Emerging Advances of the Radical Pathway Glycosylation Enabled by Bench-Stable Glycosyl Donors: Glycosyl Sulfoxides, Glycosyl Sulfones, and Glycosyl Sulfinates

Abstract

Abstract. In synthetic carbohydrate chemistry, the modification of glycosyl radicals pathway stands as a central area of focus. The radical-based reactions often demonstrate remarkable compatibility with various functional groups owing to the mild initiation conditions. In particular, the identification of novel glycosyl radical precursors, combined with advanced reaction techniques, has substantially broadened the scope of glycosyl compound synthesis. Despite the presence of versatile donors, the synthesis of noble donors is still addressed as a synthetic need and challenges associated with sugar chemistry. Currently, a new class of glycosyl radical precursors has been developed which enables the production of C-, S-, O-, and N-glycosides efficiently. In this light, we highlight strategies towards bench-stable glycosyl sulfoxides, sulphone, and sulfite donors that can enable the site-, regio- and stereoselective transformation of protected or naked sugar synthons in synthetic carbohydrate chemistry. Here, this review article covers the recent developments in the selective glycosyl radical diversification such as glycosyl alkylation, arylation, alkenylation, sulfuration, C-H activation, and DNA conjugation via the bench-stable donors along with mechanistic aspects, challenges, and future directions. 1. Introduction 2. Generation of glycosyl radical from glycosyl sulfoxide, glycosyl sulfone, and glycosyl sulfinate 3. Glycosyl radicals and the stereoselectivity 4. Early history of glycosyl sulfoxides, sulfones, and sulfinate donors 5. Generation of glycosyl radicals from glycosyl sulfoxides 6. Generation of glycosyl radicals from glycosyl sulfones 6.1 Allyl glycosyl sulfones 6.2 Heteroaryl glycosyl sulfones 7. Generation of glycosyl radicals from glycosyl sulfinates 8. Summary and Outlook