Reactions with Boron Trifluoride

Chemical Properties. In addition to the reactions Hsted in Table 3, boron trifluoride reacts with alkali or alkaline-earth metal oxides, as well as other inorganic alkaline materials, at 450°C to yield the trimer trifluoroboroxine [13703-95-2] (BOF), MBF, and MF (29) where M is a univalent metal ion. The trimer is stable below — 135°C but disproportionates to B2O2 and BF at higher temperatures (30). 

The successful labeling of the elusive 14a-position in cholestane represents a very important application of this reaction.It is known that hydroboration of the double bond in 5of-cholest-14-ene (174) occurs on the a-side. Consequently, by using deuteriodiborane (generated by the reaction of boron trifluoride etherate with lithium aluminum deuteride) and then propionic acid for hydrolysis of the alkylborane intermediate, 14a-d,-5a-cholestane (175) is obtained in 90% isotopic purity. This method also provides a facile route to the C-15 labeled analog (176) when the alkylborane derived from 5a-cholest-14-ene is hydrolyzed with propionic acid-OD. ... 

Selectivity in formation of protective groups may also be achieved by a proper choice of reaction conditions and catalyst. Thus formation of the 3-monothioketal from 3,6-diketones is achieved by dilution of the ethane-dithiol-boron trifluoride reaction mixture with acetic acid. 3-Monocyanohydrins are obtained in good yield from 3,20-diketo-(5a)-pregnanes by diluting the exchange reaction with ethanol. Similarly, dilution of the... 

Boron trichloride, reaction with 2-aminobiphenyl, 46, 66 Boron trifluoride, in preparation of ni-tronium tetrafluoroborate, 47, 56 with hydrogen fluoride in isomerization of /-cymene to tM-cymene, 47, 41... 

It is worth recalling that the phenomenon of co-catalysis (now more consistently renamed co-initiation ) was found first with boron trifluoride and with the tetrahalides of titanium and tin. It is well known that it can be interpreted by the reaction scheme (1)... 

Homoallylic amines result from the reaction of aldimines, previously activated by boron trifluoride etherate, with allylic bromides in the presence of chromium(II) chloride, e.g. equation 68194. 

Test the reaction of boron trifluoride ammine with water. Dissolve boron trifluoride ammine in a minimum amount of water and evaporate it in a water bath until almost dry. Cool the solution. Examine the separated crystals under a microscope. 

Wittig and co-workers2 have shown that triphenylborane can be readily synthesized in high yield by simple thermal decomposition of trimethylammonium tetraphenylborate. They obtained the latter compound by collecting the precipitate which was formed on mixing aqueous solutions of trimethylammonium chloride and lithium tetraphenylborate. The lithium salt was isolated from the products of the reaction of boron trifluoride-etherate with... 

Small Quantities. Wear nitrile rubber gloves, laboratory coat, and eye protection. In the fume hood, pour the boron trifluoride complex into a large evaporating dish. Cover the boron trifluoride complex with excess solid sodium carbonate or calcium carbonate. When the reaction has subsided, very slowly add the mixture to a pail of cold water. Allow to stand for 24 hours. Test the pH of the solution and neutralize if necessary. Wash the solution into the drain.2-5... 

Miscellaneous.—The 2-hydroxymethylene-ketone (310) forms a reasonably stable crystalline mesomeric complex (311) by reaction with boron trifluoride. Reaction of the complex with methyl-lithium, followed by acid, gave the 2-ethylidene-ketone (312), though in low yield. 

The 2-diazo-4,4-dimethyl-5-ene-3-one (478) is a special case, one of the main products being the l-methyl-19-nor-l(10),5-dien-3-one (480). The same product was formed when boron trifluoride reacted with the l,5-dien-3-one (479), pointing to this being an intermediate in the diazo-ketone reaction. With boron trifluoride. 

In the second approach (B), because of a low initial yield in the first method, the acid-catalysed reaction of the phenol in dioxane containing boron trifluoride etherate with the prenyl alcohol was used. In this way 2-geranyl, 2-farnesyl, 2-phytyl and 2-nonaprenylphenol were obtained in unstated yields, accompanied by the 4-isomer in each case. In the third strategy (C) the prenyl bromide was... 

An excellent in situ preparation of diborane results from the reaction of boron trichloride (BCI3) or boron trifluoride (BF3) with sodium borohydride in the presence of alkenes, as shown above. This reagent gave virtually instantaneous conversion of an alkene to a trialkylborane at ambient temperatures, when done in a ether solvent. When diborane was isolated and purified it also reacted with alkenes, rapidly and quantitatively in ether solvents. 

Solution The reaction of ethyl fluoride (CHaCHaF) and boron trifluoride (BF3) with mesitylene... 

It might surprise you to learn that the reaction of gaseous boron trifluoride (BF3) with gaseous ammonia (NH3) to form BF3NH3 is a Lewis acid-base reaction. 

A common method for preparing alkynyl(phenyl)iodonium tetrafluoroborates involves the reaction of iodosylbenzene in the presence of triethyloxonium tetrafluoroborate or boron trifluoride etherate with alkynyl-silanes. For example, the complex of iodosylbenzene with triethyloxonium tetrafluoroborate (362) reacts with alkynylsilanes in dichloromethane at room temperature to afford alkynyl(phenyl)iodonium tetrafluoroborates 363 in good yield [496]. A variation of this procedure employs the complex of iodosylbenzene with boron trifluoride etherate (364) followed by treatment with aqueous NaBp4 [493,497] or sodium arylsulfonates to furnish, respectively, the appropriate alkynyl(phenyl)iodonium tetrafluoroborates 363 [483,487] or organosul-fonates 365 [488,489] (Scheme2.102) [498,499],... 

Derivatives of azete are only known as unstable reaction intermediates. Oxetane and azetidine are considerably less reactive than their three-membered counterparts (oxetane reacts with hydroxide anion 10 times more slowly than does oxirane), but nonetheless do undergo similar ring opening reactions for example, oxetane reacts with organolithium reagents, in the presence of boron trifluoride, or with cuprates, and azetidine is opened on heating with concentrated hydrochloric acid. 

The reaction of boron trifluoride etherate with a solution of lithium tetrahydroborate in a simple ether or in dioxan (278, 280) is of importance, not only as the first reaction of this kind to be discovered, but also as the first reaction of any kind found to produce... 

Borane is a useful and selective reducing agent. It is prepared by the reaction of boron trifluoride etherate with sodium borohydride. The borane produced, as the etherate, may be distilled as the dimer, which is a colorless, toxic gas (B2Hg). Collection of the dimer distillate in tetrahydrofuran (THF) again forms the monomer, in this case as the BHs- THF complex. The latter is commercially available as a 1.0 M solution. 

B-l-Alkynyl-9-BBN, easily and quantitatively prepared by the reaction of boron trifluoride-diethyletherate with the corresponding lithium methyl alkynyldial-kylborinate [12], undergoes a smooth 1,4-addition in pentane at room temperature to methyl vinyl ketone (MVK) and ketones capable of adopting cisoid conformation [13]. The reaction proceeds through srx-membered cyclic transition state to afford the enol borinate intermediate, which on hydrolysis afford y,6-acetylenic ketones, in high yields (Scheme 7.8). 

The Lewis-acid-catalysed dimerization of 3,3-dimethylcyclopropene gives tetramethyltricyclo[3,l,0,0 ]hexane (60). The most effective catalysts are alunuuium trichloride etherate or boron trifluoride etherate. With triethylaluminium, the reaction takes a different course and gives the cyclopropane (61) as the major product. 

---