Intramolecular Reactions of Cyclopropylcarbinyl, Cyclobutyl, and Allylcarbinyl Cationic Systems

Bayless, John H.; Friedman, Lester; Smith, Jason A.; Cook, Francis Bernard; Shechter, Harold

doi:10.1021/ja01081a053

Cited by 30 publications

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“…Carbene 1 comprises (cyclopropyl)carbene ( 7 ) − and cyclobutylidene ( 8 ) − units and should react according to their known rearrangement types. Examples of these include ring enlargement or ring contraction via a 1,2-C atom shift reaction and cyclopropanation via a 1,3-C–H bond insertion reaction (Scheme ).…”

Section: Results and Discussionmentioning

confidence: 99%

Tricyclo[2.1.0.0^2,5]pent-3-ylidene: Stereoelectronic Control of Bridge-Flapping within a Nonclassical Nucleophilic Carbene

Rosenberg

Brinker

2020

J. Org. Chem.

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Tricyclo[2.1.0.0 2,5 ]pent-3-ylidene is a carbene foreseen to rearrange to pyramidane ( c -C 4 H 4 )C, a highly strained molecule featuring an inverted C atom. Modeling of the carbene, using the (U)MPWB1K/cc-pVTZ//(U)MPWB1K/6-311G(d) theoretical model, indicated a large singlet–triplet energy gap (Δ E S–T = −45 kcal/mol), a high gas-phase proton affinity (PA = 258 kcal/mol), and a preference for electron-poor alkenes. These properties are consistent with those of nucleophilic carbenes. Structural differences between the C s -symmetric singlet (ω flap = ±44 deg) and C 2 v -symmetric triplet (ω flap = 0 deg) stem from nonclassical electron delocalization in the former and the lack thereof in the latter. Degenerate bridge-flapping of the singlet’s main bridge, which comprises the reactive divalent C3 atom, is computed to be slow due to a high activation barrier of the C 2 v -symmetric transition state (TS) ( E a = 17 kcal/mol). The position of the conformeric equilibrium is subject to stereoelectronic control. 1-Substituted derivatives of the carbene (R ≠ H) are sensitive to σ inductive effects. A proximal conformation is preferred when R is electron-donating and a distal one is favored when R is electron-withdrawing. Finally, carbene rearrangements via 1,2-C atom shift or enyne fragmentation were computed. The C 2 v -symmetric bridge-flapping TS has the proper geometry to initiate enyne fragmentation.

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Section: Results and Discussionmentioning

confidence: 99%

Tricyclo[2.1.0.0^2,5]pent-3-ylidene: Stereoelectronic Control of Bridge-Flapping within a Nonclassical Nucleophilic Carbene

Rosenberg

Brinker

2020

J. Org. Chem.

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“…This material was not actively sought among the products of the cyclobutyl cation although under certain conditions it becomes an important product in the deamination of cyclobutylamine. 23 The presence of bicyclobutane was detected initially in the nmr spectrum of the gaseous products of the electrolysis of cyclobutanecarboxylic acid. In addition to the expected absorptions (cyclobutane at 1.96 ppm; cyclobutene, two singlets at 4.03 and 2.54 ppm in ratio 2:1),24 two small, rather broad peaks were noted at about 0.43 and 1.4 ppm in ratio 1:2.…”

Section: Methodsmentioning

confidence: 99%

Cyclopropylcarbinyl, cyclobutyl, and allylcarbinyl cations from anodic oxidations of the carboxylic acids

Keating¹,

Skell²

1969

J. Am. Chem. Soc.

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“…In a 1964 review on carbonium ions, Deno (1) briefly stated that deoxidation with cyclopropylcarbinol-a,a-d, (1-OH-a-d,) gave principally 1,3-butadiene-1,l-d,, indicating that no isotopic scrambling has occurred in the cyclopropylcarbinyl cation produced under the conditions of very short life expected for deoxidation. A more detailed analysis of the hydrocarbon products from the alkaline deoxidation of 1-OK with bromoform was reported by Bayless et al (2). Among the 11 % yield of hydrocarbon products, 1,3-butadiene, bicyclobutane, cyclobutene, methylenecyclopropane, ethylene, and acetylene were found and their formation was attributed to processes involving highly energetic intramolecular cationic paths, such as carbonhydrogen insertion, carbon-skeleton rearrangement, and fragmentation.…”

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confidence: 87%

Deoxidation studies with cyclopropylcarbinol

Cessna¹,

Lee²

1970

Can. J. Chem.

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The liquid products from the deoxidation with cyclopropylcarbinol in KOH–CHBr3 were identified as cyclopropylcarbinyl, cyclobutyl, and allylcarbinyl alcohols, bromides, and the various ethers, with dicyclopropylcarbinyl ether as the most abundant product. In addition, small amounts of methylene bromide, cyclopropanecarboxaldehyde, and cyclobutanone were also found. The deoxidation with cyclopropylcarbinol-α-14C gave rise to isotopically scrambled cyclopropylcarbinol-x-14C, with about 22% of the 14C-label rearranged from C-α to the cyclopropyl group.

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Intramolecular Reactions of Cyclopropylcarbinyl, Cyclobutyl, and Allylcarbinyl Cationic Systems

Cited by 30 publications

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Tricyclo[2.1.0.0^2,5]pent-3-ylidene: Stereoelectronic Control of Bridge-Flapping within a Nonclassical Nucleophilic Carbene

Tricyclo[2.1.0.0^2,5]pent-3-ylidene: Stereoelectronic Control of Bridge-Flapping within a Nonclassical Nucleophilic Carbene

Cyclopropylcarbinyl, cyclobutyl, and allylcarbinyl cations from anodic oxidations of the carboxylic acids

Deoxidation studies with cyclopropylcarbinol

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Intramolecular Reactions of Cyclopropylcarbinyl, Cyclobutyl, and Allylcarbinyl Cationic Systems

Cited by 30 publications

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Tricyclo[2.1.0.02,5]pent-3-ylidene: Stereoelectronic Control of Bridge-Flapping within a Nonclassical Nucleophilic Carbene

Tricyclo[2.1.0.02,5]pent-3-ylidene: Stereoelectronic Control of Bridge-Flapping within a Nonclassical Nucleophilic Carbene

Cyclopropylcarbinyl, cyclobutyl, and allylcarbinyl cations from anodic oxidations of the carboxylic acids

Deoxidation studies with cyclopropylcarbinol

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Tricyclo[2.1.0.0^2,5]pent-3-ylidene: Stereoelectronic Control of Bridge-Flapping within a Nonclassical Nucleophilic Carbene

Tricyclo[2.1.0.0^2,5]pent-3-ylidene: Stereoelectronic Control of Bridge-Flapping within a Nonclassical Nucleophilic Carbene