Boron trichloride derivatives

Treatment of l,4 3,6-dianhydro-D-glucitol with boron trichloride gives l,6-dichloro-l,6-dideoxy-D-glucitol (20). Although methyl 6-chloro-6-deoxy-a-D-glucopyranoside (isolated as the tribenzoate) could be isolated from the reaction of methyl 3,6-anhydro-a-D-glucopyranoside with boron trichloride (21), the application to the isomeric furanoside derivative led to complex results. 

Boron trichloride appears to form with methyl /3-D-ribofuranoside a complex which, after treatment with appropriate nucleophiles, such as sodium methoxide, or the carbanion derived from diethyl 2-(ethox-ycarbonylmethyl)malonate, gives the corresponding a-glycosyl compound.147... 

Bidentate boranes with an o-phenylene backbone constitute some of the simplest examples of polydentate Lewis acids with rigid backbones. They can be prepared by the reaction of boron halides with a 1,2-dimetallated benzene derivative. Thus, the reaction of 1,2-bis(chloromercurio)benzene (5) with boron trichloride affords 1,2-bis(dichloroboryl)benzene (6, Scheme 3). ... 

When the distannyl reagent 7 is employed, the fate of the reaction apparently depends on the reaction conditions. Indeed, Eisch observed that the reaction of 7 with boron trichloride at —40 °C in hydrocarbon solvent is not always selective and leads to the formation of both a monoborylated intermediate (10) that slowly converts into 6 (Scheme 5). The outcome of these reactions is apparently further complicated by a fast methyl group transfer from the tin to the boron centers yielding the undesired monoborylated derivative 11. Eisch also found that such reactions are not limited to the case of boron trialide but can be performed with dialkyl boron halide starting materials. For example, the reaction of the distannane... 

Naphthalene-based bifunctional Lewis acids that involve boron and a heavier group 13 element have also been prepared starting from the boron/tin derivative 30 (Scheme 15). Thus, the transmetalation reaction of 30 with gallium trichloride or indium trichloride in tetrahydrofuran (THF) results in high yields of l-(dichlorogallium)-8-(dimesitylboron)naphthalenediyl 35 and l-(dichloroindium)-8-(dimesitylboron)... 

The thiophene derivatives are relatively stable in the pure state. The fluorine atoms of the trifluoromethylmercapto group can be quantitatively substituted with chlorine by boron trichloride with HjOg, oxidation to the sulfone takes place. Further substitution is achieved in both cases in the presence of perfluorosulfonic acids ... 

All derivatives, sulfenylated at the nitrogen atom, are stable for a prolonged period of time only at low temperature. 5-Trifluoromethyl-mercaptouracil is an extraordinarily stable compound. In contrast to 5-bromouracil (129), the substituent cannot be exchanged by amines. Nevertheless, a complete fluorine-chlorine exchange can be brought about with the aid of boron trichloride, just as with other aromatic CF3S compounds (170) ... 

Methylbenzofuran-3-carbaldehydes undergo ready condensation with Meldrum s acid (isopropylidene malonate) to afford arylmethylene derivatives 83. These on flash vacuum pyrolysis at 500-600 C give 3-dibenzofuranols 84 (Scheme 21). The arylmethylene derivative, e.g., 85, presumably undergoes conversion to a methylene ketene (86, Scheme 22) on pyrolysis, which undergoes a [1,5-H] shift and subsequent cyclization and tautomerization, yielding the dibenzofuranol 87. The derived methyl ether 88 has been converted by mild acetylation with acetyl chloride and aluminum chloride and subsequent boron trichloride-induced demethylation to the natural product ruscodibenzofuran (8). A limitation is imposed on this method because 3-acetyl-2-methyldibenzofurans fail to condense with Meldrum s acid so that l-methyl-3-dibenzofuranols are not available by this method. ... 

Treatment of 118 with 2-fluorobenzyl bromide 119 afforded a mixture of 120 and 121. The mixture was separated by flash chromatography. The A -protective group in 118 was removed to yield 122 upon treatment of 121 with boron trichloride (Scheme 2) <1995JHC1423>. Alkylation of azolopytidazin-7-ones with alkyl halides in DMF in the presence of potassium carbonate afforded the corresponding 6-alkyl derivatives in 55-72% yield <2002FA89>. 

