Pinacol diboron

A reaction vessel was charged with the step 3 product (1.77 mmol), bis(pinacolate)-diborone (3.72 mmol), [1,1 -bis(diphcnyl-phosphino)-ferroccnc]palladium dichloride (0.11 mmol), l,l -bis(diphenylphosphino)ferrocene (0.11 mmol), and 15 ml of... 

Allylmetal compounds can be prepared by the Pd-catalysed allylation of dimetal compounds. The phenylallylboronate 195 is prepared by the reaction of 2-phenylallyl acetate with bis(pinacolate)diboron (194) catalysed by ligandless Pd in DMSO [95], A good synthetic route to the allylsilane 197 is the reaction of Me3SiSiMe3 with geranyl trifluoroacetate (196) catalysed by ligandless Pd via transmetallation of the n-allylpalladium intermediate at room temperature in DMF [96],... 

Addition of bis(pinacolate)diboron (206) to dienes is catalysed by Pt complexes. The 1 1 adduct 207 is obtained with Pt(Ph3P)4, whereas Pt(dba)2 without phosphine is a very active catalyst and the 1,8-adduct 208 is obtained at room temperature [90],... 

Boronic acids and boronate esters are usually prepared from lithium compounds, for example, from pyrimidines lithiated at the 5-position (Scheme 99). Boronates can also be obtained conveniently by Pd(0)-catalyzed couplings with, for example, pinacol diboron. 

Figure 22.1 (a) An example of SPC using AA/BB monomers (a phenylene pinacol diboronate and anthracene-1,8-ditriflate) ... 

The new boronation reaction is not confined to haUde-starting materials Aryl triflates also react with pinacol diboron and related diboron reagents. These developments have changed the face of organic synthesis by making a wide variety of boronic acids and esters readily available in the... 

Addition of a boron-boron bond across a carbon-carbon triple bond is known for some 40 years since the finding that diboron tetrahalides add to alkenes and alkynes in the absence of catalysts.36 Although the reaction seemed to be potentially attractive, the instability of diboron tetrahalides was the critical drawback for the practical use in synthesis. In 1993, much more stable pinacol ester derivative of diboron was found to add to alkynes in the presence of platinum catalysts such as Pt(PPh3)4, Pt(CH2=CH2)(PPh3)2, and Pt(CO)2(PPh3)2 (Figure 1, Scheme 2).37,38 Other... 

A solution of the pinacol ester of diboronic acid (1 mmol), l-bromo-3,4-methylenedioxy benzene (2 mmol), 10% Pd/C (80mg) and CS2CO3 (3.7 mmol) were dissolved in 10ml methyl alcohol and heated to 55 °C 16 hours. GC analysis indicated that the product constituted of 83.5% 2-(bisl,3-benzodioxole and 16.5% l-bromo-3,4-methylenedioxy)benzene. 

The total synthesis of the proteasome inhibitor cyclic peptide TMC-95A was accomplished by. S.J. Danishefsky and co-workers. The biaryl linkage in the natural product was constructed by a Suzuki cross-coupling between an aryl iodide and an arylboronic ester derived from L-tyrosine. The required arylboronic pinacolate substrate was prepared using the Miyaura boration. The aryl iodide was exposed to b/s(pinacolato)diboron in the presence of a palladium catalyst and potassium acetate in DMSO. The coupling proceeded in high yield and no symmetrical biaryl by-product was observed. 

Ishiyama, T., Ishida, K., Miyaura, N. Synthesis of pinacol arylboronates via cross-coupling reaction of bis(pinacolato)diboron with chloroarenes catalyzed by palladium(0)-tricyclohexylphosphine complexes. Tetrahedron 2001, 57, 9813-9816. 

Preparation of C2 oxazolylboronic acids is troublesome, likely due to the ring-opening liability of 2-lithiooxazoles. The C4 position can be made into a oxazolylboronate by palladium-catalyzed reaction of a C4 triflate with bis(pinacolato)diboron/ The C4 boronate can also be prepared through lithium-halogen exchange of a C4 bromide and reaction with B(0/-Pr)3 and pinacol. C2-TIPS protected oxazole can be lithiated at the C5 position and trapped with B(OzPr)3 to form the C5 boronic acid. °... 

Several new synthetic methods of arylboronates, such as pinacol ester, have been developed. A convenient preparative method of arylboronates 4 is Pd-catalyzed cross-coupling of aryl halides and triflates with bis(pinacolato)diboron (3), which can be handled easily in air. The best ligand for the coupling is DPPF [12]. In addition, one-pot biaryl synthesis can be carried out most conveniently without isolation of the boronate 4 to provide 5 [13], Ligandless Pd(OAc)2 is active for... 

The Pd-catalyzed cross-coupling reaction of the pinacol ester of diboronic acid with aryl halides and triflates gives a direct procedure for various functionalized arylboronic esters (Table 6), which are useful for highly efficient and selective carbon-carbon bond formation by Pd catalysts (Sect. III.2.2). The combination of PdCl2(dppf) with KOAc (and dppf) is effective in the carbon-boron bond formation. KOAc is essential not only to accelerate the reaction but also to prevent the formation of biaryl by-products. 

Table 10. Iridium-catalysed borylation of arenes with pinacol ester of diboron (350)...

Esterification of arylboronic acids Preparation of phenyl-1,4- diboronic acid bis-pinacol ester (266) 18/... 

A suspension of phenyl-1,4-diboronic acid [18] (366, 1.00 g, 6.03 mmol), pinacol (1.71 g, 14 mmol, 2.32 eq.) and anhydrous magnesium sulfate (2.00 g, 16 mmol) in anhydrous methanol (10 ml) was stirred overnight (approx. 24 h) at 30 C. The solvent was evaporated under reduced pressure and the residue was extracted with ethyl acetate (30 ml). The organic phase was washed with water (10 ml), dried (MgS04) and then concentrated in vacuo. The crude product was purified by silica gel chromatography (petroleum ether / dichloromethane, 7 3 to pure dichloromethane) to... 

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