Related reactions with alkynes

A reaction closely related to olefin metathesis is alkyne polymerization, which occurs between a metal carbene and an alkyne [64]. After initial alkyne coordination to the metal center, [2 -I- 2] cycloaddition leads to a metallacyclobutene complex instead of the metallacyclobutane formed in olefin metathesis (Fig. 4.20) 

By analogy to olefin metathesis, alkyne metathesis occurs between a complex containing a metal-carbon triple bond - a metal carbyne (or alkylidyne) - and an alkyne substrate [66]. As illustrated in Fig. 4.21, this mechanism parallels the Chauvin mechanism for olefin metathesis after alkyne coordination to the metal center, [2 - - 2] cycloaddition between the metal carbyne and the alkyne yields a metallacyclobutadiene, which rearranges and fragments productively to afford a new carbyne and a new alkyne (Fig. 4.21) [54]. 

Recent developments in catalyst design have produced efficient new molybde- 

The ROMP of cyclic alkynes like cyclooctyne may be used to make alkyne-containing polymers in a reaction similar to olefin ROMP (Fig. 4.24) [71]. Additionally, Bunz and co-workers have pioneered the application of acychc 

Transition Metal-Carbene Complexes in Olefin Metathesis 

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Dipolar cycloaddition of ethyl 2-diazo-4,4,4-trifluoroacetoacetate 201 with isobutyl vinyl ether produced dihydrofuran 202 which underwent elimination affording 2-trifluoromethylfuran 203 [130], A related reaction with alkynes directly... 

The reaction of alkoxyarylcarbene complexes with alkynes mainly affords Dotz benzannulated [3C+2S+1C0] cycloadducts. However, uncommon reaction pathways of some alkoxyarylcarbene complexes in their reaction with alkynes leading to indene derivatives in a formal [3C+2S] cycloaddition process have been reported. For example, the reaction of methoxy(2,6-dimethylphenyl)chromium carbene complex with 1,2-diphenylacetylene at 100 °C gives rise to an unusual indene derivative where a sigmatropic 1,5-methyl shift is observed [60]. Moreover, a related (4-hydroxy-2,6-dimethylphenyl)carbene complex reacts in benzene at 100 °C with 3-hexyne to produce an indene derivative. However, the expected Dotz cycloadduct is obtained when the solvent is changed to acetonitrile [61] (Scheme 19). Also, Dotz et al. have shown that the introduction of an isocyanide ligand into the coordination sphere of the metal induces the preferential formation of indene derivatives [62]. 

Protonic acid and Lewis acids can activate carbonyls to facilitate the addition of nucleophile attacks in aqueous media. The Prins reaction, reaction with alkyne, and Friedel-Crafts-type reactions have been discussed in related chapters in detail. 

Reduction with metals in weakly acidic solvents is not restricted to arenes. A useful related reaction reduces alkynes to trans-alkenes, and provides a useful alternative to catalytic hydrogenation, which favors formation of cw-alkenes (Section 11-2A) ... 

In a related reaction, terminal alkynes react with silanes (R3SiH) in the presence of an iridium catalyst to give the 1-trialkylsilyl alkyne. similar products are obtained when terminal alkynes react with A-trialkylsilylamines and ZnCl2. " ... 

When applied to triple bonds, hydrocarboxylation gives a,p-unsaturated acids under very mild conditions. Triple bonds give unsaturated acids and saturated dicar-boxylic acids when treated with carbon dioxide and an electrically reduced nickel complex catalyst. Alkynes also react with NaHFe(CO)4, followed by CuCl2 2 H2O, to give alkenyl acid derivatives. A related reaction with CO and palladium catalysts in the presence of SnCE also leads to conjugated acid derivatives. Terminal alkynes react with CO2 and Ni(cod)2, and subsequent treatment with DBU (p. 1132) gives the a,p-unsaturated carboxylic acid. ... 

At this stage, the hydroamination of both terminal and internal alkynes with primary and secondary amines can be achieved by judicious choice of substrate and catalyst. Notably, hydroamination with primary aUcylamines using late transition metals is rarely reported [187, 189-191], although the related reaction with anihne derivatives can be mediated by complexes of groups 9-12 metals. Once again, to reduce the nucleophilicity of the amine partner, protected amines are often used as alternative substrates. 

Mainly for practical reasons, other topics are discussed in other parts. In addition to Pd-catalyzed cross-coupling involving allyl, propargyl, and allenyl derivatives discussed in Sects, ni.2.9 and m.2.10, allylpalladation and related reactions with alkenes, alkynes, and other 7r-compounds, which can best be viewed as carabopalladation processes, are discussed in Sect. IV.4, while carbonylation and related reactions of allylpalladium and related derivatives are discussed in Sect. VI.3. 

Hydrosoluble iridium alkyl complexes may also be prepared by hydrolysis of alkynes and alkenes promoted by water-soluble precursors. The reaction with alkynes follows the well-known mechanism demonstrated by Bianchini et al. for ruthenium complexes.A reasonable mechanism, related to that of hydrolytic breakage, has been proposed by Chin etal. to account for the hydrolysis of ethene promoted by [Cp"lr(TPPMS)Cl2] 344 in the presence of silver salts in water. Scheme 37 describes the Chin s hydrolysis of alkynes, leading to [Cp Ir(TPPMS)(CO)(CH2R)] (69 R=Ph, Bz, Bu, />-Tol) via the aquo complex [Cp Ir(TPPMS)(OH2)OTf 345... 

The solid-phase synthesis of a library of isocoumarins was reported by Hernandez and colleagues (Scheme 3.62). Resin-bound 2-bromobenzoates 354 underwent Sonogashira reaction with alkynes to provide 2-(alk-l-ynyl) benzoates 355. Electrophile-induced halocylization reactions then gave access to a library of 58 isocoumarins (and related stmetures). 

Addition Reactions of //-Phosphonates and Related Reagents with Alkynes. 169... 

Ni- and Pt-Cycles as intermediates in reactions of Ni(0)- and Pt(0)-complexes with benzyne or related small-ring alkynes 97CB1029. 

A related unprecedented double insertion of electron-deficient alkynes has also been reported in the reactions of the linear Pt2Pd heterotrimetallic complex 64 with 65 (RO2CCSCR) (Scheme 24) [95,96]. A series of unsymmetri-cal A-frame clusters 68 has thus been obtained in which a first insertion of the alkyne takes place site-selectively into the Pt-Pd bond vs the Pt-Pt bond (66). After a zwitter-ionic polar activation of the resulting inserted alkene (67), a subsequent reaction with the phosphine unit of the dpmp allows one to obtain the products 68 via the nucleophilic migration of the terminal P atom from the Pd center to the CH terminal carbon (formation of the P-C bond). 

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