Boronic isolation

Few medicines based on boron are known, in general boric acid or a boronic acid serve to esterify an a-diol or an ortho-diphenol. This is the case for the emetic antimony borotartrates of the ancient pharmacopoieas, for the injectable catecholamine solutions, for tolboxane " , that is close to meprobamate and that was commercially available as a tranquilhzer some decades ago, or also for the phenylbo-ronic esters of chloramphenicol. " Boromycine was the first natural product containing boron isolated. " It is a complex between boric acid and a polyhydroxylated tet-radentate macrocycle. " Another natural product is aplas-momycin with antibiotic properties. " " ... 

This compound, which contains atoms arranged tetrahedrally around the boron atom, can readily be isolated from a mixture of dimethyl ether and boron trichloride. On occasions a chlorine atom, in spite of its high election affinity, will donate an electron pair, an example being found in the dimerisation of gaseous monomeric aluminium chloride to give the more stable Al2Clg in which each aluminium has a tetrahedral configuration ... 

A mixture of an acid anhydride and a ketone is saturated with boron trifluoride this is followed by treatment with aqueous sodium acetate. The quantity of boron trifluoride absorbed usually amounts to 100 mol per cent, (based on total mola of ketone and anhydride). Catalytic amounts of the reagent do not give satisfactory results. This is in line with the observation that the p diketone is produced in the reaction mixture as the boron difluoride complex, some of which have been isolated. A reasonable mechanism of the reaction postulates the conversion of the anhydride into a carbonium ion, such as (I) the ketone into an enol type of complex, such as (II) followed by condensation of (I) and (II) to yield the boron difluoride complex of the p diketone (III) ... 

Concerning my research during my Dow years, as I discuss iu Chapter 4, my search for cationic carbon intermediates started back in Hungary, while 1 was studying Friedel-Crafts-type reactions with acyl and subsequently alkyl fluorides catalyzed by boron trifluoride. In the course of these studies I observed (and, in some cases, isolated) intermediate complexes of either donor-acceptor or ionic nature. 

The cr-complexes (iv) are thus the intermediates corresponding to the substitution process of hydrogen exchange. Those for some other substitutions have also been isolated in particular, benzylidyne trifluoride reacts with nitryl fluoride and boron trifluoride at — ioo°C to give a yellow complex. Above — 50 °C the latter decomposes to hydrogen fluoride, boron trifluoride, and an almost quantitative yield of tn-nitrobenzylidyne trifluoride. The latter is the normal product of nitrating benzylidyne trifluoride, and the complex is formulated as... 

Chiral 2-oxazolidones are useful recyclable auxiliaries for carboxylic acids in highly enantioselective aldol type reactions via the boron enolates derived from N-propionyl-2-oxazolidones (D.A. Evans, 1981). Two reagents exhibiting opposite enantioselectivity ate prepared from (S)-valinol and from (lS,2R)-norephedrine by cyclization with COClj or diethyl carbonate and subsequent lithiation and acylation with propionyl chloride at — 78°C. En-olization with dibutylboryl triflate forms the (Z)-enolates (>99% Z) which react with aldehydes at low temperature. The pure (2S,3R) and (2R,3S) acids or methyl esters are isolated in a 70% yield after mild solvolysis. 

Step 3. Boron is ion implanted around the perimeter of the resist-protected area to form a "typ isolation border (the channel stopper or chanstop). The boron cannot penetrate through the resist. 

Fig. 9. Fabrication sequence for an oxide-isolated -weU CMOS process, where is boron and X is arsenic. See text, (a) Formation of blanket pod oxide and Si N layer resist patterning (mask 1) ion implantation of channel stoppers (chanstop) (steps 1—3). (b) Growth of isolation field oxide removal of resist, Si N, and pod oxide growth of thin (<200 nm) Si02 gate oxide layer (steps 4—6). (c) Deposition and patterning of polysihcon gate formation of -source and drain (steps 7,8). (d) Deposition of thick Si02 blanket layer etch to form contact windows down to source, drain, and gate (step 9). (e) Metallisation of contact windows with W blanket deposition of Al patterning of metal (steps 10,11). The deposition of intermetal dielectric or final...

In the case of the fibrous laminate not much work has been done, but it has been observed that a significant loss of stiffness in boron—aluminum laminate occurs when cycled in tension—tension (43,44). Also, in a manner similar to that in the laminated PMCs, the ply stacking sequence affects the fatigue behavior. For example, 90° surface pHes in a 90°/0° sequence develop damage more rapidly than 0° pHes. In the case of laminates made out of metallic sheets, eg, stainless steel and aluminum, further enhanced resistance against fatigue crack propagation than either one of the components in isolation has been observed (45). 

