Boron trifluoride complexes with ethers

Takahashi and coworkers described the one-pot synthesis of core 2 branched oligosaccharides [236], It was found that boron trifluoride complexed with a tri-methylsilyl ether would enhance the nucleophilidty of the silyl ether. As a result, glycosylations of the 6-O-TMS modified acceptor with a glycosyl fluoride provided... 

Boron trifluoride is used as a Lewis acid catalyst in a wide variety of reactions. Like diborane, BF3 is a toxic gas, but BF forms a stable complex with ethers, allowing it to be conveniently stored and measured. The complex of BF3 with diethyl ether is called boron trifluoride etherate. ... 

Boron trifluoride forms a range of complexes with ethers, nitriles and amines. It is commercially available as the adduct Et20 BF3 (12.11). Being a liquid at 298 K, it is a convenient means of handling BF3 which has many applications as a catalyst in organic reactions, e.g. in Friedel-Crafts alkylations and acylations. 

A typical initiator for TXN polymerization is boron trifluoride, usually in the form of its complexes with ethers, esters or amines. Such stable, easily available complexes are conveniently handled and can be purified by distillation 49). 

The complexes of urea and thiourea with boron trifluoride have been studied and, as with other boron trifluoride complexes, the shifts are very similar namely 19 2+0-3 p.p.m. [with respect to (MeO)aB]. A similar shift was observed for the more complex adducts with cadmium chloride or nickel bromide. It was found that dimethyl ether-boron trifluoride (shift of 17-6) and di-t-butylthiourea-boron... 

Boron Trifluoride Ltherate. Boron fluoride ethyl ether boron fluoride etherate ethyl ether-boron trifluoride complex. C4HltBF30 mol wt 141.94. C 33.85%, H 7.10%, B 7.62%. F 40.16%, O 11.27%. (CH,CHj),O.BF,. Prepd by vapor-phase reaction of anhydr ether with BF, Lauben gayer, Finlay, J. Am. Chem. Soc. 65, 884 (1943). 

A variation of the above reaction involves the boron trifluoride etherate-catalyzed condensation of gi OT-dihydroper-oxides 240 with dimethyl and diethyl acetals 243 (method C, Scheme 45) <2004S2356>. The gi OT-dihydroperoxides 240 were prepared from cycloalkanone dimethyl or diethyl acetals 242 by treatment with hydrogen peroxide catalyzed by boron trifluoride complexes <2003TL7359> or similarly from appropriate enol ethers <2004RCB681>. 

Boron trtfluorlde forms complexes with ether, acidic acid, phenol, etc. Forms monohydrate and/or dIhydrate with substandard water. The cfihydrate is a corrosive liquid with melting point at 6 C. TLV is maximum and must not be exceeded. Lung edema symptoms usually develop several hours later and are aggravated by ph ical exertion rest and hospitalization essential. Do not spray leaking cylinder wittt water (to avoid corrosion). The boron trifluoride dltq rate has HI no. 80 and UN no. 2851. 

Boron trifluoride complexes easily with ethers. The complexes are stabilized by symbiosis of F and O ligands around the boron. Dialkyl ethers are ruptured by BBrj to furnish alkyl bromides (2, 3). This is a consequence of the mutual weakening of B-Br and O-R bonds (both are hard-soft pairs) on coordination. The splitting of the bromide ion from the complexes and its return attack on the alkyl group of the oxonium intermediates are favored on HSAB grounds. 

Catalytic curing agents initiate resin homopolymerization, either cationic or anionic, as a consequence of using a Lewis acid or base in the curing process. The Lewis acid catalysts frequently employed are complexes of boron trifluoride with amines or ethers. 

Kawakami, Suzuki and Yamashita showed that compound 7, among many others, could be polymerized to derivatives of the corresponding open-chained species by treatment with boron trifluoride ether complex. Yamashita and Kawakami formed these same sorts of materials by heating the glycols and paraformaldehyde in the presence of toluenesulfonic acid. This led to prepolymers which were then thermally depolymerized to afford the cyclic oligomers which were separated by fractional distillation. 

The product of this reaction, a Lewis acid-Lewis base complex called infonnally boron trifluoride etherate, may look unusual but it is a stable species with properties different from those of the reactants. Its boiling point (126°C) for exanple, is much higher than that of boron trifluoride—a gas with a boiling point of — 100°C—and diethyl ether, a liquid that boils at 34°C. 

A solution of 3 g of the nitrile, water (5 moles per mole of nitrile), and 20 g of boron trifluoride-acetic acid complex is heated (mantle or oil bath) at 115-120° for 10 minutes. The solution is cooled in an ice bath with stirring and is carefully made alkaline by the slow addition of 6 A sodium hydroxide (about 100 ml). The mixture is then extracted three times with 100-ml portions of 1 1 ether-ethyl acetate, the extracts are dried over anhydrous sodium sulfate, and the solvent is evaporated on a rotary evaporator to yield the desired amide. The product may be recrystallized from water or aqueous methanol. Examples are given in Table 7.1. 

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. 

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). 

In acid solution 1-acyl-1//-azepines and alkyl l//-azepine-l-carboxylates undergo rapid aromatization to A-arylcarbamates,115,139,142 whereas 1/Z-azepine-l-carbonitrile suffers quantitative rearrangement and hydrolysis to phenylurea.163 Rearrangement of ethyl l//-azepine-l-carboxylate to ethyl A-phenylcarbamate is also rapid (5 min) and quantitative with boron trifluoride-diethyl ether complex in benzene.245... 

The dehydrogenation of 2,3-dihydro- and 2,5-dihydro-l//-l-benzazepines to 3//-l-benz-azepincs with heterocyclic enamines in the presence of boron trifluoride diethyl ether complex has been achieved in moderate yields (30-35%).241 In contrast, electrochemical oxidation of 2,5-dihydro-1 H- -benzazepines in buffered acetic acid solution furnishes initially 5//-l-benz-azepines in 35-45% yield.242... 

Indole and dimethyl acetylenedicarboxylate yield 2-(indol-3-yl)-2,3-dihydro-l//-l-ben-zazepine (mp 240-242 C) by addition of indole to the initially formed l//-l-benzazepinc,21 whereas 1,3-dimethylindole (10, R = H) fails to react with the diester under a variety of conditions.145 However, in the presence of boron trifluoride-diethyl ether complex at room tem-... 

The reaction of benzopentathiepin with alkenes [(fl-but- -ene, ( )-hex-3-ene, cyclopentene or cyclohexene] in the presence of the boron trifluoride-diethyl ether complex results in the formation of 3,4-dihydro-l,2,5-benzotrithiepins, e.g. formation of 3.407... 

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