Showing papers on "Boron tribromide published in 1998"
35 citations
TL;DR: The 2-fluoroethyl group was easily introduced, in good yields, by the treatment of the NH group with potassium carbonate and 2-bromo-1fluoroethane as mentioned in this paper.
18 citations
TL;DR: In this paper, arylethanals were treated with boron tribromide and cycled by a tandem aldol condensation-intramolecular Friedel-Crafts cyclization or a condensation at the O-position followed by a double Friedelcrafts alkylation.
12 citations
TL;DR: In this article, 2-bromo-5-iodo-hydroquinone dialkylethers are prepared by stepwise halogenation and alkylation of hydroquinone monoalkylether using simple and easily performable reactions.
Abstract: 2-Bromo-5-iodo-hydroquinone dialkylethers are prepared by the stepwise halogenation and alkylation of hydroquinone monoalkylethers using simple and easily performable reactions. Boron tribromide induced cleavage of the dipropoyl ether gives the parent compound 2-bromo- 5-iodo-hydroquinone in good yields.
11 citations
TL;DR: Condensation of 4-nitro-1-pentanal and 4 -nitropentanal 3-methylbutanal with 3,5-difluoro-4-methoxyphenylhydrazine afforded 4,6diffluoro-5methoxy-3-(2′ -nitro)propylindole 4a and 4, 6-defluoro -5methyl-2′-ethylindoles 4b, respectively, in one step.
4 citations
TL;DR: A palladium-catalyzed cross-coupling reaction has been developed for the rapid synthesis of 3-hydroxybenzo[c]phenanthrene and 12-hydroxymethyltriphenylphosphonium bromide and phenyllithium as mentioned in this paper.
Abstract: A new strategy which involves a palladium-catalyzed cross-coupling reaction has been developed for the rapid synthesis of 3-hydroxybenzo[c]phenanthrene (5) and 12-hydroxybenzo[g]chrysene (6). These phenolic compounds are the key intermediates for the synthesis of highly carcinogenic fjord-region diol epoxide metabolites 3 and 4 of benzo[c]phenanthrene (1) and benzo[g]chrysene (2). The cross-coupling reaction of 2-bromo-5-methoxybenzaldehyde (9) with naphthalene-1-boronic acid (7) and phenanthrene-9-boronic acid (8) produced 2-(1-naphthyl)-5-methoxybenzaldehyde (10) and 2-(9-phenanthryl)-5-methoxybenzaldehyde (11), respectively, in quantitative yields. After reaction of these aldehydes with trimethylsulfonium iodide under phase-transfer conditions or with the Wittig reagent obtained from (methoxymethyl)triphenylphosphonium bromide and phenyllithium to generate an oxiranyl or methoxyethene side chain, the acid-catalyzed cyclization with methanesulfonic acid (or boron trifluoride) produced 3-methoxybenzo[c]phenanthrene (16) and 12-methoxybenzo[g]chrysene (17) in 61-64% yields. Finally, demethylation of these methoxy derivatives 16 and 17 with boron tribromide resulted in the formation of the hydroxy analogues 5 and 6, respectively. The availability of this short and high-yielding regiospecific method for the synthesis of phenols 5 and 6 should allow the preparative-scale synthesis of the fjord-region diol epoxides 3 and 4. These diol epoxides are required as starting compounds for the synthesis of site-specifically modified oligonucleotides which are critically needed to elucidate the mechanism of carcinogenesis at the molecular level.
4 citations
TL;DR: In this article, the reaction of boron tribromide-methyl sulfide complex with 6methoxy-5amidoquinolines provides oxazolo(4,5f) quinolines.
3 citations
TL;DR: In this article, the enantiomeric purity of 2,6-dibromo-L-tyrosine was determined by HPLC with a chiral stationary column and was found to be more than 95% (ee).
Abstract: (2S)-2-Amino-3-(2′,6′-dibromo-4′-hydroxy)phenylpropionic acid (2,6-dibromo-L-tyrosine) 1a has been synthesized by two methods. The first is by enantioselective hydrolysis of the N-trifluoroacetyl derivative of the racemic 2,6-dibromotyrosine with carboxypeptidase A. The kinetic parameters of activity of carboxypeptidase A against N-trifluoroacetyl-2,6-dibromo-L-tyrosine have also been estimated (Vmax, 0.32 mM min–1 mg–1; Km 16.15 mM). The second is an asymmetric synthesis by Schollkopf’s bis-lactim ether method. Alkylation of the lithiated bis-lactim ether of cyclo(-D-Val-Gly) 6 with 2,6-dibromo-4-methoxybenzyl bromide and subsequent hydrolysis with aqueous trifluoroacetic acid gives 2,6-dibromo-4-methoxy-L-tyrosine methyl ester 8. Demethylation of the ester 8 with boron tribromide affords the amino acid 1a. The enantiomeric purity of 2,6-dibromo-L-tyrosine 1a obtained by both methods has been determined by HPLC with a chiral stationary column and is found to be more than 95% (ee).
