Dimethyl ether, with boron trifluoride

Boron trifluoride, with dimethyl ether and epichloro-hydrin to give trimethyl-oxonium tetrafluoroborate,... 

The movement of electrons in Lewis acid-base reactions can be seen clearly with electrostatic potential maps. In the reaction of boron trifluoride with dimethyl ether, for instance, the ether oxygen atom becomes more positive and the boron becomes more negative as electron density is transferred and the B-0 bond forms (Figure 2.6). 

Active Figure 2.5 The reaction of boron trifluoride, a Lewis acid, with dimethyl ether, a Lewis base. The Lewis acid accepts a pair of electrons, and the Lewis base donates a pair of nonbonding electrons. Note how the movement of electrons from the Lewis base to the Lewis acid is indicated by a curved arrow. Note also how, in electrostatic potential maps, the boron becomes more negative (red) after reaction because it has gained electrons and the oxygen atom becomes more positive (blue) because it has donated electrons. Sign in atwww. thomsonedu.com to see a simulation based on this figure and to take a short quiz. 

Reaction of 2-cyanomethyl-4H-l,3-benzothiazin-4-one with benzoylace-tonitrile at 160°C yielded 8-cyano-7-imino-9-phenyl-7//,ll//-pyrido[2,l-6][l,3]benzothiazin-l 1-one (85MI1 86MI2). Reaction of 2-ethoxy-2,3 dihydro-4//-l,3-benzothiazin-4-one with 1,2,3,4-tetramethylbutadiene and 2,4-dimethyl-l,3-pentadiene in the presence of boron trifluoride in diethyl ether gave rise to 6,7,8,9-tetramethyl- and 7,9)9-trimethyl-5a,6,9,ll-tetrahydropyrido[2,l-6][l,3]benzothiazin-ll-one, respectively (73JHC149). 

Any of these BH3 compounds adds readily to most alkenes at room temperature or lower temperatures. The reactions usually are carried out in ether solvents, although hydrocarbon solvents can be used with the borane-dimethyl sulfide complex. When diborane is the reagent, it can be generated either in situ or externally through the reaction of boron trifluoride with sodium borohydride ... 

Boron trifluoride reacts with dimethyl ether to form a compound with a coordinate covalent bond ... 

Trimethyloxonium fluorohorate [1, 1232]. In the preparation cited in ref. 1, the reagent was prepared by the reaction of dimethyl ether with triethyloxonium fluoro-borate. In a new procedure,2 the reagent is prepared by the reaction of epichloro-hydrin with dimethyl ether and boron trifluoride etherate. This procedure dispenses with the intermediate preparation of triethyloxonium fluorohorate. Prepared by the newer method, the salt can be stored for as long as a year in a dessicator over Drierite at — 20°. 

The dimethyl acetal (94) is readily prepared from the 22-aldehyde (93) by direct reaction with methanol in the presence of hydrogen chloride. Ena-mines (95) are formed without a catalyst even with the poorly reactive piperidine and morpholine.Enol acetates (96) are prepared by refluxing with acetic anhydride-sodium acetate or by exchange with isopropenyl acetate in pyridine.Reaction with acetic anhydride catalyzed by boron trifluoride-etherate or perchloric acid gives the aldehyde diacetate. 

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-... 

Indole and dimethyl acetylenedicarboxylate yield 2-(indol-3-yl)-2,3-dihydro-l//-l-ben-zazepine (mp 240-242 C) by addition of indole to the initially formed l//-l-benzazepinc,21 whereas 1,3-dimethylindole (10, R = H) fails to react with the diester under a variety of conditions.145 However, in the presence of boron trifluoride-diethyl ether complex at room tem-... 

Note It is reported that the use of chlorobenzene as solvent is essential when the reagent is to be used to detect aromatic amines [1]. In the case of steroids, penicillins, diuretics and alkaloids the reaction should be accelerated and intensified by spraying afterwards with dimethylsulfoxide (DMSO) or dimethylformamide (DMF), indeed this step makes it possible to detect some substances when this would not otherwise be possible [5,9-11] this latter treatment can, like heating, cause color changes [5,9]. Penicillins and diuretics only exhibit weak reactions if not treated afterwards with DMF [10, 11]. Steroids alone also yield colored derivatives with DMSO [9]. Tlreatment afterwards with diluted sulfuric acid (c = 2 mol/L) also leads to an improvement in detection sensitivity in the case of a range of alkaloids. In the case of pyrrolizidine alkaloids it is possible to use o-chloranil as an alternative detection reagent however, in this case it is recommended that the plate be treated afterwards with a solution of 2 g 4-(dimethyl-amino)-benzaldehyde and 2 ml boron trifluoride etherate in 100 ml anhydrous ethanol because otherwise the colors initially produced with o-chloranil rapidly fade [12]. 

Methyl cc-D-glucofuranosidurono-6,3-lactone (26) may be obtained exclusively by reaction of 4 with trimethyl orthoformate in the presence of boron trifluoride etherate.28 Its 2,5-dimethyl ether (27) is formed by methyl iodide-silver oxide methylation29,30 (Purdie-Ir-... 

The value of methylation studies in structural determination of carbohydrates is well known. Methylation of sucrose has generally been achieved by the use of dimethyl sulfate-sodium hydroxide,34,35 methyl iodide-silver oxide-acetone,20 sodium hydride-methyl io-dide-N,N-dimethylformamide,35 or diazomethane-boron trifluoride etherate.36,37 The last method (already applied to monosaccharides38,39) has been found particularly useful for sucrose, because it proceeds without concomitant migration of acyl groups. The reaction of 2,3,6,T,3, 4, 6 -hepta-0-acetylsucrose (21) and 2,3,4,6,1, 3, 4 -hepta-O-acetylsucrose (22) with diazomethane in dichloromethane in the presence of a catalytic proportion of boron trifluoride etherate for 0.5 h at —5° gave the corresponding 4-methyl (23) and 6 -methyl (24)... 

Epichlorohydrin, 54, 20 with boron trifluoride diethyl etherate and dimethyl ether to give trimethylox-onium tetrafluoroborate, 51, 142... 

Electrolytic reduction, apparatus, 52, 23 Enol acetates, acylation of, 52,1 Enol esters, preparation, 52, 39 Epichlorohydrin, with boron trifluoride diethyl therate and dimethyl ether to give trimethyloxonium tetra-fluoroborate, 51,142 ESTERIFICATION OF HINDERED ALCOHOLS f-BUTYL p-TOLUATE,... 

Methoxy-6-propyl-l,4-benzoquinone (170, Scheme 43) with hydrogen chloride undergoes dimerization and yields the biquinone 171 and the di-benzofuran 172. 2-Hydroxy-3,6-dimethyl-1,4-benzoquinone (173, Scheme 44), however, on treatment with boron trifluoride etherate in ether, or with concentrated sulfuric acid in acetic acid at room temperature, yields the extended quinone 174, which on reductive acetylation affords the dibenzo-furan 175. 

Methylation of carbazole phenolic oxygen has been achieved using dimethyl sulfate without reaction at nitrogen. Demethylation of carbazole methyl ethers has been achieved with hydrobromic acid-acetic acid, boron trichloride,and pyridine hydrochloride. Selective demethylation of methoxyl ortho to an aldehydo function has been achieved using boron trifluoride. ° ° Partial demethylation of 1-methoxy-3-formylcarbazole occurred during Wolff-Kischner reduction." ... 

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