β‐Selective Glycosylation by Using O ‐Aryl‐Protected Glycosyl Donors

Site-Selective O-Arylation of Carbohydrate Derivatives through Nickel-Photoredox Catalysis

Site-selective O-arylations of glycoside-derived diols have been achieved by couplings with bromoarenes upon irradiation with blue LEDs in the presence of an iridium photocatalyst and a nickel complex. The use of hexamethylenetetramine (hexamine) in place of quinuclidine, along with the application of a methoxy-substituted 2,2'-bipyridine ligand, provided improvements in yield for this relatively challenging substrate class. Selective arylation took place at the less sterically hindered OH group, as determined by the substitution pattern and configuration of the glycoside substrate. Percent buried volume calculations were used to quantify the relative levels of steric hindrance at the two reactive sites.

Recent advances in the direct O-arylation of carbohydrates

Methods for the O-arylation of hydroxyl and hemiacetal groups in carbohydrates via C(sp2)-O bond formation are discussed. Such methods provide an alternative disconnection to the traditional approach of nucleophilic substitution between a sugar-derived electrophile and a phenol or phenoxide nucleophile. They have led to new opportunities for stereoselectivity, site-selectivity and chemoselectivity in the preparation of O-aryl glycosides and carbohydrate-derived aryl ethers, compounds that are useful for a broad range of applications in medicinal chemistry, glycobiology and organic synthesis.