Ruthenium(II)-Catalyzed Selective Intramolecular [2 + 2 + 2] Alkyne Cyclotrimerizations

Abstract

In the presence of a catalytic amount of Cp*RuCl(cod), 1,6-diynes chemoselectively reacted with monoalkynes at ambient temperature to afford the desired bicyclic benzene derivatives in good yields. A wide variety of diynes and monoynes containing functional groups such as ester, ketone, nitrile, amine, alcohol, sulfide, etc. can be used for the present ruthenium catalysis. The most significant advantage of this protocol is that the cycloaddition of unsymmetrical 1,6-diynes with one internal alkyne moiety regioselectively gave rise to meta-substituted products with excellent regioselectivity. Completely intramolecular alkyne cyclotrimerization was also accomplished using triyne substrates to obtain tricyclic aromatic compounds fused with 5-7-membered rings. A ruthenabicycle complex relevant to these cyclotrimerizations was synthesized from Cp*RuCl(cod) and a 1,6-diyne possessing phenyl terminal groups, and its structure was unambiguously determined by X-ray analysis. The intermediary of such a ruthenacycle intermediate was further confirmed by its reaction with acetylene, giving rise to the expected cycloadduct. The density functional study on the cyclotrimerization mechanism elucidated that the cyclotrimerization proceeds via oxidative cyclization, producing a ruthenacycle intermediate and subsequent alkyne insertion initiated by the formal [2 + 2] cycloaddition of the resultant ruthenacycle with an alkyne.

Efficient Activation of 2‐Iminomethylpyridine/Cobalt‐Based Alkyne [2+2+2] Cycloaddition Catalyst by Addition of a Silver Salt

“…of 3-hexyne with an Ru catalyst gave only 13 % of the desired product. [7] Very recently, Takeuchi and co-workers recommended a slow addition technique for such reactions to minimize the self-addition of the diyne: thus, they employed an [Ir-A C H T U N G T R E N N U N G (cod)Cl] 2 /dppe catalyst for the cyclotrimerization using the procedure of slow addition (7 h) of diyne to the mixture of monoyne (3 equivs.) and catalyst to provide the corresponding benzene derivative in good yield.…”

Reactivity of Electron-Deficient Alkynes on Gold Nanoparticles

“…[19][20][21][22][23][24][25][26] In many cases, arene-type ligands have been employed as electron-donors to stabilize the metal charge. 19b, [22][23][24] We added electron-rich arenes in the reaction medium to test a possible enhancement of the cyclotrimerization reaction and the results in Figure 2 show that Au supported-solids become in general more active for the cyclotrimerization of 1 in the presence of methoxy-substituted arenes.…”

Bio- and air-tolerant carbon–carbon bond formations via organometallic ruthenium catalysis

“…14 ). We observed that [2+2+2] cycloaddition of dimethyl acetylenedicarboxylate (2) using catalyst 1 (1 mole %) 15 was not only air-tolerant 16 but also proceeded in presence of water without any added organic co-solvent (Scheme 1, 17 . Under these mild aerobic conditions, the starting material was consumed within 5.5 h and hexamethyl mellitate 3 was isolated in 76% yield.…”