Homodimerization, alkynes

Scheme 94 Total synthesis of the natural compound dehydrohomoancepsenolide (473) through sequential application of chemoselective ruthenium-catalyzed RCM and tungsten-catalyzed alkyne homodimerization [191]...

In 2012, Zhang and coworkers published an intermolecular version of Gagosz s alkyne-homodimerization. This paper did not provide new mechanistic insights but focused on the synthetic aspects of that chemistry [35]. 

To see whether water could be activated and added to Jt-systems other than alkynes, the metal-catalyzed hydrolysis of nitriles was studied [20]. For this purpose novel homodimeric and heterodimeric bis(acetylacetonato)ruthenium(ii) complexes bearing the 6-diphenylphosphino-N-pivaloyl-2-aminopyridine (10a) and 3-diphenylphosphinoisoquinolone (Ila) ligands were prepared. The molecular structures of these precatalyst were studied in solution and also in the solid state and revealed some unusual hydrogen-bonding patterns, in particular for the heterodimeric system in which the acetylacetonato ligand is involved (Scheme 2.7). 

Half-sandwich lanthanide alkyl complexes and, subsequently oranolanthanide amides were found to be highly efficient catalysts for the cross-coupling reactions of carbodiimides with alkynes and amines, respectively [136, 137]. Although the half-sandwich lanthanide alkyl complexes can also catalyze the dimerization of alkynes, no homodimerization product is observed in the reaction of alkynes with carbodiimides. These reactions offer a wide scope for the substrates of terminal alkynes and amines, respectively [138]. 

Trost and co-workers found that the Pd(OAc)2 tris(2,6-dimethoxyphenyl)phosphine (TDMPP) system catalyzes the homodimerization of terminal alkynes 1 to produce conjugated enynes 2 (Scheme This method is very simple and efBcient reactions are... 

More recently, Gevorgyan and Yamamoto proposed a Pd-catalyzed trimerization of alkynes as a sequential approach to the multisubstituted benzenes 17 and 18 (Scheme In the first step of the sequence, a donor alkyne 1 would undergo either homodimerization to produce 2 or cross-coupling with an acceptor alkyne 3 to form an enyne 4. Enynes 2 and 4, after completion of the first step of the sequence, would undergo [4 + 2] benzannelation with the enynophile 16 to afford the tetra- or pentasubsdtuted benzenes 17 and 18, respectively (Scheme 6) (for the Pd-catalyzed [4 + 2] benzannelation of conjugated enynes, see Sect. IV.10.2). 

Another example of Pd(0)-catalyzed dimerizations of alkynes was reported by Ishikawa and co-workers. Terminal silylacetylenes 19, containing at least one phenyl group at the silyl moiety, in the presence of Pd(PPh3)4 underwent homodimerization in a head-to-head fashion to produce the corresponding bis-silylenynes 20 in reasonable yields (Scheme 7). The preferred anti-Markovnikov-type regiochemistry in these cases and also in the Pd(+2)-catalyzed homodimerization of trimethylsilylacetylene was explained with steric factors. ... 

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