Cross with vinyl boronate

This reaction has the advantage that only one product (11) (head-to-head coupling product) is formed. Additional results are shown in Table 5. Aromatic bromides and iodides easily react with vinylic boron compounds, but organic chlorides do not participated, except the reactive allylic and benzylic derivatives. Heteroaromatic halides can be used as coupling partners. Or// o-substituents on benzene ring do not give difficulty. Thus, the cross-coupling reaction is used for the synthesis of benzo-fused heteroaromatic compounds (eq 5) (6). 

Vinylation can also be done by Pd-catalysed cross-coupling in which one component is used as a halide or triflate and the other as a stannane (Stille reaction) or boronic acid (Suzuki reaction). Entry 9, Table 11.3, is an example of the use of a vinylstannane with a haloindole. lndole-3-boronic acids, which can be prepared by mcrcuration/boration, undergo coupling with vinyl triflates (Entry 10). 

The procedure described here Is an example of a general method for preparing conjugated alkadienes by the palladium-catalyzed reaction of 1-alkenylboranes or boronates with vinylic halides. Hydroboratlon of l-a1kynes with catecholborane Is a standard method for obtaining (E)-l-alkenylboronates (1). Several different types of alkenylboranes and boronates (2-4) are now available as reagents for the cross-coupling reaction with vinyl halides. 

The benzene derivatives containing the fluorinated sulfone have been prepared either by nucleophilic substitution of the 4-fluorophenyl derivative (e.g. 1) or by starting with the appropriately substituted sodium thiophenoxide and reacting with perfluoroalkyl iodide follow by oxidation with either MCPBA or chromium oxide (12. li.) The biphenyl derivatives have been prepared by palladium catalyzed cross coupling chemistry of the 4-bromophenyl derivative (e.g. 2) with substituted phenyl boronic acid (yields 37-84%) (JLH, .). Compound 16 has been prepared by palladium catalyzed cross coupling of (4-bromophenyl)perfluorohexyl sulfone with vinyl anisole in 37 % yield (JJL). The vinyl sulfones, 7 and 9, have been prepared by condensation of CH3S02Rf (JJL) with the appropriate aldehyde (yields 70,and 73%) following a literature procedure (1 ). Yields were not optimized. 

Hydroboration of allenes 65 with pinacolborane in the presence of Pt(DBA)2 and a trialkylphosphine provides either the allyl boronate 66 or the vinyl boronate 67 regioselectively, depending on the stereoelectronic factors of the phosphine employed (Equation 2) <1999CL1069>. Allyl and vinyl boronates are synthetically important because of their ability to undergo nucleophilic addition to carbonyl compounds as well as transition metal-catalyzed cross-coupling. 

The reaction of vinyl-substituted silanes and octavinylsilsesquioxane with vinyl-substituted amides, amines (carbazole) as welt as boronates catalyzed by I proceeds effectively to yield under optimum conditions stereo- and/or regio-selectively l-silyl-2-/V- and 1,1-silylboryl-substituted ethenes. 1-silylvinyl carbazole can also be obtained via cross-metathesis of vinylsilane with vinylcarbazole, but only in the presence of the 2nd generation Grubbs catalyst (IV). 

Asymmetric hydrogenation of bromo-substituted aromatic a-enamides 14 affords the corresponding bromo-amino acid derivatives 15, which subsequently is subjected to Pd-catalyzed cross-coupling with aryl and vinyl boronic acids. In addition to diverse phenylalanine derivatives 16, a broad array of other novel aromatic and heterocyclic amino acids have been produced rapidly from a small number of bromo-functionalized intermediates [24], This same two-step process may be applied to the production of many other classes of aromatic and heterocyclic chiral building blocks, such as arylalkylamines, amino alcohols, diamines, and directly on peptides as well. 

The dotted arrows on the transmetallation step 243 show only what joins to what and are not intended as a serious mechanism. Indeed a better mechanism might involve addition of RO to the boron atom before transmetallation. This process can be used to couple aryl to aryl, vinyl to vinyl, and aryl to vinyl (either way round ). As boron compounds are much less toxic than tin compounds, the Suzuki coupling is often preferred industrially. Because each partner in the coupling reaction is marked in a different way - one with a boron atom and one with a halide - we can be sure that we shall get cross coupling reactions only. 

Pd catalyzed cross-coupling reactions of aryl, alkynyl or vinyl halides with aryl or vinyl boronic acids (see 1st edition). 

The reaction is not restricted to forming biaryls. Aryl boronic acids can also react with vinyl halides and vinyl triflates in the presence of palladium (0). Thallium (I) ethoxide is known to promote Suzuki cross coupling reactions for vinyl or arylboronic acids with vinyl and aryl halide partners. 3 synthetic example is... 

The Suzuki method for cross-coupling involves use of an arylboronic acid as the nucleophilic component. These conditions have been successfully applied to indoles. Indole-3-boronic acids, which can be prepared via electrophilic mercuration, can be coupled with vinyl triflates (Scheme 130) <93TL2235>. 

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