A quarter of a century of explorations in organozirconium chemistry

Abstract

Systematic explorations of organozirconium chemistry over the past quarter of a century have led to the discoveries and development as well as structural and mechanistic clarifications of novel Zr-catalyzed and -promoted carbon-carbon bond-forming reactions including (i) Ni- or Pd-catalyzed cross-coupling reaction of organozirconiums, (ii) Zr-catalyzed carboalumination of alkynes, (iii) Zr-catalyzed asymmetric carboalumination of alkenes, (iv) generation and carbometallative ring expansion of zirconacyclopropanes and zirconacyclopropenes and a myriad of their transformations and (v) various organozirconium migratory insertion reactions.

5.34 Early Transition Metal Mediated Reductive Coupling Reactions

“…As shown, the substrate bearing a trimethylsilyl (TMS)-and t-butyldimethylsilyl (TBDMS or TBS)-substituent undergoes cyclization/aldehyde addition to deliver a product where C-C bond formation has occurred at the site a-to the TMS group (in preference to the TBDMS group). 4 or ClTi(Oi-Pr) 3 (1 equivalent) Although the yield for the product was reported to be only 41% (half of that observed for other examples), and a precise selectivity was not given for this process, the authors report that the other possible regioisomer 'could not be isolated. ' In related studies targeting intermolecular functionalization of metallacyclopentadienes generated from Ti-mediated diyne cyclization, it has been demonstrated that site-selective allylation is possible (Scheme 5B).…”

“…The air-stable precatalyst Cp 2 TiCl 2 has been shown to be competent in cyclization chemistry. Here, cyclization of enynes to bicyclic iminocyclopentenes proceeds with 10 mol% of 'finely ground' Cp 2 TiCl 2 , 20 mol% n-BuLi, and 115 mol% Et 3 2. Although previous attempts to accomplish CO insertion into intermediate titanacyclopentenes derived from enyne cyclization with Cp 2 TiCl 2 /2EtMgBr in tetrahydrofuran (THF) met with failure, 28,37,38 it has been found that the commercially available precatalyst Cp 2 Ti(CO) 2 can be employed to catalyze cyclization and carbonylation to deliver bicyclic cyclopentenones (5 -20 mol% Cp 2 Ti(CO) 2 , 18 psig CO, PhMe, 90 1C).…”

“…This finding stemmed from the discovery and development of a new hydroxycyclopropane-forming reaction, now termed the Kulinkovich reaction, 1 where the addition of two equivalents of a suitable Grignard reagent to Ti(Oi-Pr) 4 results in an activated organometallic complex that ultimately adds to a carboxylic ester en route to the formation of a hydroxycyclopropane (Scheme 1). 2 Like the established reactivity of the 'Negishi reagent' (n-Bu 2 ZrCp 2 ), 3,4 it has been proposed that the Kulinkovich reaction proceeds through the intermediacy of a similar metallacyclopropane, formed from decomposition of the initially formed (alkyl) 2 Ti(Oi-Pr) 2 species. 5 In short, each s C-Ti bond of the resulting metallacyclopropane engages in nucleophilic addition to the carboxylic ester, resulting in the formation of a hydroxycyclopropane.…”

“…34.3.8.2 Single and double asymmetric hydroxyl-directed imine-alkene coupling 1719 5. 34.3.8.3 Imine-alkene coupling by formal metallo [3,3] Glossary Chemoselectivity A preference for reactivity at a particular functional group of a molecule possessing multiple functional groups. When this term is used to describe selective reaction at one functional group in a molecule possessing other similar groups (one alkene of a polyene), the term 'site selectivity' is used.…”

Zirconocene catalysis in the synthesis of 1,4-dimagnesium reagents: using competitive inhibition to suppress β-hydrogen abstraction

“…Zirconocene complexes have been widely employed as reagents for the modification and elaboration of alkenes [1,2]. There are many examples of both stoichiometric and catalytic reactions in which zirconocene dichloride acts as a precursor in the formation of reduced zirconium intermediates that carbometallate or couple alkenes [3][4][5].…”