Search

As shown by X-ray crystallography, crystals of 3β-acetoxy-16,17-seco-17,20-dioxopregn-5-ene-16-nitrile are dimorphic. The regioselectivity of the Norrish–Yang type II photocyclization under visible light of this steroidal 1,2-diketone, which bears primary, secondary, and tertiary nonequivalent abstractable γ-hydrogens, dramatically increases in the crystalline state of both polymorphs. X-ray crystallography and molecular mechanics calculations reveal crystal structure–solid state photochemistry relationships., Financial support by the Investigation Programs of the Ministerio de Economía y Competitividad (CTQ2010-18244) is acknowledged. D.A.-D. thanks the Ministerio de Economía y Competitividad for a fellowship. The authors acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI).

A simple epimerization of C-(α-D-Gly p )methanol into C-(β-L-Gly p )methanol compounds is described. The radical sequence involved homolytic cleavage of the C5–H bond by 1,5-hydrogen atom transfer promoted by the 1’-O-yl radical and subsequent hydride addition with inversion of configuration. This methodology allows the preparation of rare C-(β-L-Ido p )-, C-(β-L-Altp)-, C-(β-L-Gulp)-, C-(β-L-Allp)methanol glycosides starting from carbohydrates of the D-series. It can also be applied to transform L- into D-configured C-glycosyl compounds, as illustrated by the formation of C-(β-D-6dGulp)- and C-(β-D-6dAltp)methanol from readily accessible L-rhamno and L-fuco analogs, respectively. In further development of this procedure compounds with C-(β-L-Araf)- and C-(β-L-5dRibf)methanol structures have also been synthesized. The alkoxyl radicals were generated by reaction of the corresponding N-alkoxyphthalimides with nBu3SnH(D) and in comparative terms, by visible light-photocatalysis using the Hantzsch ester/fac-Ir(ppy)3 procedure. The influence of the sugar ring conformation and the electronegativity of the substituents on the stereochemical outcome will be addressed., The authors gratefully acknowledge the financial support from the Investigation Programs of the Ministerio de Economia y Competitividad (CTQ2010-18244), Fundación CajaCanarias (2015-BIO08), the European Regional Development Funds (ERDF) and the Gobierno de Canarias (ProID2017010017). ASM is grateful to the CSIC JAE Predoc Program (Spanish Research Council). The authors acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI).

The anomeric alkoxyl radical β-fragmentation (ARF) of carbohydrates possessing an electron-withdrawing group (EWG) at C2, promoted by PhI(OAc)2/I2, gives rise to an acyclic iodide through which a pentavalent atom of phosphorus can be introduced via the Arbuzov reaction. After selective hydrolysis and subsequent cyclization, the phosphonate or phosphinate intermediates can be converted into 2-deoxy-1-phosphahexopyranose and 2-deoxy-1-phosphapentopyranose sugars. The ARF of carbohydrates with an electron-donor group (EDG) at C2 proceeds by a radical-polar crossover mechanism, and the cyclization occurs by nucleophilic attack of a conveniently positioned phosphonate or phosphinate group to the transient oxocarbenium ion. This alternative methodology leads to 5-phosphasugars with a 4-deoxy-5-phosphapentopyranose framework. The structure and conformation of the 2-oxo-1,2-oxaphosphinane and 2-oxo-1,2-oxaphospholane ring systems in different carbohydrate models have been studied by NMR and X-ray crystallography., Financial support by the Investigation Programs of the Ministerio de Economía y Competitividad (No. CTQ2010-18244), Fundación CajaCanarias (No. 2015-BIO08) and the Gobierno de Canarias (No. ProID2017010017) is acknowledged. D.H.-G. thanks the Ministerio de Economía y Competitividad for a fellowship.