Ammino-derivatives of Boron Salts—Derivatives of Boron Fluoride, Trichloride, Tribromide, Tri-iodide. 

A variation of this route was applied to the preparation of a-methylenecyclo-pentane 179, an intermediate that was employed for the synthesis of prostaglandin PGF2o, (180) (Scheme 6.82). The acetonide-protected oxime-diol 175 [derived from propanal (174)] was treated with sodium hypochlorite without the addition of base. This led to the tricyclic adduct 176 with high stereoselectivity. One of the side chains was subsequently elaborated and the fully protected cyclopentano-isoxazo-line (177), when exposed to Raney Ni/boron trichloride, gave the 2-hydroxymethyl-cyclopentanone (178). This compound was dehydrated using mesyl chloride/ pyridine to furnish enone (179) (324). In another related synthesis of PGF2q, the p-side-chain (3-hydroxyoctenyl) was introduced prior to the cycloaddition (325). 

Rapid Claisen rearrangement of allyl phenyl ether and meta-substituted derivatives has been reported to occur with poor regioselectivity at 250 °C in dicationic ionic liquids, especially (24).23 Claisen rearrangement of resorcinol allyl ethers (25) was found to have poor regioselectivity under thermal or microwave conditions, but it was further found that selectivity for the 6-substituted product (26) over (27) could be improved to 13 1 using boron trichloride and an appropriately protected ether (25 ... 

Chemical methods are generally based on the reaction of surface hydroxyl groups with a selectively reacting compound to form a covalently bonded surface species of well known composition. As reactive compounds, diborane,4,5 boron trichloride,6,7 diazomethane,8 organosilanes,3,6,9,10,11,12,13,14 and organometallic compounds15 have been employed. a0H is then derived from the amount of the chemisorbed species as well as the amount of volatile reaction products. 

Di(silyl)benzene gives the di(chlorosilyl)benzene reagent upon treatment with boron trichloride (Scheme 3). Contrary to the parent compound, this derivative is readily solvolyzed and gives cyclic siloxanes, silthianes, silazanes and silylphosphines on contact with water, hydrogensulfide, ammonia, amines, or phosphines, respectively. 

The structures of l,8-di(silyl)naphthalene and its mono- and di(p-anisyl) derivatives have been determined and are shown in Fig. 3-5. While the naphthalene part of the molecules appears to be largely undistorted, the two silyl groups are clearly bent away from each other in the molecular plane in order to avoid closer repulsive contacts. This steric crowding enhances the chemical reactivity of the molecule and makes the eompound a versatile starting material for numerous derivatives. For substitution control the conversion into the symmetrical dichlorosilane is possible using boron trichloride (Scheme 5). 

Ebelman and Bouquet prepared the first examples of boric acid esters in 1846 from boron trichloride and alcohols. Literature reviews of this subject are available. B The general class of boric acid esters includes the more common orthoboric acid based trialkoxy- and triaryloxyboranes, B(0R)3 (1), and also the cyclic boroxins, (ROBO)3, which are based on metaboric acid (2). The boranes can be simple trialkoxyboranes, cyclic diol derivatives, or more complex trigonal and tetrahedral derivatives of polyhydric alcohols. Nomenclature is confusing in boric acid ester chemistry. Many trialkoxy- and triaryloxyboranes such as methyl, ethyl, and phenyl are commonly referred to simply as methyl, ethyl, and phenyl borates. The lUPAC boron nomenclature committee has recommended the use of trialkoxy- and triaryloxyboranes for these compounds, but they are referred to in the literature as boric acid esters, trialkoxy and triaryloxy borates, trialkyl and triaryl borates or orthoborates, and boron alkoxides and aryloxides. The lUPAC nomenclature will be used in this review except for relatively common compounds such as methyl borate. Boroxins are also referred to as metaborates and more commonly as boroxines. Boroxin is preferred by the lUPAC nomenclature committee and will be used in this review. 

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