Z‐Selective (Cross‐)Dimerization of Terminal Alkynes Catalyzed by an Iron Complex

Abstract

Efficient iron-catalyzed homocoupling of terminal alkynes and cross-dimerization of aryl acetylenes with trimethylsilylacetylene is reported. The complex [Fe(H)(BH4 )(iPr-PNP)] (1) catalyzed the (cross-)dimerization of alkynes at room temperature, with no need for a base or other additives, to give the corresponding dimerized products with Z selectivity in excellent yields (79-99 %).

Iron‐Catalyzed gem‐Specific Dimerization of Terminal Alkynes

“…Similar to Z and E 1,3‐enynes, geminal ( gem ) 1,3‐enynes are useful synthons for complex organic architectures ,,–. Nevertheless, to the best of our knowledge, iron‐catalyzed gem ‐selective alkyne dimerization has not been reported . Gem ‐selective alkyne dimerization has been reported with palladium, rhodium, early metal, and aluminum catalysts .…”

“…In summary,t he deprotonation of 1 gave cyclometalated complex 2,w hich is an efficient catalyst for the homo-and cross-dimerization of terminal alkynes in the absence of additives.O ur catalytic system is compatible with ab road range of substrates and exclusively gives the gem products, thus making it complementary to Milsteins Z-selective iron catalyst. [7] Our preliminary mechanistic study and computation have allowed us to propose apossible mechanism, which will be studied in further detail. Such studies,a long with the design of more active iron catalysts,a re underway in our laboratory.…”

“…[1a, 4, 5] In contrast, only af ew examples of iron-based catalysts have been reported. [6,7] Thef irst reported iron-catalyzed alkyne dimerization uses FeCl 3 as the catalyst in the presence of aligand and large excess of KO t Bu;this reaction requires an extremely high catalyst loading (30 mol %) and high temperatures,and gives E enyne products. [6a] Recently,Milstein and co-workers reported aw ell-defined iron(II)-pincer catalyst that can achieve Z-selective alkyne dimerization of arylal-kynes under mild conditions at 1-3 mol %catalyst loadings in the absence of any additive.…”

Cobalt‐Catalyzed Dimerization and Homocoupling of Terminal Alkynes

“…[3][4][5] In particular,d irect dimerization [6] and Glaserh omocoupling [7] of terminal alkynes are of significant interestd ue to their atom-economy assembling av ariety of useful organic compounds, such as 1,3-diynes [8] and 1,3-enynes. [9] In addition, these products are valuable building blocks for the synthesis of polysubstituted aromatic rings, drug intermediates and natural products.I np reviousr eported works, dimerizationo ft erminal alkynes often gave E-1,3-enynes [10] and Z-1,3-enynes, [11] and only af ew examples has been reportedg iving high selectivity.A lso, to our knowledge,t he efficient Glaser homocoupling of terminal alkynes catalyzed by cobalt complexes has rarely been developed.[12]Thus, we envisionedt hat cobaltc omplexes promoted reaction of terminal alkynes would provide alternative access to 1,3-diynes and Z-selective 1,3-enynes through fine tuningo f the ligand structure. In this regard,w eh erein describe cobaltcatalyzed dimerization/homocoupling of terminala lkynes in the presence of tBuOK, depending on the cobalt complexes and reaction conditions.…”

Terminal Alkyne Coupling Reactions through a Ring: Mechanistic Insights and Regiochemical Switching

“…[1,2] These reactions involve the formal addition of the C(sp) À H bond of one alkyne across the C Cb ond of the other, aprocess that can in principle result in three different regioor stereochemical isomers: gem-, E-, and Z-enynes.W ith the additional possibility for the substrates to be consumed through competing metal-catalysed reaction pathways-for instance leading to butatrienes,a renes,o ro ther polyenesthe widespread application of terminal alkyne coupling reactions in organic synthesis rests on the development of catalysts that can enforce high reaction control. [4] Building on early landmarks, [5] rhodium-based catalysts are of notable contemporary interest. [4] Building on early landmarks, [5] rhodium-based catalysts are of notable contemporary interest.…”