A tandem 1,5-hydrogen atom transfer/radical oxidation/nucleophilic cyclization mechanism is proposed for the intramolecular hydrogen abstraction reaction promoted for primary carboxamidyl radicals. The electron-withdrawing capacity of the C-5 substituent can switch the reaction to give exclusively bicyclic spirolactams (6-oxa-1-azaspiro[4.5]decan-2-one) when R(1) = H or spirolactones (1,6-dioxaspiro[4.5]decan-2-one) when R(1) = OAc. With a substituent of medium polarity (R(1) = OMe), a mixture of lactones and lactams is formed.
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 alpha-D-Glcp-(1-->4)-beta-D-Glcp, alpha-L-Rhamp-(1-->4)-alpha-D-Galp or alpha-D-Manp-(1-->4)-beta-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 alpha-L-Rhamp-(1-->4)-alpha-D-Glcp or alpha-D-Manp-(1-->4)-alpha-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.
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.
The preparation of 2-amino-C-glycosides of the hexahydro-2H-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.
CO Me [Ru(bpy) 3 ](BF 4 ) 2 iPr 2 NEt, hn CO 2 Me AcO AcO AcO 21 EtO 2 C CO 2 Et Me N Me 28 H AcO 23 65 Scheme 7 Synthesis of C-ketosides by intermolecular addition of C-glycos-1-yl radicals to double bonds.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.