The 18-electron electrocyclisation of vinylogous fidecene. an unusual sequence of pericyclic processes

Beck, Andreas; Knothe, Lothar; Hunkler, Dieter; Prinzbach, Horst

doi:10.1016/s0040-4039(00)87360-8

Cited by 9 publications

(7 citation statements)

References 9 publications

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“…The cis product ( 2- cis ) that would be formed from a symmetry-allowed disrotatory pathway was not observed. Similarly, in 1982, Prinzbach and co-workers reported that a related system containing a hendecafulvene linked to a fulvene undergoes a symmetry-forbidden conrotatory 18π electrocyclization (Figure b) . These results are in violation of the outcome that would be expected from the Woodward–Hoffmann rules. , Perhaps the most famous quote in the history of orbital symmetry“Violations.…”

Section: Introductionmentioning

confidence: 98%

Violations. How Nature Circumvents the Woodward–Hoffmann Rules and Promotes the Forbidden Conrotatory 4n + 2 Electron Electrocyclization of Prinzbach’s Vinylogous Sesquifulvalene

et al. 2021

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Woodward and Hoffmann, in their treatise on orbital symmetry in 1969, stated "Violations. There are none!" Prinzbach reported in 1978 that the electrocyclization of vinylogous sesquifulvalene occurs exclusively through the Woodward−Hoffmann orbital-symmetry-forbidden 14π-electron conrotatory pathway, despite the availability of a variety of orbital-symmetry-allowed processes. Prinzbach later demonstrated that an 18π-electron homologue exhibits the same forbidden behavior. And yet, the analogous vinylogous pentafulvalene and heptafulvalene both follow the orbital symmetry rules, each proceeding through its allowed conrotatory 12π and 16π process, respectively. We report the investigation of these reactions with ωB97X-D DFT. The physical origins of the flagrant Prinzbach violations of the Woodward−Hoffmann orbital symmetry selection rules have now been elucidated by these calculations in conjunction with extensive analyses and comparisons to electrocyclizations that obey the Woodward−Hoffmann rules. This remarkable reversal of the Rules (the 14π-electron-forbidden process is found to be 11 kcal/mol more energetically facile than the allowed process) occurs due to the high degree of polarization of this hydrocarbon, such that conrotatory electrocyclization of vinylogous sesquifulvalene behaves like a cyclopentadienide combining with a tropylium. These results are compared to other forbidden pericyclic processes driven by steric constraints and strain release or by diradical character of the reactants that facilitates the formation of diradical transition states for symmetry-forbidden reactions. We predict how strong donor−acceptor substitution can modify nodal properties to level the difference between allowed and forbidden electrocyclic reaction barriers, and we provide computational predictions of two such cases.

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Section: Introductionmentioning

confidence: 98%

Violations. How Nature Circumvents the Woodward–Hoffmann Rules and Promotes the Forbidden Conrotatory 4n + 2 Electron Electrocyclization of Prinzbach’s Vinylogous Sesquifulvalene

et al. 2021

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“…Prinzbach et al [17] reported the only example of a 18π-electrocyclizations to the best of our knowledge. The authors described the reaction of a vinilogous fidecene to form the pentacyclic compound 23 under drastic reaction conditions.…”

Section: π-Electrocyclizationsmentioning

confidence: 93%

“…Prinzbach et al [17] . reported the only example of a 18π‐electrocyclizations to the best of our knowledge.…”

Section: Higher‐order Electrocyclizationsmentioning

confidence: 94%

“…Our calculations also show that this high-order electrocyclization is endergonic in both cases, being symmetryforbidden conrotatory process slightly less favored than the disrotatory pathway. However, the small energetic difference is [17] not high enough to expect a thermodynamically controlled process where initial formation of kinetically favored cis-INT11 would evolve towards trans-INT11. Moreover, hydrogen-β conformation is the same in both cis-and trans-INT11.…”

Section: π-Electrocyclizationsmentioning

confidence: 97%

“… 18π‐elecrocyclization key step associated with the synthesis of compound 23 reported by Prinzbach et al [17] . All the stationary points were located and characterized at the B3LYP‐D3BJ/6‐31G(d) level of theory.…”

