Modulable Photocatalyzed Strategies for the Synthesis of α-<i>C</i>-Glycosyl Alanine Analogues via the Giese Reaction with Dehydroalanine Derivates
Lorenzo Poletti, Alessandro Massi, Daniele Ragno, Federico Droghetti, Mirco Natali, Carmela De Risi, Olga Bortolini, Graziano Di Carmine
Abstract
High Resolution Image Download MS PowerPoint Slide Herein, we present the α-selective Giese reaction between pyranosyl/furanosyl bromides and dehydroalanine analogues, which provides access to a library of highly valuable α- C -glycosyl alanines. The key C -glycosyl radical is generated through photocatalysis by either the new generation copper(I) complex [(DPEPhos)(bcp)Cu]PF 6 or [Ru(bpy) 3 ](BF 4 ) 2 . The reactions proceed smoothly, affording the desired α- C -glycosyl alanines in up to 99% yield when diethyl 1,4-dihydro-2,6-dimethyl-3,5-pyridinedicarboxylate [Hantzsch ester (HE)] is used as an additive. N, N -Diisopropylethylamine (DIPEA) has been selected as a reductant in both protocols. A mechanistic study by means of transient absorption spectroscopy unveils a halogen-atom transfer (XAT) process in C -glycosyl radical formation.