Ruthenium alkyne-coupling reactions

A cross-coupling reactions of terminal alkynes with terminal alkenes 32 supported on Merrifield-resin (Scheme 4.5) in the presence of Grubs ruthenium initiator [Cl2(PCy3)2Ru = CHPh] provided efficient access to supported 1,3-dienes 33 which were transformed into octahydrobenzazepinones 34 via MeAlCl2 catalyzed Diels-Alder reaction [27]. 

Denmark pursued intramolecular alkyne hydrosilylation in the context of generating stereodefined vinylsilanes for cross-coupling chemistry (Scheme 21). Cyclic siloxanes from platinum-catalyzed hydrosilylation were used in a coupling reaction, affording good yields with a variety of aryl iodides.84 The three steps are mutually compatible and can be carried out as a one-pot hydro-arylation of propargylic alcohols. The isomeric trans-exo-dig addition was also achieved. Despite the fact that many catalysts for terminal alkyne hydrosilylation react poorly with internal alkynes, the group found that ruthenium(n) chloride arene complexes—which provide complete selectivity for trans-... 

A concise total synthesis of dehydrohomoancepsenolide is achieved in an optically active form. The key steps are alkene metathesis and alkyne metathesis. A three-component coupling reaction affords dienyne 137, which undergoes ring-closing alkene metathesis in the presence of the first-generation ruthenium carbene complex to give 138,... 

Interestingly, the in situ generated ruthenium acetylide complex C5Me5(PPh3)Ru-C=CPh catalyzed the cross-coupling reaction of terminal and internal alkynes to yield functionalized enynes [87] (Eq. 65). A coordinatively unsaturated enynyl complex is postulated as an intermediate in this mechanism. 

The precatalyst Cp RuCl(COD) allowed the head-to-head oxidative dimerization of terminal alkynes and the concomitant 1,4-addition of carboxylic acid to stereoselectively afford 1-acyloxy-l,3-dienes in one step under mild conditions [89] (Eqs. 67,68). The first step of the reaction consists in the oxidative head-to-head alkyne coupling via the formation of a ruthenacycle intermediate that behaves as a mixed Fischer-Schrock-type biscarbene ruthenium complex, allowing protonation and nucleophilic addition of the carboxylate. 

As described in the section Reactions Involving Addition of Water to Alkynes, the reaction of terminal alkynes, water, and a-vinyl ketones afforded 1,5-diketones in DMF-H20 (Eq. 12). Under similar conditions, in the presence of halide, ruthenium-catalyzed three-component coupling of alkyne, an enone, and halide ion formed vinyl halide (Eq. 17) [35]. 

As far as alkynes are concerned, C-C coupling reactions have been reported to be catalyzed by rhodium or ruthenium clusters. Phenylacetylen can be coupled to diisopropyl carbodiimide to give 93... 

The ruthenium catalyst 2 was recently used by Trost et al. also for coupling reactions of alkenes 9 with alkynes 10. [5] These reactions lead to the branched coupling products 11 as well as the lineaer isomers 12 (Scheme 4). 

The catalytic C-C coupling of alkynes has been widely reported for rhodium and ruthenium complexes (e.g., see [113-120]) however, examples of iridium catalysts are less frequent [121-123]. The low activity observed for Ir complexes could be attributed to the greater tendency of rhodium and ruthenium to form vinyUdene complexes [124—127], since it is generally accepted that the formatiOTi of Z-enynes occurs via vinyUdene intermediates [117-120]. In this regard, the intermetalUc cooperation makes it possible to form the Ir-vinylidene intermediates required for the formation of Z-enynes and, ultimately, C-C coupling reactions. 

In 2006, Trost and co-workers reported a one-pot synthesis of enantiopure N- and O-heterocyclic compounds using the combination of an achiral ruthenium catalyst and a chiral palladium complex. After the completion of the ruthenium-catalysed alkene-alkyne cross-coupling reaction between the... 

Scheme 3.10 Tandem alkene-alkyne cross-coupling reaction-intramolecular het-erocyclisation reaction catalysed hy a combination of ruthenium catalysis and chiral palladium catalysis.

Surprisingly, coupling reactions between the hexamethylbenzene-ruthenium-allyl compound 59 and various alkynes generate complexes 60, in whieh one methyl substituent of the hmb ligand has been replaced by hydrogen (Equation (6)). " Presumably, this dealkylation proeess involves an / <7<9-hexamethyl-T/ -cyclohexadienyl intermediate. ... 

A f/oro-mthenacyclopentadiene complex 55 was obtained by the reaction of 7 with linear alkanes (Equation (18))." During this reaction, six C-H bonds of alkane were successively cleaved. Such multiple C-H bond cleavage was rationalized by the cooperative action of the neighboring ruthenium centers of the ttimetallic framework, which promotes the incorporation of alkane into the reaction field of the cluster. Such closo-typc metallacyclopentadiene complexes have been intensively studied using carbonyl clusters, and often prepared by the coupling reaction between the two alkyne ligands of the bis(/r3-7 ( )-alkyne) complex, so-called violet isomer.The /i3-sulfido complex 9 obtained by the reaction of 7 with thiophenol also reacts with alkane to yield a /ts-alkylidyne complex. ... 

The same ruthenium(II) catalytic system with 1 equiv. of Cu(0Ac)2-H20 oxidant was used to generate 2-pyridones directly firom acrylamides by C-H and N-H bond functionalization and annulation with alkynes. This reaction offers improved substrate scope with respect to the similar reaction reported with rhodium catalyst [(Eq. 88)] [177]. The reaction is applicable to dialkylacetylenes. Alkylphenyla-cetylenes lead to regioselective annulation with an (aryl)C-N linkage formation, consistent with the coupling of the electron-deficient alkyne carbon with the electron-rich carbon of the Ru-C bond. 

---