Ferrocenium complex aided O -glycosylation of glycosyl halides

A new strategy for the activation of glycosyl halide donors to be utilized in glycosylation reactions is presented, utilizing the ferrocenium (Fc) complexes [FcB(OH) 2 ]SbF 6  and FcBF 4  as promoters. The scope of the new system has been investigated using glycosyl chloride and glycosyl fluoride donors in combination with common glycosyl acceptors, such as protected glucose. The corresponding glycosylation products were formed in 95 to 10% isolated yields with  α / β  ratios ranging from 1/1 to  β  only (2 to 14 h reaction time at room temperature, 40 to 100% ferrocenium promoter load).