3- pyridylboronic acid

Bromoquinolines behave in the Suzuki reaction similarly to simple carbocyclic aryl bromides and the reaction is straightforward. Examples include 3-(3-pyridyl)quinoline (72) from 3-bromoquinoline (70) and 3-pyridylboronic acid (71) (91JOC6787) and 3-phenyl-quinoline 75 from substituted 3,7-dibromoquinoline 73 and (2-pivaloylaminophenyl)boronic acid 74 (95SC4011). Notice that the combination of potassium carbonate and ethanol resulted in debromination at the C(7) position (but the... 

SYNTHESIS OF 3-PYRIDYLBORONIC ACID AND ITS PINACOL ESTER. APPLICATION OF 3-PYRIDYLBORONIC ACID IN SUZUKI COUPLING TO PREPARE 3-PYRIDIN-3-YLQUINOLINE... 

B. 3-(4,4,5,5-Tetramethyl-[l,3,2]dioxaborolan-2-yl)pyridine. A 250-mL, one-necked, round-bottomed flask equipped with a magnetic stirbar and a Dean-Stark trap fitted with a condenser capped with a nitrogen inlet adaptor is charged with tris(3-pyridyl)boroxin-0.85 H20 (3.0 g, 9.1 mmol), pinacol (4.07 g, 34.4 mmol) (Note 6), and 120 mL of toluene. The solution is heated at reflux for 2.5 hr in a 120°C oil bath. The reaction is complete when the mixture changes from cloudy-white to clear. The solution is then concentrated under reduced pressure on a rotary evaporator to afford a solid residue. This solid is suspended in 15 mL of cyclohexane (Note 7) and the slurry is heated to 85°C, stirred at this temperature for 30 min, and then allowed to cool slowly to room temperature. The slurry is filtered, rinsed twice using the mother liquors, washed with 3 mL of cyclohexane, and dried under vacuum to afford 4.59 g (82%) of 3-pyridylboronic acid pinacol ester as a white solid (Note 8). 

An alternate approach to the formation of pyridylboronic acids is the cross-coupling of a halopyridine with a diboronate ester (usually bis(pinacolato)diboron, 7.7.)9 The analogous reaction of 2-chloropyridine led to pyridine formation through protodeboronation. The product of the reaction, either after hydrolysis to the boronic acid or in the ester form, can be further reacted with another aryl halide to give a biaryl. In certain cases the reaction might also be carried out in a one-pot manner.10... 

There are many examples of the Suzuki coupling in which the pyridine motif is employed as a nucleophile in the form of a pyridylboron reagent. With the growing number of commercially available pyridylboronic acids, more and more applications using this approach are expected. 

A pyridylboronic acid derivative 181 has also been attached to a solid-support and does... 

The viability of pyridylboronic acids was investigated as potential intermediates in the preparation of heteroarylpyridines [80]. Boronic acid 227 was prepared from 226 and coupled to 3-bromoquinoline to generate 228. 

An example of transfer of the phenyl group from triphenylphosphine (e) is seen in the coupling of the phenyldiethanolamine ester of 2-pyridylboronic acid, where this side reaction represents about 20% of the product, however using tri-o-tolylphosphine circumvents the problem (4.2.7.6). 

The bipyridyl 74 was prepared by the coupling of 3-pyridylboronic acid 72 with 2-bromo-5-methoxypyridine 73 in good yield. Similarly heteroarylpyridines were prepared [74]. Coupling of the jS-chloro-a,y3-unsaturated aldehyde 75 occixrred in water without a co-solvent in the presence of Bu4NBr [75]. 

Me (2), 4-F (1.7). For arylboronic acids sensitive to water, the reaction under nonaqueous conditions is desirable. The coupling of 2-formyl-phenylboronic acid with 2-iodotoluene at 80 °C in an aqueous solution of Na COj and DME results in a 54% yield of biaryl accompanied by benzaldehyde (39%). The yield, however, improves to 89% with the 1,3-propandiol ester of boronic acid and anhydrous K3PO4 suspended in DMF at 80 °C (Eq. 36). 2-Pyridylboronic acid is highly susceptible to... 

Czamik devised an elegant improvement on PBA-TOMA as a carrier admixture by synthesizing the lipophilic alkylated pyridylboronic acids 3 (75). Functioning as covient versions of PBA-TOMA, carriers 3 were found to transport nucleosides up to eight-fold better (e,g, a BLM containing 0.5 mM of carrier 3 enhanced uridine transport to over 100 times the rate of background diffusion). At pH 7, compounds 3 exist as zwitterions, thus the principal binding equilibrium is that shown in equation 1. 

The 4-pyridylboronic acid and the 3-pyridylboronic acids led to dimeric cobaloximes 161 and 162 by a reaction with cobaloxime compounds. The bridges consisted in the axial pyridyl fragment and the boron inserted inside the dioxime macrocycles. In the case of 3-aminophenylboronic acid, a trinuclear arrangement 163 was observed (Scheme 23). ... 

Conceptually, this was first demonstrated using a metallated porphyrin that was functionalized with 2 diols (zinc dicatechol porphyrin) (Fig. 5). After addition of 3-pyridylboronic acid, absorption spectroscopy indicated that the pyridyl moiety was coordinated to the Zn-porphyrin. The observed affinity constant for this interaction, however, was more than 30 times what was expected for a simple pyridyl-Zn-porphyrin complex. It was, therefore, reasoned that the diols reacted with the boronic acids to afford the esters that would result in a cyclic structure (Fig. 5). Indeed, vapor phase osmometry (VPO) confirmed the 2 2 dimeric nature of the complex. Here the ester served as the key covalent linkage, though associated coordination was required between the metal and pyridine to create the cyclic structure. 

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