allylic cations particularly show great stability with generally insignificant 1,3-overlap, except in the case of cyclobutenyl cations 230 The formation of allyl cations from halocyclopropanes via ring opening of the unstable cyclopropyl cations also has been investigated 159 …”

Section: Alkenyl Cationsmentioning

confidence: 99%

“…The simplest 2p monohomoaromatic cation, the homocyclopropenyl cation (C 4 H 5 þ , cyclobutenyl cation, 578), along with its analogs, has been prepared and studied by Olah et al 230,1010 The experimental evidence for the existence of 1,3-overlap has been derived from 1 H and 13 C NMR data. Monohomoaromatic Cations.…”

Section: Homoaromatic Cationsmentioning

confidence: 99%

Carbocations in Superacid Systems

Oláh¹,

Prakash²,

Molnár³

et al. 2008

Superacid Chemistry

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“…Because of its importance, the phenomenon of homoaromaticity has been the subject of a wealth of experimental and theoretical studies aiming both at the evaluation of various manifestations of this phenomenon [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] and, also, to the design of new tools and procedures allowing estimating the extent of the effects responsible for its existence. An example can be, e.g., the early studies [10][11][12][13] in which qualitative molecular orbital (MO) diagrams and perturbational MO (PMO) theory were used to estimate the energetic impact of homoaromatic stabilization.…”

Section: Introductionmentioning

confidence: 99%

Multicenter Bond Indices As a New Means for the Quantitative Characterization of Homoaromaticity

2005

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This study reports the use of multicenter bond indices as a new tool for the quantitative characterization of homoaromaticity. The approach was applied to the series bicyclic systems whose homoaromaticity was recently discussed in terms of traditional aromaticity index, namely, NICS. In this study we found that the multicenter bond indices are indeed able to quantify the degree of homoaromaticity of the studied systems as reflected in the classification of these molecules into classes of homoaromatic, non-homoaromatic, and anti-homoaromatic systems suggested on the basis of NICS values.

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Novel aromatic systems. II. Cyclobutenyl cations and the question of their homoaromaticity. Preparation and study of the homocyclopropenium ion, the simplest homoaromatic system

Cited by 99 publications

References 1 publication

Generation of perfluoro- and 1-chloropolyfluorobenzocycloalken-1-yl cations and their relative stability

Generation of perfluoro- and 1-chloropolyfluorobenzocycloalken-1-yl cations and their relative stability

Carbocations in Superacid Systems

Multicenter Bond Indices As a New Means for the Quantitative Characterization of Homoaromaticity

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