Abstract

Without the stereodirecting ability of 2-substituents, strategies to prepare 2-deoxyglycosides selectively in high alpha- or beta-anomeric forms rely heavily on indirect sequences from glycals or latent 2-deoxysugars. As such, these require a
subsequent reductive step that would be unsuitable for many complex natural products and for any viable total synthesis program. A case in point is that of the kedarcidin chromophore and its alpha-linked 2,6-dideoxysugars, L-mycarose
and L-kedarosamine. In particular, direct and efficient alpha-selective methods for allo-configured systems are especially difficult to realise. Herein we describe a direct, potent, and mild protocol to efficiently generate alpha-L-mycarosides from thioglycosides by using AgPF6, which is exemplified by the alpha-mycosylation of an advanced kedarcidin substructure. Although the present method is applicable to other 2-deoxy systems, such as the synthesis of alpha-L-kedarosaminides, normal 2-oxythioglycosides remain inert to AgPF6 and can be used as acceptors armed with strategic anomeric linkages.