Coupling reactions vinyl

Furthermore, coupling to form C-aryl glucals, as precursors to C-aryl glycosides, was carried out both from the C-metallated glucal154 and onto the C-iodo glucal (equations 90 and 91)155. A synthesis of vineomycinone B2 methyl ester has resulted from this chemistry. A vinyl-vinyl coupling reaction has also formed the cornerstone of aryl steroid synthesis (equation 92)156. 

The mechanism originally proposed for the vinylic coupling reactions involved decomposition of a diolefin tr-complex 281, 282). However, the information developed since then on reactions of vinylic Pd(II) compounds suggests that these compounds are intermediates in the coupling reaction. The vinyl Pd(II) compounds could either oxidatively couple, since this is known to occur, or the vinyl Pd(II) intermediate could add across the olefinic double bond ... 

Scheme 7 Vinyl-vinyl coupling reaction on transition metal complexes...

There are a host of palladium-catalyzed C-C coupling reactions that have been developed since the mid-1960s, but only a couple of specific examples will be covered here (cf. Ref 14, 14a). Tsuji discovered Pd-catalyzed tr-allyl and carbon nucleophile coupling reactions in 1965.Mizoroki and Heck " separately developed vinylic coupling reactions (Equation (16)) in the early 1970s, and this is commonly referred to as a Heck reaction or coupling. 

The Li compound 588 formed by the ort/io-lithiation of A. A -dimethylaniline reacts with vinyl bromide to give the styrene derivative 589(433]. The 2-phe-nylindole 591 is formed by the coupling of l-methyl-2-indolylmagnesium formed in situ from the indolyllithium 590 and MgBr2, with iodobenzene using dppb[434]. 2-Furyl- and 2-thienyllithium in the presence of MgBr2 react with alkenyl halides[435]. The arylallenes 592 and 1,2,4-alkatrienes are prepared by the coupling reaction of the allenyllithium with aryl or alkenyl halides[436]. 

Lithiation at C2 can also be the starting point for 2-arylatioii or vinylation. The lithiated indoles can be converted to stannanes or zinc reagents which can undergo Pd-catalysed coupling with aryl, vinyl, benzyl and allyl halides or sulfonates. The mechanism of the coupling reaction involves formation of a disubstituted palladium intermediate by a combination of ligand exchange and oxidative addition. Phosphine catalysts and salts are often important reaction components. 

Indoles with carbocyclic halogen or triflate substituents are potential starting materials for vinylation, arylation and acylation via palladium-catalysed pro-cesses[l]. Indolylstannanes. indolylzinc halides and indolylboronic acids are also potential reactants. The principal type of substitution which is excluded from such coupling reactions is alkylation, since saturated alkyl groups tend to give elimination products in Pd-catalysed processes. 

Cross-coupling reactions of aromatic or vinylic halides and olefins catalyzed by palladium. 

Reductive coupling reaction of fluonnated vinyl iodides or bromides has been used as a route to fluorinated dienes [246, 247, 248, 249, 250. Generally, the vinyl iodide is heated with copper metal in DMSO or DMF no 1 ntermediate perfluorovmy I-copper reagent is detected. Typical examples are shown m equations 163-165 [246, 247, 249. The X-ray crystal structure of perfluorotetracyclobutacyclooctatetraene, prepared via coupling of tetrafluoro-l,2-diiodocyclobutene with copper, is planar... 

Stannyl cuprates couple widi vinyl halides or trlGales [16c-d, 85], and a vinyl stannane produced diis way has been used in die syntliesis of 7-[f )-alkylidetie]-cepbalosporlns [117]. Vinyl substitution reactions slariing Grom ddiydrofciraiis are... 

A number of StHle coupling reactions have been reported by Handy et al. [95]. With PdCl2(PhCN)2/Ph3As/Cul in [BMlM][Bp4], good yields and good catalyst recyclability (up to five times) were reported for the reaction between a-iodenones and vinyl and aryl stannanes (Scheme 5.2-19). However, the reported reaction rates were significantly lower than those obtained in NMP. 

This organometallic coupling reaction is useful in organic synthesis because it forms carbon-carbon bonds, thereby making possible the preparation of larger molecules from smaller ones. As the following examples indicate, the coupling reaction can be carried out on aryl and vinylic halides as well as on alkyl halides. 

The Ni(ii)/Cr(n)-mediated coupling reaction employs an excess of chromium(ii) chloride and a catalytic amount of nickel(n) chloride (0.1 %). The preferred solvent for this reaction is usually DMF, although THF, DMF/THF, or DMF/Me2S may also be used. The ability to activate the vinyl iodide (or related) substrate at ambient... 

TABLE 3. Cross-coupling reaction of vinyl sulfones with Grignard reagents12 ... 

Our group has recently developed an alternative method for alkyl-(hetero)aryl- as well as aryl-heteroaryl cross coupling reactions catalyzed by iron salts.3 4 This methodology was inspired by early reports of Kochi et al.5>6 on iron-catalyzed cross coupling of vinyl halides and is distinguished by several notable advantages. 

Radical-based carbonylation procedures can be advantageously mediated by (TMSlsSiH. Examples of three-component coupling reactions are given in Reactions (74) and (75). The cascade proceeds by the addition of an alkyl or vinyl radical onto carbon monoxide with formation of an acyl radical intermediate, which can further react with electron-deficient olefins to lead to the polyfunctionalized compounds. ... 

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