The preparation of urea by Wöhler constituted a landmark achievement in organic chemistry, and it laid the ground for the early days of target-oriented organic synthesis.1 Since then, significant progress has been achieved in this discipline; many powerful single bond forming reactions and asymmetric variants have been developed. These discoveries have paved the way for the stereoselective assembly of complex organic molecules, a task deemed inconceivable by early practitioners. A great many strategies were invented by chemists in order to facilitate the synthesis of complex natural products.2 One avenue in emulating nature’s efficiency would * To whom correspondence should be addressed. E-mail: dennis.hall@ ualberta.ca. † Novartis Institute for Biomedical Research. ‡ Department of Chemistry, University of Alberta. Chem. Rev. 2009, 109, 4439–4486 4439

Natural product synthesis using multicomponent reaction strategies.

Palladium-catalyzed alkynylation.

Transition Metal Catalyzed Cycloisomerizations of 1,n-Allenynes and -Allenenes

Stereocontrolled synthesis of tetrasubstituted olefins.

Publisher Summary This chapter discusses the chemistry of cationic dicyclopentadienyl group 4 metal–alkyl complexes. Neutral, d 0 group 4 metal alkyl complexes of general form Cp 2 M(R) 2 (R = H, hydrocarbyl) or Cp 2 M(R)(X) (X = anionic, two–electron donor) comprise the most extensively studied class of group 4 organometallics (I). For many years, it has been suspected that cationic d 0 metal–alkyl species Cp 2 M(R) + are involved in metallocene-based Ziegler–Natta olefin polymerization catalyst systems of the general type Cp 2 MX 2 /AIR n X 3 – n . Several key advances in the early 1980s generated renewed interest in the proposal that Cp 2 M(R) + ions are active species in the soluble catalyst systems. A simple but key point in the development of this chemistry was the realization that noncoordinating, nonreactive counterions, such as BPh 4 – are required for the isolation of stable salts. In 1976, Kaminsky reported the isolation of [(C 5 H 5 ) 2 Zr(CH 2 C(H)– (AIEt 2 ) 2 )][C 5 H 5 ] from the reaction of (C 5 H 5 ) 4 Zr and AIEt 3 . Cationic Cp 2 M(R)(L) + complexes exhibit a variety of interesting structural features, which result from the high Lewis acidity of the cationic d 0 metal centers. The tetrahydrofuran (THF) ligands in these complexes are labile and generally undergo rapid (nuclear magnetic resonance (NMR) time scale) exchange with free THF by dissociative or associative mechanisms at ambient temperature. Cationic, d 0 Cp 2 M(R)(L) + and base-free Cp 2 M(R) + complexes are easily prepared from readily available Cp 2 M(R) 2 compounds. There is strong evidence that Cp 2 M(R) + ions are the active species in Cp 2 MX 2 -based Ziegler–Natta olefin polymerization catalysts.

Chemistry of Cationic Dicyclopentadienyl Group 4 Metal-Alky I Complexes

Metal-promoted cyclization. 19. Novel bicyclization of enynes and diynes promoted by zirconocene derivatives and conversion of zirconabicycles into bicyclic enones via carbonylation

Clean and convenient procedure for converting primary alkyl iodides and .alpha.,.omega.-diiodoalkanes into the corresponding alkyllithium derivatives by treatment with tert-butyllithium

Zirconocene-promoted stereoselective bicyclization of 1,6- and 1,7-dienes to produce trans-zirconabicyclo[3.3.0]octanes and cis-zirconabicyclo[4.3.0]nonanes

Metal-promoted cyclization. 28. Regioselective and diastereoselective alkyl-alkene and alkene-alkene coupling promoted by zirconocene and hafnocene

Strictly regio-controlled method for α-alkenylation of cyclic ketones via palladium-catalyzed cross coupling

Douglas R. Swanson

Papers

Metal-promoted cyclization. 19. Novel bicyclization of enynes and diynes promoted by zirconocene derivatives and conversion of zirconabicycles into bicyclic enones via carbonylation

Clean and convenient procedure for converting primary alkyl iodides and .alpha.,.omega.-diiodoalkanes into the corresponding alkyllithium derivatives by treatment with tert-butyllithium

Zirconocene-promoted stereoselective bicyclization of 1,6- and 1,7-dienes to produce trans-zirconabicyclo[3.3.0]octanes and cis-zirconabicyclo[4.3.0]nonanes

Metal-promoted cyclization. 28. Regioselective and diastereoselective alkyl-alkene and alkene-alkene coupling promoted by zirconocene and hafnocene

Strictly regio-controlled method for α-alkenylation of cyclic ketones via palladium-catalyzed cross coupling