Visible-Light-Mediated β-C(sp³)–H Amination of Glycosylimidates: En Route to Oxazoline-Fused/Spiro Nonclassical Bicyclic Sugars

Abstract

A straightforward route has been developed for the diastereoselective synthesis of nonclassical conformationally constrained oxazoline-fused and spiro bicyclic sugars bearing a quaternary center via selective β-C–H amination of appropriately positioned glycosylimidates. The desired transformation proceeds via the generation of imidate N-radicals under visible-light conditions followed regioselective intramolecular N–C bond formation. The reactions tolerate broad functional groups under the optimized conditions. Furthermore, the synthetic utility of oxazoline-fused bicyclic sugar moiety is demonstrated through the glycosylation reactions.

Radical‐Mediated Non‐Dearomative Strategies in Construction of Spiro Compounds

“…important from the point of view of modern medicine incorporation of heterocycle into carbohydrate skeleton is being recognized as the most challenging for organic and medicinal scientists [74] . In light of this facts, Shaw and Kumar described recently a diastereoselective synthesis of oxazoline‐based spirocyclic sugars 194 based on visible‐light‐mediated β‐C( sp 3 )−H amination of glycosylimidates 193 [75] . In the presence of iodine source and under blue LED irradiation appropriate non‐classical spirocyclic sugars 194 were obtained in a stereoselective fashion with a reasonable yields (62–63%, Scheme 53).…”

Radical Dehydroxymethylative Fluorination of Carbohydrates and Divergent Transformations of the Resulting Reverse Glycosyl Fluorides

“…[8] Thes econd class capitalizes on derivations of furanos-4-yl and pyranos-5-yl radicals [9] as exemplified by the oxidative radical decarboxylation of uronic acids promoted by Pb(OAc) 4 , [10] (diacetoxyiodo)benzene (DIB)/I 2 , [11] and iridium-based photoredox catalysis, [12] the radical dehydroxymethylation of furanoses mediated by DIB/I 2 , [13] and 1,5hydrogen atom transfer (HAT) of the imine radical of 6-Otrichloroacetimides. [14] Ferriersp hotobromination and ensuing displacement is the third widely used protocol for the synthesis of reverse glycosides. [15] Despite their reliability, these methods suffer from the tedious synthesis of sensitive alkenes from sugar alcohols,harsh conditions,and/or narrow substrate scopes.…”

Radical Dehydroxymethylative Fluorination of Carbohydrates and Divergent Transformations of the Resulting Reverse Glycosyl Fluorides

“…The first involves the functionalization of polar intermediates, for example, the iodofluorination of furanosyl‐4‐ exo ‐olefins, nucleophilic ring opening of 5,6‐epoxides of pyranosyl‐5‐ exo ‐olefins, and enolate capture by electrophiles . The second class capitalizes on derivations of furanos‐4‐yl and pyranos‐5‐yl radicals as exemplified by the oxidative radical decarboxylation of uronic acids promoted by Pb(OAc) 4 , (diacetoxyiodo)benzene (DIB)/I 2 , and iridium‐based photoredox catalysis, the radical dehydroxymethylation of furanoses mediated by DIB/I 2 , and 1,5‐hydrogen atom transfer (HAT) of the imine radical of 6‐ O ‐trichloroacetimides . Ferrier's photobromination and ensuing displacement is the third widely used protocol for the synthesis of reverse glycosides .…”