Difluoro boron

Boron tnfluonde also reacts with hydroxy acndones to form difluoro boron complexes [111] (Table 28) Another route to fluoroboraties involves transhalogen-ation by fluonnation of the correspondmg chloro- and bromoboranes with lithium or potassium fluonde under mild conditions [112] (Table 29)... 

In recent years, the use of organotrifluoroborate reagents (RBF3K) in Suzuki coupling reactions been shown to solve many of the problems described above. These reagents were originally developed by Vedejs in 1995 as air-stable precursors to aryl(difluoro)boron Lewis acids,and are typically prepared in high yield by treatment of boronic acids or esters with... 

Figure 8 View of a Zn(II)-based MOF that combines a tetracarboxylate-derived porphyrin with a bis-pyridyl substituted BODIPY (difluoro-boron-dipyrromethene) ligand. (Reprinted with permission from Ref 41. Copyright (2011) American Chemical Society.)...

Diethyl (7,8-difluoro-3-methyl-3,4-dihydro-2//-benzoxazin-4-yl)methy-lenemalonate was cyclized in boiling acetic anhydride on the action of boron trifluoride in THF to give a pyrido[l,2,3-de]-l,4-benzoxazine-6-... 

The cyclization of the racemic methyl ester of 1727 (R = Me) and its (S) enantiomer by boron trifluoride gave 9,I0-difluoro-7-oxopyrido[l,2,3-carboxylic acid and its optically active form, respectively [89J AP( K)228974]. 

Adducts of type 13, arising from the rearrangement of the allylic intermediate, have never been observed. The product distribution in methanol depends, however, on the reaction conditions. When the addition of XeF2 is carried out in the presence of boron trifluoride as a catalyst, the formation of the complex b has been suggested. This complex would react with 2,3-dimethylbutadiene as a positive oxygen electrophile to give, besides 1,2- and 1,4-difluoro derivatives, 1,4- and 1,2-fluoromethoxy products with a predominance of the anti-Markovnikov adduct (equation 26). 

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. 

The hydrogen fluoride catalyzed fluorination of norbornene by xenon difluoride at room temperature leads to a mixture of at least seven components,39 but under milder conditions (— 78 to 26 C, 22 hours) the reaction affords a mixture of two main products 2-e,xo-5-cxo-difluoro-norbornane and 2-c-wfo-5- Yo-difluoronorbornane, ratio 2 1, in a total yield of 51-76%. If the same reaction is carried out in a limited temperature range between — 46 and — 39 C the yield of these products decreases, their ratio becomes equal, and the main product is 2-exo-l-ff //-difluoronorbornane (42 %).40 The structure dependence of the fluorination products of norbornene with xenon difluoride was studied. Solvent, temperature, reaction duration, catalyst (hydrogen fluoride, boron trifluoride, trifluoroacetic acid, pentafluorobenzenethiol) and the routes of product isomerization were analyzed.41-42... 

Difluoro-l-silacyclobutane is obtained by the exchange of two chlorine atoms for fluorine in the 1,1-diehloro analog using antimony(III) fluoride in w-xylene yield 46% bp 36 -38 C.64 Antimony(lll) fluoride is supposed to interact, through its lone electron pair, with coordinative-ly unsaturated silicon rather than with chlorine atoms at silicon. Because of this Si —Cl compounds are fluorinated slower than C — Cl derivatives in the presence of boron trifluoride.65... 

Apparently chlorine and trifluoromethanesulfonate groups attached to boron and silicon can be replaced by fluorine in lithium fluoride at lower temperatures than that reported for C-X (X = halogen) exchange. Dichloroborane 5 is converted to the difluoro derivative 6 with lithium fluoride in diethyl ether at 0-22°C.7... 

In another example it has been shown that boron trifluoride is the catalyst of choice to convert dichloromaleic anhydride (9) with sulfur tetrafluoride into 3.4-dichloroperfluoro-2,5-dihy-drofuran (10). In its absence only the formation of a,/i-dichloro->, , -difluoro-y-crotonolactone is observed. 3,4-Dichloroperfluoro-2,5-dihydrothiophene can be prepared in the same manner. 11... 

