Fragmentation of carbohydrate anomeric alkoxy radicals: a new synthesis of chiral 1-halo-1-iodo alditols

10 pages, 3 tables, 2 schemes.-- PMID: 14673851 [PubMed].-- Supporting information (52-page PDF file) available at: http://www.wiley-vch.de/contents/jc_2111/2003/f5294_s.pdfTreatment of 1,2-fluorohydrins, 1,2-chlorohydrins, 1,2-bromohydrins, and 1,2-iodohydrins of the D-gluco, D-galacto, D-lacto, L-rhamno, D-allo, L-arabino, 3-deoxy-D-gluco, and 3,4-dideoxy-D-gluco families of carbohydrates with the (diacetoxyiodo)benzene/iodine system afforded 1-fluoro-1-iodo, 1-chloro-1-iodo, 1-bromo-1-iodo, and 1,1-diiodo alditols, respectively, in excellent yields. The reaction was achieved by radical fragmentation of the C1bond;C2 bond, triggered by the initially formed anomeric alkoxy radical, and subsequent trapping of the C2-radical by iodine atoms. This methodology is compatible with the stability of the protective groups most frequently used in carbohydrate chemistry. The potential utility of these 1-halo-1-iodo alditols as chiral synthons was evaluated by their transformation into alk-1-enyl iodides and in the Takai E-olefination reaction.This work was supported by the Investigation Programs nos. PPQ2000-0728, BQU2000-0650, and BQU2001-1665 of the Dirección General de Investigación Científica y Técnica, Spain. C.R.-F. thanks the Dirección General de Universidades e Investigación del Gobierno de Canarias for a fellowship

Fragmentation of carbohydrate anomeric alkoxy radicals: a new synthesis of chiral 1-halo-1-bromo compounds

4 pages, 2 tables.-- Printed version published Aug 11, 2003.The reaction of 1,2-halohydrins derived from easily available carbohydrates with (diacetoxyiodo)benzene (DIB) in the presence of bromine is a mild procedure for the synthesis of 1-deoxy-1-halo-1-bromo-alditols with one carbon less than the original carbohydrate. The reaction goes through β-fragmentation of the intermediate anomeric alkoxyl radicals. These 1-halo-1-bromo polyhydroxy compounds may be valuable synthetic intermediates in organic synthesis.This work was supported by the Investigation Programmes no. BQU2000-0650 and BQU2001-1665 of the Dirección General de Investigación Cientı́fica y Técnica, Spain. C.R.-F. thanks the Dirección General de Universidades e Investigación del Gobierno de Canarias for a fellowship

Synthesis of highly functionalized chiral nitriles by radical fragmentation of beta-hydroxy azides. Convenient transformation of aldononitriles into 1,4- and 1,5-iminoalditols

8 pages, 2 tables, 5 schemes.-- PMID: 15549818 [PubMed].-- Printed version published Nov 26, 2004.Supporting information available: Detailed experimental procedures and spectral and analytical data for several compounds.-- Available at: http://pubs.acs.org/doi/suppl/10.1021/jo049026pThe synthesis of highly functionalized nitriles by an alkoxyl radical fragmentation of cyclic β-hydroxy azides is described. The alkoxyl radicals were generated by reaction of the alcohols with (diacetoxyiodo)benzene and iodine under mild conditions compatible with the presence of sensitive substituents and the protective groups most frequently used in carbohydrate chemistry. To explore the scope and limitations of this methodology, experiments were carried out using a variety of β-hydroxy azides of the carbohydrate (1−6, 33, and 41), monoterpenoid (21 and 22), and steroid (23−25) families of natural products. Of special interest are the aldopentonitriles (15−18, 34, and 42) and aldotetrononitriles (19 and 20) synthesized from the corresponding 2-azido-2-deoxycarbohydrates. To demonstrate the versatility of these aldononitriles as chiral synthons, 1,4-imino-1-deoxysugar (37) and 1,5-imino-1-deoxysugar (43) analogues of the polyhydroxypyrrolidine and -piperidine types were prepared.This work was supported by the Investigation Programme Nos. BQU2000-0650, BQU2001-1665, and PPQ2000-0728 of the Dirección General de Investigación Científica y Técnica, Spain. C.R.-F. thanks the Dirección General de Investigación del Gobierno de Canarias for a fellowship

Fragmentation of carbohydrate anomeric alkoxy radicals. synthesis of polyhydroxy piperidines and pyrrolidines related to carbohydrates

6 pages, 1 table, 4 schemes.-- PMID: 11262138 [PubMed].-- Printed version published Mar 9, 2001.Supporting information available at: http://pubs.acs.org/doi/suppl/10.1021/jo0057452Imino sugars of the piperidine and pyrrolidine types can be specifically obtained when protected 5-amino-5-deoxyfuranopentoses, 5-amino-5-deoxyfuranohexoses, 6-amino-6-deoxyfuranohexoses, and 6-amino-6-deoxypyranohexoses undergo a tandem alkoxy radical β-fragmentation−intramolecular cyclization reaction. The reaction is promoted by the system: iodosylbenzene−iodine under mild conditions. The tert-butoxycarbonyl, benzyloxycarbonyl, and diphenylphosphinoyl radicals have been studied as amino-protecting groups. Using this methodology, polyhydroxylated pyrrolidines of the d-erythrofuranoses 34 and 35, d-threofuranose 36, l-xylofuranose 42, and d-arabinofuranose 43 series and polyhydroxylated piperidines of the d-arabinopyranose type 37 and 38 were obtained.This work was supported by the Investigation Program No. PB96-1461 of the Dirección General de Investigación Científica y Técnica, Spain and Program Nos. 93/030 and 93/014 of the Dirección General de Universidades e Investigación del Gobierno de Canarias. C.C.G. and C.R.-F. thank the Ministerio de Educación y Ciencia, Spain, and the Dirección General de Universidades e Investigación del Gobierno de Canarias, respectively, for fellowships