Vinyl bromide reaction with aldehydes

Next, the building blocks were coupled (Scheme 9.13). Transmetallation of vinyl iodide 555, followed by reaction with aldehyde 563 gave a product mixture of two diastereomeric alcohols. Deprotection of the alkyne with ensuing protection of the alcohol afforded compound 565. The open chain precursor 566 was obtained using a Suzuki coupling of bromide 551 with the vinyldisiamylborane, which was prepared in situ, followed by deprotection of the alcohol and the carboxylic acid. Once again, Mitsunobu macrocycUzation was applied to obtain the macrolide. After... 

Hydrogen bromide adds to acetylene to form vinyl bromide or ethyHdene bromide, depending on stoichiometry. The acid cleaves acycHc and cycHc ethers. It adds to the cyclopropane group by ring-opening. Additions to quinones afford bromohydroquinones. Hydrobromic acid and aldehydes can be used to introduce bromoalkyl groups into various molecules. For example, reaction with formaldehyde and an alcohol produces a bromomethyl ether. Bromomethylation of aromatic nuclei can be carried out with formaldehyde and hydrobromic acid (6). 

The bisfunctionalization of alkynes by both C02 and another electrophile can also be achieved, as shown in Scheme 9.17,17a The titanium-carbon bond in the titanacycle complex 31, which was formed by reaction of C02 with the titanacyclopropene 30, can be substituted with various electrophiles. For example, its reaction with NBS or I2 afforded the synthetically useful vinyl bromide or iodide 32, respectively, while the reaction with D20 yielded the /3-deuterated a,/ -unsaturated carboxylic acid. When an aldehyde such as PhCHO was used as an electrophile, butenolide 33 was produced after acidic workup. 

Tellurophosphoranes, obtained through a transylidation reaction between tellurenyl halides and phosphoranes, react with aldehydes to give the expected vinylic tellurides as an E Z isomeric mixture (method a). One other methodology involves the treatment of equimolar amounts of phenyl tellurenyl bromide and phosphonium salts with t-BuOK followed by an aldehyde (method b). Under these lithium-salt-free conditions, (Z)-vinylic tellurides are the main products. ... 

Allylcopper/zinc reagents can be prepared directly by reaction of vinyl copper reagents with (iodomethyl)zinc iodide, the Simmons-Smith reagent. These allylcopper/zinc reagents do not couple with an alkyl iodide or benzyl bromide, but react readily with electrophiles such as aldehydes, ketones, or imines.3 This approach to organodimetallic reagents is apparently limited (see Iodomethylzinc iodide, this volume). 

These reagents can be obtained by reaction of vinyl Grignard reagents with allylic zinc bromides in THF at - 35 to 0°. Reaction of 1 with ClSn(CH3)3 provides an a-trimethyltin-zinc reagent (2) that is oxidized by air to an aldehyde or ketone (3). ... 

Lithiation of compound 560 with s-BuLi-TMEDA in THF at —78 °C following an inverse addition protocol provided the anion 561. It reacts with primary alkyl iodides and triflates, silyl chlorides, diphenyl disulfide, epoxides, aldehydes, ketones, imines, acyl chlorides, isocyanates and sulfonyl fluorides to yield the expected compounds 562 (Scheme 152). The transmetallation of compound 561 with ZnBr2 allowed the palladium-catalyzed cross-coupling reaction with aryl and vinyl bromides837. When the reaction was quenched with 1,2-dibromotetrafluoroethane, the corresponding bromide 562 (X = Br) is obtained838. 

Reaction of vinyl or aryl iodides or bromides with chromium(II) chloride produces chromium(III) species that react chemoselectively with aldehydes to give allylic or benzylic alcohols, respectively, in high yields. 

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