Substitution of hydrogen by fluorine in compounds with acidic a-hydrogens can be achieved with xenon difluoride and some catalysts. Thus, room-temperature fluorination of 1,3-diketones, e g. 20, with xenon difluoride in the presence of the insoluble cross-linked polysty-rene-4-vinylpyridine, either complexed with boron trifluoridc or Nafion-H, as catalyst, gives mono and difluoro products.27-28... 

This alkoxyfluorination leads to alkoxy fluoro and difluoro compounds. The product distribution depends on the reaction conditions. Similarly, fluoro halides are obtained in addition to alkoxy halides using a combination of boron trifluoride and alkyl hypohalite.50... 

BORONCOMPOUNDS - BORON OXIDES, BORIC ACID AND BORATES] (Vol 4) 6a,9-Difluoro-llb,21-dihydroxy-16a,17-[(l-methylethylidene)bis(oxy)] -pregna-l,4-dienes-3,20-dione. See Fluocmolone acetomde. 

Chlorodifluoroamine has been prepared by reaction of difluoro-amine with boron trichloride,1 phosgene (carbonyl chloride),2 or hydrogen chloride 2 treating a mixture of sodium azide and sodium chloride with fluorine 3 reaction of chlorine trifluoride with ammonium fluoride 4 reaction of chlorine with diflu oro-amine in the presence of potassium fluoride 5 and photolysis of tetrafluorohydrazine and sulfinyl chloride (thionyl chloride).6... 

Arsine—boron tribromide, 0101 Bis(5,5-difluoro-/V-sulfimido)sulfur tetrafluoride, 4375... 

By cocondensation of boron monofluoride with alkynes, Timms (17) obtained 1,4-difluoro-1,4-diborines (1,4-difluoro-1,4-dibora-2,5-cyclo-hexadienes). With the l,4-difluoro-2,3,5,6-tetramethyl-l,4-diborine (18a)... 

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 1,1-difluoro olefins (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 l,3-dichloro-2-propanol derivative and ethyl-... 

Earlier studies have already demonstrated that in acid-catalyzed fluorination of norbornene, 2,3-difluoro products were also formed via radical intermediates, their amounts depending significantly on the presence of oxygen as scavenger69. Catalyst and temperature also had a significant effect on the reaction pathways, boron trifluoride ether-ate favoring the formation of l-endo-S-exo-axid. 2-exo-5-ex0-difluoro norbornane, while pentafluorothiophenol favored the formation of fluoronortricyclane70-72. 

Korytnyk and coworkers have shown that reactions of xenon difluoride with acetylated glycals in the presence of boron trifluoride are a convenient route for the synthesis of 1,2-difluoro sugars, while the addition of fluorine to the double bond occurred predominantly from the less hindered side and cis adducts were mainly formed75, 76. Stereoselective transformation of tri-O-acetyl-D-galactal with xenon difluoride at -20 to +5 °C, without a catalyst in CFC13, after hydrolysis, afforded 2-deoxy-2-fluoro-D-galactose in 63% yield77. 

As an intermediate of their synthesis of [2.2]metaparacyclophane-quinones, Tashiro et al. obtained 70, that could not be completely demethylated with boron tribromide [37], Using the tert-butyl group as a positional protecting group, these authors also tried the synthesis of [2.2]metacyclophanes 72a/b containing in-traannular halide-substituents [38], The preparation of the difluoro compound... 

Boron trifluoride-triethylamine effects a ring-opening elimination of 4,4-difluoro-3-trifluoromethyl-l,2-oxathietane 2,2-dioxide to give fluorosulfonyl-trifluoromethylketene. Eliminations occur from intermediate 3-sultones, obtained by addition of sulfur trioxide to alkenes, to give alkenesulfonic acids. ... 

Both chlorines in the iminium chloride (27) can be replaced by fluorine, bromine or iodine, giving compounds (58)-(60) (Scheme 3) if the salt is treated with the corresponding hydrogen halide under anhydrous conditions. By chloro-iodo exchange with HI from the 3-chloroacrylamide chloride the corresponding amide iodide (61 equation 37) was prepared. Dimethylformamide chloride (27) is converted by methyl iodide to dimethylformamide iodide (59). Remarkably the difluoro compound (60) is a nonionic, distillable liquid which can be ionized by addition of boron trifluoride. ... 

Arsine-boron tribromide, 0101 Bis(S,S-difluoro-A-sulflmido)sulfur tetrailuoride, 4381... 

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