Vinylboronic acids, vinylation with

A dramatic rate enhancement was realized by Kishi using TlOH as a base. The coupling can be achieved even at 0°C and a wide variety of sensitive functional groups can be readily incorporated into the synthetic protocols because of these mild conditions. Kishi utilized these conditions in the synthesis of Palytoxin via the coupling of vinylboronic acid 102 with the vinyl iodide 103 (Scheme 28.25). However, TlOH is air and moisture sensitive and has a limited shelf life. In this regard, Roush found TlOEt to be superior to TlOH due to its ready availability and greater stability. " ... 

The adducts derived from catechol borane are hydrolyzed by water to vinylboronic acids. These materials are useful intermediates for the preparation of terminal vinyl iodides. Since the hydroboration is a syn addition and the iodinolysis occurs with retention of the alkene geometry, the iodides have the -configuration.214... 

Z,E)-2-Bromo-l,3-dienes. 1,1-Dibromoalkenes and E-vinylboronic acids couple to (Z,E)-2-bromo-1,3-dienes in the presence of this Pd(0) catalyst and TlOH as base, conditions developed earlier for coupling of vinyl bromides with vinyl-... 

This is an indirect method to obtain an anti Markovnikov addition of HI to terminal acetylenes. Chlorination929 and bromination930 (with bromine or with sodium bromide931) of vinylboronic acids results in inverted vinyl halides. This allows the three-step stereospecific inversion of ( )vinyl bromide into the [Z] isomer (equation 137)932. 

Trialkylboranes were converted into alkyl phenyl selenides and alkyl phenyl tellurides by reactions with PhSeSePh and PhTeTePh in the presence of stoichiometric amounts of air.550 Vinyl selenides and tellurides were synthesized by treating vinylboronic acids or esters with phenylselenyl chloride in ionic liquids (Equation (114))551 or by palladium-catalyzed coupling reaction of diorgano ditellurides (Equation (115)).552... 

Alkenylboron derivatives are readily available by stereo-defined hydroboration of alkynes and used for the preparation of styrene derivatives by alkenyl-aryl coupling. Vinylboronic acid (81), the most simple alkenylboronic acid, is difficult to handle, because it undergoes uncontrollable polymerization. Its anhydride, 2,4,6-trivinylcyclotriboroxane (82)-pyridine complex, is stable, and can be used conveniently for the coupling. Vinylation of 2-bromoanisole with 82 proceeds in refluxing DME using K2CO3 as a base fo provide 2-vinylanisole (83) [80]. 

Suzuki-Miyaura coupling that is the reaction of an aryl- or vinylboronic acid with an aryl or vinyl halide catalyzed by a palladium(O) complex (Figure 1.1) [63]. 

A Chan-Lam-Evans coupling has also been designed as a new method to access O-vinyl-iV-arylhydroxylamines under mild conditions that avoid the use of strong bases as described previously for the Bartoli-indole synthesis and related preparations of oxindoles (see Section 14.2.3). Anderson and coworkers have shown that treatment of iV-arylhydroxamic acids with vinylboronic acids leads directly to the synthesis of a-(o-anilido)ketones such as 90 f Scheme... 

Vinylboronic acids, easily prepared by hydroboration of acetylenes, react with iodine monochloride at low temperatures to give good yields of -vinyl iodides (Scheme 31). This mild alternative to an earlier approach is compatible with hydroxy, alkoxy, and carbomethoxy groups. Following monocarbozirconation, treatment of 1-pentynyldimethylalane (50) with iodine gives l,l-di-iodo-2-methylpent-l-ene (51) in 92% yield. ... 

Trifluoroacetic anhydride (30mol%) has been reported to catalyse the Michael-type vinylation of enones (468) with vinylboronic acids (466) (R = RCH=CH). The reaction... 

With the role of the base established, another issue in the Suzuki-Miyaura reaction was to elucidate whether the mechanism for the transmetalation step involved either one or two phosphine ligands in the Pd catalytic species. On this issue, Maseras et al. reported a thorough computational study at DFT-B3LYP level of the full catalytic cycle for the coupling of vinyl bromide and vinylboronic acid H2C=CHB(0H)2 catalyzed by both [Pd(PH3)2] and [PdfPHj)] [71]. Moreover, alternative mechanisms for the transmetalation step depending on the cis or trans... 

However, most asymmetric 1,3-dipolar cycloaddition reactions of nitrile oxides with alkenes are carried out without Lewis acids as catalysts using either chiral alkenes or chiral auxiliary compounds (with achiral alkenes). Diverse chiral alkenes are in use, such as camphor-derived chiral N-acryloylhydrazide (195), C2-symmetric l,3-diacryloyl-2,2-dimethyl-4,5-diphenylimidazolidine, chiral 3-acryloyl-2,2-dimethyl-4-phenyloxazolidine (196, 197), sugar-based ethenyl ethers (198), acrylic esters (199, 200), C-bonded vinyl-substituted sugar (201), chirally modified vinylboronic ester derived from D-( + )-mannitol (202), (l/ )-menthyl vinyl ether (203), chiral derivatives of vinylacetic acid (204), ( )-l-ethoxy-3-fluoroalkyl-3-hydroxy-4-(4-methylphenylsulfinyl)but-1 -enes (205), enantiopure Y-oxygenated-a,P-unsaturated phenyl sulfones (206), chiral (a-oxyallyl)silanes (207), and (S )-but-3-ene-1,2-diol derivatives (208). As a chiral auxiliary, diisopropyl (i ,i )-tartrate (209, 210) has been very popular. 

The (E) and (Z) forms of the vinylboron compounds 278 and 279 can be prepared by hydroboration of alkynes and haloalkynes, and their reactions with the (E)- or (Z)-vinyl iodides or bromides 280 and 281 proceed without isomerization the four possible isomers 282-285 can be prepared in high purity. However, for the efficient preparation of the (Z,Z)-dienes 287, the diisopropyl ester of (Z)-alkenylboronic acid 286 should be used. Other boron compounds give poor yields... 

Benzylic boronic esters [52]can be obtained from bromomethyl boronic esters and aryl or vinyl stannanes [53]. Alkyl and vinyl boronic esters are accessible through hydroboration of alkynes with dialkylboranes followed by oxidation with acetaldehyde [43]. Alternatively, vinylboronates can be obtained directly from alkynes in a reaction -with catecholborane without a subsequent oxidation step [53]. Further diversification in the boronic acid derivatization is achieved by binding the boronic acids bearing another derivatizable functional group (for instance an amine) to suitable polymeric supports. The modified boronic acid may then be... 

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