The generation and fate of 2,3,6-icosa-O-methyl-β-cyclomaltoheptaos-6-O-yl radical under reductive conditions is described. Two radical cascade reactions are involved: the main one is triggered by a 1,8-HAT of the hydrogen at 5C. The radical can reach the anomeric hydrogen at 1C three sugar units ahead using a six-step sequence. The different hydrogen donor ability of the group 14 hydrides permits one to selectively stop the cascade at 5C, 2C, and 4C to obtain β-CD with a β-l-Idop unit, acyclic hepta-, and hexa-saccharide structures, respectively., Financial support by the Investigation Programs of theMinisterio de Economía y Competitividad (No. CTQ2010-18244), Fundación CajaCanarias (No. 2015-BIO08) and the Gobierno de Canarias (No. ProID2017010017) is acknowledged.

A simple method to modify the primary face of cyclodextrins (CDs) is described. The 6I‐O‐yl radical of α‐, β‐, and γ‐CDs regioselectively abstracts the H5II, located in the adjacent D‐glucose unit, by an intramolecular 1,8‐hydrogen‐atom‐transfer reaction through a geometrically restricted nine‐membered transition state to give a stable 1,3,5‐trioxocane ring. The reaction has been extended to the 1,4‐diols of α‐ and β‐CD to give the corresponding bis(trioxocane)s. The C2‐symmetric bis(trioxocane) corresponding to the α‐CD is a stable crystalline solid whose structure was confirmed by X‐ray diffraction analysis. The calculated geometric parameters confirm that the primary face is severely distorted toward a narrower elliptical shape for this rim., Financial support by the Investigation Programs of the Ministerio de Economía y Competitividad (CTQ2010‐18244) and the COST Action CM1201 “Biomimetic Radical Chemistry” is acknowledged. D.A.‐D. thanks the Ministerio de Economía y Competitividad for a fellowship.

The excitation of the innermost carbonyl of nono‐2,3‐diulose derivatives by irradiation with visible‐light initiates a sequential Norrish type II photoelimination and aldol cyclization process that finally gives polyfunctionalized cyclopentitols. The rearrangement has been confirmed by the isolation of stable acyclic photoenol intermediates that can be independently cyclized by a thermal 5‐(enolexo)‐exo‐trig uncatalyzed aldol reaction with high diastereoselectivity. In this last step, the large deuterium kinetic isotope effect found for the 1,5‐hydrogen atom transfer seems to indicate that the aldol reaction runs through a concerted pericyclic mechanism. Owing to the ready availability of pyranose sugars of various configurations, this protocol has been used to study the influence of pyranose ring‐substituents on the diastereoselectivity of the aldol cyclization reaction. In contrast with other pyranose ring contraction methodologies no transition‐metal reagents are needed and the sequential rearrangement occurs simply by using visible light and moderate heating (0 to 60 °C)., This work was supported by the Investigation Programs (CTQ2010‐18244) of the Ministerio de Economía y Competitividad and (SolSub20081000192) of the Gobierno de Canarias. D.A.‐D. thanks the Ministerio de Economía y Competitividad for a fellowship. C.R.‐F. thanks the Programa I3P‐CSIC for a postdoctoral contract.

A simple and efficient radical C–H functionalization to access modified cyclodextrins (CDs) has been developed. The well-defined conformation of glycosidic and aglyconic bonds in α-, β-, and γ-CDs favors the intramolecular 1,8-hydrogen atom transfer (HAT) promoted by the 6I-O-yl radical, which abstracts regioselectively the hydrogen at C5II of the contiguous pyranose. The C5II-radical evolves by a polar crossover mechanism to a stable 1,3,5-trioxocane ring between two adjacent glucoses or alternatively triggers the inversion of one α-d-glucose into a 5-C-acetoxy-β-l-idose unit possessing a 1C4 conformation. The 6I,IV- and 6I,III-diols of α- and β-CDs behave similarly to the monoalcohols, forming mostly compounds originating from two 1,8-HAT consecutive processes. In the case of 6I,II-diols the proximity of the two 6-O-yl radicals in adjacent sugar units allows the formation of unique lactone rings within the CD framework via a 1,8-HAT−β-scission tandem mechanism. X-ray diffraction carried out on the crystalline 1,4-bis(trioxocane)-α-CD derivative shows a severe distortion toward a narrower elliptical shape for the primary face., Financial support by the Investigation Programs of the Ministerio de Economía y Competitividad (CTQ2010-18244), Fundación CajaCanarias (2015-BIO08) and the COST Action CM1201 “Biomimetic Radical Chemistry” is acknowledged. D.A.-D. thanks the Ministerio de Economía y Competitividad for a fellowship.

