Zur Chemie cyclischer π‐Elektronensysteme, IV. Stabile Chinotropilidene

Föhlisch, Baldur; Bürgle, Peter; Krockenberger, D.

doi:10.1002/cber.19681010814

Cited by 28 publications

(11 citation statements)

References 20 publications

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“…[1,7] A coexistence of A in a rapid equilibrium was also proposed in organic solvents, while A was described to be predominant in liquid sulfur dioxide. [1,7] A coexistence of A in a rapid equilibrium was also proposed in organic solvents, while A was described to be predominant in liquid sulfur dioxide.…”

Section: Introductionmentioning

confidence: 97%

“…[2][3][4] 1 has also been shown to serve as a mild halogenating agent and activator in Swern-type oxidation reactions. [1] In the case of 1, their NMR spectroscopic data as well as a later NMR study by In solution, there is a highly dynamic equilibrium involving both the ionic halotropylium halide form and different isomers of the covalent dihalocycloheptatriene form. In principle, there are five possibilities (see Scheme 1): An ionic halotropylium halide structure (A) and four isomeric covalent dihalocycloheptatriene structures (B-E).…”

Section: Introductionmentioning

confidence: 99%

“…[1] In recent years, both these compounds have found synthetic use as precursors for carbocyclic carbene complexes. [1] In recent years, both these compounds have found synthetic use as precursors for carbocyclic carbene complexes.…”

Section: Introductionmentioning

confidence: 99%

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The Ambivalent Nature of Halogenated Tropone Derivatives: Dihalocycloheptatriene vs. Halotropylium Halide

2017

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Although dichlorocycloheptatriene and dibromocycloheptatriene have been known for a long time, their exact structure remained uncertain so far. In this computational and crystallographic study, we elucidate the nature of these compounds in solution and in the solid state. In the latter case, both compounds exist as halotropylium halides, which also feature Br–Br halogen bonds in the case of bromotropylium bromide. In solution, there is a highly dynamic equilibrium involving both the ionic halotropylium halide form and different isomers of the covalent dihalocycloheptatriene form. The presence of the 7,7‐dihalocycloheptatriene isomer, which until now has been the most commonly used representation in literature, can be excluded.

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Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

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The Ambivalent Nature of Halogenated Tropone Derivatives: Dihalocycloheptatriene vs. Halotropylium Halide

2017

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“…According to Scheme 9,possible precursors of nonaheptafulvalene (20)have been prepared by acylation of tropone with acetyl fluoroborate (to give 29a)a nd oxalyl dibromide [51] (to give 29b), however synthetic attempts towards nonaheptafulvalene (20)failed due to the easy valence isomerizations of the cyclononatetraene units of 37a…”

Section: 3synthesis Of Heptafulvene (3a)mentioning

confidence: 99%

Low‐Temperature Olefin Syntheses in View of Parent Fulvenes and Fulvalenes

Neuenschwander

2015

Helvetica Chimica Acta

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Parent fulvenes and fulvalenes are thermallyu nstable cross-conjugated olefins for which lowtemperature syntheses are indispensable. In this review 5syntheses (inthe temperature range between À 100 and À 108)are discussed:1. Reaction of sodium cyclopentadienidew ith 1-acetoxy-1-chloroalkanes or 1-acetoxy-1-bromoalkanes (26)gives acetoxy-alkyl-cyclopentadienes (27)which are easily converted to pentafulvenes (2)by low-temperature HOAc-elimination with NEt 3 .T his synthesis has been applied to parent pentafulvene (2a), heptafulvene(3a), nonafulvene (4a)a nd sesquifulvalene (19a)(Schemes 8 -11).2. Based on an early quantitative oxidative coupling of cyclononatetraenide (8)t og ive dihydrononafulvalene (38)( Scheme 10), ag eneral synthetic plan for fulvalenes has been outlined (Scheme 11)a nd applied to the synthesis of pentafulvalene (12), nonapentafulvalene (16)a nd nonafulvalene (14). Several applications of oxidative couplings of Hückel anions are discussed (Schemes 20 and 21).3. Tr ifunctional cyclopropanes 67 (inm ost cases 1,1-dibromo-2-X-cyclopropanes) are attractive precursors of parent triafulvene (1a)a nd calicene (17)(Scheme 18). Contrary to classical procedures they are transformed into nucleophiles (67 ! 68)b yh alogen-lithium exchange,m ethylation( 68 ! 69) and HBr-eliminationt og ive 1-methylidene-2-X-cyclopropaneso ft ype 71.B ys ubsequentH Xeliminationtriafulvene (1a)has been synthesized and trapped as a[4þ2]-cycloadduct 73 (Scheme 20). Furthermore,c alicene precursors 77 are available by using cyclopentenone as an electrophilic cyclopentadiene equivalent.4. Similarly,1 -lithio-1-bromo-2-X-cyclopropanes 68 are directly transformed into triafulvalene precursors 81 (Scheme 26)b yanovel CuCl 2 -catalyzed oxidative coupling.5. In view of the synthesiso fp arent triafulvene( 1a), triafulvalene( 11)a nd calicene (17), retroDielsÀAlder reactionso fs table precursors -p repared by low-temperature reactions( described in chapters 3 and 4)-have been explored.

