Coupling vinyl, palladium

Recently, Larock and coworkers used a domino Heck/Suzuki process for the synthesis of a multitude of tamoxifen analogues [48] (Scheme 6/1.20). In their approach, these authors used a three-component coupling reaction of readily available aryl iodides, internal alkynes and aryl boronic acids to give the expected tetrasubsti-tuted olefins in good yields. As an example, treatment of a mixture of phenyliodide, the alkyne 6/1-78 and phenylboronic acid with catalytic amounts of PdCl2(PhCN)2 gave 6/1-79 in 90% yield. In this process, substituted aryl iodides and heteroaromatic boronic acids may also be employed. It can be assumed that, after Pd°-cata-lyzed oxidative addition of the aryl iodide, a ds-carbopalladation of the internal alkyne takes place to form a vinylic palladium intermediate. This then reacts with the ate complex of the aryl boronic acid in a transmetalation, followed by a reductive elimination. 

The formation of spirolactams 47-49 could be rationalized in terms of a sequence domino cyclization of a-allenols-cross coupling reactions. A palladium (Il)-catalyzed mechanism for the domino sequence leading to spiranic adducts 47-49 is proposed in Scheme 17. It could be presumed that the initially formed allenepalladium complex 50 undergoes an intramolecular attack by the hydroxyl group (oxypalladation), giving rise to the spirocyclic vinylic palladium species 51. 

Suzuki coupling)A palladium-catalyzed substitution that couples an aryl or vinyl halide with a alkyl, aryl, or vinyl boronic acid or boronate ester, (p. 794)... 

Figure 7 Probable reaction path for vinyl-alkynyl coupling on palladium.

Vinyl triflates (C=C-0S02CF3) react with vinyl tin derivatives in the presence of palladium catalysts to form dienes, in what is known as the Stille coupling. Vinyl triflates can be prepared from the enolate by reaction with Al-phenyl trifli-... 

In 1991, a new C-N-C bond formation reaction using a nitrogenation-transmetalation process was described. Ketones and aryl or vinyl halides couple to give divinyl or arylvinyl amines in the presence of the titanium isocyanate complex [3THF MgaClaO TiNCO] and a palladium catalyst, via transmetallation of the titano imine complex with aryl or vinyl palladium bromide. Moderate to good yields of the desired products were observed (Scheme 2.176). 

Csp-Csp Cross-coupling. The palladium and copper cocatalyzed cross-coupling between vinyl/aryl halides or triflates and terminal acetylenes, known as the Sonogashira reaction, is the most straightforward and powerful method for the construction of Csp -Csp bonds with retention of the vinyl stereochemistry and has been widely reviewed (eq 26). ... 

Tetrakis(triphenylphosphine)palladium couples vinyl halides with Grignard reagents and organolithium reagents. 

A concise route to oxygen-containing helical tetrasubstituted alkenes via a palladium-catalyzed domino reaction with Sonogashira coupling/ carbopalladation/C-H functionalization sequence has been developed by Tietze and coworkers (Scheme 3.12) [30].lnthiswork, the in s/fM-generated vinyl palladium intermediate from alkyne plays a vital role in the C—H activation. The reaction is efficient, and a mixture ofZ- and -isomers of the helical alkenes was afforded under the typical condition (44—96% yields, ElZ =1.5 1 to 1 1.6). 

In 2006, Bout and Suffert combined Stille coupling with a preceding intramolecular alkyne insertion into a vinylic palladium bond and developed a new application of the 4-exo-dig cyclocarbopalladation of acyclic y-bromopropargylic diols 120 [48] (Scheme 6.30). This strategy is an efficient route to cyclobutanediol derivatives 121. The efficiency of the reaction is improved greatly by the use of brief microwave irradiation at 130 °C. Further 6ii-electrocyclization occurred, providing new bicyclic systems 123 instead of trienes 122, when the reaction was conducted in the presence... 

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. 

In related work, 3-chloromethylcephems were coupled with tributyl(tnfluoro-vinyl)stannane catalyzed by tri(2-furyl)phosphine palladium(O) [7S, 19] (equation 13). 

The above procedure was used for the preparation of all compounds except 104p, which was obtained from 104r by palladium-catalyzed coupling with tributylvinyl-stannane followed by palladium-catalyzed cyclopropanation of the resulting vinyl intermediate with diazomethane (Scheme 32) (99BMC3187). 

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