Radical-mediated bromination of carbohydrate derivatives: searching for alternative reaction conditions without carbon tetrachloride (original) (raw)
Related papers
Organic & Biomolecular Chemistry, 2013
Exo-and endocyclic double bonds of glycals and terminal double bonds of enoses were reacted with various thiols by irradiation with UV light in the presence of a cleavable photoinitiator. The photoinduced radical-mediated hydrothiolation reactions showed highly varying overall conversions depending not only on the substitution pattern and electron-density of the double bond but also on the nature and substitution pattern of the thiol partner. Out of the applied thiols thiophenol, producing the highly stabilized thiyl radical, exhibited the lowest reactivity toward each type of alkene. In most cases, the hydrothiolations took place with full regio-and stereoselectivities. Successful addition of 1,2 : 3,4-di-O-isopropylidene-6-thio-α-D-galactopyranose to a 2,3-unsaturated N-acetylneuraminic acid derivative, providing a (3 → 6)-S-linked pseudodisaccharide, demonstrated that the endocyclic double bond of Neu5Ac-2ene, bearing an electron-withdrawing substituent, shows sufficient reactivity in the photoinduced thiolene coupling reaction. † Electronic supplementary information (ESI) available. See
Carbohydrate Research, 2006
ABSTRACT: The dithionite-mediated addition of BrCF(2)Cl to 3,4-di-O-pivaloyl-D-xylal (1) generated preferably 1-CF(2)Cl-substituted products, that is, (2-bromo-2-deoxy-3,4-di-O-pivaloyl-beta-D-xylopyranosyl)-chlorodifluoromethane and (2-deoxy-3,4-di-O-pivaloyl-beta-D-threo-pentopyranosyl)-chlorodifluoromethane. Selected chlorodifluoromethyl-substituted monosaccharide derivatives were hydrodechlorinated or alkylated at the CF(2)Cl-group using tin reagents under radical reaction conditions. Thus, hydrodechlorinations of (2,3,4-tri-O-acetyl-6-deoxy-alpha-L-galactopyranosyl)-chlorodifluoromethane and of methyl 3,4-di-O-acetyl-2-C-chlorodifluoromethyl-2,6-dideoxy-alpha/beta-L-glucopyranoside are reported using tri-n-butyltin hydride initiated by AIBN. UV-initiated allylations are reported for reactions of (2-deoxy-3,4-di-O-pivaloyl-beta-D-threo-pentopyranosyl)-chlorodifluoromethane, (2,3,4-tri-O-acetyl-6-deoxy-alpha-L-galactopyranosyl)-chlorodifluoromethane, 1,3,4,6-tetra-O-acetyl-2-C-chlorodifluoromethyl-2-deoxy-alpha-D-glucopyranose, 1,3,4,6-tetra-O-acetyl-2-C-chlorodifluoromethyl-2-deoxy-alpha-D-mannopyranose and methyl 3,4-di-O-acetyl-2-C-chlorodifluoromethyl-2-deoxy-alpha/beta-D-rabinopyranoside with allyltri-n-butyltin.
Carbohydrate Research, 2006
The dithionite-mediated addition of BrCF 2 Cl to 3,4-di-O-pivaloyl-D D-xylal (1) generated preferably 1-CF 2 Cl-substituted products, that is, (2-bromo-2-deoxy-3,4-di-O-pivaloyl-b-D D-xylopyranosyl)-chlorodifluoromethane and (2-deoxy-3,4-di-O-pivaloylb-D D-threo-pentopyranosyl)-chlorodifluoromethane. Selected chlorodifluoromethyl-substituted monosaccharide derivatives were hydrodechlorinated or alkylated at the CF 2 Cl-group using tin reagents under radical reaction conditions. Thus, hydrodechlorinations of (2,3,4-tri-O-acetyl-6-deoxy-a-L L-galactopyranosyl)-chlorodifluoromethane and of methyl 3,4-di-O-acetyl-2-C-chlorodifluoromethyl-2,6-dideoxy-a/b-L L-glucopyranoside are reported using tri-n-butyltin hydride initiated by AIBN. UVinitiated allylations are reported for reactions of (2-deoxy-3,4-di-O-pivaloyl-b-D D-threo-pentopyranosyl)-chlorodifluoromethane, (2,3,4-tri-O-acetyl-6-deoxy-a-L L-galactopyranosyl)-chlorodifluoromethane, 1,3,4,6-tetra-O-acetyl-2-C-chlorodifluoromethyl-2-deoxya-D D-glucopyranose, 1,3,4,6-tetra-O-acetyl-2-C-chlorodifluoromethyl-2-deoxy-a-D D-mannopyranose and methyl 3,4-di-O-acetyl-2-Cchlorodifluoromethyl-2-deoxy-a/b-D D-rabinopyranoside with allyltri-n-butyltin.
Radical mediated-direct conversion of aldehydes into acid bromides
Tetrahedron Letters, 2007
A method of preparing acid bromides directly from aldehydes with Br 3 CCO 2 Et under radical conditions was developed. Aromatic aldehydes with electron-donating group were found to be more reactive than aromatic aldehydes with electron-withdrawing group and aliphatic aldehydes under reaction conditions.
Synthesis of bromodeoxy sugars from hexoses, alditols, and aldonic acids
Pure and Applied Chemistry, 2000
Reaction of hexoses, anhydroalditols, and aldonic acids with hydrogen bromide in acetic acid leads to the formation of acetylated bromodeoxy compounds. The reaction proceeds by partial acetylation and formation of acetoxonium ions followed by substitution with bromide. Hexoses react only in the furanose form to give 6-bromo compounds. Most l,-and 1,5-anhydrides of hexitols give mono-or dibromides. Aldonic acids, or their lactones, yield mono-or dibromolactones with bromine at C-2 and at the primary carbon atom. Some aspects of the chemistry of the bromolactones are discussed.
Facile synthesis of sugar lactols via bromine-mediated oxidation of thioglycosides
Journal of Carbohydrate Chemistry, 2019
Synthesis of a variety of sugar lactols (hemiacetals) has been accomplished in moderate to excellent yields by using bromine-mediated oxidation of thioglycosides. It was found that acetonitrile is the optimal solvent for this oxidation reaction. This approach involving bromine as oxidant is superior to that using N-bromosuccimide (NBS) which produces byproduct succinimide often difficult to separate from the lactol products.
2018
Department of Chemistry, Shri Mathuradas Mohota College of Science, Nagpur-440 009, Maharashtra, India E-mail: madhudash2001@yahoo.co.in Fax: 91-712-2744992 Department of Chemistry, R.T.M. Nagpur University, Nagpur-440 033, Maharashtra, India Regional Forensic Science Laboratory, Govt. of Maharashtra, Amravati-444 603, Maharashtra, India Taywade College, Koradi, Dist. Nagpur, Maharashtra, India Manuscript received 05 March 2018, revised 16 March 2018, accepted 11 April 2018 1,3-Disubstituted/unsubstituted barbituric acids on treatment with KBr-H<sub>2</sub>O<sub>2</sub> as a greener brominating reagent give mono and dibromo barbituric acids. With aqueous HCl selective bromination and without aqueous HCl complete bromination of active methylene group of barbituric acids took place. The reaction of monobarbituric acids with thiosemicarbazide and thioglyoxalic acid under refluxing in aqueous medium, simple C-S coupling products were obtained. The spiro C-N cou...