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“…[38,39] However, the synthesis of 4-(dibenzo[a,d]cyclohepten-5-ylidene)cyclohexa-2,5-dienone (14) by deprotonation of the 5-(p-hydroxyphenyl)dibenzo[a,d]cyclohepten-5-ylium salt with triethylamine, has been reported. [40] We have previously reported the synthesis of the two novel tricyclic seven-membered B-ring p-QMs, 4-(6H-dibenzo[b,e]thiepin-11-ylidene)cyclohexa-2,5-dienone (1) and its oxygen analogue 2 under relatively mild reaction conditions ( Figure 1). [41] We now report on the synthesis of a range of novel tricyclic p-QMs containing central sevenmembered rings where, in the latter compounds, the heteroatoms in 1 and 2 have been substituted by carbon atoms and a couple of carbocyclic ring systems.…”

Section: Introductionmentioning

confidence: 99%

The Synthesis of Novel p‐Quinone Methides: O‐Dealkylation of5‐(p‐Alkyloxyaryl)‐10,11‐dihydrodibenzo[a,d]cyclohepten‐5‐ols and Related Compounds

Taljaard¹,

Taljaard²,

Imrie³

et al. 2005

Eur J Org Chem

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The synthesis of a series of novel tricyclic p‐quinone methides (p‐QMs) from 5‐(p‐alkyloxyaryl)‐10,11‐dihydrodibenzo[a,d]cyclohepten‐5‐ol and related substrates in moderate‐to‐good yields is reported. The reaction is proposed to proceed under mild acidic conditions by O‐dealkylation of the p‐alkoxy group on the p‐position of the pendant 5‐aryl ring on the B‐ring of the tricyclic system.The effect of different alkyl groups on the oxygen atom, as well as substituent groups on the phenyl ring flanking the O‐alkyl group has also been investigated The mechanism of the reaction is discussed in terms of the relatively high intermediate cation stabilities, the possible intermediacy of a hemiketal, as well as conformational effects. Various modifications to the central seven‐membered B‐ring to introduce more rigidity to the tricyclic system have been made and the scope of the reaction further elaborated. Furthermore, the single crystal structure of dienone 14 has been determined and the p‐quinone methide shown to be non‐planar, which would account for the relative conformational rigidity of these systems and their ability to accommodate the planar cyclohexa‐2,5‐dienone moiety and thus explain the stability of these systems relative to their 5‐ and six‐membered B‐ring counterparts. These compounds may be useful for the synthesis of novel dyes or compounds which may exhibit photochromic and thermochromic properties. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

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Zur Chemie cyclischer π‐Elektronensysteme, IV. Stabile Chinotropilidene

Cited by 28 publications

References 20 publications

The Ambivalent Nature of Halogenated Tropone Derivatives: Dihalocycloheptatriene vs. Halotropylium Halide

The Ambivalent Nature of Halogenated Tropone Derivatives: Dihalocycloheptatriene vs. Halotropylium Halide

Low‐Temperature Olefin Syntheses in View of Parent Fulvenes and Fulvalenes

The Synthesis of Novel p‐Quinone Methides: O‐Dealkylation of5‐(p‐Alkyloxyaryl)‐10,11‐dihydrodibenzo[a,d]cyclohepten‐5‐ols and Related Compounds

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