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 ‐Alt p )‐, C ‐(β‐ l ‐Gul p )‐, C ‐(β‐ l ‐All p )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 ‐6dGul p )‐ and C ‐(β‐ d ‐6dAlt p )methanol from readily accessible l ‐ rhamno and l ‐ fuco analogs, respectively. In further development of this procedure compounds with C ‐(β‐ l ‐Ara f )‐ and C ‐(β‐ l ‐5dRib f )methanol structures have also been synthesized. The alkoxyl radicals were generated by reaction of the corresponding N ‐alkoxyphthalimides with n Bu 3 SnH(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.

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.

The 1,5-HAT-1,2-(ester)alkyl radical migration (Surzur-Tanner rearrangement) radical/polar sequence triggered by alkoxyl radicals has been studied on a series of C-glycosyl substrates with 3-C-(α,β-d,l-glycopyranosyl)1-propanol and C-(α-d,l-glycopyranosyl)methanol structures prepared from chiral pool d- and l-sugar. The use of acetoxy and diphenoxyphosphatoxy as leaving groups provides an efficient construction of 10-deoxy-1,6-dioxaspiro[4.5]decane and 4-deoxy-6,8-dioxabicyclo[3.2.1]octane frameworks. The alkoxyl radicals were generated by the reaction of the corresponding N-alkoxyphthalimides with group 14 hydrides [n-Bu3SnH(D) and (TMS)3SiH], and in comparative terms, the reaction was also initiated by visible light photocatalysis using the Hantzsch ester/fac-Ir(ppy)3 procedure. Special attention was devoted to the influence of the relative stereochemistry of the centers involved in the radical sequence on the reaction outcome. The addition of BF3•Et2O as a catalyst to the radical sequence resulted in a significant increase in the yields of the desired bicyclic ketals.

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.

The generation and fate of 2I–VII,3I–VII,6II–VII-icosa-O-methyl-β-cyclomaltoheptaos-6I-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 5VIIC. The radical can reach the anomeric hydrogen at 1VC 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 5VIIC, 2VIC, and 4VIC to obtain β-CD with a β-l-Idop unit, acyclic hepta-, and hexa-saccharide structures, respectively.

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.

A simple method to modify the primary face of cyclodextrins (CDs) is described. The 6(I)-O-yl radical of α-, β-, and γ-CDs regioselectively abstracts the H5(II), 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.

Trabajo presentado en el WG4/WG2 Meeting COST Action CM1201 celebrado en Kildare (Irlanda) del 23 al 25 de julio de 2015.

A direct approach to β-iodophosphonates and β-iodophosphine oxides from 2,3-dideoxy-3-phosphoryl carbohydrate derivatives has been achieved by using the anomeric alkoxyl radical 1,2-fragmentation protocol. The reaction has been conducted on carbohydrate derivatives under mild conditions with (diacetoxyiodo)benzene and molecular iodine. Subsequent dehydroiodination afforded the corresponding vinylphosphonates and vinylphosphine oxides.

Trabajo presentado en EuCheMS Conference on Organic Free Radicals (ECOFR 2014) celebrado en Praga (Republica Checa) del 29 de junio al 04 de julio de 2014.

Trabajo presentado en EuCheMS Conference on Organic Free Radicals (ECOFR 2014) celebrado en Praga (Republica Checa) del 29 de junio al 04 de julio de 2014.

Trabajo presentado en EuCheMS Conference on Organic Free Radicals (ECOFR 2014) celebrado en Praga (Republica Checa) del 29 de junio al 04 de julio de 2014.

Trabajo presentado en las X Jornadas de Carbohidratos de la Real Sociedad Espanola de Quimica celebrado en Logrono, La Rioja (Espana) del 28 al 30 de mayo de 2014.

Comunicacion presentada en el XI Congreso de Estudiantes de la Facultad de Quimica celebrado en La Laguna (Espana) del 31 de marzo al 2 de abril de 2014.

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.

Trabajo presentado en EuCheMS Conference on Organic Free Radicals (ECOFR 2014) celebrado en Praga (Republica Checa) del 29 de junio al 04 de julio de 2014.

Trabajo presentado en EuCheMS Conference on Organic Free Radicals (ECOFR 2014) celebrado en Praga (Republica Checa) del 29 de junio al 04 de julio de 2014.