The nitrogen-centred radical generated by reaction of an N-phosphoramidate or N-cyanamide, attached to a tri- or tetramethylene tether extended from the C-1 of a carbohydrate, with (diacetoxyiodo)benzene (DIB) and iodine can undergo a regio- and stereoselective intramolecular hydrogen atom transfer (HAT) reaction to furnish four different oxa-azaspirobicyclic systems: 1-oxa-6-azaspiro[4.4]nonane, 1-oxa-6-azaspiro[4.5]decane, 6-oxa-1-azaspiro[4.5]decane and 1-oxa-7-azaspiro[5.5]undecane. A tandem 1,5- or 1,6-HAT-oxidation-nucleophilic cyclisation mechanism is proposed., This work was supported by the research programmes BQU2000-0650 and BQU2001-1665 of the Dirección General de Investigación Científica y Técnica, Spain. I.P.-M. thanks the I3P-CSIC programme for a fellowship.

The preparation of 2-amino- C -glycosides of the hexahydro-2 H -furo[3,2- b ]pyrrole and octahydropyrano[3,2- b ]pyrrole systems is described. A tandem 1,5-hydrogen atom transfer–radical oxidation–nucleophilic cyclisation mechanism is proposed for the intramolecular hydrogen atom transfer reaction promoted by carbamoyl and phosphoramidyl radicals employing hipervalent iodine oxidants.

The primary alkoxyl radical generated by reaction of 1-(2-hydroxyethyl)-glycosides with (diacetoxyiodo)benzene (DIB) and iodine can undergo regioselective intramolecular hydrogen abstraction (IHA) reactions to furnish four different dioxabicyclic systems derived from carbohydrates. The results strongly suggest that the regiocontrol and feasibility of the cyclisation are dependant not only on geometric and stereoelectronic factors, but also on polar and thermochemical factors. The correct selection of the substituents at the precursors can favour the 1,6-IHA against the 1,5-IHA pathway.

A simple synthesis of all eight C-22, C-23, and C-25 diastereoisomers of the cephalostatin north 1 side chain has been accomplished from (25R)-5α-spirostan-3β-ol (tigogenin). The synthesis involves selective hydroxylations at C-23 and C-25 and reductive opening of the 1,6-dioxaspiro[4.5]decane spirostan system to give a conveniently protected 5α-furostan-3β,23,25,26-tetrol. The construction of the required 1,6-dioxaspiro[4.4]nonane system entailed an intramolecular hydrogen abstraction reaction promoted by the C-25 alkoxyl radical as the key step. Acid-catalyzed isomerization of the spiroketal unit suggested that 22R isomers are the thermodynamic products while the 22S isomers are the result of kinetic control. The acid-catalyzed equilibrium between 1,6-dioxaspiro[4.4]nonane and 1,6-dioxaspiro[4.5]decane systems was also studied. In the 1,6-dioxaspiro[4.4]nonane units, the observed 3J23,24 coupling constants suggest that the five-membered puckered ring-F undergoes substantial conformational changes on going from 22S to 22R isomers.

