Boronate residues

The interpretation proposed for the LnB phases can be extended to alkaline-earth and potassium hexaborides. These dissociate through metal evaporation, yielding a j3-rhombohedral boron residue at the mp for CaB , SrB5 and BaB , and at 750°C for KBft. 

Furyllithium reacts rapidly with trialkylborons though the furylborons 91 believed to be formed are not actually isolated. Treated with an electrophile (iodine or A-chlorosuccinimide), they transfer one alkyl residue to the furan ring and eject the boron residue in a reaction well known in other series (Scheme 46). The 2-alkylfurans are indeed produced in excellent yields and the method is better than many other syntheses.236... 

Results of chronic feeding studies using mallards demonstrate that diets containing 13 mg B/kg FW produce no adverse effects, but those containing 30 or 100 mg B/kg FW are associated with elevated tissue boron residues and growth reduction, and diets containing 1000 mg B/kg are fatal... 

Palm128 Hydrogen peroxide Chlorine and boron residue... 

Use Weed killer and soil sterilant, fungus control on citrus fruits (FDA tolerance 8 ppm of boron residue). 

As indicated at the beginning, the presented discussion of CPG is selective. It focuses on the many properties distinguishing CPGs from silica gels. These differences are found in the porous structures of these materials and - mainly - in their surface properties. Both are built of Si02 and have surface covered with hydroxyl groups, but boron residue remaining... 

Z)-2-Bromoalkenyl boronates.- Tl of alkynes with BBr, and subsequent queo atom and the boron residue can be selecir are useful synthetic intermediates. 

E)-Alkenyl iodides. (2-Stannylalkenyl)boranes undergo replacement of the boron residue with iodine and protodestannylation with retention of configuration. The bimetallic compounds are readily obtained from the reaction of alkynylborates with organotin chlorides. 

A solution of 2,3-dibromo-5-methoxyaniline (32 g, 0.17 mol) in CHjClj (300 ml) was stirred and cooled in an icc bath. Boron trichloride (1 M in CH2CI2, 180 ml, 0.18 mol), chloroacetonitrile (14.3 g, 0.19 mol) and TiC (1 M in CH CIj, 190ml, 0.19 mol) were added. The resulting mixture was refluxed for 1.5 h. The solution was cooled to room temperature and poured carefully on to a mixture of icc and 20% aq. HCl (700 ml). The organic layer was separated and the CH Clj removed by distillation. The residue was heated to 90°C on a water bath for 30 min. The solution was cooled and the solid collected by filtration. It was partitioned between ether (1.41) and 1 N NaOH (500 ml). The ether layer was washed with brine, dried over Na2S04 and evaporated. The residue was recrystallized from ethanol to give 2-amino-3,4-dibromo-6-methoxy-a-chloroacetophenone (55 g) in 90% yield. 

Cmde diketene obtained from the dimeriza tion of ketene is dark brown and contains up to 10% higher ketene oligomers but can be used without further purification. In the cmde form, however, diketene has only limited stabHity. Therefore, especiaHy if it has to be stored for some time, the cmde diketene is distiHed to > 99.5% purity (124). The tarry distiHation residue, containing trike ten e (5) and other oligomers, tends to undergo violent Spontaneous decomposition and is neutralized immediately with water or a low alcohol. Ultrapure diketene (99.99%) can be obtained by crystallization (125,126). Diketene can be stabHized to some extent with agents such as alcohols and even smaH quantities of water [7732-18-5] (127), phenols, boron oxides, sulfur [7704-34-9] (128) and sulfate salts, eg, anhydrous copper sulfate [7758-98-7]. 

A typical cationic polymeriza tion is conducted with highly purified monomer free of moisture and residual alcohol, both of which act as inhibitors, in a suitably dry unreactive solvent such as toluene with a Eriedel-Crafts catalyst, eg, boron triduoride, aluminum trichloride, and stannic chloride. Usually low temperatures (—40 to —70°C) are favored in order to prevent chain-transfer or sidereactions. 

Na2B0402 10H2O, and cmde oil residue (41) in a rotary kiln heated to 1038°C. Borax is fed at the rate of 1360 kg/h and sprayed with 635 kg/h of 17% residue cmde oil. The heated mixture then reacts with CI2 at 760°C in a separate reactor to yield BCl. On a smaller scale, BCl can be prepared by the reaction of CI2 and a mixture of boron oxide [1303-86-2] 2 3 coke, and lampblack in a fluidized bed (42). Other methods for the preparation... 

To a 3QQ-mL, round-bottomed flask fitted with a water separator, (Note 1) which contains 15 g of Linde 4A molecular sieve l/16-1nch pellets and Is filled with toluene, are added 7.3 g (0.04 mol) of cyclododecanone, 11.4 g (0.16 mol) of pyrrolidine, 100 mL of toluene, and 0.57 g (0.004 mol) of boron trifluoride etherate. The solution is heated under reflux for 20 hr. The water separator is replaced by a distillation head, and about 90 mL of the toluene is removed by distillation at atmospheric pressure. The residue containing l-(N-pyrrolidino)-l-cyclododecene (1) is used in the next step without further purification (Note 2). 

A suspension of lithium aluminum deuteride (1.6 g) in dry tetrahydrofuran (60 ml) is added dropwise to a stirred and cooled (with ice-salt bath) solution of 5a-androst-l4-ene-3j3,17j3-diol (179, 1.6 g) and boron trifluoride-etherate (13.3 g) in dry tetrahydrofuran (60 ml). The addition is carried out in a dry nitrogen atmosphere, over a period of 30 min. After an additional 30 min of cooling the stirring is continued at room temperature for 2 hr. The cooling is resumed in a dry ice-acetone bath and the excess deuteriodiborane is destroyed by the cautious addition of propionic acid. The tetrahydrofuran is then evaporated and the residue is dissolved in propionic acid and heated under reflux in a nitrogen atmosphere for 8 hr. After cooling, water is added and the product extracted with ether. The ether... 

