Diethyl ether reaction with boron trifluoride

Alkyl nitrites can also be used in anhydrous media and, for example, 4-hydroxyben-zenediazonium tetrafluoroborate is isolated in 89% yield after diazotization with isopcntyl nitrite, hydrogen fluoride and boron trifluoride in ethanol/diethyl ether.96 Diazotization can also be performed in dichloromethane or ethers (diethyl ether, tetrahydrofuran, 1,2-dimethoxyethane) with terl-butyl nitrite and boron trifluoride-diethyl ether complex which generates nitrosyl fluoride in situ.229 Excess boron trifluoride is used to trap water and tert-butyl alcohol, so that the reaction can be considered as being performed under complete anhydrous conditions. Yields are higher in dichloromethane, but 1,2-dimethoxyethane is preferred for less soluble amines. This procedure has been successfully applied to the synthesis of mono-and difluorobenzo[c]phcnanthrenes.230... 

Boron trifluoride, BF3, and diethyl ether, ( 2115)20, react to produce a compound with the formula BF3 ( 2115)20. A coordinate covalent bond is formed between the boron atom on BF3 and the oxygen atom on ( 2115)20. Write the equation for this reaction, using Lewis electron-dot formulas. Label the... 

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. ... 

B. 3-(1,1-Dimethylethyl) 4-methyl-(S)-2,2-dimethyloxazolidine-3,4-dicarbox-ylate (3). To a solution of N-Boc-L-serine methyl ester (10.0 g, 45.6 mmol) in acetone (165 mL) is added 2,2-dimethoxypropane (50 mL, 400 mmol) and boron trifluoride etherate (BF3-OEt2, 0.35 mL, 2.8 mmol) (Notes 9 and 10). The resulting orange solution is stirred at room temperature for 2.5 hr when TLC analysis indicates the reaction to be complete (Note 11). The reaction mixture is treated with 0.9 mL of 99% triethylamine and the solvent is removed under reduced pressure. The residual brown syrup Is partitioned between diethyl ether (150 mL) and saturated aqueous sodium bicarbonate solution (250 mL). The aqueous layer is extracted with diethyl ether (2 x 150 mL) and the combined organic phases are dried with anhydrous sodium sulfate and concentrated under reduced pressure (7 mm and 65°C bath temperature) to give 10.4-10.8 g (88-91% crude yield) of oxazolidine methyl ester 3 as a pale yellow oil (Note 12). Analysis of crude 3 by 1H NMR indicates a chemical purity of > 95%. The product can be used without further purification. 

Boron, a Group 3A element, has three electrons in its valence shell, and after forming single bonds with three fluorine atoms to give BFj, boron still has only sbc electrons in its valence shell. Because it has an empty orbital in its valence shell and can accept two electrons into it, boron trifluoride is electron deficient and, therefore, a Lewis add. In forming the O—B bond, the oxygen atom of diethyl ether (a Lewis base) donates an electron pair and boron accepts the electron pair. The reaction between diethyl ether and boron trifluoride is dassified as an acid-base reaction according to the Lewis model, but because there is no proton transfer involved, it is not classified as an add-base reaction by the Bronsted-Lowry model. Said another way, all Bronsted-Lowry acids are protic acids Lewis adds maybe protic acids or aprotic acids. 

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. 

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). 

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... 

Since the preformed aggregate Bu3Cu2Li showed a diastereoselectivity of 83 17 in the presence of boron trifluoride16, the low diastereoselectivity noted above was presumably due to a faster addition reaction of butyllithium, which is formed by the treatment of the Gilman cuprate with the boron trifluoride-diethyl ether complex16,, s. 

The diastereofacial selectivity of Lewis acid promoted reactions of allylsilancs with chiral aldehydes has been thoroughly investigated58. Aldehydes with alkyl substituted a-stereogenic centers react with a mild preference for the formation of Cram products, this preference being enhanced by the use of boron trifluoride-diethyl ether complex as catalyst58. 

The use of boron trifluoride-diethyl ether complex as the Lewis acid in these reactions promotes silyl group migration and gives rise to the formation of tetrahydrofurans with excellent stereoselectivity82. 

