Nickel‐Catalyzed Asymmetric Addition of Alkyne CH Bonds across 1,3‐Dienes Using Taddol‐Based Chiral Phosphoramidite Ligands

Abstract

Much interest has been focused on the catalytic, direct conversion of alkyne C À H bonds through C À C bond-forming reactions without the stoichiometric generation of acetylides. [1] One of the most widely used procedures for such an atom-economical process is the nucleophilic alkynylation of carbonyl compounds, a,b-unsaturated carbonyl compounds, or related electrophiles, in which catalytically generated metal acetylides often play a key role. [2, 3] Recent attention has focused on the development of asymmetric variants of these nucleophilic alkynylation reactions for the synthesis of highly functionalized chiral alkyne derivatives. [4,5] Besides these nucleophilic alkynylation reactions, hydroalkynylation, i.e. the addition of alkyne C À H bonds, across unactivated carbon-carbon multiple bonds has attracted increasing attention. [1b] After extensive studies on the homoand cross-dimerization reactions of alkynes using rhodium, palladium, and nickel catalysts, [6] hydroalkynylation has been extended to carbon-carbon double bonds, such as those in allenes and cyclopropenes. [7,8] However, the scope of the hydroalkynylation reaction is still significantly limited. [9,10] As a consequence, no successful catalytic asymmetric hydroalkynylation reactions have been established, except for the rhodium-catalyzed hydroalkynylation of allenes. [10] We recently showed that bulky triisopropylsilylacetylene underwent addition to C = C bonds in 1,3-dienes, norbornene, styrenes, and methylenecyclopropanes in the presence of nickel triorganophosphine catalysts. [9] The relatively narrow scope for the choice of phosphine ligands in these reactions could be a major difficulty in applying this system to asymmetric synthesis. Herein, we report the nickel-catalyzed asymmetric hydroalkynylation reactions of 1-aryl-1,3-butadienes involving the essential use of taddol-derived phosphoramidite ligands (taddol = 2,2-dimethyl-a,a,a',a'-tetraphenyldioxolane-4,5-dimethanol). In addition to the significance of the chiral ligands, the use of a terminal alkyne that contains an a-siloxy-sec-alkyl group on the alkynyl carbon is important to achieve sufficient reaction efficiency.

Nickel-catalysed migratory hydroalkynylation and enantioselective hydroalkynylation of olefins with bromoalkynes

“…The semi-hydrogenation of alkyne (5a) by DIBAL-H (diisobutylaluminum hydride) could be highly stereoselective, giving the Z-alkene (9). In addition, oxidative cleavage of the triple bond in 5e could afford the corresponding chiral carboxylic acid (10).…”

Urea Azines (Bisguanidines): Electronic Structure, Redox Properties, and Coordination Chemistry

“…Later the same group (Nishimura and Hayashi) developed a cobalt‐Josiphos‐type catalyst system for handling substrates without such a neighboring coordinating group 10. In 2010, Suginome showed the first nickel‐catalyzed asymmetric addition of a terminal alkyne CH bond to 1,3‐dienes 11. The trans ‐configuration of the dienes and unique α‐siloxy‐α,α‐ sec ‐alkyl‐containing alkynes were found to be crucial reaction partners for achieving high enantioselectivity.…”

Asymmetric Hydroalkynylation of Norbornadienes Promoted by Chiral Iridium Catalysts

“…It was found that the allene moiety had to contain the coordinating diphenylphosphinyl group (P(O)Ph 2 ). In 2010, Shirakura and Suginome pioneered the nickel‐catalyzed enantioselective addition of the CH bond of a terminal alkyne across a 1,3‐diene (Scheme ) 9. The trans diene was demonstrated to be crucial for obtaining high enantioselectivity (up to 93 % ee ) and reactivity.…”