Eine neue Fulvensynthese

Schaltegger, H.; Neuenschwander, Markus; Meuche, Doris

doi:10.1002/hlca.19650480433

Cited by 58 publications

(18 citation statements)

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“…54a is very reasonable,a nd after protonation the substituted 1,2-di(cyclopentadienyl)ethane 55 was isolated. After another deprotonation 27 )of 55 ! 54b,intramolecular oxidative coupling was induced to give 56 which easily isomerized to the substituted dihydrofulvalene 57 by acid or base catalysis 28 ).…”

Section: à3mentioning

confidence: 99%

“…Them ain advantages were the low reaction temperature,t he use of aprotic solvents and the simple aprotic workup conditions (if needed). This was the only method giving spectroscopically pure pentafulvene (2a)on ag ram scale [27] [28], and the method could be applied to 1,2-benzofulvenes and 1,2,3,4-dibenzofulvenes as well [33],iftriethylamine was replaced by stronger bases in the last step.I th as to be noted, however, that for 6,6-disubstituted pentafulvenes the Thiele sequence or its modifications have to be favored.…”

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confidence: 99%

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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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Section: à3mentioning

confidence: 99%

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confidence: 99%

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

Neuenschwander

2015

Helvetica Chimica Acta

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“…Reaction of the cyclopentadienide 6-Li with N-chlorosuccinimide gave chloropentacyclopropylcyclopentadiene (19) in 95% yield. Hydride abstraction from 6-Li with triphenylmethyl tetrafluoroborate yielded the interesting tetracyclopropylcyclopropylidenecyclopentadiene 18 (37%).…”

Section: Cyclopentadienyl Cations 33mentioning

confidence: 99%

“…The first fulvenes, 6,6-dialkylfulvenes, were prepared as early as 1906 by Thiele et al from sodium cyclopentadienide and ketones [16]. The parent hydrocarbon 27 and many other derivatives have been thoroughly studied since the 1960s [17][18][19]. Diazocyclopentadiene (28), which is also easily prepared from cyclopentadienide, is a heteroanalogue of fulvene.…”

Section: Fulvene and Spiroannelated Cyclopentadiene Derivativesmentioning

confidence: 99%

Oligounsaturated Five‐Membered Carbocycles – Aromatic and Antiaromatic Compounds in the Same Family

Haag

Meijere

2002

Modern Arene Chemistry

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Most compounds containing oligounsaturated five-membered carbocycles ranging from cyclopentadiene to C 20 fullerene display interesting electronic and structural properties. This chapter describes recent developments in this area, starting with stabilized cyclopentadienyl cations, then discusses several fulvenes as well as spiroannelated cyclopentadiene derivatives and eventually linearly as well angularly fused oligocyclic five-membered ring systems. Among these oligounsaturated di-, tri-, and oligoquinanes, the features of the rather unstable pentalene and acepentalene are discussed with respect to their generation and electronic ground states. Structural properties, including those of the stable dilithium diides as well as several metal complexes are presented. Finally, the generation and characterization of the highly unstable C 20 fullerene, which sets a new benchmark for this class of molecules, are highlighted. 2.1

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“…Thus even derivatives of azete are difficult to prepare and are very reactive [9,10], while 2-azirine and oxirene are still unknovvn [11]. Cyclopentadienone (ER--5.3 kcal/mole) has been obtained only as an extremely reactive intermediate which cannot be isolated since it dimerizes so readily [12]; note that the isoconjugate hydrocarbon, fulvene, for which ER = 1.1 kcal/mole, is relatively stable [13][14][15], Similar remarks apply to cyclopropenone (Er = -3.0 kcal/mole) which has only recently been prepared and resisted ali attempts to isolate it from solution because it polymerized so readily [16]; cyclopropenone bears the same relation to the aromatic ion, cyclopropenium, that tropone does to tropylium, and it had been suggested that it might, like tropone, be aromatic. It has, however, become increasingly evident that tropone is not an aromatic compound, a conclusion confirmed by calculations which will be reported elsevvhere [17].…”

Section: Fij = K S Tjmentioning

confidence: 99%