Cycloaddition Reaction of Zirconacyclopentadienes to Alkynes:  Highly Selective Formation of Benzene Derivatives from Three Different Alkynes

Abstract

Zirconacyclopentadienes reacted with acetylenecarboxylates in the presence of a stoichiometric amount (2 equiv) of copper chloride to give benzene derivatives in high yields along with the formation of a copper mirror on the wall of the reaction vessel. Reactions of unsymmetrical zirconacyclopentadienes prepared from two different alkynes with acetylenecarboxylates gave benzene derivatives from three different alkynes in high yields with high selectivities. Preparation of unsymmetrical zirconacyclopentadienes and benzene derivatives formation can be done in one-pot. The structure of the reaction product of the unsymmetrical zirconacyclopentadiene having a trimethylsilyl group and a methyl group in the α- and β-position, respectively, with acetylenedicarboxylate was determined by X-ray analysis. It indicated that the regiochemistry of those substituents was maintained during the reaction. When the coupling reaction of zirconacyclopentadienes with acetylenedicarboxylate in the presence of copper chloride was carried out at −78 °C, linear trienes were obtained as the intermediates in high yields after hydrolysis. Warming the mixture without hydrolysis gave the desired benzene derivatives in high yields. Use of an unsymmetrical zirconacyclopentadiene afforded a mixture of two isomers of the linear triene as intermediates after hydrolysis. When the mixture of the two isomers was warmed to room temperature without hydrolysis, both isomers gave the same benzene derivative. In the presence of a catalytic amount of copper chloride (10 mol %), this cycloaddition proceeded to give benzene derivatives in good yields without formation of the copper mirror. The reaction under the catalytic conditions at −78 °C also gave a linear triene after hydrolysis.

Zirconocene‐Mediated Intermolecular Coupling of Si‐tethered Diynes with Alkynes, Ketones, Aldehydes, and Isocyanates by means of Novel Skeletal Rearrangement of Zirconacyclobutene–Silacyclobutene and Zirconacyclohexadiene–Silacyclobutene Fused‐Ring Intermediates

“…(2) in Scheme 4]. [14][15][16][17] In this work, we found that three triple bonds out of four [shown in Eq. (3) in Scheme 4] could be highly selectively integrated into a benzene derivative; one of the triple bonds in bis(alkynyl)siScheme 2.…”

“…[2,14,16] In our work, treatment of zirconacyclopentadiene derivatives 4, generated in situ from bis(alkynyl)silane 1 and monoalkynes via zirconacyclobutene intermediates 2, with one equivalent of DMAD in the presence of CuCl afforded benzene derivatives 14 in high isolated yields (Scheme 5). The structure of 14 b has been determined by single-crystal X-ray structural analysis (Figure 1).…”

“…[16] However, formation of benzene derivatives 14 from the sixmembered zirconacycles 5 is not clear yet. A novel skeletal rearrangement must be involved in this CuCl-mediated benzene formation reaction.…”

Synthesis of Co-oligomers of Thiophene Derivatives from Oligoynes via Zirconacyclopentadiene

“…Previously we reported that coupling of a zirconacycle with a third alkyne like dimethyl acetylenedicarboxylate (DMAD) in the presence of CuCl gives benzene derivative. 7 A similar procedure worked in 2a to afford phenylenethiophene co-oligomer 4a in 68% isolated yield. By employing different kinds of third alkyne we could produce a large variety of phenylene derivatives, furthermore, the functional groups on the phenylene unit could be utilized for further structural modification.…”

Hexasubstituted Donor–Acceptor Benzenes as Nonlinear Optically Active Molecules with Multiple Charge‐Transfer Transitions

“…Initial attempts to cyclotrimerise 6 with catalysts [50±52] such as [Pd(PhCN) 2 Cl 2 ], [53] Me 3 SiCl and Pd/C, [54] [Cp 2 ZrCl 2 ] [55,56] and [Co 2 (CO) 8 ], [57] failed without any reaction. Ligands with high steric hindrance (1,1'-bis(diphenylphosphino)ferrocene nickel(ii) chloride, dichloro-bis(tri-n-butylphosphine)nickel-(ii)) were also tried without the desired result.…”