Modulable Photocatalyzed Strategies for the Synthesis of α-C-Glycosyl Alanine Analogues via the Giese Reaction with Dehydroalanine Derivates

Herein, we present the & alpha;-selective Giese reactionbetweenpyranosyl/furanosyl bromides and dehydroalanine analogues, which providesaccess to a library of highly valuable & alpha;-C-glycosylalanines. The key C-glycosyl radical is generatedthrough photocatalysis by either the new generation copper(I) complex[(DPEPhos)(bcp)Cu]PF6 or [Ru(bpy)(3)](BF4)(2). The reactions proceed smoothly, affording the desired & alpha;-C-glycosyl alanines in up to 99% yield whendiethyl 1,4-dihydro-2,6-dimethyl-3,5-pyridinedicarboxylate [Hantzschester (HE)] is used as an additive. N,N-Diisopropylethylamine (DIPEA) has been selected as a reductant inboth protocols. A mechanistic study by means of transient absorptionspectroscopy unveils a halogen-atom transfer (XAT) process in C-glycosyl radical formation.