A series of four α-diketones placed as 1α-pyruvoyl tethers on D-glucopyranose and D-glucopyranosiduronic acid skeletons was prepared in order to determine the influence of captodative and stereoelectronic effects on the regioselectivity of the hydrogen atom transfer (HAT) in Norrish typeII photochemical processes. We observed that the 1,5-HAT regioselectivity can be switched between the two potentially abstractable syn-1,3-diaxial hydrogens at H6 and H8. Highly unusual photoproducts from Norrish typeII photoelimination and Norrish-Yang photocyclization initiated by the excited internal carbonyl group were obtained, in some cases in excellent synthetic yield. The 1,5-HAT transition state in the Norrish typeII photoelimination was investigated by photochemical experiments in the crystalline state.

A series of four α‐diketones placed as 1α‐pyruvoyl tethers on D‐glucopyranose and D‐glucopyranosiduronic acid skeletons was prepared in order to determine the influence of captodative and stereoelectronic effects on the regioselectivity of the hydrogen atom transfer (HAT) in Norrish type II photochemical processes. We observed that the 1,5‐HAT regioselectivity can be switched between the two potentially abstractable syn‐1,3‐diaxial hydrogens at H6 and H8. Highly unusual photoproducts from Norrish type II photoelimination and Norrish–Yang photocyclization initiated by the excited internal carbonyl group were obtained, in some cases in excellent synthetic yield. The 1,5‐HAT transition state in the Norrish type II photoelimination was investigated by photochemical experiments in the crystalline state., This work was supported by the Investigation Programs of the Ministerio de Economía y Competitividad (CTQ2010‐18244) and of the Gobierno de Canarias (SolSub20081000192). D.A.‐D. thanks the Ministerio de Economía y Competitividad for a fellowship. C.R.‐F. thanks the Programa I3P‐CSIC for a postdoctoral contract.

The excitation of the innermost carbonyl of nono-2,3-diulose derivatives by irradiation with visible-light initiates a sequential Norrish typeII photoelimination and aldol cyclization process that finally gives polyfunctionalized cyclopentitols. The rearrangement has been confirmed by the isolation of stable acyclic photoenol intermediates that can be independently cyclized by a thermal 5-(enolexo)-exo-trig uncatalyzed aldol reaction with high diastereoselectivity. In this last step, the large deuterium kinetic isotope effect found for the 1,5-hydrogen atom transfer seems to indicate that the aldol reaction runs through a concerted pericyclic mechanism. Owing to the ready availability of pyranose sugars of various configurations, this protocol has been used to study the influence of pyranose ring-substituents on the diastereoselectivity of the aldol cyclization reaction. In contrast with other pyranose ring contraction methodologies no transition-metal reagents are needed and the sequential rearrangement occurs simply by using visible light and moderate heating (0 to 60 degrees C).

A previously developed 1,8-hydrogen atom transfer (HAT) reaction promoted by 6-O-yl alkoxyl radicals between the two pyranose units in Hexp-(1→4)-Hexp disaccharides has been extended to other systems containing at least a furanose ring in their structures. In Penf-(1→3)-Penf (A) and Hexp-(1→3)-Penf (B) disaccharides, the 1,8-HAT reaction and concomitant cyclization to a 1,3,5-trioxocane ring are in competition with radical β-scission of the C4–C5 bond and formation of dehomologated products. The influence of the stereoelectronic β-oxygen effect on the β-scission and consequently on the 1,8-HAT reaction has been studied using the four possible isomeric d-furanoses. d-xylo- and d-lyxo-derivatives afforded preferentially 1,8-HAT products, whereas d-arabino- and d-ribo-derivatives gave exclusively direct β-scission of the alkoxyl radical. When the 6-O-yl radical is on a pyranose ring, as occurs in Penf-(1→4)-Hexp (C), it has been shown to provide the cyclized products exclusively., This work was supported by the Research Programs SolSubC200801000192 of the Gobierno de Canarias and CTQ2010-18244 of the Ministerio de Ciencia e Innovación, cofinanced by the Fondo Europeo de Desarrollo Regional (FEDER). I.P.-M. thanks the Spanish Ministerio de Ciencia e Innovación for the Research Program PIE 200930I138. S.G. thanks the Gobierno de Canarias for a postdoctoral contract.