Section: Higher‐order Electrocyclizationsmentioning

confidence: 99%

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Higher‐Order Electrocyclizations in Biological and Synthetic Processes

de Cózar,

Arrieta,

Arrastia

et al. 2023

ChemPlusChem

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In general, electrocyclizations follow the Woodward‐Hoffmann's rules of conservation of orbital symmetry. These rules have been extensively verified in low‐order processes, both in thermal and photochemical reactions, up to eight π‐electrons. However, when the number of π‐electrons in the system increases, some deviations of that general rules can be found. This focused review highlights the main features of reported higher‐order electrocyclizations involving 10, 12, 14, 16 and 18 π‐electrons. Some of these examples constitute useful intermediates in the synthesis of biologically active compounds. When computational studies were not included in the reported examples, DFT calculations have been performed to be included in this review. Analysis of the respective pericyclic topologies shows the importance of computational tools for understanding the selectivity observed experimentally.

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Cyclisch gekreuzt‐konjugierte Bindungssysteme, 41. Sechzehn‐Elektronen‐Elektrocyclisierung in vinylogen Heptafulvalenen

et al. 1983

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Das vinyloge Heptafulvalen 3 geht thermisch leicht (E, = 22 k 1.5 kcal . mol-', log A = 10.8) und perispezifisch die ,,symmetrieerlaubte" conrotatorische 16-Elektronen-Elektrocyclisierung zu trans-12a,l2b-Dihydrobenzo[l,2: 3.4ldicyclohepten (14) (Rontgenstrukturanalyse) ein. Im Diazageriist 4 (Troponazin) ist die analoge 16 n-Cyclisierung (zu 21) wahrscheinlich aus thermodynamischen Griinden nur unter Saurekatalyse praparativ realisierbar. Die Bemiihungen zum Nachweis der tricyclischen 16n-Annulene 15 bzw. 23 blieben erfolglos. Cyclic Cross-Conjugated Bond Systems, 41 1) Sixteen-Electron Electrocyclisation of Vinylogous HeptafulvalenesThe vinylogous heptafulvalene 3 easily (E, = 22 k 1.5 kcal . mol-', log A = 10.8) and perispecifically undergoes the thermal symmetry-allowed conrotatory 16-electron electrocyclisation yielding trans-l2a, 12b-dihydrobenzo[3,2: 3,4]dicycloheptene (14) (crystal structure analysis). Probably for thermodynamic reasons the analogous 16n-cyclisation in the diazaframework 4 (tropone azine) (to 21) proceeds only under acid catalysis. Efforts to identify the tricyclic 16n-annulenes 15/23 have been unsuccessful to date. a,o,B) zu den Tricyclen C stabilisieren. In der Tat erfolgt im vinylogen Pentafulvalen 1 (A, m = n = 2)3*4) und im vinylogen Sesquifulvalen 2 (A, m = 2, n = 3)@ die 12%-bzw. 14n-Elektrocyclisierung so leicht, daD in verdiinnter Losung die fur die geringe Stabilitat einfacher Fulvalene verantwortlichen Konkurrenzprozesse kaum abtraglich werden.In beiden Fallen erfolgt der RingschluD -unabhangig von der Zahl der in den Ubergangszustanden B beteiligten x-Elektronen -unter sterischer Kontrolle strikt conrotatorisch. Bei den Versuchen, die aus 1 und 2 gewonnenen Tricyclen C -bzw. ihre unter H-Verschiebung entstandenen Isomeren -zu dehydrieren, wurde deutlich, daB die 0 Verlag

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The 18-electron electrocyclisation of vinylogous fidecene. an unusual sequence of pericyclic processes

Cited by 9 publications

References 9 publications

Violations. How Nature Circumvents the Woodward–Hoffmann Rules and Promotes the Forbidden Conrotatory 4n + 2 Electron Electrocyclization of Prinzbach’s Vinylogous Sesquifulvalene

Violations. How Nature Circumvents the Woodward–Hoffmann Rules and Promotes the Forbidden Conrotatory 4n + 2 Electron Electrocyclization of Prinzbach’s Vinylogous Sesquifulvalene

Higher‐Order Electrocyclizations in Biological and Synthetic Processes

Cyclisch gekreuzt‐konjugierte Bindungssysteme, 41. Sechzehn‐Elektronen‐Elektrocyclisierung in vinylogen Heptafulvalenen

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