Synthesis and chemistry of cubanes

Griffin, G. W.; Marchand, Alan P.

doi:10.1021/cr00095a003

Cited by 173 publications

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References 34 publications

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“…[D 3d ]-Octahedrane (1) is a more difficult case than cubane because cage opening would be highly favorable, in contrast to cubane in which breaking just one CÀC bond causes only little structural changes. [40] To emphasize the power of this method further, the PTC pro- …”

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Preparation and Reactivity of [D_3d]‐Octahedrane: The Most Stable (CH)₁₂ Hydrocarbon

Meijere

Lee

Кузнецов

et al. 2005

Chemistry A European J

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The synthesis of the (CH)12 hydrocarbon [D(3d)]-octahedrane (heptacyclo[6.4.0.0(2,4).0(3,7).0(5,12).0(6,10).0(9,11)]dodecane) 1 and its selective functionalization retaining the hydrocarbon cage is described. The B3LYP/6-311+G* strain energy of 1 is 83.7 kcal mol(-1) (4.7 kcal mol(-1) per C-C bond) which is significantly higher than that of the structurally related (CH)16 [D(4d)]-decahedrane 2 (75.4 kcal mol(-1); 3.1 kcal mol(-1) per C-C bond) and (CH)20 [I(h)]-dodecahedrane 3 (51.5 kcal mol(-1); 1.7 kcal mol(-1) per C-C bond); the heats of formation for 1-3 computed according to homodesmotic equations are 52, 35, and 4 kcal mol(-1). Catalytic hydrogenation of 1 leads to consecutive opening of the two cyclopropane rings to give C2-bisseco-octahedrane (pentacyclo[6.4.0.0(2,6).0(3,11).0(4,9)]dodecane) 16 as the major product. Although 1 is highly strained, its carbon skeleton is kinetically quite stable: Upon heating, 1 does not decompose until above 180 degrees C. The B3LYP/6-31G* barriers for the S(R)2 attack of the tBuO. and Br3C. radicals on a carbon atom of one of the cyclopropane fragments (Delta(298) = 27-28 kcal mol(-1)) are higher than those for hydrogen atom abstraction. The latter barriers are virtually identical for the abstraction from the C1-H and C2-H positions with the tBuO. radical (DeltaG(298) = 17.4 and 17.9 kcal mol(-1), respectively), but significantly different for the reaction at these positions with the Br3C. radical (DeltaG(298) = 18.8 and 21.0 kcal mol(-1)). These computational results agree well with experiments, in which the chlorination of 1 with tert-butyl hypochlorite gave a mixture of 1- and 2-chlorooctahedranes (ratio 3:2). The bromination with carbon tetrabromide under phase-transfer catalytic (PTC) conditions (nBu4NBr/NaOH) selectively gave 1-bromooctahedrane in 43 % isolated yield. For comparison, the PTC bromination was also applied to 2,4-dehydroadamantane yielding 54 % 7-bromo-2,4-dehydroadamantane.

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Preparation and Reactivity of [D_3d]‐Octahedrane: The Most Stable (CH)₁₂ Hydrocarbon

Meijere

Lee

Кузнецов

et al. 2005

Chemistry A European J

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“…Are there any other rearrangement paths for protonated cubane? Herein we address both computationally and experimentally the question to what extent the cubane cage is able to survive electrophilic attack [16] and what the most favorable paths for the reaction of 1 with a proton are.Despite enormous strain, cubane [15,17,18] is kinetically quite stable because breaking just one CÀC bond causes only minor structural changes and hence only little relief of strain. However, cleavage of a second CÀC bond is highly exothermic and followed by rapid rearrangements.…”

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“…In contrast, mild radical reagents [21] lead to substitution products with conservation of the cubane cage. [22] Electrophilic cubane conversions are limited to reactions of soft electrophiles like metal ions, [18] and a number of fascinating rearrangements (e.g., to syn-tricyclooctadiene (2) with Pd 2+ and to cuneane (3) with Ag + and Li + ) are preparatively useful. [18,23] The attack of a proton on cubane is highly exergonic and all of our and previous [9,15,16,24] ]oct-5-yl cation (5) [25] upon optimization without symmetry constrains.…”

