Remote inductive effects in the solvolysis of secondary and tertiary 2-norbornyl derivatives. Evidence for nonclassical stabilization of the 2-norbornyl cation

Lenoir, Dieter; Apeloig, Yitzhak; Arad, Dorit; Schleyer, Paul von Ragué

doi:10.1021/jo00238a033

Cited by 54 publications

(12 citation statements)

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“…This raises the intriguing possibility that by measuring accurate structures of series of such compounds, with R constant and varying leaving groups -OX, it may be possible to identify structural changes in R associated with the need to accommodate the developing positive charge. Nowhere would a positive result of this sort be more interesting than in the series of structures which give rise to the so-called 'non-classical' carbonium ions [for a useful recent summary and list of references see Lenoir, Apeloig, Arad &von Schleyer (1988)], so we have attempted to apply our 'variable oxygen probe' to several such systems. We report results with derivatives of bicyclo[2.2.1]heptan-2-ol, and the structure of the p-toluenesulfonate (2) of endo-borneol.…”

mentioning

confidence: 99%

Bond length and reactivity. Structure of 2-endo-bornyl p-toluenesulfonate

Jones¹,

Schmidt‐Bäse²,

Edwards³

et al. 1992

Acta Crystallogr C

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confidence: 99%

Bond length and reactivity. Structure of 2-endo-bornyl p-toluenesulfonate

Jones¹,

Schmidt‐Bäse²,

Edwards³

et al. 1992

Acta Crystallogr C

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“…[4,13] To confirm the structure of the stereoisomers of 17, we carried out an alternative synthesis (Scheme 5), starting from the known ene ketal (AE )-24. [14] After acidic hydrolysis of (AE )-24, the obtained ketone was submitted to the McMurry reduction. In this way, a new mixture of stereoisomers of 17 was obtained and characterized by 1 H and 13 C NMR spectroscopy.…”

Section: Resultsmentioning

confidence: 99%

“…The mixture was allowed to cool to room temperature and was poured onto ice water (10 g). The organic phase was separated and analyzed by GC-MS, and was shown to contain mainly compounds 14, 18, and (AE ) (1 n, 1.8 mL) was added to a cold (0 8C) solution of acetal (AE )-24 (298 mg, 1.79 mmol), prepared as described, [14] in THF (31 mL), and the mixture was allowed to warm to room temperature and was stirred at this temperature for 45 h. Saturated aqueous NaHCO 3 solution (15 mL) was added to give pH 8. The organic phase was separated and the aqueous phase was extracted with diethyl ether (3 50 mL).…”

Section: Methodsmentioning

confidence: 99%

Dehalogenation of 1,3‐Diiodotricyclo[3.3.0.0^3,7]octane: Generation of 1,3‐Dehydrotricyclo[3.3.0.0^3,7]octane, a 2,5‐Methano‐Bridged [2.2.1]Propellane

Ayats

Camps

Fernández

et al. 2007

Chemistry A European J

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Compounds isolated from the reaction of (+/-)-1,3-diiodotricyclo[3.3.0.0(3,7)]octane with molten sodium or tBuLi suggest the intermediate formation of (+/-)-1,3-dehydrotricyclo[3.3.0.0(3,7)]octane. Worthy of note is the formation of stereoisomeric bi(5-methylenebicyclo[2.2.1]hept-2-ylidene) derivatives, probably by coupling of two units of (+/-)-1,3-dehydrotricyclo[3.3.0.0(3,7)]octane of the same or different absolute configuration followed by fragmentation, processes that have been studied by theoretical calculations.

