J. Am. Chem. Soc.

1967

DOI: 10.1021/ja00987a034

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Stable carbonium ions. XXXIV. 1-Methylcyclopentyl cation

George A. Oláh¹,

J. Martin Bollinger²,

Chris A. Cupas³

et al.

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Cited by 77 publications

(50 citation statements)

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“…Involvement of corner-protonated cycloCyclopentene (I), cyclohexene (2), cyclododecene (5), propanes (Scheme 1) can lead to ring-contracted and rearrangement products and consecutive protonation-deprotonations can produce all products. Ring contraction of the cyclohexyl, cycloheptyl, and cyclooctyl cations to tertiary species is exactly what is observed for the species in strongly acidic media (10,11). Rings smaller than C5 were not observed, presumably 1-methylcyclopentene ( l a ) , 1-methylcyclohexene (2a), I-ethylcyclohexene (2d) (containing -10% other products), and a variety of other alkylated C-5 and C-6 cycloalkenes can be perlabellkd.…”

Section: Resultssupporting

confidence: 63%

Protium–deuterium exchange of cyclic and acyclic alkenes in dilute acid medium at elevated temperatures

1985

Can. J. Chem.

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, 530 (1985). A modification of the high temperature -dilute acid (HTDA) method for deuterium labelling of aromatic compounds has been applied to the H-D exchange of a number of cyclic and acyclic alkenes. Cyclopentene, cyclohexene, cyclododecene, and tetramethylethylene have been completely exchanged in excellent yield. 1-Methylcyclopentene and I-methylcyclohexene have also been perdeuterated and cycloheptene and cyclooctene partially labelled but require spinning band distillation or preparative glpc for separation from rearrangement products. A variety of C5-C8 acyclic alkenes have also been treated under HTDA conditions. NICK HENRY WERSTIUK et GEORGE TIMMINS. Can. J. Chem. 63, 530 (1985).On a applique une modification de la methode a haute ternpkrature en milieu acide diluk, dkveloppke pour marquer des composCs aromatiques avec du deuterium, a I'Cchange H-D d'un certain nombre d'alcknes cycliques et acycliques. Le cyclopentkne, le cyclohexkne, le cyclodeckne et le tCtramkthylkthylkne s'kchangent tous completement avec d'excellents rendements. Le methyl-l cyclopentkne et le methyl-I cyclohexkne sont aussi perdeutkrks alors que le cycloheptbne et le cyclooctkne ne sont que partiellement marquis; toutefois, dans ces cas, il faut faire appel soit a des distillations a l'aide de bande tournante soit a la cpg preparative pour sCparer les produits desires des produits de transposition. On a aussi trait6 de la m&me manikre un certain nombre d'alcknes acycliques comptant de 5 a 8 C.[Traduit par le journal] IntroductionIn an attempt to develop high temperature -dilute acid exchange (HTDA) (1 -6) into a general technique for preparing deuterated (or tritiated) organic compounds we have extended our studies from aromatic compounds to alkenes.Early attempts to label alkenes using heterogeneous platinum catalysis resulted in extensive (up to 100%) disproportionation with only low levels of deuterium incorporation (7). Also, radiation induced methods such as the Wilzbach technique for tritium labelling lead to addition products in preference to substitution (8). In attempting to avoid some of these problems, Calf et al. (9) carried out exchange reactions in dilute DCI/D20 at temperatures of 110-130°C. They were successful in achieving incorporations of up to 35 at.% D.In this paper we describe deuterium labelling of alkenes using a modification of the HTDA method (1 -5). Exchange reactions were carried out with dilute DCI/DIO in sealed Pyrex tubes at elevated temperatures (165-280°C) in the presence and absence of decalin as a cosolvent and with or without mixing by shaking. In general, reactions were run to near equilibration (92-95 at.% D) with the deuterium pool in one cycle. For example, cyclopentene was labelled with 7.38 D atoms of deuterium per molecule (92.2 at.%; entry 5, Table I) in one cycle, whereas, Calf et al. (9) reported the incorporation of only 2.39 D atoms at 130°C.

“…Involvement of corner-protonated cycloCyclopentene (I), cyclohexene (2), cyclododecene (5), propanes (Scheme 1) can lead to ring-contracted and rearrangement products and consecutive protonation-deprotonations can produce all products. Ring contraction of the cyclohexyl, cycloheptyl, and cyclooctyl cations to tertiary species is exactly what is observed for the species in strongly acidic media (10,11). Rings smaller than C5 were not observed, presumably 1-methylcyclopentene ( l a ) , 1-methylcyclohexene (2a), I-ethylcyclohexene (2d) (containing -10% other products), and a variety of other alkylated C-5 and C-6 cycloalkenes can be perlabellkd.…”

Section: Resultssupporting

confidence: 63%

Protium–deuterium exchange of cyclic and acyclic alkenes in dilute acid medium at elevated temperatures

1985

Can. J. Chem.

