Die als Synthesebausteine neuerdings sehr begehrten l-Chroma-1J-butadiene und 1 -Chroma-l,3,5-hexatriene 3 lassen sich aus reaktiven Aldehyden und (C0)Fr = C(OC2H5)CH3 (1) durch Kondensation rnit (C2H5)3N/(CH3hSiC1 leicht herstellen.1 -Metallabutadiene (Alkenylcarben-Komplexe) und 1 -Metallahexatriene (Alkadienylcarben-Komplexe) sind vielseitig verwend bare Ausgangsmaterialien fur Diels-Alder-Reaktionen2), Cyclohexadienon-Anellier~ngen~), zur Darstellung von Pyrrolen4) und 6-Carbolinen') sowie fur Transmetallierungen?Der erste Vertreter dieser Verbindungsklasse wurde 1968 durch Radikal-induzierte Umlagerung eines C-Methylketenimin-Chromkomplexes erhalten')'. Mittlenveile kennt man mehrere allgemein anwendbare Darstellungsverfahren*), von denen vor allem die Carbonyl-Olefinierung von (Alkyla1koxycarben)-Komplexen, deren a-Wasserstoffe beachtliche Aciditaten aufweisen*), wichtig ist. Konjugierte Basen von 1 (pKB = 89') reagieren allerdings nur rnit besonders aktiven Elektrophilen'O). Entsprechend sind Aldol-Kondensationen") damit bisher stets zweistufig durchgefuhrt worden, wobei mit n-BuLi bei -78 "C aus 1 zunachst ein Carbanion-Aquivalent erzeugt und dieses dann in Gegenwart von Lewissauren rnit der Carbonylkomponente kondensiert wurde.

The procedure for a metal-mediated cyclopentadiene annelation to enolizable cycloalkanones is described. Its key step is based on the cyclization of a 1-metalla-1,3,5-hexatriene intermediate, which is generated from the 1-metalla-1,5-hexadien-3-yne (CO) 5 MdC(OEt)Ct CC(∼)dCH(∼) (3; M ) Cr, W) precursor. Addition of secondary amines 4a,b to [2-(1-cyclopentenyl)ethynyl]carbene complexes 3a,b (M ) W, Cr) affords the 4-amino-1-metalla-1,3,5-hexatrienes (3E)-5a-d, which cyclize spontaneously to the η 1 (C,M)-cyclopentadiene complexes 6a-d. The ring closure is highly stereoselective and involves an anti addition (!) of the MdC bond to the terminal CdC bond of the 1-metalla-1,3,5-hexatriene unit. Ligand displacement from compound 6a is achieved by protonation to give an iminium salt 7a. Addition of aniline to compounds 3a,b yields 4-(NH-amino)-1-metalla-1,3,5-hexatrienes (3Z)-10a,b, which subsequently cyclize to cyclopentenimine(N,M) complexes syn-11a,b and anti11a,b and finally afford the cyclopentenimine 12 by oxidative ligand disengagement. Addition of secondary phosphanes 13a,b to compound 3a produces a mixture of the isomeric cyclopentadiene(P,W)-tungsten complexes anti-14a,b, anti-15a,b, and anti-16b. X-ray structure analyses are reported of compounds (3E)-5a, 6c, anti-11a, anti-16b, and anti17a.(1-Alkynyl)carbene complexes (CO) 5 MdC(OEt)CtCR (M ) W, Cr) have been applied as stoichiometric reagents in a number of high-yield transformations of potential usefulness to organic synthesis. 2 It has been shown recently that cyclopentadienes can be generated in a [3 + 2] fashion from reaction of (1-alkynyl)carbene complexes with cycloalkenylamines (∼)CHdC(∼)NR 2 in solvents such as dichloromethane. 6-Amino-1-metalla-1,3,5-hexatrienes (CO) 5 MdC(OEt)CHdC(Ph)C(∼)dC(∼)-(NR 2 ) (M ) W, Cr) were found to be key intermediates in these transformations ()"alkene route to cyclopentadienes"). 3 An alternate route to the formation of cyclopentadienes by [3 + 2] cycloaddition is based upon the reaction of the (2-amino-1-alkenyl)carbene-chromium complexes ()4-amino-1-chroma-1,3-butadienes) (CO) 5 CrdC(OEt)CHdC(R′)NR 2 with alkynes RCtCH, and the 6-amino-1-chroma-1,3,5-hexatrienes (CO) 5 Crd C(R)CHdC(OEt)CHdC(R′)NR 2 (generated by insertion of the CtC into the CrdC bond) are thought to be key intermediates ()"alkyne route to cyclopentadienes"). 2a A strong driving force for the cyclization of 1-metalla-1,3,5-hexatrienes to cyclopentadienes is provided by amino substituents and not only 6-amino-(vide supra) but also 2-amino-and 4-amino substituents were found to enhance this reaction. Examples of the latter type comprise cyclization both of the 2-amino-1-tungsta-1,3,5-hexatriene (CO) 5 WdC(NEt 2 )C(Me)dC(OEt)CHdCHPh (generated by insertion of the 1-aminoalkyne Et 2 NCt CMe into the WdC bond of the 1-tungsta-1,3-butadiene (CO) 5 WdC(OEt)CHdCHPh) 4a as well as the 4-amino-1-tungsta-1,3,5-hexatriene (CO) 5 WdC(OEt)CHdC(NEt 2 )-C(Me)dCHPh (generated by insertion of the 1-aminoalkyne Et 2 NCtCMe into the CdC bond of the 1-tungsta-1,3-buta...

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Aus Wolfram‐Aryl‐ und ‐Alkylcarben‐Komplexen lassen sich mit Tetrachlorgoldsäure die entsprechenden Gold(I)‐Carben‐Komplexe (2a–e, 4) in guten Ausbeuten synthetisieren. Die Carbenübertragung auf das Gold erfolgt unter Konfigurationserhaltung am Carbenliganden. Der Mechanismus der Reaktion sowie spektroskopische Daten der Komplexe werden diskutiert.