Arylboron derivatives

The reaction of [ Co"(DMG)2py 2] with B( -C4H,)3 in benzene followed by extraction with CH2Cl2/aq. NaOH produces [ -BuCo(DMG)2py] the reaction is less successful with [pyCo "(DMG)2Cl] 161). This may be a convenient method using the more stable arylboron derivatives, but is probably experimentally more difficult than the Grignard route if a lower alkyl is to be introduced, because the lower alkylboron compounds inflame spontaneously in air, though they do not react with water, while the aryls are stable in air. 

A diastereoselective Rh(I)-catalysed conjugate addition reaction of aryl- and alkenyl-boronic acids to unprotected 2-phenyl-4-hydroxycyclopentenone (207) has been investigated. The free OH group on the substrate was found to be responsible for the (g) stereochemistry, which is cis for arylboronic derivatives (208). In the case of the alkenylboronic compounds, the stereochemistry can be tuned to either a cis (with a base as additive) or trans addition (209) (with CsF as additive), without the need for protecting groups.249... 

The first synthetic method preparing biaryls by using a coupling reaction of arylboron derivatives with aryl halides was reported in 1981 (Scheme 2-38) [99]. After this discovery, various modifications of the reaction conditions have been explored. A combination of Pd(PPh3)4 or PdCl2(PPh3)2 and aqueous Na2C03 in dimethoxyethane (DME) works satisfactorily in most cases [1(X), 101]. 

The relative stereochemistry of the hydroxy groups in the tetrahy-droaromatic rings in (330) and (331) was established by the ready formation of acetonide and arylboronate derivatives (28S, 555). The absolute configuration of the quinone (330) was shown to be (15,35) by degradation to the (i )-lactone (333) via the corresponding 1-deoxy derivative (332) as shown in Scheme 58. The lactone (333) was prepared... 

Bumagin, N.A. Nikitin, K.V. Beletskaya, I.P. (1990) Competitive carbonylation and cross-coupling of the aryl halide and arylboron derivatives system catalysed by palladium compounds, Dokl Akad Nauk SSSR, 320,619-22. 

Aryl-5-oxo-1,2,3,5-tetrahydropyrido[ 1,2,3-i/e]quinoxaline-6-carboxy-mides were prepared from 7-chloro derivatives and arylboronic acids in the presence of Na2C03, diphenylphosphinated divinylbenzene-crosslinked polystyrene and Pd(PPh3)4 catalyst. 7-Chloro derivatives were obtained from 7-hydroxy derivatives by heating in POCI3 at 50°C for 3 h (01MIP12). 

For the synthesis of a suitable arylboron compound, usually an aryl halide is converted to an aryllithium or aryl Grignard derivative, and then reacted with a trialkoxyborane to yield an arylboronic ester, e.g. the phenylboronic acid diisopropyl ester 13 from bromobenzene 11 ... 

The Suzuki reaction97 allows tire coupling of two aromatic rings by reaction of an arylboronic compound with a iodo or bromo aryl derivative. The tetrakis (U iphenylphosphine) Pd is the catalyst working in the basic medium. This reaction was recently used98 in aqueous media for the preparation of different isomers of diphenyldicarboxylic acids (Fig. 5.21) but also for the synthesis of soluble rodlike polyimides99 by coupling the 3,6-diphenyl- V, V,-bis(4-bromo-... 

As first described by Krizan and Martin,6 the in situ trapping protocol, i.e., having the base and electrophile present in solution simultaneously, makes it possible to lithiate substrates that are not applicable in classical ortho-lithiation reactions.7 Later, Caron and Hawkins utilized the compatibility of lithium diisopropylamide and triisopropyl borate to synthesize arylboronic acid derivatives of bulky, electron deficient neopentyl benzoic acid esters.8 As this preparation illustrates, the use of lithium tetramethylpiperidide instead of lithium diisopropylamide broadens the scope of the reaction, and makes it possible to functionalize a simple alkyl benzoate.2... 

The use of expensive and unstable ZnPli2 in the preparation of chiral di-arylmethanol derivatives, with electronically and sterically similar aryl rings, made this approach less attractive for the enantioselective synthesis. In order to avoid this inconvenience, other alternative preparations of arylzinc reagents were evaluated.As a first choice, Yus et al. proposed the use of arylboronic adds as a viable source of phenyl (Scheme 4.19). Thus, the reaction of various boronic acids with an excess of ZnEt2 at 70 °C gave the corresponding arylzinc intermediates (probably aryl(ethyl)zincs), which were trapped by reaction with dif-... 

General procedure for the reaction of an o-substituted aryl iodide with an arylboronic acid. Synthesis of terphenyl derivatives. 

A similarly high performance has been reported for oxime-derived (125) and benzylsulfide-derived (126) palladacycles.438 These precatalysts are effective in the cross-coupling of arylboronic acids,438,439 organotin compounds,440 and terminal acetylenes441 with aryl iodides and bromides, and of activated aryl chlorides. SC-palladacycles can effect the Suzuki-Miyaura reaction even at room temperature. 

Today, the Suzuki cross coupling of aryl halides and arylboronic acids is also carried out in aqueous-biphasic operation starting from chlorinated derivatives instead of their more costly bromo or iodo equivalents (Equation 5.6, [39]). 

Table 9 Reaction of arylboronic acids with 3,5-dihalo-1,2,4-triazole derivatives under Suzuki coupling conditions (Equation 25)...

Recently, a rhodium-catalyzed tandem cyclization has been reported with an arylboronic ester bearing a pendant Michael-type acceptor olefin and acetylenic65 or olefinic66 derivatives. This transformation proceeds in a water-containing medium as solvent and proton source. This catalyst system is optimized with electron-rich and bulky ligands to stabilize the rhodium intermediate and decrease the protonolysis of boron derivatives in a protic solvent. 

Vinyl- or arylboronic acids also react with allenes, affording 1,3-dienes or styrene derivatives, respectively.89 This palladium-catalyzed addition proceeds with good regioselectivity and high stereoselectivity in favor of the formation of (ft)-trisubstituted isomer. 

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