Effective 1,4-asymmetric induction has been observed in reactions between 2-(alkoxyethyl)-2-propenylsilanes and aldehydes. The relative configuration of the product depends on the Lewis acid used. Titanium(IV) chloride, in the presence of diethyl ether, gave 1,4-ijn-products with excellent stereoselectivity with boron trifluoride-diethyl ether complex, the amt-isomer was the major product, but the stereoselectivity was less83. 

Excellent chelation control was observed using tributyl(2-propenyl)stannane and a-benzyloxy-cyclohexaneacetaldehyde with magnesium bromide or titanium(IV) chloride, whereas useful Cram selectivity was observed for boron trifluoride-diethyl ether complex induced reactions of the corresponding ferr-butyldimethylsilyl ether89. 

The boron trifluoride-diethyl ether complex induced reaction of 2-butenyl(tributyl)-stannane and 3-(/er/-butyldimethylsilyloxy)-2-methylpropanal gave predominantly the nonchelation-controlled yyn-product93, whereas with the analogous 3-benzyloxyaldehyde, 2-propenyl-tin trichloride, generated in situ from tributyl(2-propenyl)stannanc and tin(IV) chloride, gave the chelation-controlled product93. 

The reaction between 5-methyl-2-(l-methyl-1 -phenylethyl)cyclohexyl 2-oxoacetate and 2-buteny](tributyl)stannane promoted by boron trifluoride-diethyl ether complex showed a strong preference for 57-facial attack, with syn selectivity69. 

The stereoselectivity of these intermolecular reactions between 1-alkoxyallylstannanes and aldehydes induced by boron trifluoride-diethyl ether complex is consistent with an open-chain, antiperiplanar transition state. However, for intramolecular reactions, this transition state is inaccessible, and either (Z)-.yyn-products are formed, possibly from a synclinal process105, or 1,3-isomerization competes113. Remote substituents can influence the stereoselectivity of the intramolecular reaction114. 

Boron trifluoride-diethyl ether complex induced reactions of both (E)- and (Z)-tributyI(3-methoxy-2-propenyl)stannane with aldehydes give. vj-w-products with useful slereoselectivi-... 

Much better results are achieved in the addition of butyllithium to oxime ethers 4a, 4b and 4c activated by boron trifluoride-diethyl ether complex (BF3 OEt2) at — 78 °C (above a reaction temperature of — 30 °C complex mixtures of products are obtained) using toluene as the solvent. Furthermore, the stereoselectivity depends on the E/Z ratio of the starting oxime ethers. The reaction appears to be highly stereoselective, with the diastereoselectivity of the... 

An interesting example from carbohydrate chemistry is the boron trifluoride-diethyl ether complex catalyzed nucleophilic addition of silyl enol ethers to chiral imines (from n-glyceralde-hyde or D-serinal)22. This reaction yields unsaturated y-butyrolactones with predominantly the D-arabino configuration (and almost complete Cram-type erythro selectivity). 

Another AMPA-derived procedure took advantage of the neat reaction between the N-carbamoyl-HHT 59 and diethyl phosphite catalyzed by boron trifluoride etherate to generate the AMPA carbamate 60. Subsequent alkylation with ethyl bromoacetate and base produced the glyphosate triester carbamate 61, which was hydrolyzed to GLYH3 (59). 

To achieve these lactose-purpurinimide conjugates 89-93, in the macrocycle positions 3, 8, 12, the purpurin-18-methyl ester 81 had to undergo several chemical transformations to obtain the desired hydroxymethyl group.68 Such alcohol derivatives were reacted with lactose octaacetate in the presence of boron trifluoride diethyl etherate to induce the acetylated lactose-purpurinimide derivative which, after deacetylation reaction conditions, yielded the desired compounds in excellent amounts (Scheme 12). 

Under the catalysis of mercuric oxide and boron trifluoride-diethyl ether, the reaction of methanol with 1,2-hexadiene afforded 2,2-dimethoxyhexane [6]. Hydration with sulfuric acid led to methyl n-butyl ketone [6],... 

Isopropylidene amino(ethoxycarbonylmethyl)methylenemalonate (1611) and boron trifluoride etherate were heated under reflux in ethanol for 48 hr. When the reaction mixture was treated with aqueous potassium carbonate, the triester (1612) was obtained in 40% yield, while after evaporation of the solvent and treatment of the residue with water, diethyl 3-oxoglutarate was isolated in 22% yield (8IS 130). 

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