Lewis acids boron trifluoride

Covalent fluondes of group 3 and group 5 elements (boron, tin, phosphorus, antimony, etc ) are widely used m organic synthesis as strong Lewis acids Boron trifluoride etherate is one of the most common reagents used to catalyze many organic reactions. A representative example is its recent application as a catalyst in the cycloadditions of 2-aza-l,3-dienes with different dienophiles [14] Boron trifluoride etherate and other fluonnated Lewis acids are effective activators of the... 

The pharmaceutical interest in the tricyclic structure of dibenz[6,/]oxepins with various side chains in position 10(11) stimulated a search for a convenient method for the introduction of functional groups into this position. It has been shown that nucleophilic attack at the carbonyl group in the 10-position of the dibenzoxepin structure renders the system susceptible to water elimination. Formally, the hydroxy group in the enol form is replaced by nucleophiles such as amines or thiols. The Lewis acids boron trifluoride-diethyl ether complex and titanium(IV) chloride have been used as catalysts. 

The Lewis acid, boron trifluoride, enhances selectivity, but not reactivity. 

The alcohol in hemiacetal/acetal formation can be replaced with a thiol (R-SH). In addition, a glycol can be replaced with a dithiol, and then you can follow a procedure similar to the one outlined in Figure 10-21. This procedure leads to an easy method for reducing a carbonyl (Figure 10-22). The reaction with a thiol is in the presence of the Lewis acid boron trifluoride, BFj. 

In this procedure, the ketone is first converted to its enol acetate by reaction with acetic anhydride in the presence of a proton acid. Since this enol acetylation is performed under equilibrating conditions, the more stable enol acetate (usually the more highly substituted isomer) is produced. Acetylation of this enol acetate, catalyzed by the Lewis acid boron trifluoride, usually leads to the formation of the enol acetate of a /3-diketone which is cleaved by boron trifluoride to form acetyl fluoride and the borofluoride complex of the /3-diketone. Thus, this procedure offers a convenient and general synthetic route... 

The carbon-sulfur bond of thiazines can be reductively cleaved (Sections 7.06.5.7 and 7.06.6.7) and 2//-thiazines, being imines, can be hydrolyzed (Section 7.06.5.5). Saturated thiazines (thiomorpholines) are stable toward alkaline hydrolysis <1981CPB1554> and Lewis-acidic boron trifluoride <1980JHC449>. 

Figure 5.19. Illustration of the formation of a donor-acceptor complex by the sequential adsorption of trimethylamine and boron trifluoride. The Lewis-basic trimethylamine forms a dative bond with the electrophilic Si dimer atom, and the Lewis-acidic boron trifluoride bonds to the nucleophilic Si dimer atom [278].

Several catalysts and initiator systems have been tested for the polymerization of GlcAnBzl3, including the following Lewis acids boron trifluoride and its etherate, phosphorus pentafluoride, titanium tetrachloride, and antimony pentachloride and pentafluoride. Several cationic initiators have also been used, including (triphenylmethyl) antimony hexachloride, 2,3,4,6-tetra-O-acetyl-D-glucopyranosyl hexa-fluorophosphate, acetyl hexafluorophosphate, pentamethylbenzyl hexa-fluorophosphate (most of which were generated in situ), and triethyl-... 

Concerning electrophilic side reactions, intramolecular Friedel-Crafts condensations have been reported for example, fluorenone is formed from 2-benzoylbenzenediazonium tetrafluorobo-rate.241 The strong Lewis acid boron trifluoride can also be responsible for side reactions, such as the extensive formation of tars from nitro-substituted arenediazonium tetrafluorobor-ates or the acidic hydrolysis of ester substituents, especially in the case of 2-(ethoxycar-bonyl)benzenediazonium tetrafluoroborate.105,242... 

Compounds containing carbon-carbon double bonds m y also act as Lewis bases. The rather high solubilities of the inorganic Lewis acids, boron trifluoride, aluminum bromide, and silver perchlorate, in benzene derivatives and in olefinic compounds suggest acid-base interactions. Addition compounds formed from silver perchlorate and a number of such hydrocarbons have been isolated it has been shown that the silver ion is not bonded to any single carbon atom but sits astride the two -electron dumbbells as shown in Figure 5-1. Thus, such adducts are... 

As in acidolysis (Chap. 6.1), thioacidolysis proceeds mainly by cleavage of arylglycerol-/ -aryl ether linkages. In contrast to acidolysis, however, thioacidolysis is performed in anhydrous media. The ether-cleaving reagent combines a hard Lewis acid, boron trifluoride etherate, and a soft nucleophile, ethanethiol (Node et al. 1976, Fuji et al. 1979). 