A tandem 1,5-, 1,6- or 1,8-intramolecular hydrogen atom transfer (HAT)/intermolecular radical allylation using mono- or (1→4)-O-disaccharide models is described. It is a simple, sequential, stereocontrolled methodology for C-C bond formation by remote free radical functionalization, giving access to interesting carbohydrate structures carrying differently functionalized tethers. A tandem intramolecular hydrogen atom transfer (HAT)/intermolecular radical allylation is described. This process occurs by a completely regio- and stereoselective route that provides a simple methodology for C-C bond formation on remote positions without modifying the remainder of the carbohydrate., This work was supported by the Research Programs of the Gobierno de Canarias (SolSubC200801000192 and CTQ2010‐18244) of the Ministerio de Ciencia e Innovación, cofinanced by the Fondo Europeo de Desarrollo Regional (FEDER). I. P.‐M. thanks the Spanish Ministerio de Ciencia e Innovación for the Research Program PIE 200930I138. L. M. Q. thanks the Consejo Superior de Investigaciones Científicas (CSIC) (Program I3P) for fellowships.

This article reviews the progress in the area of radicals in carbohydrate chemistry with special attention to new developments published during the past decade. No attempt has been made to present a comprehensive review of the literature but, rather, some specific examples are given to highlight the most synthetically valuable processes. The major focus is on inter- and intramolecular carbon–carbon bond-forming radical reactions, with emphasis on the preparation of C-glycosides, C-ketosides, C-disaccharides, and branched-chain sugars, as well as on the synthesis of polyfunctionalized carbocycles by radical cyclization of acyclic carbohydrate derivatives. We also describe methods for the formation of carbon–hydrogen bonds, and synthesis in which a heteroatom-centered radical plays a clear role in the carbon–heteroatom (C–N, C–P, C–O, C–S/Se, and C–Br) bond formation. Finally, a few selected examples of alkoxyl radical β-fragmentation reactions, carried out under oxidative or reductive conditions, are included to illustrate their potential in the preparation of chiral synthons. Keywords: carbohydrates; radicals; C-glycosides; C-disaccharides; carbasugars; glycos-1-yl radicals; carbon-centered radicals; heteroatom-centered radicals

3 pages, 2 schemes.-- PMID: 11950346 [PubMed].-- Printed version published Apr 18, 2002.-- Supporting information available at: http://pubs.acs.org/doi/suppl/10.1021/ol025580e, A simple transformation of the eight-carbon side chain of a natural spirostan sapogenin into the cephalostatin north 1 spiroketal moiety is described. This methodology, based on an intramolecular hydrogen abstraction reaction promoted by alkoxy radicals, permits the synthesis of C-22 and C-25 stereoisomers of the dioxaspiro[4.4]nonane cephalostatin ring system. The acid-catalyzed isomerization of the spirocenter in the different isomers is studied., This work was supported by Investigation Programmes BQU2000-0650 and BQU2001-1665 of the Dirección General de Investigación, Spain. I.P.-M. thanks the Cooperativa Farmacéutica de Tenerife (COFARTE), Spain, for a fellowship.