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The Protonation of Cubane Revisited

et al. 2004

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Protonation of saturated hydrocarbons is the simplest and practically most important electrophilic reaction.[1] Small alkanes like methane, ethane, and isobutane [2] form welldefined protonated species, and their experimental proton affinities (PAs) are excellently reproduced computationally. [3][4][5] However, the current data on the protonations of strained hydrocarbons are rather controversial, and facile rearrangements are thought to account for the difficulties encountered in measuring the PAs.[6] Cyclopropane (strain energy(E str ) = 27.2 kcal mol À1 ) is an exception because the number of energetic downhill paths is very limited and the barrier for the ring opening of corner-protonated C 3 H 7 + to the 2-propyl cation is high. The experimental PA of cyclopropane (179.4 kcal mol À1 [7] ) is well reproduced computationally (179.3 kcal mol À1 at CCSD(T)/cc-pVTZ//CCSD(T)/cc-pVDZ for corner-protonated C 3 H 7 + ).[8] In contrast to cyclopropane which displays secondary CÀH bonds only, a surprisingly small range of PAs is characteristic for a number of hydrocarbons with tertiary C À H bonds. These hydrocarbons differ considerably in their strain energies, for example, dodecahedrane (PA = 201.7 kcal mol À1 , [9] E str = 65.4 kcal mol), adamantane (PA = 175.7 kcal mol À1 , [11] E str = 6.3 kcal mol À1 [12] ), and cubane [13] (PA = ca 200 kcal mol À1 , [7,9] E str = 161 kcal mol À1 [14] ). For these systems the question remains: How much does the strain energy affect the proton affinity of a saturated hydrocarbon and to what extent should isomerizations be considered? The experimental PA of cubane (1) measured by ion-cyclotron resonance spectroscopy [9] is surprisingly low and was recently questioned by Koppel et al. [15] on the basis that 1 rearranges rapidly to cuneane so that the PA is attributed to the energy change of the entire protonation/rearrangement/deprotonation process. However, cuneane is also highly strained, so where one does stop? Are there any other rearrangement paths for protonated cubane? Herein we address both computationally and experimentally the question to what extent the cubane cage is able to survive electrophilic attack [16] and what the most favorable paths for the reaction of 1 with a proton are.Despite enormous strain, cubane [15,17,18] is kinetically quite stable because breaking just one CÀC bond causes only minor structural changes and hence only little relief of strain. However, cleavage of a second CÀC bond is highly exothermic and followed by rapid rearrangements. For instance, thermolysis [16,19] and single-electron oxidation [20] of 1 leads to cyclooctatetraene. In contrast, mild radical reagents [21] lead to substitution products with conservation of the cubane cage. [22] Electrophilic cubane conversions are limited to reactions of soft electrophiles like metal ions, [18] and a number of fascinating rearrangements (e.g., to syn-tricyclooctadiene (2) with Pd 2+ and to cuneane (3) with Ag + and Li + ) are preparatively useful. [18,23] The attack of a proton on cubane i...

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“…[1,14 -16] Our group has successfully utilized these techniques in the elucidation of numerous PCU derivatives synthesized in our laboratory. [17 -24] As part of our ongoing program in this field, the NMR assignment of eight novel PCU derivatives (1)(2)(3)(4)(5)(6)(7)(8) is reported (Fig. 1).…”

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Synthesis and NMR assignment of pentacycloundecane precursors of potential pharmaceutical agents

Onajole

Makatini

Gasqui

et al. 2010

Magnetic Reson in Chemistry

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The synthesis and complete NMR elucidation of eight novel pentacycloundecane (PCU) derivatives are reported. These compounds are precursors in the synthesis of PCU-based anti-tuberculosis (TB) agents and potential human immunodeficiency virus (HIV) protease inhibitors. Two-dimensional (2D) NMR techniques were used to assign the NMR spectra for these compounds. Substitution of the cage molecule at (C-8/11) further complicates the assignment, since some of the substituted alkyl chain groups overlap with the cage proton signals. The side chain heteroatoms also introduce a rare through-space deshielding effect to some of the carbon atoms of the cage skeleton. Ring strain in the rigid cage skeleton appears to induce drastic electronic changes in some parts of the cage framework. This observation is more dramatic for the C-4 methylene group of the cage diols and the cage ethers.

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Synthesis and chemistry of cubanes

Cited by 173 publications

References 34 publications

Preparation and Reactivity of [D_3d]‐Octahedrane: The Most Stable (CH)₁₂ Hydrocarbon

Preparation and Reactivity of [D_3d]‐Octahedrane: The Most Stable (CH)₁₂ Hydrocarbon

The Protonation of Cubane Revisited

Synthesis and NMR assignment of pentacycloundecane precursors of potential pharmaceutical agents

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Synthesis and chemistry of cubanes

Cited by 173 publications

References 34 publications

Preparation and Reactivity of [D3d]‐Octahedrane: The Most Stable (CH)12 Hydrocarbon

Preparation and Reactivity of [D3d]‐Octahedrane: The Most Stable (CH)12 Hydrocarbon

The Protonation of Cubane Revisited

Synthesis and NMR assignment of pentacycloundecane precursors of potential pharmaceutical agents

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Preparation and Reactivity of [D_3d]‐Octahedrane: The Most Stable (CH)₁₂ Hydrocarbon

Preparation and Reactivity of [D_3d]‐Octahedrane: The Most Stable (CH)₁₂ Hydrocarbon