Ru(II)-Catalyzed Cycloadditions of 1,6-Heptadiynes with Alkenes:  New Synthetic Potential of Ruthenacyclopentatrienes as Biscarbenoids in Tandem Cyclopropanation of Bicycloalkenes and Heteroatom-Assisted Cyclocotrimerization of 1,6-Heptadiynes with Heterocyclic Alkenes

Abstract

The ruthenium(II)-catalyzed tandem cycloaddition of 1,6-heptadiynes with bicyclic alkenes, such as bicyclo[3.2.1]heptenones and norbornene derivatives, furnishes the 1:2 adducts between the diynes and two molecules of the bicycloalkenes together with common [2 + 2 + 2] cyclocotrimerization products. The structure of a representative tandem 1:2 adduct between dimethyl dipropargylmalonate and 2,4-dimethylbicyclo[3.2.1]-oct-6-en-3-one was unequivocally determined by X-ray analysis and was concluded to involve an unusual 1,2-dicyclopropylcyclopentene skeleton. On the basis of the spectroscopic analogy, the previously communicated structures of the tandem cycloadducts between the diynes and norbornene derivatives were corrected. The formation of the tandem double-cyclopropanation products from the diynes is chemical evidence of a biscarbenoid hybrid structure, 1,3,5-metallacyclopentatriene, of the corresponding 2,4-metallacyclopentadiene intermediates. The selectivity for the formation of the tandem cyclopropanation adducts was increased in the order of (η 5 -C 9 H 7 )Ru(PPh 3 ) 2 Cl > CpRu(cod)Cl > Cp*Ru(cod)Cl, indicative of the η 5 f η 3 ring slippage of the cyclopentadienyl type ligands playing a key role in the tandem cyclopropanation. On the other hand, the normal [2 + 2 + 2] cyclocotrimerization between 1,6-heptadiynes and alkenes was selectively catalyzed by Cp*Ru(cod)Cl, in the case of cyclic or linear alkenes possessing heteroatoms at the allylic position. The latter heteroatom-assisted cyclocotrimerization was also catalyzed by a paramagnetic dinuclear ruthenium(III) complex, [Cp*RuCl 2 ] 2 , at lower temperature.

Addition of Diazoalkanes to Enynes Promoted by a Ruthenium Catalyst: Simple Synthesis of Alkenyl Bicyclo[3.1.0]hexane Derivatives

“…The formation of intermediates D and E corresponds to alkene and enyne metathesis key steps. The novelty of this catalytic reaction is related to the last step: a promoted reductive elimination from E to give 2, rather than the classical formation of the enyne metathesis product the alkenylcycloalkene F. On interaction of ruthenium-carbene moiety with an alkene, this reductive elimination step is favoured [20] probably because of the steric hindrance of the C 5 Me 5 -Ru group, as we showed that [Cp*RuCl(cod)] also catalyzed the same reaction but afforded derivatives of 2 in lower yield.…”

Ruthenium‐Catalyzed Cycloaddition of 1,6‐Diynes and Nitriles under Mild Conditions: Role of the Coordinating Group of Nitriles

“…Ruthenium-catalyzed cycloaddition of dicyanides: To A C H T U N G T R E N N U N G achieve a selective and efficient pyridine formation, we employed a neutral ruthenium(ii) complex, [Cp*RuClA C H T U N G T R E N N U N G (cod)] (1), having both an electron-donating planar ligand (Cp* = pentamethylcyclopentadienyl) and a readily leaving supporting ligand (cod = 1,5-cyclooctadiene), as this proved to be an efficient precatalyst for the cycloaddition of the a,w-diynes with alkenes, [11] alkynes, [12] isocyanates and isothiocyanates, [13] or tricarbonyl compounds. [14] The reaction of dimethyl dipropargylmalonate (2 a) and two equivalents of acetonitrile in the presence of 1 mol % 1 in 1,2-dichloroethane (DCE) at room temperature (around 25 8C), however, gave only a mixture of dimers and trimers of 2 a. Diyne 2 a was recovered quantitatively if the reaction was carried out with acetonitrile as a solvent.…”

“…In contrast to 3 b, dicyanides connecting a more rigid tether gave better results. For example, ortho-, meta-, and para-dicyanobenzenes 3 d-3 f were allowed to react with 2 a, delivering the corresponding pyridines 4 ad-4 af in 43-61 % yield (runs [10][11][12]. In these cases, the product yields appeared to depend on the distance between the two cyano groups.…”

Indenylmetal Catalysis in Organic Synthesis

“…[56] When dimethyl dipropargylmalonate 67 is reacted with an excess of norbornene and chloro(η 5 -indenyl)ruthenium(1,5-cycloocatdiene) 70 , polycyclic 68 is formed as the primary reaction product, with minor amounts of diene 69 . However, when indenyl complex 70 is exchanged for its cyclopentadienyl analogue 71 , more of the diene is formed in proportion to 68 .…”