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

Abstract

Ah ighly E-selective cross-dimerization of terminal alkynes with either terminal silylacetylenes,tert-butylacetylene, or 1-trimethylsilyloxy-1,1-diphenyl-2-propyne in the presence of adichlorocobalt(II) complex bearing asterically demanding 2,9-bis(2,4,6-triisopropylphenyl)-1,10-phenanthroline,a ctivated with two equivalents of EtMgBr,g ives av ariety of (E)-1,3-enynes.Awell-characterized diolefin/cobalt(0) complex, with divinyltetramethyldisiloxane,a cted as ac atalytically active species without any activation, clearly indicating that ac obalt(0) species is involved in the catalytic cycle.

Catalytic Hydrogen Transfer Reactions

“…The 2,9‐diaryl‐1,10‐phenanthroline ligands have also been used by other groups into cobalt‐catalyzed dimerization of terminal alkynes and ferrous metal‐catalyzed ethylene oligomerization. [ 35 ] The potential of these ligands in open‐shell catalyst‐promoted hydride transfer could be expected.…”

Pd‐Catalyzed Tandem Pathway for Stereoselective Synthesis of (E)‐1,3‐Enyne from β‐Nitroalkenes by Using a Sacrificial Directing Group

“…Additionally, transition metal (Rh, Ru, Pd, etc .) catalyzed homo‐ and cross‐coupling of two alkynes yield the head‐to‐tail gem‐1,3‐enynes and head‐to‐head E / Z ‐1,3‐enynes albeit suffers with the regio‐ and stereoselectivity issues for instability of alkynes (Figure 1B–a) [24–32] . In 1968, Wilkinson and Singer pioneered a stereoselective dimerization of propargylic alcohol to head‐to‐head ( E )‐1,3‐enyne using of RhCl(PPh 3 ) 3 in benzene [33] .…”

Asymmetric Synthesis of 3-Methyleneindolines via Rhodium(I)-Catalyzed Alkynylative Cyclization of N-(o-Alkynylaryl)imines

“…9 The transition-metal-catalyzed hydroalkynylation of internal alkynes with terminal alkynes has been extensively studied for its perfect atom economy in the synthesis of functionalized alkynes. 10 Due to the wealth of carbo-and heterocycles in natural products, it is of great importance to develop efficient asymmetric annulation protocols; however, the synthesis of enantioenriched heterocycles via transition-metal-catalyzed alkynylative tandem reactions of alkynes is quite limited. 11 Consequently, we proposed the rhodium-catalyzed enantioselective alkynylative cyclization of N-(o-alkynylaryl)imines, even though several challenges were encountered in this process (Scheme 1d).…”