Boron oxide fluorides, preparation

Large quantities of boron chloride are best prepared by the chlorination of a mixture of boron oxide (or borax) and carbon. Smaller amounts may be obtained (1) by the chlorination of amorphous boron or metallic borides or (2) by the reaction between boron oxide and phosphorus (V) chloride in a sealed tube. A more convenient laboratory method for the preparation of boron chloride makes use of the reaction between boron fluoride and aluminum chloride. For the preparation of boron bromide, the reaction of boron fluoride and aluminum bromide is recommended as much less troublesome than other methods. Potassium tetrafluoborate may be used in place of the boron fluoride in each of these syntheses. 

Besides acetophenone, this reaction was also applied to p-chloro- andp-methoxyacetophenone, and even to an aliphatic ketone, acetone (although the yield was stated to be only half as large as that obtained from mesityl oxide, i.e., less than 30%, Dorofeenko and co-workers reported a 45% yield of 2,4,6-trimethylpyrylium perchlorate from acetone, acetic anhydride, and perchloric acid), and is the standard method for preparing pyrylium salts with identical substituents in positions 2 and 4. The acylating agent may be an anhydride in the presence of anhydrous or hydrated ferric chloride, or of boron fluoride, or the acid chloride with ferric chloride.Schneider and co-workers ... 

Mesitaldehyde may be prepared from mesitylmagnesium bromide by the reaction with orthoformate esters3 or ethoxy-methyleneaniline 3 from acetylmesitylene by oxidation with potassium permanganate,4 from mesitoyl chloride by reduction,5 from mesityllithium by the reaction with iron pentacarbonyl and from mesitylene by treatment with formyl fluoride and boron trifluoride,7 by treatment with carbon monoxide, hydrogen chloride, and aluminum chloride,8 or by various applications of the Gatterman synthesis.9-11... 

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-... 

Very many acidic solids and liquids, immiscible with hydrocarbons, will catalyse the oligomerisation of isobutene at ambient temperatures. Among the more common are syncatalysts prepared from boron fluoride and a protonic substance BH (B = OH, CHsO, C2H50, t-C4H90, CH3C02, etc.) mineral acids natural and synthetic alumino-silicates, (e.g., Fuller s earth, bentonite, attapulgite) and metal oxides containing small quantities of water. 

The introduction of fluorine into activated arenes is achieved by the combination thallium(III) trifluoroacetate/potassium fluoride/ boron trifluoride. Thallium(III) is hereby an oxidative fluo-rinating reagent.910 Representative compounds prepared in this way are listed below. 

The usual method of preparing boron trifluoride from calcium fluoride, boric oxide, and sulfuric acid is unsatisfactory, since yields are low, much silicon fluoride contaminates the product, and a solid residue which is difficult to remove remains in the generator. 

Oxidative fluorodesulfuriztuion can also be achieved by the action of nitrosonium tetrafluo-roborate, as oxidant, and hydrogen fluoridc/pyridine, as a source of fluoride ions, on aryl sulfides. The starting compounds are easily prepared from ketones or aldehydes and ben-zenethiol using boron trifluoride monohydratc as catalyst, and subsequent reduction with triethylsihine. - ... 

These complexes, which are readily synthesized by transmetalation see Transmetalation) from the appropriate Cp metal and MX4 (L = U) or (jj -L)MX3 (L L ), represent a large family of qnite always air-stable componnds. The bromides and iodides are also obtained from chlorine exchange reactions with the appropriate boron trihalide. The flnorides can be obtained by metathesis see Metathesis) of chlorides derivatives with MesSnF. With only one equivalent of tin reagent per mole of dichloride, partial fluorination occms affording mixed hahde metallocenes. The fluorides are also prepared by chloride/fluoride, by chloride/NMe2 followed by NMe2/fluoride exchange, and by oxidative addition see Oxidative Addition). ... 

These two milestone syntheses were soon followed by others, and activity in this field continued to be driven by interest in the biologically active esters of cephalotaxine. In 1986, Hanaoka et al. (27) reported the stereoselective synthesis of ( )-cephalotaxine and its analog, as shown in Scheme 4. The amide acid 52, prepared by condensation of ethyl prolinate with 3,4-dimethoxyphenylacetyl chloride, followed by hydrolysis of the ethyl ester, was cyclized to the pyrrolobenzazepine 53 by treatment with polyphos-phoric acid, followed by selective O-alkylation with 2,3-dichloropropene (54) in the presence of sodium hydride. The resulting enol ether 55 underwent Claisen rearrangement on heating to provide C-allylated compound 56, whose reduction with sodium borohydride yielded the alcohol, which on treatment with 90% sulfuric acid underwent cationic cyclization to give the tetracyclic ketone 57. Presumably, this sequence represents the intramolecular version of the Wichterle reaction. On treatment with boron tribromide, ketone 57 afforded the free catechol, which was reacted with dibromometh-ane and potassium fluoride to give methylenedioxy derivative 58, suited for the final transformations to cephalotaxine. Oxidation of ketone 58... 

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