Eine neue Fulvensynthese. 4. Mitteilung

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.

Section: Syntheses With Trifunctionalmentioning

confidence: 99%

mentioning

confidence: 99%

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

Neuenschwander

2015

“…*) Uber die Synthese von Acetoxy-chlor-methanen aus aliphatischen Aldehyden und Ketonen wurde bereits im Rahmen der Synthese von Fulvenen kurz berichtet [12] [13]. -lo+ 5" ausreagieren und kontrolliert das Produkt im 'H-NMR -Spektrum Der Katalysator wird bei -10" uber 10 g A1203 basisch I abfiltriert (doppelwandige gekuhlte Chromatographiesaule), das Produkt mit insgesamt 20 ml abs CHzC12 eluiert und das Eluat bei 0"/10 Torr i RV eingedampft.…”

Section: Verbindungunclassified

Chloracylierung und Bromacylierung von Carbonylverbindungen: Eine in Vergessenheit geratene Carbonylreaktion. I. Präparative Anwendungsbreite

Neuenschwander

Bigler

Christen

et al. 1978

“…6-Methylfulvene [26] was prepared from AcCl and acetaldehyde which formed, under catalysis of ZnCl,, 1-chloroethyl acetate. Reaction of 1-chloroethyl acetate with sodium cyclopentadienide gave, after treatment with Et,N, 6-methylfulvene.…”

mentioning

confidence: 99%

Substituent Effects on Fe⁺‐Mediated [4+2] Cycloadditions in the Gas Phase

Schroeter¹,

Schalley²,

Schröder³

et al. 1997

(1 6.1V.97)The Fe+-mediated [4+2] cycloaddition of dienes with alkynes has been examined by four-sector ion-beam and ion cyclotron resonance mass spectrometry. Prospects and limitations of this reaction were evaluated by investigating several Me-substituted ligands. Me Substitution at C(2) and C(3) of the diene, i.e., 2-methylbuta-l,3-diene, 2,3-dimethylbuta-l,3-diene, hardly disturbs the cycloaddition. Similarly, variation of the alkyne by use of propyne and but-2-yne does not affect the [4+2] cycloaddition step, but allows for H/D exchange processes prior to cyclization. In contrast, Me substituents in the terminal positions of the diene moiety (e.g., penta-l,3-diene, hexa-2,4-diene) induce side reactions, namely double-bond migration followed by Introduction. -In addition to its widespread analytical applications, in the last two decades mass spectrometry developed to one of the most important techniques for the examination of ion-molecule reactions in the gas phase [l]. The particular notion of investigating processes under these 'artificial' conditions is that here intrinsic features of reactants can be uncovered, while, in the condensed phase, solvents, ligands, and counter ions largely complicate and obscure the mechanistic pattern. Of course, there are also problems even under the otherwise ideal gas-phase conditions ; for example, an in-depth investigation of stereochemical properties by mass spectrometry (MS) is quite challenging [2]. In fact, the differentiation of stereoisomers by MS techniques is often not trivial. While in most cases stereo-differentiation concerns cyclic compounds [2] [3], strategies have been developed recently, which allow for stereochemical probes of acylic compounds by means of 'bare' transition-metal ions [4].-Transition-metal-ion-mediated coupling reactions have been already investigated in the gas phase