Acids Boron trifluoride etherate

B-Homosteroids have also been prepared by acid-catalyzed reaction of diazomethane with a,/5-unsaturated ketones. 3/ -Hydroxycholest-5-en-7-one acetate (57) reacts with diazomethane in the presence of concentrated fluoroboric acid, boron trifluoride etherate or aluminum chloride to give 3yS-hydroxy-B-homo-cholest-5-en-7a-one acetate (67). The 7a-keto group is reported to be chemically less reactive than an 11-keto group. 

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... 

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). 

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. 

Whereas empirical force-field calculations predict a ring A boat conformation for lanost-8-en-3-one, combined empirical force-field-extended Hiickel molecular orbital calculations favour a ring A chair conformation. Europium-shift n.m.r. results indicate that the molecule adopts the latter conformation. Studies on the peracetic acid-boron trifluoride etherate Baeyer-Villiger oxidation of 4,4-dimethyl-3-keto-triterpenoids to 5-lactones (18) and their subsequent ring contraction to y-lactones have been reported. Dehydrogenation of lanost-8-en-3j8-ol with 2,3-dichloro-5,6-dicyanobenzoquinone afforded, in addition to the corresponding 7,9(1 l)-diene, the aromatic seco-lanostane derivatives (19)... 

Preparation.1 The reagent (1) is prepared by the addition of methanol to 2-methyI-l-buten-3-yne using a catalyst prepared from red mercuric oxide, trichloroacetic acid, boron trifluoride etherate, and methanol. 

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. 

Production of alpha-terpinyl alkyl ethers Beta Excellent yields in continuous reactor Eliminates use of HCl, H2SO4, AICI3, toluene, sulfonic acid, boron trifluoride etherate, and acidic cation resins as catalysts... 

Reactions of free ketones with imines are far more restricted than those with preformed iminium salts. Examples of ketone-imine condensations are included in several reviews - and are limited to the use of arylimines, mainly benzylideneaniline. Blatt and Gross have noted that the reproducibility of uncatalyzed additions of ketones to Schiff bases is poor but can be improved by the addition of small amounts of hydrochloric acid. The highest yields of 3-amino ketones are obtained using 10 mol % of concentrated hydrochloric acid and 95% ethanol as solvent, and by performing the reaction at room temperature. The reaction, however, is of limited applicability, as it is restricted to methyl ketones and cycloalkanones. Deamination leading to unsaturated ketones is a major side reaction. In addition to hydrochloric acid, boron trifluoride etherate has been used as a catalyst in reactions of aromatic imines with methyl ketones, cyclic ketones and an epoxy ketone. ... 

Amidation of carboxylic acids. Boron trifluoride etherate has been used as a reagent for reaction of carboxylic acids with primary or secondary amines to form amides. The reaction is accelerated by bases (triethylamine, DBU) and by azeotropic removal of the water formed. The reaction is conducted in refluxing benzene or toluene. Yields are generally in the range of 50-85%. 

A new method for the selective demethylation of alkyl methyl phosphates employs a mixture of dimethyl sulphide and methanesulphonic acid. Boron trifluoride etherate catalyses the regio- and stereo-specific alkenylation of phenolic ethers by diisopropyl prenyl or geranyl phosphates (84) in low to moderate yields. 2-(Diethoxyphosphinyl)-1,3-butadienes, e.g., (85), are cleaved by organocopper reagents in some cases this reaction is accompanied by alkylation and rearrangement to an allene structure. ... 

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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