Boron forms strong bonds to fluorine (644kJmol ), usually combining with three or four fluorides in its compounds or salts. Several binary fluorides of boron are known including boron trifluoride, BF3, a stable gas of great industrial importance as a Lewis acid. Boron trifluoride is synthesized industrially by reaction of hydrofluoric acid with borates or boric oxides (equation 42). ... 

Cobalt-complexed propargylic aldehydes can be alkylated using both cyclic and acyclic trimethylsilyl enol-ethers and -esters in the presence of a Lewis acid. Boron trifluoride etherate is the most frequently employed Lewis acid. 

Starling from the cycloadduct of juglone and acetoxybutadiene [35]. The Diels-Alder reaction gave regio- and stereoselectively the adduct in the presence of the Lewis acid, boron trifluoride. 

The following test systems were selected Lewis acids-. Boron trifluoride etherate, titanium tetrachloride, aluminum trichloride, zinc dichloride, and zinc diiodide Amines Benzylamine, butylamine, morpholine, and dipropylamine. The distribution of these items in the corresponding score plots are shown in Fig. 16.7. 

Whereas these and other reports did not indicate the possibility of 1,4-cuprate additions to activated dienes, Yamamoto and co workers" showed in their seminal contributions that this is indeed feasible while the reaction of methyl sorbate with the Gilman cuprate M-Bu2CuLi provided exclusively the 1,6-addition product, the reagent formed from butylcopper and the Lewis acid boron trifluoride led to the 1.4-adduct as the major product (equation 15). The synthetically veiy useful organocopper compounds RCu have been named Yamamoto reagents. In certain cases, the regioselectiv-... 

As shown in Fig. 8, two possibilities are conceivable for the addition step of the imine to the lanthanoid-phosphite complex Ha. To determine whether structure V or VI seems to be the more reasonable in the addition reaction of a dimethyl phosphite with the C=N double bond of cyclic imines, several hydrophos-phonylation experiments using different types of phosphites were carried out in the presence or absence of the Lewis acid boron trifluoride. As it was shown that a high level of Lewis acid activation of the imine is required independently from the nucleophilicity of the phosphorus nucleophile which was used, a transition state of type VI appeared to exist as the dominant transition state structure. 

The next most popular esterification catalyst is the Lewis acid boron trifluoride (BFj), which is commercially available as a 14% solution in methanol for making methyl esters. The analogous BCI3 reagents are also available and almost equally useful. BCI3 is also available as the 2-chloroethanol complex, as mentioned above, and BFj as the n-propanol and n-butanol complexes. 

Epoxides can be isomerized to carbonyl compounds by Lewis acids. Boron trifluoride is frequently used as the reagent. Carbocation intermediates appear to be involved, and the structure and stereochemistry of the product are determined by the factors which govern substituent migration in the carbocation. Clean, high-yield reactions can be expected only where structural or conformational factors promote a selective rearrangement. 

Keywords free radical, initiator, accelerator, crosslinking, gelation, inhibition, peroxide, hydroperoxide, amine, anhydride, amide, Lewis acid, boron trifluoride, pot life, exotherm. 

General Discussion. 2,4-Pentadienyltrimethylsilane is used as a stable (storable) nucleophilic substitute for pentadienyllithium. This compound reacts with Lewis acid (boron trifluoride etherate, iodotrimethylsilane, titanium(IV) chloride) activated electrophiles in the same manner as allylsilanes (eq 1). Generally only e-substitution is observed (cf. Table 1). ... 

TiCU is a powerful activator of carbonyl groups and promotes nucleophilic attack by a silyl enol ether. The product is a titanium salt of an aldol which, on hydrolysis, yields a p-hydroxy ketone. TiCU is generally the best catalyst for this reaction. The temperature range for reactions with ketones is normally 0-20 °C aldehydes react even at —78 °C, which allows for chemoselec-tivity (eq 9). In a- or p-alkoxy aldehydes, the aldol reaction can proceed with high 1,2- or 1,3-asymmetric induction. With the nonchelating Lewis acid Boron Trifluoride Etherate, the diastere-oselectivity may be opposite to that obtained for the chelating TiCU or Tin(IV) Chloride (eq 10). ... 

Cationic polymerization of comb LCPs was first reported by Percec who used the Lewis acid boron trifluoride etherate as initiator. This approach, illustrated in Fig. 7.22, gave useful solution preparations of polyvinylethers (R = H) and polypropenylethers (R = CH3). Recently Sagane and Lenz demonstrated that the use of the cationic initiator system HI/U brought about living polymerizations of similar monomers and greatly improved the molecular mass distribution of the products. 

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