Boron trifluoride catalysis

Fluorochloro, fluorobromo, and fluoroiodoalkanes react selectively with aromatics under boron trifluoride catalysis to provide chloro-, bromo- and iodoalkylated products (48). The higher reactivity of the C—F bond over C—Cl, C—Br, and C—I bonds under Lewis acid catalysis results in the observed products. 

Other THF polymerization processes that have been disclosed in papers and patents, but which do not appear to be in commercial use in the 1990s, include catalysis by boron trifluoride complexes in combination with other cocatalysts (241—245), modified montmorrillonite clay (246—248) or modified metal oxide composites (249), rare-earth catalysts (250), triflate salts (164), and sulfuric acid or Aiming sulfuric acid with cocatalysts (237,251—255). 

Alkyl tertiary alkyl ethers can be prepared by the addition of an alcohol or phenol to a tertiary olefin under acid catalysis (Reycler reaction) sulfuric acid, phosphoric acid, hydrochloric acid, and boron trifluoride have all been used as catalysts ... 

Lewis acids are defined as molecules that act as electron-pair acceptors. The proton is an important special case, but many other species can play an important role in the catalysis of organic reactions. The most important in organic reactions are metal cations and covalent compounds of metals. Metal cations that play prominent roles as catalysts include the alkali-metal monocations Li+, Na+, K+, Cs+, and Rb+, divalent ions such as Mg +, Ca +, and Zn, marry of the transition-metal cations, and certain lanthanides. The most commonly employed of the covalent compounds include boron trifluoride, aluminum chloride, titanium tetrachloride, and tin tetrachloride. Various other derivatives of boron, aluminum, and titanium also are employed as Lewis acid catalysts. 

Ketals other than ethylene ketals are prepared by the orthoformate procedure with heating. Thioketals are obtained from dithiols, monothiols and hemithioketals by the boron trifluoride-catalysis method. Hemi-thioketals have also been prepared in high yield by the exchange proce-dure.""""... 

Phenacyl benzoate condenses with acetamide in boiling xylene under boron trifluoride etherate catalysis to give a high yield of 2,4-diphenyloxazole in a general synthesis of diaryloxazoles (Scheme 7) <96T10131>. 

Similarly, and in contrast to the behavior of its secondary isomer, 2-adaman-tanol, 1-adamantanol undergoes smooth, quantitative reduction to adamantane in less than an hour at room temperature in dichloromethane solution containing triethylsilane under the catalysis of either free boron trifluoride129 or boron trifluoride etherate (Eq. 13).143... 

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)... 

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],... 

Tetrahydropyrimidines 949 are produced by the formal [4- -2] cycloaddition of A -tosylazetidines 948 with nitriles under the influence of boron trifluoride or zinc triflate catalysis <2004OL4829, 2005JA16366, 2006TL5393>. 

Nucleophilic substitution can occur at an sp -hybridized carbon in dihydrooxazines. 3-Methoxydihydrobenzoxazine 154 was treated with trimethylsilyl cyanide with boron trifluoride catalysis (Equation 7) to give the 3-cyanohenzox-azine 155 <1986H(24)3483>, and the N-acetylated derivative of 154 reacted similarly <1983JHC45>. 

The material is prepared by acetylation of diisoamylene with acetic anhydride or acetyl chloride under boron trifluoride etherate catalysis [23a]. 

The ring enlargement of 2,3-divinylcyclobutanones has been catalyzed by boron trifluoride or trifluoroacetic acid.110 This acid catalysis, however, usually gives lower yields than the thermal reaction and favors rearrangement to five- or six-membered rings. 

No reaction occurred when trifluorovinyllithium was treated with epoxides or oxetanes, but with boron trifluoride catalysis the corresponding trifluorovinyl-ated alcohols were obtained in good yields [119] (Scheme 43). 

Chlorodifluoromethylketones underwent aldol reactions (Eq. 124) via zinc enolates, to afford good yields of a,a-difluoro-/ -hydroxy ketones, in a study by the Kyoto group [327]. Copper(I) or silver salt catalysis was essential and boron-trifluoride additive appeared to exert a key role in the conversion to the enolate. Earlier [328], chlorodifluoromethyl ketones had been converted to the di-fluoroenoxy silanes by the action of zinc in the presence of chlorotrimethyl silane. A difluoroenoxy silane was used by McCarthy and co-workers [329] to synthesise a kynureninase inhibitor (Eq. 125) Lewis acid-mediated reaction with a chloroglycinate installed the key carbon-carbon bond. 

We also studied the effect of catalyst concentration on the reaction and determined that the reaction could take place without catalysis, but that its speed was highly dependent upon the concentration of catalyst, both in the case of 72% perchloric acid and in the case of the boron trifluoride etherate. A workable level for the perchloric acid catalyst was found to be in the order of 3-4 grams per mole of the acid-ester charge. A catalyst level for the boron trifluoride etherate of 40 grams per mole of the acid component charge was satisfactory. 

Acid-catalysis was demonstrated for the addition of phenol to epichlorohydrin by Levas and Lefebre,1 1 using boron trifluoride. Although some unidentified higher-boiling products accompanied the desired adduct, this procedure was deemed superior to that reported by Boyd and Marie 8 under alkaline conditions, which requires as much as 6 weeks for completion. Bradley and co-workers M have objected, on the other hand, that the boron trifluoride-catalyged process involves an excessively large phenol epichlorohydrin ratio and is therefore uneconomical. 

Oxiranes exhibit 1,3 [e,n] capacity. Therefore, seven-membered ring systems can be synthesized on reaction with hetero- 1,3-dienes. The reaction is catalyzed by 4-dimethylaminopyndine. On catalysis with boron trifluoride, the regioche-mistry is reversed [263] (equation 58). 

The direct hydration of a C—C triple bond has been recently reviewed.302,303 Hydration is possible under acid or metal catalysis, as well as by photohydration. Hydration under acid catalysis is generally done with sulfuric acid, although other acid systems such as phosphoric acid/boron trifluoride have been reported.304 It is established that acid catalysis occurs by a vinyl cationic intermediate which reacts with... 

The addition of carboxylic acids to alkynes affords enol esters which are useful as intermediates in organic synthesis.470 As in the addition to alkenes, a catalyst is usually required for high conversions of alkynes to enol esters. Simple acid catalysis has been employed (equation 279),471 but the more common catalysts are Lewis acids, such as boron trifluoride etherate,472 silver nitrate,473 zinc acetate474 and zinc oxide (equations 280 and 281),47S-476... 

By use of the Ferrier reaction with boron trifluoride catalysis, the formation of both the epimeric a-linked hex-2-enopyranosides 105 [64] and 106 [65] is achieved. 

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