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“…However, as shown in 3 p , for C(7), namely -0.96 [Id], is practically the same as for the more remote C(4) and C(5). ") See the recent comprehensive literature review in [22].…”

Section: Discussion -The K(rel) Values Inmentioning

confidence: 99%

Norbornanes. Part 21. Bridging strain in norbornyl and oxanorbornyl cations

Flury

Grob

Wang

et al. 1988

Helvetica Chimica Acta

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(1 1. V. 88)Further evidence is presented that the 2-norbomyl cation is stabilized primarily by C(2)-C{6) bridging, and that C(2)-C(7) bridging leads to prohibitive strain. Thus, a comparison of the heats of hydrogenation of nortricyclene 17 and bicycl0[3.2.0.0~.~]heptane 18 indicates that the strain energy of the latter is ca. 21.5 kcal/mol higher than that of 17. Furthermore, 6-exo-2-oxabicyclo[2.2. ljheptyl sulfonates 8 ionize with strong O(2) participation to the bridged oxonium ion 12. In contrast, 2-endo-7-oxabicyclo[2.2.1]heptyl sulfonates 11 ionize without O(7) participation to form the unbridged carbenium ion 15.As pointed out in [la], displacement (&2) reactions of bi-and tricyclic halides and sulfonates with nucleophilic solvents are sterically hindered, if the nucleofuge is adjacent to a bridgehead atom. In these cases, solvolysis reactions occur via carbenium ions (&1) and tend to be slow unless assisted by bridging of the cationic center by neighboring atoms.In carbocyclic compounds, bridging involves weak bonding between the electrophilic cationic center and neighboring C-atoms, thereby generating some of the strain associated with the subdivision of cyclic structures into smaller rings [2]. Differential bridging of neighboring C-atoms, therefore, accounts for the frequently different rates and products of epimeric bi-and tricyclic sulfonates [lb], such as the exo-and endo-2-norbornyl p -bromobenzenesulfonates (brosylates) and p -toluenesulfonates (tosylates) 1 (X = BsO) and 2 (X = TsO), respectively, which differ by factors of more than 3002).In their original communications [3], Winstein and Trifan attributed the higher rate of 1-OBs to anchimeric assistance of exo-ionization by the antiperiplanar C( 1)-C(6) bonding electrons, i.e. by so-called CT participation3), which is absent in the endo-epimer 2-OBs. According to a modified version of this rationale [6], the transition state for exo-ionization is stabilized by C,C hyperconjugation with the strained and antiperiplanar C( 1)-C(6) CT bond. Thus, both interpretations stress the role of the C( 1)-C(6) bonding electrons in controlling the relative rates of I-OBs and 2-OBs. On the other hand, the role of the equally strained C( 1)-C(7) bond, which is somewhat deflected from the plane ') 2, 3,The IUPAC name for norbornane: 8,9,1U-trinorbornane. The rate ratio at 25"is 350 in AcOH [3], 580 in 80% EtOH [lb], and cn. 2000 in H2O [4].For a definition of u participation, see [5].

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Remote inductive effects in the solvolysis of secondary and tertiary 2-norbornyl derivatives. Evidence for nonclassical stabilization of the 2-norbornyl cation

Cited by 54 publications

References 3 publications

Bond length and reactivity. Structure of 2-endo-bornyl p-toluenesulfonate

Bond length and reactivity. Structure of 2-endo-bornyl p-toluenesulfonate

Dehalogenation of 1,3‐Diiodotricyclo[3.3.0.0^3,7]octane: Generation of 1,3‐Dehydrotricyclo[3.3.0.0^3,7]octane, a 2,5‐Methano‐Bridged [2.2.1]Propellane

Norbornanes. Part 21. Bridging strain in norbornyl and oxanorbornyl cations

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Remote inductive effects in the solvolysis of secondary and tertiary 2-norbornyl derivatives. Evidence for nonclassical stabilization of the 2-norbornyl cation

Cited by 54 publications

References 3 publications

Bond length and reactivity. Structure of 2-endo-bornyl p-toluenesulfonate

Bond length and reactivity. Structure of 2-endo-bornyl p-toluenesulfonate

Dehalogenation of 1,3‐Diiodotricyclo[3.3.0.03,7]octane: Generation of 1,3‐Dehydrotricyclo[3.3.0.03,7]octane, a 2,5‐Methano‐Bridged [2.2.1]Propellane

Norbornanes. Part 21. Bridging strain in norbornyl and oxanorbornyl cations

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Dehalogenation of 1,3‐Diiodotricyclo[3.3.0.0^3,7]octane: Generation of 1,3‐Dehydrotricyclo[3.3.0.0^3,7]octane, a 2,5‐Methano‐Bridged [2.2.1]Propellane