Boron trifluoride alkylation with

The boron trifluoride-alkyl thiol reagent combination also operates on the basis of nucleophilic attack on an oxonium ion generated by reaction of the ether with boron trifluoride.90... 

The boron trifluoride alkyl fluoride (chloride) complexes gave no evidence of alkylcarbonium ion formation. It must, however, be emphasized that (a) the physical investigation of the binary system was carried out at such low temperatures (generally below —100°) that ionization of the halides could hardly be expected (with exception of highly reactive tertiary halides) (b) the methods used could not he relied on to detect a small ionization equilibrium even if it existed. 

To add rings B and A to the diketone (100), Stork [13] first used the comparatively readily accessible [1053] 4-chloromethyl-3-methylisoxazoles as alkylating agents. The alkylation of the sodium enolate of the bicyclic diketones (100) with 3,5-dimethyl-4-chloromethylisoxazole led to compound (376) in good yield. The reduction of the A -bond in it did not affect the isoxazole ring, forming the trans-decalone (377). The transformation of the isoxazolylmethyl residue into the desired tricyclic system (383) was readily effected by the action of boron trifluoride etherate with subsequent treatment with bases in this case an intermediate was the diketone (380). 

Concerning my research during my Dow years, as I discuss iu Chapter 4, my search for cationic carbon intermediates started back in Hungary, while 1 was studying Friedel-Crafts-type reactions with acyl and subsequently alkyl fluorides catalyzed by boron trifluoride. In the course of these studies I observed (and, in some cases, isolated) intermediate complexes of either donor-acceptor or ionic nature. 

Adberabibty of the film may be enhanced by its treatment with flame, electric discharge, boron trifluoride gas, activated gas plasma, dichromate sulfuric acid, and a solution of alkab metal ia Hquid ammonia (84—87). A coating of polyurethane, an alkyl polymethacrylate, or a chlotinated adhesive can be apphed to PVF surfaces to enhance adhesion (80,88,89). 

Catalysts used in the polymerization of C-5 diolefins and olefins, and monovinyl aromatic monomers, foUow closely with the systems used in the synthesis of aHphatic resins. Typical catalyst systems are AlCl, AIBr., AlCl —HCl—o-xylene complexes and sludges obtained from the Friedel-Crafts alkylation of benzene. Boron trifluoride and its complexes, as weU as TiCl and SnCl, have been found to result in lower yields and higher oligomer content in C-5 and aromatic modified C-5 polymerizations. 

Isopropylnaphthalenes can be prepared readily by the catalytic alkylation of naphthalene with propjiene. 2-lsopropylnaphthalene [2027-17-0] is an important intermediate used in the manufacture of 2-naphthol (see Naphthalenederivatives). The alkylation of naphthalene with propjiene, preferably in an inert solvent at 40—100°C with an aluminum chloride, hydrogen fluoride, or boron trifluoride—phosphoric acid catalyst, gives 90—95% wt % 2-isopropylnaphthalene however, a considerable amount of polyalkylate also is produced. Preferably, the propylation of naphthalene is carried out in the vapor phase in a continuous manner, over a phosphoric acid on kieselguhr catalyst under pressure at ca 220—250°C. The alkylate, which is low in di- and polyisopropylnaphthalenes, then is isomerized by recycling over the same catalyst at 240°C or by using aluminum chloride catalyst at 80°C. After distillation, a product containing >90 wt % 2-isopropylnaphthalene is obtained (47). 

Catalysts. Nearly aU. of the industrially significant aromatic alkylation processes of the past have been carried out in the Hquid phase with unsupported acid catalysts. For example, AlCl HF have been used commercially for at least one of the benzene alkylation processes to produce ethylbenzene (104), cumene (105), and detergent alkylates (80). Exceptions to this historical trend have been the use of a supported boron trifluoride for the production of ethylbenzene and of a soHd phosphoric acid (SPA) catalyst for the production of cumene (59,106). 

Alkylation of furan and thiophene has been effected with alkenes and catalysts such as phosphoric acid and boron trifluoride. In general, Friedel-Crafts alkylation of furans or thiophenes is not preparatively useful, partly because of polymerization by the catalyst and partly because of polyalkylation. 

The most important reaction with Lewis acids such as boron trifluoride etherate is polymerization (Scheme 30) (72MI50601). Other Lewis acids have been used SnCL, Bu 2A1C1, Bu sAl, Et2Zn, SO3, PFs, TiCU, AICI3, Pd(II) and Pt(II) salts. Trialkylaluminum, dialkylzinc and other alkyl metal initiators may partially hydrolyze to catalyze the polymerization by an anionic mechanism rather than the cationic one illustrated in Scheme 30. Cyclic dimers and trimers are often products of cationic polymerization reactions, and desulfurization of the monomer may occur. Polymerization of optically active thiiranes yields optically active polymers (75MI50600). 