Extraintestinal features may be observed in patients with ulcerative colitis (UC). We describe a 69-year-old woman who was initially diagnosed as having polymyalgia rheumatica (PMR). Prednisone was progressively tapered to complete discontinuation a year and a half after PMR diagnosis. However, at that time, she started to complain of asthenia, abdominal cramping and pain on the left side, weight loss and bloody diarrhoea. A colonoscopy confirmed a diagnosis of left-sided UC. She experienced several flares of the disease that required admission and treatment with high-dose corticosteroids and azathioprine. Colectomy was performed as the disease became refractory to these therapies. Four months after surgery, when the patient was not receiving any corticosteroid therapy, she started to feel dull and achy pain in the thighs along with claudication of the lower limbs. An 18F-fluorodeoxyglucosepositron emission tomography with CT (FDG PET/CT) disclosed an inflammatory process with mild-moderate diffuse increased metabolism in the thoracic aorta and markedly increased FDG uptake in the in the femoral and posterior tibial arteries on both sides. Treatment with the anti-TNF-alpha monoclonal antibody-adalimumab (40 mg every 2 weeks subcutaneously) along with prednisone (initial dose 15 mg/day) yielded rapid improvement of symptoms. Also, a new FDG PET/CT performed 4 months later disclosed marked decrease of FDG uptake in the involved arteries.This report emphasises the importance of suspecting the presence of large- and medium-vessel vasculitis in a patient with UC presenting with musculoskeletal features. It also highlights the beneficial effect of TNF-antagonists in vasculitis associated to UC.

The C-radical originated by β-fragmentation of carbohydrate anomeric alkoxy radicals, generated under reductive conditions by treatment of N-phthalimido glycosides with allyltri-n-butyltin/AIBN, may subsequently undergo an intermolecular allylation to give hept-1-enitol derivatives. These compounds can be useful chiral synthons for the synthesis of polyhydroxylated compounds.

[reaction: see text] The alkoxy radical generated by reaction of 3,7-anhydro-2-deoxyoctitols with (diacetoxyiodo)benzene (DIB) and iodine abstracts regioselectively either the proton at C7 or that at C4 depending on the electronegativity of the substituent at C4. The correct election of this substituent can switch the reaction to give 2,9-dioxabicyclo[3.3.1]nonane or hexahydro-2H-furo[3,2-b]pyran ring systems.

The nitrogen-centred radical generated by reaction of an N-phosphoramidate or N-cyanamide, attached to a tri- or tetramethylene tether extended from the C-1 of a carbohydrate, with (diacetoxyiodo)benzene (DIB) and iodine can undergo a regio- and stereoselective intramolecular hydrogen atom transfer (HAT) reaction to furnish four different oxa-azaspirobicyclic systems: 1-oxa-6-azaspiro[4.4]nonane, 1-oxa-6-azaspiro[4.5]decane, 6-oxa-1-azaspiro[4.5]decane and 1-oxa-7-azaspiro[5.5]undecane. A tandem 1,5- or 1,6-HAT-oxidation-nucleophilic cyclisation mechanism is proposed.

The glycopyran-6-O-yl radical promoted hydrogen atom transfer reaction (HAT) between the two pyranose units of ¿-D-Manp-(1-4)-¿-D-Glcp and ¿-D-Manp-(1-4a)-4a-carba-¿-D-Glcp disaccharides provides supporting chemical evidence for the conformational differences between O- and C-glycosyl compounds. In the O-disaccharide the 6-alkoxyl radical, generated under oxidative or reductive conditions, abstracts exclusively the hydrogen at C-5' via a completely regioselective 1,8-HAT reaction. This may be attributable to the conformational restriction of the glycosidic and aglyconic bonds due principally to steric and stereoelectronic effects. On the contrary, very little regioselectivity is observed in the homologous C-disaccharide and a mixture of compounds generated by 1,5-, 1,6-, and 1,8-HAT processes where the abstraction occurs at hydrogen atoms positioned at C-4a, C-1', and C-5', respectively, has been obtained. This study has been extended to simpler O- and C-glycosides, where the aglycon was a straight n-alkyl alcohol tether of five atoms; in general, all of the results obtained are shown to be consistent with a major conformational flexibility of the C-glycosidic bond., This work was supported by the Spanish Ministerio de Educación y Ciencia (MEC); Research Programs CTQ2004‐06381/BQU, CTQ2004‐02367/BQU and CTQ2007‐67492/BQU, cofinanced by the Fondo Europeo de Desarrollo Regional (FEDER). I. P.‐M. and L. M. Q. thank the CSIC (Program I3P) for fellowships.

