Arylboronic acid derivatives

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... 

Table 6. Aryl Fluorides by Reaction of Arylboronic Acid Derivatives with Cesium Fluoroxysul-fate ...

Coupling of Aryl Compounds With Arylboronic acid Derivatives Aryl-de-halogenation, and so on Aryl-de-boronylation, and so on... 

The Suzuki reaction of arylboronic acid derivatives with aryl halides is one of the most powerful methods for construction of an unsymmetrically substituted biaryl derivative [11, 23, 85]. Due to the importance of substituted biaryls as building blocks for pharmaceuticals, there is currently a great deal of interest in the coupling of economically attractive aryl halides with arylboronic acids [86-98]. 

Unfortunately, 1,3,2-dioxaborinanes proved to be ineffective in the Hg(II)-catalyzed conversion of arylboronic acid derivatives to aryllead triacetates, in contrast to other arylboronate species... 

Upon investigating the literature, Lauren noted that arylboronic acids substituted with electron-withdrawing groups often experience extensive protodeboronation and poor yields under the standard Suzuki conditions that utilize aqueous NaaCOs as a base. A solution to this problem lies in either the use of a milder base or nonaqueous conditions. Therefore, Lauren chose to employ NaHCOj as a base. The arylboronic acid derivative of 6-bromopiperonal was coupled with the suitably elaborated aryl iodide to provide the desired biaryl ( )-3 in moderate yields (Eq. 15). 

Pd-catalyzed cross-coupling of an iodoaro-matic moiety with an arylboronic acid. The Suzuki reaction has been employed to modify shorter peptides and the WW domain portion of the protein Pinl (residues 6-39) (- peptidyl prolyl cisitrans isomerases) in aqueous solution (Na2PdCl4 as the catalyst) under mild conditions, without changing its structure and function. Conjugation of fluorophores was achieved by coupling appropriate arylboronic acid derivatives to a p-iodophenylalanine residue in the peptide [S. Kotha, K. Lahiri, Biopolymers 2003, 69, 517 A. Ojida et al., Tetrahedron Lett. 2005, 46, 3301). 

Representative results reported in biaryl coupling are sununarized in Table 5. The reaction conditions are not optimized in most cases, and the procedures are still being improved. However, finding arylboronic acid derivatives, aryl electrophiles, and their coupling procedures can be useful. 

The use of a-imino esters with bulky arylboronic acids (with ortho substituents or a naphthyl group) also proceeded successfully to afford the corresponding a-amino esters with high enantiose-lectivity. Both electron-rich and electron-poor arylboronic acid derivatives can be used. The utility of this reaction was demonstrated by the same group, in the concise asymmetric synthesis of the 1-naphthyl-a-amino acid and the corresponding amino alcohol, in just one step without any racem-ization occurring (Scheme 6.30) [38]. 

Baoeffl/, [59] andKappeefaZ. [60] independendy reported the synthesis of diarylmethanol derivatives using nickel catalysts, 2ildehydes, and arylboronic acid derivatives. While Bao and coworkers used Ni(C10, )2 OH O along with as base, with a maximum yield of 92%, Kappe and coworkers... 

Michaelis and Becker noted the toxicity of phenylboronic acid against microorganisms and its relative harmlessness against higher animals more than a century ago [198]. The antimicrobial properties of simple arylboronic acid derivatives were fur-... 

Cholesteryl arylboronic acid derivatives have been used to extract sugars into organic solvents, and the aldose-cholesteryl boronic acid complexation results in a UV-visible absorption shift characteristic of the aldose enantiomer used. ... 

---