Organoboron acids

In 1975, Heck described the first non-catalytic example of this reaction, nsing organoboronic acids as precursors and stoichiometric amounts of palladium acetate... 

Much attention has recently been focused on organoboronic acids and their esters because of their practical usefulness for synthetic organic reactions including asymmetric synthesis, combinatorial synthesis, and polymer synthesis [1, 3, 7-9], molecular recognition such as host-guest compounds [10], and neutron capture therapy in treatment of malignant melanoma and brain tumor ]11]. New synthetic procedures reviewed in this article wiU serve to find further appHcations of organoboron compounds. 

The regioselectivity of palladium-catalyzed additions of organoboronic acids to unsymmetrical alkynes is strongly dependent on steric and electronic effects (Scheme 12).62 Multi-component reaction has been reported for the synthesis of tetrasubstituted alkenes.58 The aryl group from an aryl iodide is generally added to the less hindered... 

Nitroalkenes are good candidates for the rhodium-catalyzed asymmetric 1,4-addition of organoboronic acids. Hayashi et al. reported that the reaction of 1-nitrocyclohexene with phenylboronic acid in the presence of rhodium/ -BINAP catalyst gave 99% ee of 2-phenyl-1-nitrocyclohexane (Scheme 38).117... 

Organoboronic acids are stable in the presence of oxygen and moisture, permitting a protic or even aqueous reaction medium. 

Palladium- and copper-catalysed cross-coupling of organotellurium dichlorides with organostannanes and organoboronic acids... 

Figure 3.15. Scope of Rh/(S)-binap-catalyzed asymmetric 1,4-addition of organoboronic acids to a,P-enones.

Figure 3.44. Scope of Rh/47-catalyzed asymmetric ring-opening of oxabicyclic alkenes with organoboronic acids.

Tab. 3.1 Asymmetric conjugate addition of organoboronic acids to a,j8-unsaturated ketones catalyzed by RhjacacjjCjHJj/jSj-BINAP [6],...

Due to the tendency of organoboronic acids to undergo cyclic trimerization with loss of water to form organoboroxines, the determination of the exact stoichiometry of the organoboronic adds is usually difficult Use of more stable organoboroxines 10, which have similar reactivity to organoboronic acid, can avoid this problem. 

The rhodium-catalyzed asymmetric conjugate addition is applicable to a,yS-unsaturated esters (Scheme 3.8). Hayashi reported [20] that the reachon of 5,6-dihydro-2H-pyran-2-one 19a with phenylboronic acid gave a 94% yield of phenylated lactone (S)-20am with 98% enanhomeric excess. For the linear enoates, organoboronic acids did not give... 

Scheme 3.13 Catalytic cycle for the rhodium-catalyzed addition of organoboronic acids to oxanorbornenes [27, 28].

The reaction mechanism proposed for the addition of organostannanes [29] is similar to that for organoboronic acids. An example of the reaction of methyl vinyl ketone 42 is outlined in Scheme 3.15. The catalytic cycle involves a cationic rhodium complex G, phenylrhodium H, and oxa-n -allylrhodium I. Stannyl enol ether 44 is formed by the reaction of oxa-n -allylrhodium I with Me3SnBF4, which upon hydrolysis gives the ketone 43. The lower yields in the absence of water were explained by the further reaction of 44 with methyl vinyl ketone 42. The rapid hydrolysis with water may prevent such oligomerization. 

There is one report of vinyl substitution with an organosodium derivative.47 Organoboronic acids, also, have been used.48... 

Suzuki reaction A palladium catalyzed reaction that results in the formation of new carbon to carbon bonds by reacting an organohalide or organotriflate with an organoboronic acid. 

Alkynals and alkynones have been alkylatively cyclized in a palladium(0)-catalysed trans-addition of organoboronic acids.349... 

Use of a classical heteronuclear NMR method to study intermediates on cycle directly the Rh-catalysed asymmetric addition of organoboronic acids to enones... 

A major advantage of this MCR is that organoboronic acids are readily available in a large variety of structural configurations and they can be formed in isomeri-cally pure forms. As a result of their widespread utility in Suzuki-Miyaura coupling [27, 28] and other reactions [29, 30], a variety of aryl and heteroaryl [31] boronic adds are now commercially available and can be employed in this MCR process. Most of these compounds are also air and water stable as well as non-toxic and environmentally friendly. They also tolerate many functional groups, thereby... 

The Suzuki Coupling, which is the palladium-catalysed cross coupling between organoboronic acid and halides. Recent catalyst and methods developments have broadened the possible applications enormously, so that the scope of the reaction partners is not restricted to aryls, but includes alkyls, alkenyls and alkynyls. Potassium trifluoroborates and organoboranes or boronate esters may be used in place of boronic acids. Some pseudohalides (for example triflates) may also be used as coupling partners. 

Tempesti et al. (238) used organoboronic acids (lib) for the immobilization of Mo(VI). It is assumed that the interaction of Mo occurs through a condensation with the supported acid. Reactions reported with the bimetallic material showed an activity and selectivity comparable to those of homogeneous bimetallic analogs. In a comparable approach, Mo was anchored to immobilized phosphorus-containing acids, for example, of cellulose phosphate (11c) (239) or phosphonate resins (11a) (240). 

A. R. Martin, Y. Yang, Palladium Catalyzed Cross-Coupling Reactions of Organoboronic Acids with Organic Electrophiles "Acta Chem. Scand. 1993, 47, 221-230. 

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