Carbometallation of Alkenes and Alkynes

Stereoselective Synthesis of (E)- and (Z)-Acetals of Pent-2-en-4-yn-1-al and Related Dienynes and Dienediynes

“…However, through the alkynylcopper intermediate in agreement with the absence of 5 when the reaction was performed without an increase in the concentration of the reagents induced the formation of the desilylated compound 8a-E and of the subcuprous iodide (Entry 3). [20] Another possibility might be the carbopalladation of 1,4-bis(trimethylsilyl)but-1,3-diyne sequent homocoupling product 9a-EE (Entry 5). On the other hand, the increased reactivity allowed the achieveby a vinylpalladium compound resulting from the oxidative addition of 3a-E on PdL 2 .…”

Titanium 3,3′-Modified-Biphenolate Complexes Atropisomerically Controlled by TADDOLs: Novel Chiral Lewis Acid Catalysts for Asymmetric Methylation with an Achiral Methyl-Titanium Reagent

“…For example, catalytic asymmetric alkylation with diethylzinc reagent has been successfully reported, using chiral aminoalcohol-zinc catalysts by Oguni, 9 Soai, 10 Noyori, 11 and Knochel. 12 In sharp contrast, only low levels of enantioselectivity (up to 59% ee) 13 were obtained in the methylation reaction with dimethylzinc even by using similar aminoalcohol-zinc catalysts (Scheme 4), presumably because of low steric demand of dimethylzinc reagent. Thus, we developed chiral BIPOLate/TADDOLate-Ti catalysts (1) to give enhanced enantioselectivities up to 100% ee, in a combination with a highly nucleophilic but sterically demanding achiral methyl-titanium reagent.…”

Zirconocene catalyzed diastereoselective carbometalation of cyclobutenes

“…The carbometalation reaction, defined as “the addition of a carbon–metal bond of an organometallic across a carbon–carbon unsaturated system leading to a new organometallic species that can be further functionalized” – is one of the most powerful approaches that have been used extensively to perform the 1,2-bis-alkylation of alkynes. 1 In this context, organocopper, 2 as well as zirconocene-catalyzed methylalumination, 3 occupies a significant place due to its high stereoselectivity, typically controlled by the nature of the substituents on the triple bond (Scheme 1, path a for an example of carbocupration). Besides forming stereodefined polysubstituted double bonds, the carbometalation reaction of alkynes has recently been considered as a new stereodefined chemical handle to prepare reactive intermediates for the subsequent creation of more complex molecular structures possessing sp 3 -configurated stereocenters including quaternary carbon stereocenters (Scheme 1, path b).…”