Boronate chelate

Methylsulfonyl-9-(4-methylpiperazinyl)-3-methyl-2,3-dihydro-7-oxo-7//-pyrido[l,2,3- /e]-l,4-benzoxazine-6-carboxylic acid was obtained from 9-fluoro-lO-methylsulfonyl derivative with 1-methylpiperazine in MeCN at 60 °C for 16h. The boron chelate of lO-methoxylsulfonyl-9-fluoro derivatives gave the same result (99H(51)1563). 

Reduction of (3-hydroxy ketones through chelated TSs favors. yy -l,3-diols. Boron chelates have been exploited to achieve this stereoselectivity.129 One procedure involves in situ generation of diethylmethoxyboron, which then forms a chelate with the (3-hydroxyketone. Reduction with NaBH4 leads to the vyn-diol.130... 

Manaev AV, Chisova TA, Traven VF (2006) Boron chelates in the synthesis of a, P-unsatu-rated ketones of the coumarin series. Russ Chem Bull 55 2226-2232... 

In a molecule of 2-phenyl-l-boraadamantane there are two markedly different types of B-C bonds two of them are boron-alkyl and one is boron-benzyl. On treatment of THF complex 34 with 8-hydroxyquinoline at 20 °C, mpture of the 1-boraadamantane core takes place, resulting in a mixture of boron chelates 52-54 (Scheme 16). When trimethylamine adduct 16 is used as the starting compound, reaction takes place only in boiling toluene. Interestingly, all the products result from the protolysis of B-CH2 bonds only <2006UP1>. 

The protolytic cleavage of THF-2,2-dimethyl-l-boraadamantane 23 with pivalic acid also proceeds regiospecifi-cally giving rise, after treatment with 8-hydroxyquinoline, to boron chelate 55 (Scheme 17) <2004MI1>. 

SCHEME 3.47 Chemical structure of a boron chelate-based green dopant. 

SCHEME 3.73 Chemical structures of blue boron chelates. 

The BF2 chelates are hydrolytically stable (the majority of them may be recrystallized from water) whereas the BC12 chelates are easily hydrolyzed. The boric acid ester complex triptych boroxazolidines are also stable towards hydrolysis as are other aminoalcohol esters.83 A great number of the boron chelates are colored several spectrophotometric methods are based on chelate formation81 84 for the analytical determination of boric acid, organoboric acids and chelating organic compounds. The boron chelates are remarkable for their pharmacological properties as well.84 Various aspects of the boron chelates have been reviewed.81,83-86... 

The more stable boron chelates can be isolated even from aqueous solution, whereas those of lower stabilities are only accessible from non-aqueous media. Catechol- and inositol-borates (3, 5 and 6) possesses a well-defined monomeric structure,75 whereas those obtained from monosaccharides and alditols are polymeric.121 A crystal structure determination122 has been carried out for sodium scyUo-inositol diborate (6). 

Based on the excellent solubility and reducing properties of amine boranes, they are often used for the stabilization and purification of industrial materials. Further, they are applied as additives in hydrocarbon fuels and in lubricating oils, as polymerization catalysts, as ingredients in photographic processing and in the electroplating industry.169 High stability towards hydrolysis and oxidation makes cationic boron chelates useful as water-soluble dyes.170... 

We have synthesized and tested an example boron-chelating polymer based on a commercially available dendrimeric poly(amido amine) (PAMAM). Dendrimeric chelants offer several advantages over polymers typically used in PAUF. Foremost among these is the reduced viscosity of dendrimer solutions as compared to solutions of linear polymers[6]. This allows the use of higher polymer concentrations than previously feasible (though in the present study we worked at polymer concentrations of less than 5% due to the expense of the starting dendrimer). In this study, the dendrimeric chelant also serves as a convenient, monodisperse polymer with which to test the mathematical model for boron speciation which is derived from the work of Wise and Weber[l],... 

Stereoselective reduction of -hydroxy ketones." Boron chelates of p-hydroxy ketones are reduced by sodium borohydride stcrcoseicctivciy to, vvn-l,3-diols (equation I). Even higher, sy -selectivity obtains on similar reduction of. wn-a-substituted-p-hydroxy... 

The total syntheses of 3-deoxy-D-nZ 6>- and 3-deoxy-D-araZ m6>-hexose were realized via the cross-aldolization of 2,3-O-isopropylene-D-glyceraldehyde (R)-24 and 1,1-dimethoxyacetone (Scheme 13.62). The key step of the synthesis is the diastereoselective reduction of one of the aldols 179 via boron chelates. Treatment of 179 with triisobutylborane, and then with NaBH4 gives syn-1,3 181 and anti-1,3-diol 182 in a ratio 95 5. Acidic hydrolysis provides... 

Nasaraka, K, Pai, F-C, Stereoselective reduction of (3-hydroxyketones to 1,3-diols. Highly selective 1,3-asymmetric induction via boron chelates. Tetrahedron, 40, 2233-2238, 1984. 

Alkoxydialkylboranes (R OBR2) react with P-hydroxy ketones to form boron chelate intermediates that on subsequent reduction give the 1,3-syn diols. ° Methoxydiethylborane and NaBH4 are the reagents of choice for this transformation. The chelate is reduced via intermolecular hydride delivery at the face opposite from the P-R group, as shown below. 

Mass spectra of numerous boron-chelate complexes of pyridines and quinolines (five-membered chelate rings) and their N-oxides (six-membered chelate rings) have been recorded.309... 

But first consider the yield of the reaction. It is 99%. What is more, the diastereoselectivity is 99 1. If you work in a lab yourself, you might reflect on how many of your reactions go in 99% yield with such high selectivity. It really is a very good reaction indeed and this is how it works. Under the reaction conditions the cyclic intermediate 158 is formed. Methoxide has been displaced from Et2BOMe and one of the carbonyl lone pairs also gets in on the act and binds the boron in place. Reduction of 158 gives another boron chelate 159. 

These results are interpreted as shown in Figure 6.79. The formation of 6.92 takes place via a cyclic transition state Cj Si. Chelate 6.91 is disrupted in order to allow the coordination of the aldehyde to the boron atom. As usual, steric interactions are minimized in the favored transition state. In the presence of excess boron triflate or of another Lewis acid which can activate the aldehyde carbonyl group, the boron chelate is no longer disrupted. Two acyclic transition-state models, A Re and A Si, can be envisioned according to the nature of the Lewis acid [106], Open transition states are also proposed for the reactions of 6.91 with CF3CHO, which does not require electrophilic assistance [1261]. 

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