Boranes vinyl, coupling

Another solid-support Suzuki coupling is the hydroboration of vinyl polystyrene with 9-BBN in THF to provide [29] polymer supported borane. This borane is coupled to give different aryl, vinyl, or alkyl iodides. Pd(OAc)2 is employed as the catalyst for aryl iodides and PdCl2(dppf) in other cases to yield the coupled adduct in 55-85% yield (Scheme 31.7) on the basis of the mass of the product cleaved or by comparison with IR integration to standards. 

Silyl acetylenes add boranes then couple with aryl and vinyl halides catalytically (Pd) to give silyl styrenes and dienes, undergo Ti catalysed reversible hydromagnesation, and insert Zx-C of... 

Hydrozirconations of both vinyl and acetylenic boranes by Srebnik et al. led to 1,1-dime-tallo reagents, which offer the benefits as coupling partners of alkyl- and vinylboranes, respectively [59—62], Initial trials were conducted with B-alkenylborabicyclo[3.3.1]nonanes, but these led to unstable dimetallics. Replacement of the 9-BBN fragment with the pina-colborane-derived analogue produced stable dioxaborolanes 61 (Scheme 4.34). 

Palladium-catalyzed reactions of arylboronic acids have been utilized to craft precursors for constructing indole rings. Suzuki found that tris(2-ethoxyethenyl)borane (149) and catechol-derived boranes 150 readily couple with o-iodoanilines to yield 151, which easily cyclize to indoles 152 with acid [158]. Kumar and co-workers used this method to prepare 5-(4-pyridinyl)-7-azaindoles from 6-amino-5-iodo-2-methyl-3,4 -bipyridyl [159], A similar scheme with catechol-vinyl sulfide boranes also leads to indoles [160]. A Suzuki protocol has been employed by Sun and co-workers to synthesize a series of 6-aryloxindoles [161]. 

S)-(-)-CITRONELLOL from geraniol. An asymmetrically catalyzed Diels-Alder reaction is used to prepare (1 R)-1,3,4-TRIMETHYL-3-C YCLOHEXENE-1 -CARBOXALDEHYDE with an (acyloxy)borane complex derived from L-(+)-tartaric acid as the catalyst. A high-yield procedure for the rearrangement of epoxides to carbonyl compounds catalyzed by METHYLALUMINUM BIS(4-BROMO-2,6-DI-tert-BUTYLPHENOXIDE) is demonstrated with a preparation of DIPHENYL-ACETALDEHYDE from stilbene oxide. A palladium/copper catalyst system is used to prepare (Z)-2-BROMO-5-(TRIMETHYLSILYL)-2-PENTEN-4-YNOIC ACID ETHYL ESTER. The coupling of vinyl and aryl halides with acetylenes is a powerful carbon-carbon bond-forming reaction, particularly valuable for the construction of such enyne systems. 

Polystyrene-bound trialkylboranes, which can be prepared by hydroboration of support-bound alkenes with 9-BBN, undergo palladium-mediated coupling with alkyl, vinyl, and aryl iodides (Suzuki coupling Entries 1 and 2, Table 5.3 for vinylations, see Section 5.2.4). Because boranes are compatible with many functional groups and do not react with water, these coupling reactions could become a powerful tool for solid-phase synthesis. To date, however, few examples have been reported. 

Moreover, the subsequent vinyl borane 69 can undergo further transformations such as cyclopropanation, Suzuki coupling and so on. 

Vinylic ethers (44) can be synthesized in high yields by the cross-coupling of aryl or benzyl halides with tris(2-ethoxyvinyl)borane (4S) in the presence of 1 molej% of a palladium compound such as tetrakis(triphenylphosphine)palladium and a base (Eq. 108) Since vinylic ethers (44) thus obtained can readily be hydrolyzed to aldehydes, this reaction provides a convenient procedure for converting aryl or benzylic halides into the corresponding aldehydes with two more carbon atoms. 

Hydroboration of acetylenic selenides with 9-BBN led to the regio- and stereoselective formation of a-selanylalkenyl boranes which were then converted into Z-a, -disubstituted vinyl selenides by cross-coupling reaction with aryl bromides [80] (Scheme 58). With unsubstituted acetylenic selenides, an inversion of regioselectivity during the hydrozirconation was observed [81,82]. 

The introduction of the aminoethyl side chain is accomplished by Suzuki cross-coupling of dienyl triflate 10 with the alkyl borane generated by hydroboration of A -vinyl- er butyl carbamate (11) with 9-BBN. ... 

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