Alkyl-and Arylboronic Acids

A variety of alkyl- and arylboronic acids can be obtained in large quantity by the above general procedure. The reaction of organolithiums with triisopropyl borates at -78 °C is an alternative and convenient method to achieve high yields of boronic acids or their esters [9, 10] (eq (8)). 

The reaction of RMgX reagents with trialkoxyboranes can be controlled to proceed in a stepwise manner. It provides a method for alkyl- and arylboronic acids and their esters. Stoichiometric amounts of reagents or xs trialkoxyborane is used and the reaction is carried out at low... 

Some functionalized alkyl- and arylboronic acids can be prepared via transmetalation [see also Eq. (1)] ... 

X. N. Chen, G. Y. Liang, D. Whitmire, J. P. Bowen, Ah initio and molecular mechanics (MM3) calculations on alkyl- and arylboronic acids, Journal of Physical Organic Chemistry 1998, 11, 378. 

Alkyl and arylboronic acids form cyclic esters with diols. The aryl derivatives are usually crystalline, air-stable materials which resist hydrolysis under neutral or acid conditions. They have been used to characterize compounds which contain the cis diol function and to protect it during syntheses. 

A similar approach was taken for the synthesis of 45 by Miyaura. " Shaughnessy and Booth synthesized the water-soluble alkylphosphine 46, and found it to provide very active palladium catalysts for the reaction of aryl bromides or chlorides with boronic acids. The more sterically demanding ligand 47 was shown to promote the reactions of aryl chlorides with better results than 46. Najera and co-workers recently reported on the synthesis of di(2-pyridyl)-methylamine-palladium dichloride complexes 48a and 48b, and their use in the coupling of a variety of electrophiles (aryl bromides or chlorides, allyl chlorides, acetates or carbonates) with alkyl- or arylboronic acids very low catalyst loadings at Palladium-oxime catalysts 8a and 8b) have also been developed. In conjunction with... 

Reactions between a representative range of alkyl- and aryl-amines and of aliphatic and aromatic acids showed that the direct formation of amides from primary amines and carboxylic acids without catalyst occurs under relatively low-temperature conditions (Scheme 1). The best result obtained was a 60% yield of N-bcnzyl-4-phenylbutan-amide from benzylamine and 4-phenylbutanoic acid. For all these reactions, an anhydride intermediate was proposed. Boric and boronic acid-based catalysts improved the reaction, especially for the less reactive aromatic acids, and initial results indicated that bifunctional catalysts showed even greater potential. Again, anhydride intermediates were proposed, in these cases mixed anhydrides of carboxylic acids and arylboronic acids, e.g. (I).1... 

The boronate esters used for Suzuki reactions can be synthesized from commercially available alkyl-, vinyl-, and arylboronic acids. Alkyl and vinyl boronate esters are also synthesized by the hydroboration of double and triple bonds, similar to the hydrobora-tion of alkenes and alkynes in Chapters 8 and 9. Note that the boron atom generally adds to the less substituted end of a double or triple bond. Also, the B and H add to the same side of a triple bond (syn addition) to give a trans alkenylboronate ester. 

We have developed a stable CAB 2 (R = aryl) complex that can be prepared in situ by mixing tartaric acid derivative and arylboronic acid at room temperature. In contrast with 2, R = H, which is both air- and moisture-sensitive, the B-alkylated catalyst 2, R = aryl or alkyl, is stable and can be stored in closed containers at room temperature (Eq. 39). A solution of the catalyst (20 mol %) is effective in catalyzing the hetero Diels-Alder reaction of aldehydes with a Danishefsky diene to produce dihydro-pyrone derivatives of high optical purity (up to 98 % ee) (Eq. 40) [39]. The extent of asymmetric induction is largely dependent on the structure of the boronic acid. In general, bulky phenylboronic acid (R = 2,4,6-Me3CeH2, o-MeOC6H4) results in excellent asymmetric induction. 

Alternatively, the [RB(pzx)3] ligands may be prepared from the reaction of alkyl or arylboronic acids,25,27 or RB(OR)2 ester,28,2 30 with the pyrazolate ion and excess pyrazole (Equation (2)) ... 

Upon warming, alkylpalladium complex 4 underwent P-hydride elimination to generate allylbenzene and Pd(P(t-Bu)2Me)2HBr. This process was inhibited by the presence of excess P(t-Bu)2Me, consistent with a pathway that involves initial dissociation of a phosphine [45]. Oxidative-addition adduct 4 reacted with one equivalent of o-tolylboronic acid to generate the coupling product in 94% yield in addition, it served as a competent catalyst for cross-couplings of alkyl bromides and arylboronic acids. 

The Pd-catalyzed sequential reaction of the three components aryl iodide, alkyl iodide, and arylboronic acid can be performed in a one-pot operation (Scheme 17 and Table 3). ... 

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... 

Miura reported a 1,4-shift of rhodium in the reaction of norbornene with arylboronic acids (Scheme 3) where rhodium moves from an alkyl sp2-carbon to an aryl sp2-carbon, and the arylrhodium species further reacts with another molecule of norbornene.30 Polyalkylated phenyls are obtained in good yields. Cesium fluoride facilitates the transmetallation, generating the phenylrhodium complex which then coordinates to the -face of norbornene. 

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