The reactions of some fluorinated ethers may result in the elimination of alkyl fluorides In the case of 2-methoxyperfluoro-2-butene, treatment with antimony pentafluoride gives perfluoro-3-buten-2-one and methylfluoride [107] By reacting 2-chloro-l,l,2-trifluorodiethyl ether with boron trifluoride etherate or with aluminum chloride, chlorofluoroacetyl fluoride can be obtained with the elimination of ethyl fluonde [108] (equations 76 and 77)... 

In order to achieve high yields, the reaction usually is conducted by application of high pressure. For laboratory use, the need for high-pressure equipment, together with the toxicity of carbon monoxide, makes that reaction less practicable. The scope of that reaction is limited to benzene, alkyl substituted and certain other electron-rich aromatic compounds. With mono-substituted benzenes, thepara-for-mylated product is formed preferentially. Super-acidic catalysts have been developed, for example generated from trifluoromethanesulfonic acid, hydrogen fluoride and boron trifluoride the application of elevated pressure is then not necessary. 

Notable examples of general synthetic procedures in Volume 47 include the synthesis of aromatic aldehydes (from dichloro-methyl methyl ether), aliphatic aldehydes (from alkyl halides and trimethylamine oxide and by oxidation of alcohols using dimethyl sulfoxide, dicyclohexylcarbodiimide, and pyridinum trifluoro-acetate the latter method is particularly useful since the conditions are so mild), carbethoxycycloalkanones (from sodium hydride, diethyl carbonate, and the cycloalkanone), m-dialkylbenzenes (from the />-isomer by isomerization with hydrogen fluoride and boron trifluoride), and the deamination of amines (by conversion to the nitrosoamide and thermolysis to the ester). Other general methods are represented by the synthesis of 1 J-difluoroolefins (from sodium chlorodifluoroacetate, triphenyl phosphine, and an aldehyde or ketone), the nitration of aromatic rings (with ni-tronium tetrafluoroborate), the reductive methylation of aromatic nitro compounds (with formaldehyde and hydrogen), the synthesis of dialkyl ketones (from carboxylic acids and iron powder), and the preparation of 1-substituted cyclopropanols (from the condensation of a 1,3-dichloro-2-propanol derivative and ethyl-... 

In acid solution 1-acyl-1//-azepines and alkyl l//-azepine-l-carboxylates undergo rapid aromatization to A-arylcarbamates,115,139,142 whereas 1/Z-azepine-l-carbonitrile suffers quantitative rearrangement and hydrolysis to phenylurea.163 Rearrangement of ethyl l//-azepine-l-carboxylate to ethyl A-phenylcarbamate is also rapid (5 min) and quantitative with boron trifluoride-diethyl ether complex in benzene.245... 

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 syn selectivity of boron trifluoride promoted 2-butenylstannane-aldehyde reactions has been examined for a range of different systems less useful syn selectivity was observed for reactions of 2-butenylstannanes with alkyl 2-oxopropanoates68, but better selectivity was found with alkyl 2-oxoacetates69. 

Alkoxyallylstannanes are also available by boron trifluoride-diethyl ether complex induced isomerization of their 1-alkoxy isomers. This isomerization proceeds in an antarafacial manner with excellent stereoselectivity to give (Z)-3-alkoxyallylstannanes possibly via an intermolecu-lar exchange process119. Coupled with the asymmetric reduction of acylstannanes (see Section 1.3.3.3.2.3.1) this provides access to 1-alkyl-3-alkoxyallylstannanes of useful optical purity106. 

These results may be explained either by Cram s cyclic model in the case of lithium alkyls or by Cornforth s dipolar model if copper-boron trifluoride reagents are used. Boron trifluoride causes double complexation of both nitrogen and oxygen atoms which results in the formation of an adduct with rigid antiperiplanar conformation due to electrostatic repulsion (see 4 and 5)9. 

Organocopper-boron trifluoride (RCu BF3) reacts with allylic alcohols, such as 3-phenyl-2-propenol, 2-butenol, 3-buten-2-ol, 2,4-hexadienol, 3-methyl-2-butenol, to give the y-alkylation... 