A tandem 1,5 or 1,6 hydrogen atom transfer (HAT)–radical allylation using carbohydrate models is described. The HAT reaction generated a C-glycos-1-yl radical intermediate, which added to allyltri-n-butyltin with high diastereoselectivity, to give C-ketosides with the quaternary carbon carrying two differently functionalized tethers.

13 pages, 1 figure, 1 table, 7 schemes.-- PMID: 18830990 [PubMed]., Supporting information (30 pages) available at: http://www3.interscience.wiley.com/journal/121427980/suppinfo, The stereochemical and conformational factors controlling the intramolecular hydrogen-atom transfer (HAT) reaction between the two pyranose units in a (1-->4)-O-disaccharide when promoted by a primary 6-O-yl radical are studied. Models with α-D-Glcp-(1-->4)-β-D-Glcp, α-L-Rhamp-(1-->4)-α-D-Galp or α-D-Manp-(1-->4)-β-L-Gulp skeletons led exclusively to the abstraction of the hydrogen from H--C-5' and the formation, through a nine-membered transition state, of a 1,3,5-trioxocane ring system in a stable boat-chair conformation. Notwithstanding, derivatives of α-L-Rhamp-(1-->4)-α-D-Glcp or α-D-Manp-(1-->4)-α-D-Galp exclusively abstract the hydrogen from H--C-1' through a seven-membered transition state and, therefore, lead to an interglycosidic spiro ortho ester., This work was supported by Research programs CTQ2004-06381/BQU, CTQ2004-02367/BQU and CTQ2007-67492/BQU of the Ministerio de Educación y Ciencia (Spain), and cofinanced by the Fondo Europeo de Desarrollo Regional (FEDER). A.J.H., I.P.-M. and L.M.Q. thank the Program I3P-CSIC for fellowships.

3 pages, 1 table, 2 schemes.-- Printed version published Aug 25, 2008., Supporting information (16 pages) available at: http://dx.doi.org/10.1016/j.tetlet.2008.06.070, A tandem 1,5 or 1,6 hydrogen atom transfer (HAT)–radical allylation using carbohydrate models is described. The HAT reaction generated a C-glycos-1-yl radical intermediate, which added to allyltri-n-butyltin with high diastereoselectivity, to give C-ketosides with the quaternary carbon carrying two differently functionalized tethers., This work was supported by the Investigation Programmes nos. CTQ2007-67492 and CTQ2004-02367 of the Ministerio de Educación y Ciencia, Spain, cofinanced by the Fondo Europeo de Desarrollo Regional (FEDER). I.P.-M. and L.M.Q. thank the Program I3P-CSIC, for fellowships.

11 pages, 5 schemes.-- PMID: 18778104 [PubMed].-- Printed version published Oct 3, 2008., Supporting Information Available: A complete description of experimental details of precursors and copies of NMR spectra for all new compounds available at: http://pubs.acs.org/doi/suppl/10.1021/jo801499d, The stereoselective reduction of hexopyranos-5′-yl radicals in α-d-Hexp-(1→4)-d-Hexp disaccharide models is described. These radicals are generated from a 6-O-yl radical located in the other monosaccharic unit through a 1,8-hydrogen atom transfer. The reaction, which is strongly influenced by steric and stereoelectronic effects, permits in some cases the transformation of α-d-Hexp-(1→4)-d-Hexp into β-l-Hexp-(1→4)-d-Hexp disaccharides in a single step with high diastereoselectivity., This work was supported by Research programs CTQ2004-06381/BQU, CTQ2004-02367/BQU, and CTQ2007-67492/BQU of the Ministerio de Educación y Ciencia, Spain, cofinanced by the Fondo Europeo de Desarrollo Regional (FEDER). I.P.-M. and L.M.Q. thank the I3P-CSIC Program for fellowships.

