Cobalt-Catalyzed Cross Addition of Silylacetylenes to Internal Alkynes

Abstract

A CoCl2·6H2O/Zn reagent using 2-(2,6-diisopropylphenyl)iminomethylpyridine (dipimp), 1,2-bis(diphenylphosphino)ethane (dppe), or 1,2-bis(diphenylphosphino)benzene (dppPh) as a ligand effectively catalyzed the cross-addition reaction of silylacetylene to internal alkynes. The reaction of some unsymmetrical internal alkynes, such as 3-arylpropargyl alcohols, proceeded in a highly regioselective manner in the presence of dppe or dppPh but gave a nearly 1:1 mixture of regioisomers in the presence of dipimp. The results of reactions using 1-deuterated 2-silylacetylene revealed that the reaction involves a direct oxidative addition of the silylacetylenic C-H bond to cobalt.

Cobalt‐Catalyzed Formal [4+2] Cycloaddition of α,α′‐Dichloro‐ortho‐Xylenes with Alkynes

“…In the reaction, a propargylic oxygen function was important to drastically enhance the reaction. [19] Thus, propargyl ethers, even with a phenyl (2 c) and cyclopropyl group (2 d) were tolerated, giving rise to the corresponding adducts in good yields ( Table 3, entries 2 and 3). In contrast, simple alkynes, such as 2 e and 2 f showed lower reactivity (Table 3, entries 4 and 5).…”

Cobalt‐Catalyzed Formal [4+2] Cycloaddition of α,α′‐Dichloro‐ortho‐Xylenes with Alkynes

“…Similar to 2 a , 1,4‐dibenzoxybut‐2‐yne ( 2 b ) participated in the cycloaddition and provided the corresponding dihydronaphthalene 3 ab in high yield (Table 3, entry 1). In the reaction, a propargylic oxygen function was important to drastically enhance the reaction 19. Thus, propargyl ethers, even with a phenyl ( 2 c ) and cyclopropyl group ( 2 d ) were tolerated, giving rise to the corresponding adducts in good yields (Table 3, entries 2 and 3).…”

Cobalt‐Catalyzed E‐Selective Cross‐Dimerization of Terminal Alkynes: A Mechanism Involving Cobalt(0/II) Redox Cycles

“…Deuterium labeling experiments (see the Supporting Information for details), and isolation of the catalytically active 13 revealed a plausible reaction mechanism (Scheme ). The cobalt precatalyst 1 a is reduced by EtMgBr to give the cobalt(0) species A .…”