The 2‐norbornyl cation: a retrospective

Moss, Robert A.

doi:10.1002/poc.3290

Cited by 19 publications

(13 citation statements)

References 43 publications

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“…Whereas 1 – 3 are simple deprotonation products of B , 4 and 5 require a further 3,7-ring closure, leading to the non-classical cation C , which is a derivative of the 2-norbornyl cation [38]. This system either collapses by deprotonation at the methyl group to longifolene ( 4 ), or by deprotonation at C-4 with formation of a cyclopropane ring to longicyclene ( 5 ).…”

Section: Resultsmentioning

confidence: 99%

Mechanistic investigations on multiproduct β-himachalene synthase from Cryptosporangium arvum

Rinkel¹,

Dickschat²

2019

Beilstein J. Org. Chem.

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A bacterial terpene synthase from Cryptosporangium arvum was characterised as a multiproduct β-himachalene synthase. In vitro studies showed not only a high promiscuity with respect to its numerous sesquiterpene products, including the structurally demanding terpenes longicyclene, longifolene and α-longipinene, but also to its substrates, as additional activity was observed with geranyl- and geranylgeranyl diphosphate. In-depth mechanistic investigations using isotopically labelled precursors regarding the stereochemical course of both 1,11-cyclisation and 1,3-hydride shift furnished a detailed catalytic model suggesting the molecular basis of the observed low product selectivity. The enzyme’s synthetic potential was also exploited in the preparation of sesquiterpene isotopomers, which provided insights into their EIMS fragmentation mechanisms.

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Section: Resultsmentioning

confidence: 99%

Mechanistic investigations on multiproduct β-himachalene synthase from Cryptosporangium arvum

Rinkel¹,

Dickschat²

2019

Beilstein J. Org. Chem.

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“…Its single 1 H NMR analysis documents the equivalence of all 11 hydrogen atoms in super acid media. [5][6][7] Further carbocation rearrangements in the gas phase are more extensive; complex cage-opening isomerization results in formation of the 1,3-dimethylcyclopentenyl cation. 8 Degenerate rearrangements of the nine CH groups of the 9-homocubyl cation were sought in 1967 first by Schleyer, et al 9 and a few months later by Barborak and Pettit.…”

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confidence: 99%

The 9-homocubyl cation rearrangement revisited

Jalife

Martínez‐Guajardo

et al. 2015

Chem. Commun.

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“…In the longstanding question of classical vs. nonclassical bonding in the 2-norbornyl cation. [51][52][53][54] , calculations, which were later confirmed by x-ray crystallography confirm delocalized sigma bonding for this intermediate.…”

Section: Methodsmentioning

confidence: 66%

The Discrete Existence of Singlet Nitrenium Ions Revisited: Computational Studies of Non-Aryl Nitrenium Ions and Their Rearrangements

Falvey

2018

Preprint

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Nitrenium ion species are examined using computational methods (DFT, MP2, coupled-cluster, and a composite method, CBS-APNO) with a particular emphasis on non-aromatic species (i.e. those lacking an aromatic or heteroaromatic ring in direct conjugation with the formal nitrenium ion center.) Substitution of the N+ center with alkyl, alkoxy, vinyl, acyl, sulfonyl, among others, were evaluated. For these species, three properties are considered. (1) the stability of the nitrenium ions to unimolecular isomerizations such as 1,2 alkyl or H shifts. And, to the extent the singlet states could be characterized as discrete minima on the PES, (2) the effect of the substituents on singlet-triplet energy splitting as well as (3) the relative stabilities of the nitrenium ions as defined by N-hydration enthalpies (RR’N+ + H¬2O -> RR’NOH¬2+). Nearly all simple alkyl and di-alkyl nitrenium ion singlet states are predicted to rearrange without detectable barriers, largely through 1,2 H or alkyl shifts. Methyl and N-N-dimethylnitrenium ion singlet states could be characterized as formal minima on the PES. However these species show small or insignificant barriers to isomerization. Disubstituted nitrenium ions that include an alkyl group and a conjugating substituent such as alkoxyl, vinyl or phenyl, show meaningful barriers to isomerization and are thus predicted to possess non-trivial lifetimes in solution. Alkyl groups substantially stabilize the singlet state relative to the situation in the parent nitrenium ion NH¬2+ To the point where the two states are nearly degenerate. Other groups that interact with the nitrenium ion center decrease DEst in the order formoyl< vinyl < phenyl < alkoxy ~sulfonyl < cyclopropyl ~ cyclobutyl. The latter two substituents interact strongly with the (singlet) nitrenium ion center through the formation of non-classical bonding reminiscent of the bisected cyclopropylcarbinyl ion case for carbocations. When singlet state stability is evaluated in the context of N-hydration enthalpies, it is found that the ordering is acyl<br>

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The 2‐norbornyl cation: a retrospective

Cited by 19 publications

References 43 publications

Mechanistic investigations on multiproduct β-himachalene synthase from Cryptosporangium arvum

Mechanistic investigations on multiproduct β-himachalene synthase from Cryptosporangium arvum

The 9-homocubyl cation rearrangement revisited

The Discrete Existence of Singlet Nitrenium Ions Revisited: Computational Studies of Non-Aryl Nitrenium Ions and Their Rearrangements

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