Bonds reaction with alkynes

Introduction of two different chalcogen elements to the C-C unsaturated bond is of particular interest from both synthetic and mechanistic viewpoints. Therefore, extensive studies have been carried out on the development of the (RE)2/(R E )2 binary system without using RE-E R compounds, which are difficult to prepare. (Z)-l-Seleno-2-thio-1-alkenes are produced regio- and stereoselectively when a mixture of diaryl disulfides and diaryl diselenides is subjected to a rhodium-catalyzed reaction with alkynes (Equation (68)).193... 

In most of the reactions of heteroatom-substituted carbene complexes with alkynes the first event is insertion of the alkyne into the carbon-metal double bond. If vinylcarbene complexes undergo insertion reactions with alkynes, (1,3-butadien-l-yl)carbene complexes result (Figure 2.27). 

Several of the reactions described in Section 6.16.2.4.6.1 are two-step reactions. After the initial [2+1] addition of the silylene to the multiple bond, a second insertion reaction of a silylene into a reactive Si-X bond of the cyclopropane derivative takes place yielding four-membered ring compounds. Examples are the reactions with alkynes, nitriles, imines, and ketones. 

The Lewis acid-catalyzed reactions of allylsilanes with simple alkenes and alkynes introduce both allyl and silyl groups into the unsaturated bonds (Equations (53) and (54)).209 210b These allylsilylations are 7-regiospecific with respect to allylsilanes. The /raor-addition of allylsilanes occurs in the reaction with alkynes. There are two possible mechanisms for the Lewis acid-promoted allylsilylations, that is, trimethylsilyl cation- and Lewis acid-mediated pathways. 

Addition reactions occur by breaking the n bonds of the triple bond. Hydrogen, halogens, hydrogen halides and water may give addition reactions with alkynes. 

Iridacyclopentadienes 79 (R = Ph, -Tol, H, Me) on reaction with alkynes in the presence of a protonating agent in acetonitrile produce iridabenzenes by a C-C bond-forming reaction <2004GEJ4518>. (77 -Acetato)iridacyclopentadiene 80 reacts with alkynes RC=CH (R = Ph, />-Tol) to produce a variety of iridabenzenes via >-(alkynyl)(but-l,3-dien-l-yl)iridiums, which are protonated <2005OM4849>. 

However, their intermolecular addition reactions with alkynes are mostly aimed at synthesizing substituted aLkenes, ° and only very few cascade reactions that are initiated by P radical addition to C = C triple bonds have been reported. Renaud and coworkers developed a simple one-pot procedure for the cyclization of terminal alkynes mediated by dialkyl phosphites (Scheme 2.35). In this radical chain procedure, dialkyl phosphite radicals, (R0)2P =0, undergo addition to the C = C triple bond in 190, which triggers a radical translocation (l,5-HAT)/5-eAO cyclization cascade. The sequence is terminated by hydrogen transfer from dialkyl phosphite to the intermediate 194 and regeneration of P-centered radicals. 

There are few reports of reactions between alkynes and trinuclear clusters of metals other than iron, ruthenium, or osmium. Some rhodium, platinum, and mixed-metal clusters undergo metal-metal bond rupture in reactions with alkynes (54-56), while in other cases the alkyne coordinates to the trinuclear unit without causing any major changes in framework geometry (56-59), as illustrated in Eq. (3). 

Reaction with Pb—C bonds 5.6.4 Reaction with RAg S.6.4.3 Reaction with alkynes S.6.4.3 AgP C23H2o Ag2BrN C9Hij... 

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