2 citations
Patent•
10 Feb 1998
TL;DR: In this article, a method for producing 2-amino-3-carboxy-1,4-naphthoquinone with boron tribromide was proposed.
Abstract: PROBLEM TO BE SOLVED: To enable to obtain the subject compound having an activity for stimulating the proliferation of bifidobacterium in a large amount in a high yield and at a low cost by successively subjecting 1,4-dihydroxynaphthoic acid to a methyl esterification reaction, an oxidation reaction, an amination reaction and a deesterification reaction. SOLUTION: This method for producing 2-amino-3-carboxy-1,4-naphthoquinone comprises methyl-esterifying 1,4-dihydroxynaphthoic acid with diazomethane, oxidizing the obtained methyl 1,4-dihydroxynaphthoate with silver oxide in the presence of a dehydrating agent such as anhydrous magnesium sulfate, aminating the obtained 2-carboxymethyl-1,4-naphthoquinone with sodium azide and subsequently deesterifying the obtained 2-amino-3-carboxymethyl-1,4- naphthoquinone with boron tribromide. The method enables to obtain the objective compound in a far larger amount and at a far lower cost than those by a conventional method comprising culturing a bacterium belonging to the genus Propionibacterium.
2 citations
TL;DR: Unsymmetrical monohydroxypentaalkoxytriphenylenes have been conveniently prepared from the readily accessible symmetrical hexa-alkyloxytrihexylenes using boron tribromide mediated ether cleavage as discussed by the authors.
Abstract: Unsymmetrical monohydroxypentaalkoxytriphenylenes have been conveniently prepared from the readily accessible symmetrical hexa-alkyloxytriphenylenes using boron tribromide mediated ether cleavage.
1 citations
TL;DR: In this paper, 3,5-Dimethoxybenzoic acid 3 has been transformed into olivetol dimethyl ether 6 in three steps in 79% yield Directed ortho-metallation-alkylation of 6, followed by boron tribromide demethylation resulted in a simple and inexpensive synthesis of resorstatin, in 70% overall yield.
Abstract: 3,5-Dimethoxybenzoic acid 3 has been transformed into olivetol dimethyl ether 6 in three steps in 79% yield Directed ortho-metallation-alkylation of 6, followed by boron tribromide demethylation resulted in a simple and inexpensive synthesis of resorstatin, in 70% overall yield from 3
Patent•
10 Apr 1998
TL;DR: In this article, a process for the preparation of vinflunine derivatives of formula (I), their salts with acids, and their diastereoisomers and mixtures, and processes for their preparation are new.
Abstract: Antimitotic Vinca alkaloid derivatives of formula (I), their salts with acids, and their diastereoisomers and mixtures, and processes for their preparation are new. In formula (I), n = 1 or 2, R1 = H or F; R2 = Cl. Process for the preparation of vinflunine (I; n = 2; R1 = H; R2 = difluoro), by reaction of (II) in a superacid medium (HF + SbF5) at -45 to -35[deg]C, with a halide generator (chloroform, 2,2-dichloropropane, carbon tetrabromide, dibromomethane, or boron tribromide) is also claimed, where R3 = OH; R4 = H, or R3 and R4 together form a double bond.
Patent•
10 Apr 1998
TL;DR: In this article, a process for the preparation of vinflunine derivatives of formula (I), their salts with acids, and their diastereoisomers and mixtures, and processes for their preparation are new.
Abstract: Antimitotic Vinca alkaloid derivatives of formula (I), their salts with acids, and their diastereoisomers and mixtures, and processes for their preparation are new. In formula (I), n = 1 or 2, R1 = H or F; R2 = Cl. Process for the preparation of vinflunine (I; n = 2; R1 = H; R2 = difluoro), by reaction of (II) in a superacid medium (HF + SbF5) at -45 to -35 deg C, with a halide generator (chloroform, 2,2-dichloropropane, carbon tetrabromide, dibromomethane, or boron tribromide) is also claimed, where R3 = OH; R4 = H, or R3 and R4 together form a double bond.