View full text Add to dashboard Cite

, 530 (1985). A modification of the high temperature -dilute acid (HTDA) method for deuterium labelling of aromatic compounds has been applied to the H-D exchange of a number of cyclic and acyclic alkenes. Cyclopentene, cyclohexene, cyclododecene, and tetramethylethylene have been completely exchanged in excellent yield. 1-Methylcyclopentene and I-methylcyclohexene have also been perdeuterated and cycloheptene and cyclooctene partially labelled but require spinning band distillation or preparative glpc for separation from rearrangement products. A variety of C5-C8 acyclic alkenes have also been treated under HTDA conditions. NICK HENRY WERSTIUK et GEORGE TIMMINS. Can. J. Chem. 63, 530 (1985).On a applique une modification de la methode a haute ternpkrature en milieu acide diluk, dkveloppke pour marquer des composCs aromatiques avec du deuterium, a I'Cchange H-D d'un certain nombre d'alcknes cycliques et acycliques. Le cyclopentkne, le cyclohexkne, le cyclodeckne et le tCtramkthylkthylkne s'kchangent tous completement avec d'excellents rendements. Le methyl-l cyclopentkne et le methyl-I cyclohexkne sont aussi perdeutkrks alors que le cycloheptbne et le cyclooctkne ne sont que partiellement marquis; toutefois, dans ces cas, il faut faire appel soit a des distillations a l'aide de bande tournante soit a la cpg preparative pour sCparer les produits desires des produits de transposition. On a aussi trait6 de la m&me manikre un certain nombre d'alcknes acycliques comptant de 5 a 8 C.[Traduit par le journal] IntroductionIn an attempt to develop high temperature -dilute acid exchange (HTDA) (1 -6) into a general technique for preparing deuterated (or tritiated) organic compounds we have extended our studies from aromatic compounds to alkenes.Early attempts to label alkenes using heterogeneous platinum catalysis resulted in extensive (up to 100%) disproportionation with only low levels of deuterium incorporation (7). Also, radiation induced methods such as the Wilzbach technique for tritium labelling lead to addition products in preference to substitution (8). In attempting to avoid some of these problems, Calf et al. (9) carried out exchange reactions in dilute DCI/D20 at temperatures of 110-130°C. They were successful in achieving incorporations of up to 35 at.% D.In this paper we describe deuterium labelling of alkenes using a modification of the HTDA method (1 -5). Exchange reactions were carried out with dilute DCI/DIO in sealed Pyrex tubes at elevated temperatures (165-280°C) in the presence and absence of decalin as a cosolvent and with or without mixing by shaking. In general, reactions were run to near equilibration (92-95 at.% D) with the deuterium pool in one cycle. For example, cyclopentene was labelled with 7.38 D atoms of deuterium per molecule (92.2 at.%; entry 5, Table I) in one cycle, whereas, Calf et al. (9) reported the incorporation of only 2.39 D atoms at 130°C.

“…According to Olah [4], the formation of hydrocarbon ions can be obtained in the gas phase through the proton transfer between a cation precursor and its neutral species [5]. In other words, under normal conditions the proton transfer occurs by way of a generalized electrophilic reaction, in which it has been established that the hydrogen interacts with the saturated bond of the hydrocarbon [6]. However, we should assume that the interaction between the hydrocarbon ion and its neutral component may also be the result of electrostatic interactions and charge transfer.…”

Section: Introductionmentioning

confidence: 99%

Uncommon hydrogen bonds between a non-classical ethyl cation and π hydrocarbons: a preliminary study

¹

,

²

,

³

et al. 2009

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This study undertakes a theoretical investigation into uncommon hydrogen bonds between the ethyl cation (C 2 H 5 ? ) and p hydrocarbons. Firstly, it considers the hyperconjugation effect of the ethyl cation, in which the non-localized hydrogen (H ?

“…18 In the case of cation 1, we may expect that, in the absence of trapping nucleophiles, hydride shifts will lead rapidly to the tetrahydro-2H-pyran-2-ylium carbocation 3, eqn (2). Carbocation 3 is 112 kJ mol -1 more stable than 1 at the B3LYP/6-311G(d) level.…”

Section: Resultsmentioning

confidence: 99%

Searching for intermediates in Prins cyclisations: the 2-oxa-5-adamantyl carbocation

¹

,

²

,

³

et al. 2010

Org. Biomol. Chem.

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The 2-oxa-5-adamantyl carbocation 4 is shown to be a viable intermediate in several S N 1 substitution reactions. However, attempts to observe the formation of 4 from various precursors by NMR methods (which succeed for the 1-adamantyl cation 5) failed, suggesting that 4 does not survive on longer timescales. DFT calculations suggest that the retro-Prins process (b-cleavage, Grob fragmentation) to give enantiomeric (1R,5R)-and (1S,5S)-7-methylene-2-oxoniabicyclo[3.3.1]non-2-ene cations 22 is the only realistic unimolecular escape route for 4. With the 6-31G(d) basis set, B3LYP calculation predicts that 4 is only 11 kJ mol -1 more stable than 22, and the barrier separating 4 and 22 is calculated to be only 15 kJ mol -1 , so rapid equilibration of these species is likely on the laboratory time scale. The implications of this study for the mechanism of the Prins cyclisation are discussed.

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