Substituted cyclononatetraenes and nonafulvenes

Boche, Gernot; Heidenhain, Frank; Staudigl, Brigitte

doi:10.1016/s0040-4039(01)86543-6

Cited by 13 publications

(2 citation statements)

References 17 publications

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“…-Thermal stability of most cyclononatetraenes 8 and nonafulvenes 1 (as well as of nonafulvalenes of type 3) is essentially limited by the well-known disrotatory ring closure to give cis-3a,7a-dihydroindenek (from 8) and cis-3a,7a-dihydrobenzofulvenes 17 (from 1; Scheme 8). There is a Scheme 8 thumb rule [26] [ 121 stating that thermal ~tability'~) of nonafulvenes 1 qualitatively increases with increasing electron-releasing capacity of substituents R' and RZ. In fact, corresponding to the highly olefinic nature of parent la, the half lifetime of the process l a -+ 17a is only 12 rnin at 0" in CDCl, [ S ] , while T, of l b -+ 17b increases to 36 min in CDC1, at 40" [26]; Id is still much more stable with zyz of 3 days at room temperature in CDCl, [7].…”

Section: Valence Isornerization Of Nonafulvenes Andmentioning

confidence: 99%

Synthetic Attempts towards ‘Aromatic’ Nonafulvenes

Chai

Neuenschwander

1994

Helvetica Chimica Acta

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According to their spectroscopic behavior, four classes of nonafulvenes may be distinguished, but, so far, only three classes have been identified. Type-A nonafulvenes (including parent la) are typically olefinic molecules with strongly alternating bond lengths and a nonplanar nine-membered ring. Type-B nonafulvenes are characterized by four pairs of equivalent ring H-atoms and ring C-atoms. Spectra of both Type-A and Type-B nonafulvenes are not dependent on temperature and solvent polarity. However, spectra of Type-C nonafulvenes (including prototype Id with R' = R2 = NMe,) are strongly influenced by temperature and solvent polarity due to an equilibrium 1 p l * between the nonpolar olefinic 1 and dipolar planarized l*. So far, Type-D nonafulvenes occurring exclusively in the dipolar form l * were unknown. Synthetic attempts towards nonafulvenes of Type D are described and problems encountered in nonafulvene syntheses are discussed. Several new cyclononatetraenes and four new nonafulvenes (or nonafulvalenes) 31, In, 3, and 5 have been synthesized. Spectroscopic evidence shows that 11,12-bis(diethylamino)nonatriafulvalene 5 is the first Type-D nonafulvene.

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Section: Valence Isornerization Of Nonafulvenes Andmentioning

confidence: 99%

Synthetic Attempts towards ‘Aromatic’ Nonafulvenes

Chai

Neuenschwander

1994

Helvetica Chimica Acta

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“…Angesichts der heutigen Kenntnisse uber die NMR-Spektren von Nonafulvenen 20 [3] ist allerdings die Aufspaltung des 'H-NMR-Signals des postulierten Dianions 4 [8] bei 7,16 ppm sehr ungewohnlich: Fur Protonen des Typs H-C(l)/H-C(8) beobachtet man meist ein d mit einer vicinalen Kopplungskonstanten von ca. 12,5 & 0,5 Hz, da die Allyl-Kopplungen mit 1 (6,8) 1,4 Hz uberraschend klein sind und durch weitere kleine Fernkopplungen verwischt werden. Auch bei Zunahme des Cyclononatetraenid-Anteils des Neunrings andert sich das Aufspaltungsbild nicht [ 3 ] .…”

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Nonafulvalen: Synthese durch oxidative Kupplung von Cyclononatetraenid und Valenzisomerisierung

Escher

Neuenschwander

Engel

1987

Helvetica Chimica Acta

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Following a general strategy (Scheme 2) for the synthesis of fulvalenes by oxidative coupling of ffiickel anions, the synthesis of nonafulvalene (1) has been realised (Scheme 3 ) . The most tricky step is a twofold deprotonation of bi(cyclononatetraeny1) 3 with K(t-BuO) to give 4; it is only possible after equilibration 3~3 a ; otherwise, deprotonation of one cyclononatetraene unit of 3 followed by oxidative coupling with AgBF4 gives quater(cyclononatetraeny1) I2 as an isomeric mixture. The reaction of 3 with K gives potassium ccct-cyclononatetraenide 11 (M = K; Scheme 5 ) and not the dianion 4 as reported in the literature. Nonafulvalene (1) is extremely reactive due to its very easy valence isomerisation to give an isomeric mixture of tetrahydro-dibenzopentafulvalenes 13 (Scheme 4 ) . The structure of crystalline isomer (E-anti)-13 has been proved by X-ray analysis. 1.Einleitung. -Nonafulvalen (1) ist sowohl synthetisch reizvoll wie theoretisch attraktiv, denn spektroskopische Untersuchungen von 1 konnten in Analogie zu den NMR-Ergebnissen von Nonafulvenen [3] wichtige Aufschlusse uber die Geometrie sowie die Bindungslangenalternanz in diesen cyclisch gekreuzt konjugierten 71 -Systemen geben. Bisher sind jedoch nur vereinzelte hochanellierte und arylierte Nonafulvalene bekannt geworden [4], die keine sicheren Aussagen uber die Grundzustandseigenschaften und die Reaktivitat des Grundkorpers 1 zulassen. Die praparativen Erfahrungen mit einfachen Nonafulvenen [5-71 lassen vermuten, dass 1 sowohl schwer zuganglich als auch ausserst reaktiv sei und sich der Isolierung durch rasche (6n +4n + 26)-Valenzisomerisierung der beiden Neunringe entziehen konnte.Hafner et al. beobachteten 1975 [S], dass Lithium-cyclononatetraenid 2 (M = Li) in Gegenwart von I, oder SbCl, n i t rund 30% Ausbeute zu Bi(cyclononatetraeny1) 3

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