Bromo-4-methoxy-A-homo-estra-2,4,5(10)-trien-17-one (44 0. 2g), is dissolved in formic acid, 2 ml of boron trifluoride etherate is added and the mixture is stirred vigorously at 0° for 2 hr. A brown mass ca. 0.12 g) is obtained after evaporation of the solvents at reduced pressure. This material is diluted with water and extracted with chloroform. The chloroform extracts are washed successively with water and saturated salt solution, dried over anhydrous magnesium sulfate and evaporated at reduced pressure to give 95 mg of a product which is purified by filtration through a column of neutral alumina and crystallization of the residue after evaporation of the solvent from ethyl acetate-petroleum ether. The resulting A-homo-estra-l(10),2,4a-triene-4,17-dione (45), mp 143-146°, is identical to the tropone (45) prepared from monoadduct 17-ketone (43a). 

The following procedure is given in U.S. Patent 3,458,528 78 grams (0.675 mol) of 5-nitroimidazole is dissolved in 1,500 ml of acetic acid upon the addition of 72 ml (0.57 mol) of boron trifluoride etherate. 175 ml (3.5 mols) of ethylene oxide in 175 ml of hexane, in a dropping funnel topped with a cold finger, is added slowly over 1 hour to the above solution maintained at 32° to 35°C with a water cooling bath. The mixture is concentrated under high vacuum to 100 to 150 ml volume. The residue is diluted with 500 ml of water, neutralized to pH 7 with aqueous sodium hydroxide, and extracted with 1.5 liters of ethyl acetate. The extract is dried and evaporated to yield 1-(2 -hydroxyethyl)-5-nitroimidazole. 

Ethyl-2-methyl-3-(10,11) -dihydro-5H-dibenzo [a,d] cycloheptene-5-ylidene)-1 -pyrrolinium iodide (4.7 g) was dissolved in 7 cc of methanol. To this solution there were added 1.4 g of sodium boron hydride within about 80 minutes with stirring and stirring of the solution was continued for two hours to complete the reaction. The reaction mixture was acidified with 10% aqueous hydrochloric acid solution and then the methanol was distilled off. The residual solution was alkalized with 20% aqueous sodium hydroxide solution and extracted with ether. The ether layer was dried over magnesium sulfate and the ether was distilled off. The resulting residue was further distilled under reduced pressure to yield 2.0 g of 1-ethyl-2-methyl-3-(10,11 ) dihydro-5H-dibenzo[a,d]cycloheptene-5-ylidene)pyrrolidine (boiling point 167°C/4 mm Hg.). 

Reaction of methyl a-L-rhamnopyranoside with triphenylboroxole gave a syrupy boronate ester which was characterized as a crystalline phenyl-carbamate. Removal of the phenylboronic acid residue gave a product identified as methyl a-L-rhamnopyranoside 4-N-phenylcarbamate, since it was identical with that resulting from removal of the ketal group from methyl 2,3-O-isopr opylidene-a-L-rhamnopyranoside 4-N-phenylcarbamate (12). This establishes the structure of the original ester as methyl a-L-rhamnopyranoside 2,3-phenylboronate (24). 

Alternatively, diazomcthanc can be added to thioxanthylium perchlorate (4) over 30 minutes at 0°C, and the reaction solution then poured into propan-2-ol. After concentration, the residue is dissolved in acetic anhydride and treated with boron trifluoride-diethyl ether complex at 0 C, to provide dibenzo[6,/]thiepin in 55 % overall yield16 (cf. Houben-Weyl, Vol. 10/4, p 834). 

To a stirred — 78 C solution of 5.85 mL (62.5 mmol) of 3-methoxy-l-prnpene in 25 mL of THf- are added 43.1 mL (50 mmol) of 1.16 M. vcc-butyllithium in cyclohexane over a 20-25 min period. The mixture is stirred at — 78 °C for an additional 10 min, and diisopinocampheyl(methoxy)borane [50 mmol prepared from (+ )-a-pinene] in 50 mL of THF is added. This mixture is stirred for 1 h, then 8.17 mL (66.5 mmol) of boron trifluoride diethyl etherate complex are added dropwise to give a solution of diisopiuocampheyl[(Z)-3-inethoxy-2-propenyl]borane. Immediately. 2.8 mL (50 mmol) of acetaldehyde are added and the mixture is stirred for 3 h at — 78 rC and then allowed to warm to r.t. All volatile components are removed in vacuo, then the residue is dissolved in pentane. The insoluble fraction is washed with additional pentane. The combined pentane extracts are cooled to 0 JC and treated with 3.0 mL (50 mmol) of ethanolamine. The mixture is stirred for 2 h at 0rC and is then seeded with a crystal of the diisopinocampheylborane-ethanolaminc complex. The resulting crystals arc filtered and washed with cold pentane. The filtrate is carefully distilled yield 5.6 g (57%) d.r. (synjanti) >99 1 (2/ ,37 )-isomer 90% ee bp 119-120 C/745 Torr. 

The preference of the (5, .S )-boron cnolatc to attack almost exclusively the Si-face of an aldehyde is rationalized by assuming the Zimmerman-Traxler transition state model. It is postulated that the methyl group of the propyl residue directs the 3-elhylpenlane-3-thiol group towards the borolane moiety, the chirality of which is thus effectively transferred34. 

The water wash removes residual boric acid. Elemental analysis of the final product indicated that boron content was less than 0.005%. 

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