Abstract

Abstract

Abstract

In the presence of a catalytic amount of [Cp*RuCl(cod)] (Cp*=pentamethylcyclopentadienyl, cod=1,5-cyclooctadiene), 1,6-diynes were allowed to react chemo- and regioselectively with nitriles bearing a coordinating group, such as dicyanides or α-halonitriles, at ambient temperature to afford bicyclic pyridines. Careful screening of nitrile components revealed that a CC triple bond or heteroatom substituents, such as methoxy and methylthio groups, proved to act as the coordinating groups, whereas CC or CO double bonds and amino groups failed to promote cycloaddition. This suggests that coordinating groups with multiple π-bonds or lone pairs are essential for the nitrile components.

In the presence of 2–5 mol % Cp*RuCl (cod), various 1,6-diynes reacted with α-monohalo- and α,α-dihalonitriles at ambient temperature to afford 2-haloalkylpyridines in 42–93% isolated yields. The failure of acetonitrile, N,N-dimethylaminoacetonitrile, phenylthioacetonitrile, and methyl cyanoacetate as nitrile substrate clearly showed that the α halogen substitution is essential for the present cycloaddition under mild conditions. The cycloaddition of unsymmetrical diynes bearing a substituent on one alkyne terminal gave 2,3,4,6-substituted pyridines exclusively.

A trinuclear carbonylruthenium complex, [Ru₃(CO)₁₂], was treated with diynes bearing ester, phenyl, or trimethylsilyl groups on the alkyne termini to give rise to various complexes. A diyne diester afforded a dinuclear ruthenacycle complex similar to known iron ferrole complexes and a mononuclear ruthenacyclopentadiene complex. The selectivity for the formation of these products varied depending on the ratio of the diyne diester toward [Ru₃(CO)₁₂]. When a phenyl-substituted diyne was employed, a cyclopentadienone complex was formed together with the expected dinuclear ruthenacycle complex. In contrast, a bis(trimethylsilyl)diyne gave the corresponding cyclopentadienone complex as the only product. Treatment of the obtained ruthenabicycle complex with trimethylamine oxide (Me₃NO) gave a mono(trimethylamine) complex, which was further converted into various phosphane complexes upon reaction with phosphanes in refluxing THF. The corresponding monophosphane complexes were obtained for all monodentate or bidentate phosphanes except for bis(diphenylphosphanyl)methane, which afforded a bridging bis(phosphane) complex. In contrast, when an isolated monodentate phosphane complex of 1,2-bis(diphenylphosphanyl)ethane and diphenyl(2-pyridyl)phosphane was treated with Me₃NO, P-P or P-N chelate complexes were formed, respectively. The dinuclear mono(amine)ruthenacycle complex also reacted with dimethyl butynedioate (dimethyl acetylenedicarboxylate, DMAD) in refluxing THF to afford a novel μ-η²-alkyne complex together with the [2+2+2] cycloadduct between the diyne and DMAD. The highly electron-deficient character of DMAD is imperative for the formation of the μ-alkyne complex. Methyl propiolate and diphenylacetylene gave no corresponding μ-alkyne complexes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

The ruthenium-catalyzed one-pot double allylation/cycloisomerization of 1,3-diketones and methyl acetoacetate gave exo-methylenecyclopentanes in moderate to good yields with high isomer selectivity. The double allylation step effectively proceeded in the presence of a Ru^II precatalyst, [Cp*RuCl(cod)], in 1,2-dichloroethane at 90 °C. The subsequent cycloisomerization was carried out upon addition of triethylsilane as a hydride source without purification of a 1,6-diene intermediate. Detailed inspections of the reaction by ¹H NMR spectroscopy disclosed that triethylsilyl methyl ether plays an important role for the conversion of a ruthenium(IV) allyl complex formed in the double allylation step into a ruthenium(II) species required for the cycloisomerization.

In the presence of 2.5 mol % of [Pd₂(dba)₃] (dba=dibenzylideneacetone) and 5 mol % of PPh₃, nearly equimolar amounts of dimethyl nona-2,7-diyne-1,9-dioate derivatives (diyne diesters) and dialkyl acetylenedicarboxylates were allowed to react in toluene at 110 °C to afford [2+2+2] cycloadducts in moderate-to-good yields. Similarly, dimethyl trideca-2,7,12-triyne-1,13-dioate derivatives (triyne diesters) were catalytically transformed into phthalic acid ester analogues in excellent yields. To gain insight into the mechanism of these intramolecular alkyne cyclotrimerizations, stoichiometric reactions of [Pd₂(dba)₃] with a diyne diester and a triyne diester bearing ether tethers were conducted in acetone at room temperature to furnish an oligomeric bicyclopalladacyclopentadiene and a Pd⁰ triyne complex, respectively. The structures of these novel complexes were unequivocally determined by Xray structure analysis. The isolated triyne complex was heated at 50 °C or treated with PPh₃ in acetone at room temperature to afford the arene product. Furthermore, the same complex catalyzed the triyne cyclization with or without PPh₃.

In the presence of CuCl and 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone, the [4+4] coupling between zirconacyclopentadienes and 1,3-diiodobutadienes fused through an oxygen or nitrogen five-membered ring proceeded at ambient temperature to afford fully substituted polycyclic cyclooctatetraenes in good yields. The fused ring moiety of the diiodides plays a critical role. The corresponding acyclic diiodide and a cyclohexane-fused analogue gave no coupling product, and a cyclopentane derivative showed only moderate reactivity. Correlation of the structures of the diiodides and their reactivity was established by an X-ray and density functional study.

Eine ungewöhnliches Paar von siebengliedrigen Chelatringen enthält ein Palladium(IV)-Komplex, der aus den käuflichen Verbindungen [Pd₂(dba)₃], Tetrachlor-1,2-benzochinon und Norbornen in nur einem Schritt hergestellt wurde. Die Struktur des THF-Komplexes wurde röntgenkristallographisch bestimmt und besteht aus einem C₂-symmetrischen Palladaspirocyclus-Gerüst und dem Etherliganden (siehe Bild).

A pair of seven-membered chelate rings are found in the palladium(IV) complex assembled in only a single step from commercially available [Pd₂(dba)₃], tetrachloro-1,2-benzoquinone, and norbornene. The structure consists of a C₂-symmetrical palladaspirocycle framework and an ether ligand, as confirmed by X-ray analysis of the thf complex (see picture).