Nicolas L, Angibaud P, Stansfield I, Bonnet P, Meerpoel L, Reymond S, * Cossy J. * ESCPI ParisTech, Janssen Research & Development, Val de Reuil, France and Beerse, Belgium
Diastereoselective Metal-Catalyzed Synthesis of
C-Aryl and
C-Vinyl Glycosides.
Angew. Chem. Int. Ed. 2012;
51: 11101-11104
Key words
C-glycosides - cobalt - Grignard reagents
Significance
Numerous metal-catalyzed cross-coupling methods to form anomeric C–C bonds exist, which are important for the synthesis of carbohydrate analogues such as C-glycosides (see Review below). However, β-elimination is a major drawback of these reactions. The authors report a new diastereoselective cobalt-catalyzed cross-coupling between 1-bromo glycosides and aryl and alkenyl Grignard reagents with moderate to good α-selectivity.
Review
L. Somsák Chem. Rev. 2001, 101, 81–136.
Comment
The authors report that there was good α-selectivity for the cross-coupling reaction with mannose and galatose derivatives, but lower α/β ratios for glucose derivatives. Like most
cobalt-catalyzed cross-coupling reactions, the stereoselectivity of this reaction supports a radical pathway. Treatment of a δ-olefinic 1-bromoglycoside produced an epimeric mixture of the bicyclic product, which would result from the formation of an anomeric radical that leads to a 5-exo-trig cyclization followed by cross-coupling with PhMgBr.