The first definitive studies of boron hydrides were carried out by Alfred Stock in Germany starting about 1912 (1). Through extensive and now classic synthetic studies, the field of boron hydride chemistry was founded with the isolation of a series of highly reactive, air-sensitive, and volatile compounds of general composition and This accomplishment required the development of basic vacuum line techniques for the... 

The main metals in brines throughout the world are sodium, magnesium, calcium, and potassium. Other metals, such as lithium and boron, are found in lesser amounts. The main nonmetals ate chloride, sulfate, and carbonate, with nitrate occurring in a few isolated areas. A significant fraction of sodium nitrate and potassium nitrate comes from these isolated deposits. Other nonmetals produced from brine ate bromine and iodine. 

Although boronates are quite susceptible to hydrolysis, they have been found useful for the protection of carbohydrates. It should be noted that as the steric demands of the diol increase, the rate of hydrolysis decreases. For example, pin-acol boronates are rather difficult to hydrolyze in fact, they can be isolated from aqueous systems with no hydrolysis. 

Boron trifluoride etherate in benzene converts A -20-acetoximinosteroids to the 17-ketones in somewhat lower yield, but the reaction of A -20-oximino steroids with this catalyst in the presence of acetic anhydride does not give the expected product two different compounds have been isolated and identified. ... 

Boron is comparatively unabundant in the universe (p. 14) it occurs to the extent of about 9 ppm in crustal rocks and is therefore rather less abundant than lithium (18 ppm) or lead (13 ppm) but is similar to praseodymium (9.1 ppm) and thorium (8.1 ppm). It occurs almost invariably as borate minerals or as borosilicates. Commercially valuable deposits are rare, but where they do occur, as in California or Turkey, they can be vast (see Panel). Isolated deposits are also worked in the former Soviet Union, Tibet and Argentina. 

There are four main methods of isolating boron from its compounds ... 

Figure 6.7 Idealized boron environment in metal-rich borides (see text) (a) isolated B atoms in M3B and M7B3 ...

The boron trihalides are volatile, highly reactive, monomeric molecular compounds which show no detectable tendency to dimerize (except perhaps in Kr matrix-isolation experiments at 20K). In... 

A series of chiral boron catalysts prepared from, e.g., N-sulfonyl a-amino acids has also been developed and used in a variety of cycloaddition reactions [18]. Corey et al. have applied the chiral (S)-tryptophan-derived oxazaborolidine-boron catalyst 11 and used it for the conversion of, e.g., benzaldehyde la to the cycloaddition product 3a by reaction with Danishefsky s diene 2a [18h]. This reaction la affords mainly the Mukaiyama aldol product 10, which, after isolation, was converted to 3a by treatment with TFA (Scheme 4.11). It was observed that no cycloaddition product was produced in the initial step, providing evidence for the two-step process. 

Chiral boron(III) complexes can catalyze the cycloaddition reaction of glyoxy-lates with Danishefsky s diene (Scheme 4.18) [27]. Two classes of chiral boron catalyst were tested, the / -amino alcohol-derived complex 18 and bis-sulfonamide complexes. The former catalyst gave the best results for the reaction of methyl glyoxylate 4b with diene 2a the cycloaddition product 6b was isolated in 69% yield and 94% ee, while the chiral bis-sulfonamide boron complex resulted in only... 

Treatment of l,4 3,6-dianhydro-D-glucitol with boron trichloride gives l,6-dichloro-l,6-dideoxy-D-glucitol (20). Although methyl 6-chloro-6-deoxy-a-D-glucopyranoside (isolated as the tribenzoate) could be isolated from the reaction of methyl 3,6-anhydro-a-D-glucopyranoside with boron trichloride (21), the application to the isomeric furanoside derivative led to complex results. 

An unusual difluoroboryl imidate (10) was isolated during decomposition of (9) and its stability arose from a strong intramolecular bond between the pyridine N and boron. Formation of the desired 2-amino-5-fluoropyridine followed by the use of aqueous sodium hydroxide (89S905). 

Z)-2-Butenylpotassium is generated from 4.5 mL (50 mmol) of (Z)-2-butene, 2.8 g (25 mmol) or /-BuOK. and 10.8 mL (25 mmol) oT 2.3 M butyllithium in THF for 15 min at —45 JC. This solution is cooled to — 78 C and 30 mmol of a 1 M solution of methoxy(diisopinocampheyl)borane in diethyl elher is added dropwise. The mixture is stirred for 30 min at — 78 °C, then is treated with 4mL (33 mmol) of boron trifluoride-diethyl ctherate complex this removes methoxide from the intermediate ate complex. This solution is immediatelv treated with 35 mmol of an afdchyde. Isolated yields of homoallylic alcohols are 63-79%. 

MP2, MAs2 and MSb2 all have a compressed form of the marcasite structure, while the carbides MC have trigonal prismatic coordination in the WC structure. Several borides are known MB2 has nets of boron atoms. RunBg has branched chains while RU7B3 has isolated borons. 

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