Boron trifluoride, ether complexes

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 12-ketone is generally less reactive than 3-, 6- and 7-ketones but more reactive than the 11-ketone. 12-Ethylene ketals are readily prepared by the usual procedures and the 12-ketone can be selectively ketalized in the presence of a 20-ketone bearing a 17a-hydrogen or 17a-hydroxyl substituent [(81)- (82)]. ° The procedure of choice for this reaction utihzes ethylene glycol and boron trifluoride-ether complex at room temperature. 

The boron trifluoride-ether complex has been employed mainly in the opening of 5,6-epoxides. This reaction was first studied by Henbest and Wrigley and affords products depending on the nature and stereochemistry of the... 

Diethyl 7V-ethyl-A-[6-(4-ethoxycarbonyl-l-piperazinyl)-5-fluoro-2-pyri-dyl]aminomethylenemalonate (1027) was cyclized on the action of boron trifluoride etherate complex in diphenyl ether at 228-231 °C for 30 min to give the 1,8-naphthyridine derivative (1028) in 90% yield [84JAP(K)80683]. 

The 8-ester group of 7-oxopyrido[3,2,l-t/]cinnoline-8-carboxylates (68, R- + H) was hydrolyzed under basic or acidic conditions. The carboxyl group of68(R = H) was esterified and the carboxyl group was converted to a boron complex (70) by treatment with the boron trifluoride-ether complex (92EUP470578). 

Ethylenedioxy-3(5,1 la.-dihydroxy-5a-pregnan-20-one.2 A solution of 3/ , 17a-dihydroxy-5a-pregnane-12,20-dione (8.75 g) dissolved in ethylene glycol (90 ml) containing boron trifluoride-ether complex (14 ml) is kept for 16 hr at room temperature. The solution is diluted with chloroform and washed to neutrality with water. The solution is evaporated to yield a crude ketal which is purified by crystallization from chloroform-ethyl acetate or methanol mp 255-259° (softens 252°) [a]D 74° (CHC13). 

Tris(N-methylanilino)borane has previously been prepared by the reaction of boron trifluoride-ether complexes with three equivalents each of N-methylaniline and a suitable Grignard reagent,1,2 by the reaction of (N-methylanilino)potassium with boron trifluoride-ether complexes,2 and by aminolysis of boron trichloride by N-methylaniline.3 The present general procedure describes a convenient preparation of tris(N-methylanilino)-borane by the reaction of (N-methylanilino)lithium and boron trifluoride-diethyl ether in tetrahydrofuran-hexane as solvent. 

The mixture 5-8 (1 g) was either (1) dissolved in benzene (10 mL) containing toluene-p-sulfonic acid (5 mg), or (2) dissolved in anhydrous ether (20 mL) containing boron trifluoride-ether complex (2 drops). In each case, the mixture was stirred for 2 h at ambient temperature, then washed with aqueous sodium hydrogen carbonate and water, dried, and concentrated. The residue was chromatographed on a silica gel column with ether-light petroleum 1 1 to give initially 5 (0.25 g, 25%) [a]jj — 48.3° (c 0.77, CHClj). Continued elution gave a-L-g/ycero-isomer 8 (0.5 g, 55%) [ol]jj + 11.6° (c 0.78, CHClj). 

The reactivity of lead tetra-acetate in bringing about one-electron oxidations is increased by the addition of the boron trifluoride-ether complex for example, p-dimethoxybenzene is oxidized to the corresponding radical-cation (Allara et al., 1965). 

To overcome the problems derived from formation of anomeric mixtures when O-benzylated glycosyl halides are used as precursors, Ledford and Carreira52 have disclosed an elegant synthesis of 2,3,4-tri-O-benzyl-a-D-glucopyranosyl isothiocyanate (10) based on the use of l,6-anhydro-2,3,4-tri-0-benzyl-/t-i)-glucopyranose (9) as the glycosyl donor. Treatment of 9 with tetra-n-butylammonium thiocyanate and boron trifluoride-etherate complex provided 10 in 50% yield with total control of the anomeric configuration (Scheme 5). 

Acids which are particularly effective in catalyzing this condensation are /7-toluenesulfonic acid, sulfuric acid, zinc chloride, boron trifluoride-ether complexes, and acid clays [88], The preferred catalyst (0.5 to 10 parts per 100 parts monomer) is p-toluenesulfonic acid and it is important that the catalyst be nonoxidizing relative to the mercaptan group present. 

The polymerization of less reactive monomer requires higher concentration of the monomer solution. Ionic liquids as electrolytic media give positive effect on the properties of polymer films [2]. Boron trifluoride-ether complex (BF3 OEt2) is known to reduce oxidation potential of aromatic monomers when used as an electrolytic medium [3]. 

Table 5.12 Hydroboration of propenylpyridine-boron trifluoride etherate complex [38]... 

Cationic Polymerization of ll-CF-4. Cationic polymerization of ll-CF-4 was carried out with boron trifluoride ether complex in dichloromethane. The progress of the reaction was monitored by gas chromatography and liquid chromatography by using n-tetradecane as an internal standard. In Figure 3 is shown the... 

Application of this procedure for the regio- and stereoselective synthesis of vinyl azides in the presence of boron trifluoride etherate complex is summarized in eq 6. ... 

When the reaction is conducted at 150 °C an oxazolo[2,3-c]pyrimidine is obtained . However, in the presence of a catalytic amount of boron trifluoride etherate, complex heterocyclic spiro compounds are produced (2 2 adducts). ... 

Fluorination of m-carborane (2) with SbFj afforded 9-fluoro-m-carborane (36) and 9,10-difluoro-m-carborane (37) (Scheme 6.6) (Lebedev et al., 1990). The reaction of 38, which was synthesized according to the procedure discussed above for compound 14, with a boron trifluoride etherate complex afforded 2-fluoro-m-carborane (39, 65% yield) (Roscoe et al., 1970). Compound 2 was also reacted with BuLi and subsequently perchloryl fluoride in ether at -15°C to yield 1,7-difluoro-m-carborane (40), which was converted to dodecafluoro-m-carborane (41, 30% yield) by treatment with an excess of molecular fluorine in an HF suspension (Kongpricha and Schroeder, 1969). 

Alternatively, diborane may be generated in situ by adding boron trifluoride-ether complex to a solution of the olefin and sodium borohydride in diglyme ... 

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