BoronTrifluoride

Step 1 1-(p-Chlorophenyl)-3-Ethoxy-1 H-lsoindole - Crystalline triethyloxonium boron-tetrafluoride (21 g) (prepared from 23 g of borontrifluoride etherate and 11 g of epichlorohydrin) is dissolved in 100 ml of absolute methylenechloride. 3-(p-Chlorophenyl) phthalimidine (21 g) is added and the reaction mixture is stirred overnight at room temperature. The resulting solution is poured onto 50 ml of saturated Sodium carbonate, extracted with 500 ml of ether and dried. Upon evaporation of the solvent there is obtained crude material which is recrystallized from methylene chloride/hexane (1 1) to yield l-(p-chlorophenyl)-3-ethoxy-1 H-isoindole MP 102° to 103°C. 

Tetramethyl-1,3-diphenyl-2,4,6,8-tetraoxaadamantane (163, R = CH3) is made either by dimerization of an a-formyl ketone, such as a-formyl-isobutyrophenone, (164, R = CH3) with sulfuric acid186 or by dimerization of the aldehyde (165) with borontrifluoride etherate.187 The structure of the product was determined by PMR.186... 

The reaction of borontrifluoride (acid) with ammonia (base) results into a stable octet configuration between mutual sharing of a pair of electrons of latter (donor) and former (acceptor). 

A -acylaziridines substituted with an electron-withdrawing group produce a 2,4-disubstituted oxazoline as the major product. Borontrifluoride etherate (BF3 OEt2) has also been used successfully for an Al-benzoyl, but not an N-acetyl-substituted aziridine (Scheme 8.58). ... 

The step 1 product (200 mg) was treated with phenol (100 mg) and heated to 80°C and then further treated with borontrifluoride diethyletherate (0.09 mmol). The mixture immediately turned red and increased in viscosity. The vial was then heated to 105°C for 1 hour and then treated with 10 ml of distilled water and stood overnight at ambient temperature. The mixture was dissolved in 3 ml of toluene and sonicated. The soluble fraction did not show any polymer resonances by 1H-NMR spectroscopy indicating that the polymer has become crosslinked. 

Polymerization of ethylene oxide with stannic chloride also leads to a mixture of polymer and dioxane (2). However, in contrast with the borontrifluoride initiated reaction the polymers can reach a molecular weight of up to 20.000 and chain growth and dioxane formation seem to be parallel with each consuming about one half of the monomer. 

Recently it has been reported (5,66) that ethylene oxide leads to a mixture of cyclic oligomers of D. P. 3,4, 5,6,7,8 and 9 (7 4 6 6 2 1), unaccompanied by open-chain oligomers and polymers, when treated with fluorine-containing catalysts such as antimony pentafluoride or a 1 1 mixture of borontrifluoride and hydrogen fluoride. 

A number of other epoxides have been found to produce cyclic oligomers. As shown in Table 1, propylene oxide, when treated with triethyloxonium tetrafluoro-borate or borontrifluoride, produces a mixture of cyclic oligomers, the most important one being the tetramer (6, 7). 

Polymerization of 1,2-butylene oxide with triethyloxonium tetrafluoroborate or borontrifluoride leads to a mixture of polymer, dimer, tetramer and larger rings (7). 

In a review article Eastham (12) reports that treatment of isobutylene oxide with borontrifluoride leads to dimer without any polymer but the reaction conditions were not mentioned. On the other hand, Vandenberg (13) described the polymerization of the same monomer with borontrifluoride to give 60% of polymer containing substantial amounts (ca. 27%) of high boiling volatiles which were supposed to be a mixture of cyclic oligomers. 

Kern (7) and Entelis and co-workers (15-17) found tetramer and small amounts of larger rings when the monomer was treated with borontrifluoride or triethyloxonium tetrafluoroborate. With the first initiator the ratio of tetramer to polymer is greater in the early stages of the reaction than after longer reaction periods (15). From this observation it was concluded that tetramer and polymer are formed by two independent reaction paths. The ratio of oligomers to polymer increased with temperature (16)-... 

According to Entelis the formation of cyclic oligomers in the polymerization of oxiranes initiated by borontrifluoride would be an intramolecular reaction between the chain ends of the zwitter ion produced in such polymerizations ... 

Optically active tert.butyl oxirane forms a cyclic tetramer 18) with m.p. 168 °C, when treated with borontrifluoride etherate at 20 °C. The yield of tetramer is between 20 and 30%. 

Reaction of silylamines with borontrifluoride. Methyl- and silyl-... 

From four-membered rings An acid-catalyzed transformation has been observed in the conversion of l-[l-methylsulfinyl-l-(methylthio)alkyl]cyclo-butanol to 3-methyl-2-(methylthio)cyclopentanone [9]. - Rearrangement of a /3-lactone to a y-lactone derivative in the presence of magnesiumdibromide [10]. - A borontrifluoride catalyzed cyclobutene to cyclopentene rearrangement [11]. - Ring expansion of a [2+2] photoadduct to a five-membered ring [12]-... 

From ten-membered rings Borontrifluoride catalyzed conversion of germa-crane (ten-membered) to humulane (eleven-membered) in 75% yield [15]. 

Propargylic epoxides can be used as precursor for the carbocations. For example, complexation of (159) and reaction of the complex with borontrifluoride etherate give, stereoselectively, complex (160) (Scheme 231). This sequence was used in a synthesis of (—)-ichthyothereol. ... 

The reaction between epoxides and HF gives fluorohydrins and, generally, other products resulting from extensive polymerisation. However, the acidity and reactivity of HF may be decreased by the addition of a base, either an amine or KF, or by complexation with a Lewis acid, such as borontrifluoride etherate [174]. Consequently, pyridine-HF, Et3N-3HF [203] and -Pr2NH-3HF [204] efficiently cleave epoxides to give excellent yields of fluorohydrins (Figure 3.39). 

Formation of substituted products by electrophilic reactions is one of the characteristics of benzenoid compounds. It has been shown that a few dehydro-[4/j + 2]annulenes afford substituted annulenes under strictly limited reaction conditions. Monodehydro[14]annulene, on treatment at room temperature with copper(ii) nitrate-acetic anhydride, oleum-dioxane and subsequent methylation and acetic anhydride-borontrifluoride etherate, yielded monosubstituted products, 169a, 169b and 169c, respectively. The electrophilic reactions must have resulted in substitution of one of the outer protons, but the exact point of attack has not been determined . 

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