Synthesis of Boronates

Direct Condensation of Carbohydrates with Boronic Acids 

4-phenylboronate, which may be isolated in excellent yield by removal of most of the solvent and addition of dry, light petroleum.22 

Some carbohydrate derivatives are too insoluble in benzene to be so esterifled, and, for them, a suitable, alternative solvent is 1,4-dioxane, the water azeotrope of which may, by careful, fractional distillation be removed before the solvent, and the water evolved in the reaction determined, if desired, by the Karl Fischer method. Whereas methyl a-D-glucopyranoside can be esterifled by the benzene procedure, the analogous a-D-mannoside ester must be prepared by use of 1,4-dioxane or by some other variation.3 

A further method applicable to benzene-insoluble carbohydrates involves the addition of the compounds, in water, to triphenylboroxin8 (preferably in methanol23), and, under these conditions, some boronic esters have been found to precipitate. Otherwise, the reactants may be fused under vacuum7 (a procedure not in current use, and not recommended) or treated in such solvents as acetone,9,23,24 or 2-methoxyethanol.25,28 Particularly for the formation of nucleoside boronates, pyridine has often been used as the solvent, and the reactants have been heated at the boiling point, or in sealed tubes27-30 on occasion, N,N-dimethylformamide28,31 has been employed. A feature of the use of pyridine is the occasional isolation—not surprisingly—of the products as pyridine complexes.32 

A slight modification of the reaction in acetone incorporates use of sulfuric acid as a catalyst and provides, from the corresponding, free sugars, moderately efficient, one-step procedures for obtaining 1,2-0-isopropylidene-a-D-xylofuranose 3,5-phenylboronate and the D-glu- 

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Synthesis of boron heterocycles for neutron capture therapy 94YGK1044. 

The catalysis has made reactions of certain functionalized boronates possible. For example, a carbocupration and alkylation allowed the synthesis of boronate 5. Reaction with aldehydes gave a-methylene lactones with high stereoselectivity.53... 

Qualmann, B., Kessels, M.M., Musiol, H.J., Sierralta, W.D., Jungblut, P.W., and Morodeg L. (1996) Synthesis of boron-rich lysine dendrimers as protein labels in electron microscopy. Angew. Chem. Int. 

Herbert Brown United States, b. organic synthesis of boron and phospho-... 

Scheme 9.3. Synthesis of boronic acid 10 and imidazole-4-carbaldehyde 14.

The preparation of selenolopyridazines is accomplished in the usual manner by condensation of diformylselenophenes with hydrazines. Both selenolo[2,3-cf]pyridazine (432) and selenolo[3,"4-tf]pyridazine (433) are obtained in this way (72BSF3453) as crystalline compounds with m.p. 158 and 153 °C, respectively. By strict analogy with the synthesis of boron containing furo- and thieno-pyridines (Sections 3.17.2.3.1, 3.17.3.3.1), boroxazoselenolo-pyridines (e.g. 434) and borazaroselenolopyridines (435,436) could be prepared by condensation of appropriately substituted formylselenophenoboronic acids and hydroxylamine or hydrazine <72IJS(A)(2)257>. 

The Miyaura borylation reaction enables the synthesis of boronates by cross-coupling of bis(pinacolato)diboron (B2pin2) with aryl halides and vinyl halides. 

Editor s note The synthesis of boron(III) bromide using the reaction between BF, and Al2Bt is described in Inorganic Syntheses, 3, 29 (1950). The pertinent equation is... 

Molecular design and synthesis of boron carriers for neutron-capture tumor therapy 91PAC423. 

The literature contains many references to the, /V-alkylated B-trichloroborazines, (BC1NR)3, as a starting material in the synthesis of boron-substituted borazines.1 The procedure described is a modification of syntheses originally used in the preparation of 2,4,6-trichloroborazine.2... 

Some other important aspects of boric acid chemistry are summarized in Fig. 5-26. Among these is the formation of borate esters [B(OR)3, R = alkyl or aryl], usually obtained as colorless liquids, on treatment with alcohols and H2S04. The vast literature on these compounds falls generally within the purview of organic chemistry, and will not be developed here however, it will be noted that a well-known qualitative test for boron involves treatment of the sample with methanol to form B(OMe)3, which produces a bright green color in a Bunsen burner flame. A major early discovery in this area was the synthesis of boronic acids by E. Frankland in 1862, via partial oxidation of trialkylboranes, with subsequent hydrolysis of the ester ... 

The synthesis of boron-substituted ligands starts with the desired R group already attache to the boron. Anions of the type [R Bfpzy are prepared by the following reactions... 

This procednre is the method of choice for the synthesis of boronic acids. Especially good selectivity is observed with B(0 Pr)3 and XB(NR2)2 (X = Cl, Br) as the boron source. The method may also be applied to the synthesis of many diorgano-and triorganoboranes. Some recent examples of the formation of organoboranes from organolithium and organopotassium reagents, respectively, are shown in equations (3-6). ... 

An order of susceptibility to electrophilic attack may be formulated as C6H5 > CeFs > CeCls > CH3, which correlates with similar cleavage reactions of tin derivatives. These reactions have applications in the synthesis of boron and aluminium compounds. 

Synthesis of Boron-rich Building Blocks for Phosphodiester Oligomers in Boron Neutron Capture Therapy... 

Oenbrink, G. Gabel, D. Accumulation of porphyrins in cells and tissue synthesis of boronated porphyrins. Strahlenther. Onkol. 165,130,1989. 

Scheme 4 Synthesis of Boronated ACBC Derivatives 5 CONCLUSION...

Boron cluster compounds have many electron deficient sites in them and they possess polyhedral skeleton. The procedure by which the boron cluster compounds are built from small polyhedral skeletons to a big polyhedral skeleton is in wide use for the synthesis of boron neutron capture therapy. The reactivity and reaction mechanism for the formation of the boron cluster compounds from a small cluster to a big cluster have been studied. 

Cyclic boronic esters in asymmetric synthesis 88ACR294 89T1859. Cyclic a-halo boronic esters in asymmetric synthesis 89CRV1535. B-Heterocycles as structure fragments of polymers 88UK1529. B,N-Heterocycles in the synthesis of boron nitride 90CRV73. B,P-Heterocycles 90AG(E)449. 

Combustion synthesis of boron nitride powder, BN, was reported in one of the earliest works on SHS (Merzhanov and Borovinskaya, 1972). The mechanisms of combustion and product structure formation from elements were later investigated (Mukasyan and Borovinskaya, 1992). More recently, finely dispersed hexagonal boron nitride powder has been obtained from reduction-type reactions (Borovinskaya et fl/., 1991). 

SCHEME 18.28 Synthesis of boron-modified polysilazanes by ammonolysis of tris(chlorosilylethylene)boranes (M, monomer route) and by hydroboration of vinyl-substituted polysilazanes (P, polymer route). 

SCHEME 18.32 Synthesis of boron-modified polysilylcarbodiimides from trisfchloro-silyl-ethylene)boranes and bis(trimethylsilyl)carbodirmide (Bis) under sol-gel conditions. ... 

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