Palladium-catalysed arylation of peracetylated glycals, III. Crystal structure of a by-product: mechanistic implications

Abstract

Reinvestigation of the structure of (4,6-di-O-acetyl-2,3-dideoxy-α-D-erythro-hex-2-enopyranosyl)benzene, obtained by the title reaction, is described. The α anomeric configuration was clearly established by X-ray diffraction methods on the deacetylated compound. The sugar moiety exhibits a distorted half-chair 0H5 conformation. Circular dichroism data are included. These new data demonstrate the stereospecificity of intermediate arylpalladium syn addition on the α face of the glycal. The resulting adduct collapses in two different ways: syn elimination of acetatohydridopalladium leading to 3, trans elimination of palladium acetate affording 5. Keywords: C-glycosides, palladium, X-ray diffraction.