Zirconacyclopentadienes 1,1-cycloaddition

Highly functionalized benzenes and naphthalenes have been prepared by cycloaddition of zirconacyclopentadiene 32 and its benzoderivative 33 [38] with... 

Takahashi and co-workers have designed a [4 + 3]-cycloaddition based on their previously reported [4 + 4]- and [4 + 5]-reactions (Sections 10.13.2.4 and 10.13.2.7) involving zirconacyclopentadienes as four-carbon components. The zirconacyclopentadienes are prepared by the coupling of two alkynes with Cp2ZrR2 (where R = Et, Bu, or... 

Chen C, XI C, Jiang Y, Hong X (2005) 1,1-cycloaddition of oxalyl dichloride with dialkenylmetal compounds formation of cyclopentadienone derivatives by the reaction of 1,4,-dilithio-l,3-dienes or zirconacyclopentadienes with oxalyl chloride in the presence of CuCl. J Am Chem Soc 127 8024-8025... 

Although stoichiometric amounts of transition metal complexes were employed, the cross-[2+2+2] cycloaddition of three different alkynes has been achieved using zirconium and nickel complexes. The reaction of 2-butyne, 4-octyne, and Cp ZrEt selectively afforded unsymmetrical zirconacyclopentadiene. Subsequently, it reacted with 3-hexyne in the presence of NiBr fPPhjlj to give the desired hexasubstituted benzene (Scheme 21.6) [9]. 

I-2+ 2] cycloaddition of alkynes, selectivity among tliree different alkynes can be achieved by using unsymmetrical zirconacyclopentadienes, prepared from oxidative coupling of two different alkynes with Cp2Zr(II), as intermediates to react with the third alkyne in the presence of NiBr2(PPh3)2 [39]. 

Takahashi T, Xi Z, YamazaM A et al (1998) Cycloaddition reaction of zirconacyclopentadienes to alkynes highly selective formation of benzene derivatives from three different alkynes. J Am Chem Soc 120 1672-1680... 

Lithiobutadienes 35 can easily be prepared from zirconacyclopentadienes by an iodination-lithiation sequence. The dilithiobutadienes 35 generated reacted with unactivated alkynes afforded substituted benzenes 36 via a formal [4 + 2] cycloaddition (Scheme 11.14) [16]. 

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