Boronic add

Boranes. Borane (BH3) and substituted boranes reduce aldehydes and ketones in a manner similar to their addition to C=C bonds (15-16). That is, the boron adds to the oxygen and the hydrogen to the carbon ... 

Arylboron Formation Investigated in Micro Reactors Organic synthesis 40 [OS 40] Formation of phenyl esters of boronic add... 

Scheme 6.25 Nolan conditions for the Suzuki coupling between aryl chlorides and boronic adds...

Boronic add 2 was expensive and not available on scale. It would have to be prepared, thus adding extra step(s) to the route. 

The palladium-catalyzed coupling of boronic acids with aryl and alkenyl halides, the Suzuki reaction, is one of the most efficient C-C cross-coupling processes used in reactions on polymeric supports. These coupling reactions requires only gentle heating to 60-80 °C and the boronic acids used are nontoxic and stable towards air and water. The mild reaction conditions have made this reaction a powerful and widely used tool in the organic synthesis. When the Suzuki reaction is transferred to a solid support, the boronic add can be immobilized or used as a liquid reactant Carboni and Carreaux recently reported the preparation of the macroporous support that can be employed to efficiently immobilize and transform functionalized arylboronic adds (Scheme 3.12) [107, 246, 247]. 

There are several different routes to carboxamides.3 In most of these reactions, a carboxylic acid is converted to a more reactive intermediate, e.g. the acid chloride, which is then allowed to react with an amine. For practical reasons, it is preferable to form the reactive intermediate in situ.4 Arylboronic acids with electron-withdrawing groups such as (3,4,5-trifluorophenyl)boronic acid act as highly efficient catalysts in the amidation between carboxylic acids and amines.5 (3-Nitrophenyl)boronic add and [3,5-bis(triffuoromethyl)phenyl]boronic add are also effective amidation catalysts and commercially available. 

Borane attacks from the Boron adds as an electrophile and least hindered face. hydride as the nucleophile in a... 

Alkenes. Addition of diborane and organoboranes to carbon-carbon double bonds is a rapid, quantitative, and reversible transformation. Reversibility, however, is not a severe limitation under the usual reaction conditions, since thermal dissociation of organoboranes becomes significant only above 100°C. The addition is syn and occurs in an anti-Markovnikov manner that is, boron adds preferentially to the less substituted carbon atom. The attack of the reagent takes place on the less hindered side of the reacting alkene molecule. 

Place a 5 ml aliquot or less in a 50 ml volumetric flask and make to 5 ml volume with H2S04 (3.6M) if less than a 5 ml aliquot is used. The aliquot should contain 0-100 fig of boron. Add 20 ml of chilled H2S04 (18M) and swirl. Then, by pipet, add 20 ml of carminic acid (0.92 g in H2S04 (18M)). Make to volume with H2S04 (18M) and determine the absorbance in 1 cm cells in a spectrophotometer at 605 nm with a reagent blank in the reference cell. Compare with a standard curve containing 0-100 fig of boron. 

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 syn-addition of hydroboranes to alkenes occurs with predictable selectivity, wherein the boron adds preferentially to the least hindered carbon. This selectivity is enhanced if sterically demanding boranes are used. 

Rodriguez, N. Cuenca, A. Ramirez de Arellano, C. Medio-Simon, M. Asensio, G. Unprecedented Pd-catalyzed cross-coupling reaction of a-bromo sulfoxides with boronic adds. Org. Lett. 2003, 5,1705-1708. 

The boron adds to the less substituted carbon of the double bond, and, in the oxidation, the boron is replaced by an OH group. Note that the acid-catalyzed hydration of the same alkene would give the alcohol (CH3)2C(OH)CH2CH2CH2CH3 instead, according to Markovnikov s rule. 

The boron adds to the less substituted, or CH2, carbon. In the second step, the boron is replaced by the hydroxyl group. 

The boron adds to the least crowded carbon both the boron and hydrogen add to the same face of the double bond. Subsequent oxidation with H202 and HO- places a hydroxyl group in the exact position previously occupied by boron ... 

Compound 24(00) was synthesized according to Scheme 9.10. The key step was the Suzuki coupling of iodo-substituted diarylethene and p-phenylenedi-boronic add. 

Borane adds to the double bond in a single step. Boron adds to the less hindered, less substituted carbon, and hydrogen adds to the more substituted carbon. 

We know that this is not the whole story because of the stereochemistry. Hydroboration is a syn addition across the alkene. As the addition of the empty p orbital to the less substituted end of the alkene gets under way, a hydrogen atom from the boron adds, with its pair of electrons, to the carbon atom, which is becoming positively charged. The two steps shown above are concerted, but formation of the C-B bond goes ahead of formation of the C-H bond so that boron and carbon are partially charged in the four-centred transition state. 

Regioselectivity is high the boron adds to the carbon less able to support a positive charge... 

In the ad mmctricnlly ubstituted lUkcne each as l methylcycJopenlene, there nte two possible rrantuiion states transition state, boron adds to the Uss highly substituted ear-... 

The significance of this finding lies in the greater sensitivity to differences in the substitution pattern at the beta rather than alpha carbon of the trgnt, double bond undergoing hydroboration. Thus, the (fos, aw, Mg orientation of the a-CHMe (/. e. C-2 ) is reversed in cis vs. trans alkenes and the opposite relative configuration is obtained for these isomers after the boron adds to this center. Consistent with this e/ — ... 

Arylboronic acids [63,72,80,85,194] have been most extensively studied as binding sites for derivatised monosaccharides. By using an amino group in the position ortho to the boronic add the rate constant for the esterification with a diol has been increased by a factor of 10 , as mentioned above [79], It has also been shown that the flexibility of the boronic add group is crucial. If the binding interaction is too rigid or too flexible, it is detrimental to the selectivity of the... 

For the transfer of arj l and alkenyl groups to enones, Hayashi s procedure, employing the corresponding boronic adds and a rhodium-BINAP catalyst, is the method of choice at present [24, 25]. For the transfer of alkyl groups to cydic enones the use of dialkylzinc reagents in the presence of copper-phosphoramidite catalysts is superior. Although the first examples of hi ly enantiosdective 1,4-ad-ditions of R Zn reagents to nitroalkenes have been reported, similar catalytic methods for numerous other dasses of a, -unsaturated compounds still need to be devdoped. 

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