Novel zirconocene-promoted carbon-carbon bond formation via a 1,2-migration reaction of alkynylzirconium derivatives

Tandem Insertion of Halocarbenoids and Lithium Acetylides into Zirconacycles: A Novel Rearrangement to Zirconium Alkenylidenates by β‐Addition to an Alkynyl Zirconocene

“…Molecular modelling, including DFT studies showed that the trans-fused diastereoisomer had only one reasonable conformation of the bicyclic system, in which the HCCH dihedral angles made by the four adjacent protons to the bridgehead proton were around 2 1808 and 2 608, not compatible with the observed coupling pattern. [24] The cisfused isomer has two reasonable conformations, 6 kJ mol À1 apart (comparable with error in DFT calculations) with HCCH dihedral angles (less stable conformer in brackets) of 1558 (908), 368 (288), 458 (438), and 708 (1588). The observed coupling pattern is consistent with an interconverting mixture of these conformers.…”

“…Addition of nBuLi to 21 gave (Z)-1-phenylhexene (36; 73 %) only on warming to room temperature before protonolysis, presumably by initial addition to the metal to afford 34 followed by the type of 1,2-migration previously reported by Negishi and co-workers for Cp 2 Zr [24] to afford 35. The result indicates that a bulky nucleophile is important for successful b-addition to the alkyne by inhibiting direct attack on the metal.…”

“…The observed coupling pattern is consistent with an interconverting mixture of these conformers. [24] The structure of the minor product 52 was also determined by 2D NMR experiments; for example, there was a long-range ( 2 J or 3 J) correlation between the PhC=CH 2 carbon and the cyclopentyl CH 2 protons, but not between the quaternary alkyl carbon and the allylic cyclohexyl CH 2 protons. The stereochemistry of 52 was not determined.…”

Zirconocene-promoted coupling reaction of terminal acetylenes to geminal enediynes in the presence of p-chloranil

“…of LiC"CPh according to reported literature [12], with oxidants such as 1,4-benzoquinone, tetrachlorobenzoquinone (TCQ) or dichlorodicyanobenzoquinone (DDQ) were carefully examined and quenched with acid to form (2-(phenylethynyl)but-1-en-3-yne-1,4-diyl)dibenzene (2a). The product 2a was characterized by 13 C NMR spectroscopy.…”

“…Among them, interest in organozirconium chemistry has been rapidly increasing and a tremendous number of applications in synthetic chemistry have been found [11]. In a typical process, the carbon-carbon bond formation was reported by Negishi et al using zirconate complex Li[Cp 2 Zr(C"CR) 3 ] [12,13]. Three equivalents of LiC"CPh were essential to promote the carbon-carbon bond formation, however, the third LiC"CPh did not take part in forming new C-C bond.…”