4 pages, 1 table, 3 schemes.-- Printed version published Apr 26, 2007., Supporting information (complete description of experimental details and product characterization) available at: http://pubs.acs.org/doi/suppl/10.1021/ol070496q, The stereochemical and conformational factors controlling the intramolecular hydrogen atom transfer (HAT) reaction between the two pyranose units in a (1→4)-disaccharide when promoted by a primary 6-O-yl radical are studied. Models with α-d-Glcp-(1→4)-β-d-Glcp or α-l-Rhamp-(1→4)-α-d-Galp skeletons lead exclusively to the abstraction of H−C-5' and the formation, through a nine-membered transition state, of a 1,3,5-trioxocane ring system in a stable boat-chair conformation. Notwithstanding, derivatives of α-l-Rhamp-(1→4)-α-d-Glcp abstract exclusively H−C-1' through a seven-membered transition state and therefore lead to an interglycosidic spiro ortho ester., This work was supported by Research programs CTQ2004-06381/BQU and CTQ2004-02367/BQU of the Ministerio de Educación y Ciencia, Spain, cofinanced by the Fondo Europeo de Desarrollo Regional (FEDER). I.P.-M. and L.M.Q. thank the Program I3P-CSIC for fellowships.

Aziridine N-carbonyl radicals, generated by irradiating the corresponding S-oxalyl xanthates, undergo ring opening to give 2-isocyanato radicals, which can be trapped by an external olefin.

Aziridine N-carbonyl radicals, generated by irradiating the corresponding S-oxalyl xanthates, undergo ring opening to give 2-isocyanato radicals, which can be trapped by an external olefin.

A simple, highly efficient and cheap synthesis of substituted naphthalenes is reported. These aromatic compounds can be easily prepared in acidic or basic conditions from α-tetralones, obtained by a xanthate-mediated addition–cyclisation sequence., I. P.-M. thanks the Ministerio de Educación, Cultura y Deporte (Spain) for a postdoctoral fellowship and A. C.-V. thanks CONACYT (Mexico) for its generous financial support.

4 pages, 1 table, 2 schemes.-- Printed version published Jul 1, 2002., The C-radical originated by β-fragmentation of carbohydrate anomeric alkoxy radicals, generated under reductive conditions by treatment of N-phthalimido glycosides with allyltri-n-butyltin/AIBN, may subsequently undergo an intermolecular allylation to give hept-1-enitol derivatives. These compounds can be useful chiral synthons for the synthesis of polyhydroxylated compounds., This work was supported by the Investigation Programmes No. BQU2000-0650 and BQU2001-1665 of the Dirección General de Investigación Científica y Técnica, Spain. I.P.-M. thanks the I3P-CSIC Programme for a fellowship.

3 pages, 1 table, 2 schemes.-- PMID: 12027657 [PubMed].-- Printed version published May 30, 2002.-- Supporting information available at: http://pubs.acs.org/doi/suppl/10.1021/ol025981u, Erratum to this paper published in: Org. Lett. 4(19): 3337 (2002), http://dx.doi.org/10.1021/ol020134c, The alkoxy radical generated by reaction of 3,7-anhydro-2-deoxyoctitols with (diacetoxyiodo)benzene (DIB) and iodine abstracts regioselectively either the proton at C7 or that at C4 depending on the electronegativity of the substituent at C4. The correct election of this substituent can switch the reaction to give 2,9-dioxabicyclo[3.3.1]nonane or hexahydro-2H-furo[3,2-b]pyran ring systems., This work was supported by the Investigation Programs BQU2000-0650 and BQU2001-1665 of the Dirección General de Investigación Científica y Técnica, Spain. A.J.H. and I.P.-M. thank the Ministerio de Educación y Ciencia, Spain, and the Program I3P-CSIC, respectively, for fellowships.