Olivier and Berger335, who measured the first-order rate coefficients for the aluminium chloride-catalysed reaction of 4-nitroben2yl chloride with excess aromatic (solvent) at 30 °C and obtained the rate coefficients (lO5/ ) PhCI, 1.40 PhH, 7.50 PhMe, 17.5. These results demonstrated the electrophilic nature of the reaction and also the unselective nature of the electrophile which has been confirmed many times since. That the electrophile in these reactions is not the simple and intuitively expected free carbonium ion was indicated by the observation by Calloway that the reactivity of alkyl halides was in the order RF > RC1 > RBr > RI, which is the reverse of that for acylation by acyl halides336. The low selectivity (and high steric hindrance) of the reaction was further demonstrated by Condon337 who measured the relative rates at 40 °C, by the competition method, of isopropylation of toluene and isopropylbenzene with propene catalyzed by boron trifluoride etherate (or aluminium chloride) these were as follows PhMe, 2.09 (1.10) PhEt, 1.73 (1.81) Ph-iPr, (1.69) Ph-tBu, 1.23 (1.40). The isomer distribution in the reactions337,338 yielded partial rate factors of 2.37 /mMe, 1.80 /pMe, 4.72 /, 0.35 / , 2.2 / Pr, 2.55337 339. 

Further evidence against the formation of a free carbonium ion in the alkylation reaction is obtained from the fact that in the presence of boron trifluoride-phosphoric acid catalyst, but-l-ene, but-2-ene, and i-butene react at different rates with alkylbenzenes, yet they would each give the same carbonium ion. In addition, only the latter alkene gave the usual activation order (in this case the hyper-... 

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). 

Although the synthesis of multiple-pyrrolyl compounds can be achieved by SnAt reactions of perfluoroaromatics with pyrrolylsodium at ambient temperature <96JOC9012>, deleterious side reactions are often observed during attempted A-alkylations of the alkali salts of pyrrole. A protocol has therefore been developed for the preparation of N-arylmethylenepyrroles by reduction of the corresponding AT-acyl derivatives by treatment with sodium borohydride/boron trifluoride etherate in a sealed tube <96S457>. ... 

Alkylating reagents such as boron trifluoride-methanol, sulfuric acid-methanol, methanol-hydrochloric acid and methyl iodine-sodium hydride do not react efficiently with pyrithiobac. Trimethylsilyldiazomethane may be used for the methyl-ation of pyrithiobac. 

Secondary Alkyl Alcohols. Treatment of secondary alkyl alcohols with tri-fluoroacetic acid and organosilicon hydrides results only in the formation of the trifluoroacetate esters no reduction is reported to occur.1,2 Reduction of secondary alkyl alcohols does take place when very strong Lewis acids such as boron trifluoride126 129 or aluminum chloride136,146 are used. For example, treatment of a dichlo-romethane solution of 2-adamantanol and triethy lsilane (1.3 equivalents) with boron trifluoride gas at room temperature for 15 minutes gives upon workup a 98% yield of the hydrocarbon adamantane along with fluorotriethylsilane (Eq. 10).129... 

They offer the advantage that reductions can be effected under conditions that permit the conversion of substrates that may be adversely sensitive to the presence of strong Brpnsted acids. For example, in the presence of a 10% excess of triethylsilane, addition of one-half equivalent of boron trifluoride etherate to octanal results, within one hour, in the formation of a 66% yield of dioctyl ether after a basic hydrolytic workup. Benzaldehyde provides a 75% yield of dibenzyl ether under the same reaction conditions. The remainder of the mass is found as the respective alcohol.70 Zinc chloride is also capable of catalyzing this reaction. With its use, simple alkyl aldehydes are converted into the symmetrical ethers in about 50% yields.330... 

Alkar [Alkylation of aromatics] Also (incorrectly) spelled Alcar. A catalytic process for making ethylbenzene by reacting ethylene with benzene. The ethylene stream can be of ary concentration down to 3 percent. The catalyst is boron trifluoride on alumina. Introduced by UOP in 1958 but no longer licensed by them. Replaced by the Ethylbenzene process. 

A similar type of catalyst including a supported noble metal for regeneration was described extensively in a series of patents assigned to UOP (209-214). The catalysts were prepared by the sublimation of metal halides, especially aluminum chloride and boron trifluoride, onto an alumina carrier modified with alkali or rare earth-alkali metal ions. The noble metal was preferably deposited in an eggshell concentration profile. An earlier patent assigned to Texaco (215) describes the use of chlorinated alumina in the isobutane alkylation with higher alkenes, especially hexenes. TMPs were supposed to form via self-alkylation. Fluorinated alumina and silica samples were also tested in isobutane alkylation,... 

Patents assigned to Mobil (217) describe the use of boron trifluoride supported on several porous carriers. BF3 supported on silica was found to exhibit a slightly higher performance with added water in the alkylation of a mixed alkene feed at 273 K. It was also shown that self-alkylation activity was considerably lower than that with HF as catalyst. Another patent (218) describes the use of a pillared layered silicate, MCM-25, promoted with BF3 to give a high-quality alkylate at temperatures of about 273 K. BF3 was also supported on zeolite BEA, with adsorbed water still present (219). This composite catalyst exhibited low butene isomerization activity, which was evident from the inferior results obtained with 1-butene. At low reaction temperatures, the product quality was superior to that of HF alkylate. 

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