TL;DR: In this article, the enantiomeric purity of 2,6-dibromo-L-tyrosine was determined by HPLC with a chiral stationary column and was found to be more than 95% (ee).
Abstract: (2S)-2-Amino-3-(2′,6′-dibromo-4′-hydroxy)phenylpropionic acid (2,6-dibromo-L-tyrosine) 1a has been synthesized by two methods. The first is by enantioselective hydrolysis of the N-trifluoroacetyl derivative of the racemic 2,6-dibromotyrosine with carboxypeptidase A. The kinetic parameters of activity of carboxypeptidase A against N-trifluoroacetyl-2,6-dibromo-L-tyrosine have also been estimated (Vmax, 0.32 mM min–1 mg–1; Km 16.15 mM). The second is an asymmetric synthesis by Schollkopf’s bis-lactim ether method. Alkylation of the lithiated bis-lactim ether of cyclo(-D-Val-Gly) 6 with 2,6-dibromo-4-methoxybenzyl bromide and subsequent hydrolysis with aqueous trifluoroacetic acid gives 2,6-dibromo-4-methoxy-L-tyrosine methyl ester 8. Demethylation of the ester 8 with boron tribromide affords the amino acid 1a. The enantiomeric purity of 2,6-dibromo-L-tyrosine 1a obtained by both methods has been determined by HPLC with a chiral stationary column and is found to be more than 95% (ee).
TL;DR: In this article, the reaction of boron tribromide-methyl sulfide complex with 6methoxy-5amidoquinolines provides oxazolo(4,5f) quinolines.
Abstract: Reaction of boron tribromide-methyl sulfide complex with 6-methoxy-5-amidoquinolines provides oxazolo(4,5-f) quinolines. In contrast under similar conditions boron tribromide gives only 6-hydroxy-5-amidoquinolines.
TL;DR: In this article, a method for the synthesis of the biologically important intermediate, 3,5-bis(trifluoromethyl)-salicylic acid, was reported.
Abstract: A convenient method is reported for the synthesis of the biologically important intermediate, 3,5-bis(trifluoromethyl)-salicylic acid, by a sequence involving diazotization/iodination of 2-bromo-3,5-bis(trifluoromethyl)aniline, displacement of the bromide with sodium methoxide, and carboxylation of the anion generated by lithium-iodine exchange with carbon dioxide. Alternatively, the anion could be carbonylated with dimethylformamide and the resulting aldehyde oxidized with Jones reagent. Demethylation of 3,5-bis(trifluoromethyl)anisic acid with boron tribromide gave the title compound.
TL;DR: Three components (AGL01, AGL1 and AGL21) were isolated and purified by successive column chromatography on two ion exchange Sephadexes and silicic acid (Iatrobeads) and their structures were deduced to be as follows.
Abstract: Two novel series of glycosphingolipids containing inositolphosphate or methylinositolphosphate as an acidic group were found present in whole tissues of the lugworm, Tylorhynchus heterochaetus. The thin layer chromatographic pattern of the total acidic glycolipid revealed the presence of several components with positive reactions toward molybdate (phosphate) and/or both molybdate and orcinol-sulfuric acid (sugar) spray reagents. Three components (AGL01, AGL1 and AGL21) were isolated and purified by successive column chromatography on two ion exchange Sephadexes and silicic acid (Iatrobeads). From structural studies including compositional sugar analysis, hydrogen fluoride degradation, boron tribromide demethylation, methylation analysis and fast atom bombardment, their structures were deduced to be as follows : AGL01, InsMe (1→) -P-Cer; AGL1, Fuc-InsMe (1→) -P-Cer; and AGL21, Ins (1→) -P-Cer. The ceramide moieties of the inositollipids consisted mainly of C16 : 0 and C18 : 0 fatty acids and dihydroxy- (C18 : 1 and C18 : 0) sphingoids for AGL21, and 2-hydroxylated C16 : 0 and C18 : 0 fatty acids and trihydroxy- (C18 : 0) sphingoid for AGL01 and AGL1.In addition, their thin layer chromatographic behavior and the results of compositional anal-ysis indicated presence of at least four more inositollipids to possibly be Man-InsMe-P-Cer (AGL22), Fuc-Ins-P-Cer (AGL3), Man-Ins-P-Cer (AGL4) and Man (Fuc-) Ins-P-Cer (AGL5).