Ketenimine complexes are readily accessible in good yields by the addition of isocyanides to carbene complexes.[I1 They may be used, after isolation or in situ, for further transformations. Their reactivity patterns are completely different from those of ketenimines free of metals. Herein we describe novel template syntheses of four-, five-, and six-membered N-heterocycles by means of such complexes.Complex 1 reacts rapidly with alkenyl isocyanides 2 at 0°C in hexane to form the 1 : 1 adducts (3-aza-1,2,4-pentatriene complexes) 3. These can be trapped as aminocarbene complexes with protic nucleophiles."I In the absence of a suitable reactant, 3 adds a second molecule of 2 . The I-azafulvene complexes 4 and 4' and the azetidin-2-ylidene complexes 5 are thereby formed competitively by Complexes 414' precipitate directly from the reaction mixture as red crystals. They are by far more stable than metal-free 1 -azafulvenes.['] However, 4/4' cannot be separated, because they undergo interconversion in solution. The structures of the complexes were established on the basis of spectroscopic data ( Table 1).Upon hydrolysis in the presence of pyridine, 4b/4'b afford 3-amino-2-benzoyl-4-methylpyrrole 6 in 90% yield and pentacarbonyl(pyridine)tungsten 7. Thermolysis of 4a/4'a gives the pyrrolo[3,2-b]pyridine complex 9 by a metal-promoted cyclization. The reaction presumably proceeds via 8 as an intermediate.The formation of 4/4' from 1 and 2 corresponds to the synthesis of indoles from carbene complexes and aromatic isocyanides.['I The formation of azetidin-2-ylidene complexes 5, on the other hand, must be regarded as a prototype of a novel [3 + I ] cycloaddition of a ketenimine ligand to an isocyanide. The reaction is favored by the migration of the W(CO)s group from the N atom to the central C atom of the C = C = N moiety, since this results in the formation of an especially stable aminocarbene structure.Complexes 5 can be easily isolated by chromatography of the mother liquor after separation of the 4/4' crystals.Complex 5b was synthesized starting from a ca. 10 : 1 rnixture of cis-and trans-2b.I') A 15 : 1 : I mixture of three stereoisomers, which differ in the relative configurations of the C = C bonds, was obtained. As expected, the main product has a cis configuration at both C = C bonds [5b(cis/cis) : R,(petroleumether)=O. 14, m.p. = 107°C; Sb(cis/rruns): R,(petroleum ether) =0.42, m.p. = 101 " C ; 5b(trans/cis): R,(petroleum ether/ether= 50/1)= 0.7, m.p. = 80"Cl.The structure of the 3-methyl-3-ethoxyazetidin-2-ylidene-W(CO), 512, which is analogous to 5a (CH, instead of C,Hs in 5a), was determined by an X-ray crystal structure analysis (Fig. I). CI-W 2.044(6), W-C6 2.137(5), C6-C7 1.558(7), C6-NI 1.360(6), C7-C8 1.546(7), NI-C14 1.408(7), CI4-Cl5 1.295(9), NI-C8 1.430(7), C8-N2 1.260(7), N2-Cl2 1.408(8), Cl2-Cl3 1.299(9); W-C6-C7 133.0(3), W-C6-NI 137.0(4), C7-C6-N I 89.9(4).Oxidation of 5a with pyridine N-oxide 10 in toluene leads to the p-lactam 11 in 88% yield.

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Durch Drei-Komponenten-Reaktionen von 1 -Alkinen 4 (HC=C-R, R = C&, Si(CH,h, CH@CH,) mit (COhW= C(OEt)C& (1) und c-CsHll -NC (2) erhalt man CAlkyliden-2-azetidinyliden-Komplexe 5 und 6 bnv. Alkenyl(amino)carbenKomplexe 7. Die Reaktion verliuft aber einen Keteniminkomplex 3, der sich aus 1 und 2 rasch bildet. Oberlegungen zum Reaktionsablauf werden diskutiert.Keteniminkomplexe yon Cr, Mo, W'), Fe') und anderen Metallen sind durch Addition von Isocyaniden an Carbenkomplexe leicht zuganglich. Sie eignen sich als Bausteine3) fur Synthesen von N-Heterocyclen und konnen dazu haufig in situ in Drei-Komponenten-Reaktionen umgesetzt werden. Auf diesem Weg haben wir Vierring-, Fiinfring-und Sechsring-N-Heterocyclen hergestellt (Indole*), Hydantoine4', Pyrrole5', 6-Carboline6), 3-Imidazoline7), 2-Azetidinyliden-Komplexe und P-Lactame'*2a8)).Bisher beschrieben wir zwei Grundmuster zum Aufbau von Vierring-N-Heterocyclen uber Keteniminkomplexe: a) Metallinduzierte Cycloadditionen elektronenarmer Arylisocyanide mit Carbenkomplexen von Chrom, die unmittelbar zu metallfreien P-Lactamen fiihren''. b) Metallinduzierte Cycloadditionen von Alkyl-, Aryloder Alkenylisocyaniden mit Carbenkomplexen von Wolfram') bzw. Eisen'), bei denen 2-Azetidinyliden-Komplexe entstehen, die oxidativ in P-Lactame urngewandelt werden.Wir fanden, daB 2-Azetidinyliden-Komplexe 5 und 6 auch durch Drei-Koaponenten-Reaktionen von 1-Alkinen 4 rnit dem Carbenkomplex 1 und dem Isocyanid 2 bzw. durch Addition von 4 an den Keteniminkomplex 3 zuganglich sind.I3C-NMR-, IR-und Massen-Spektren yon 5 und 6 weisen auf W(CO),-Aminocarben-Komplexe hin. Die I3C-NMRSignale der Carbenkohlenstoffe werden durch Konjugation mit der C = C -OEt-Gruppe erwartungsgemao stark nach hohem Feld verschoben [(2)-5a: 6(W=C) = 263.09; vgl. 4-Imino C6Hll-NC (2) leads to the formation of 4-alkylidene-2-azetidinylidene complexes 5 , 6 and alkenyl(amin0)carbene complexes 7, respectively. The reaction proceeds via a ketene imine complex 3, which is formed rapidly from 1 and 2.

Azafulven‐ und Azetidinyliden‐Komplexe wie 1 bzw. 2 entstehen aus Carben‐Komplexen und zwei Äquivalenten Alkenylisocyanid. Aus 1 ist der Pyrrolopyridin‐Komplex 3 zugänglich. 2 läßt sich oxidativ zum β‐Lactam 4 spalten.

Carbene complexes 1 react with isocyanides 2 to give ketenimine complexes 312' in good yields. Complexes 3 prove to be versatile synthons for organic reactions. [',41 They are capable of undergoing novel [2 + 2]-, [31 [3 + 21-, and [4 + 21-cycloadditions, all of which are characteristically controlled by the carbonylmetal fragment.H,, 2-Thienyl; R' = CeH,. o-CH~O-C~HI. c-C~H,, In inert solvents, 3 is slowly converted at 40-70°C into 1,2-bis(imino)cyclobutane complexes 5 and M(C0)6 by a template-controlled symmetric [2 + 21-cycloaddition of two C=C bonds, presumably via the intermediates 4.['] 4 5 3a reacts rapidly with the C=O and C=N-groups of aldehydes 6a and isocyanates 6b, respectively, undergoing [3 + 21 c y~l o a d d i t i o n~~~ to give the oxazolidine complexes 7a-c and imidazolidine complexes 7d-i, respectively. In each case formation of a M = C bond to the central C atom of the CCN moiety takes place (Table 1). 9s c-C6H,, 6