Photoinitiated Thiol-Ene Reactions of Various 2,3-Unsaturated O-,C- S- and N-Glycosides – Scope and Limitations Study

Kelemen, Viktor and Csávás, Magdolna and Hotzi, Judit and Herczeg, Mihály and Herczegh, Pál and Borbás, Anikó (2020) Photoinitiated Thiol-Ene Reactions of Various 2,3-Unsaturated O-,C- S- and N-Glycosides – Scope and Limitations Study. Chemistry an Asian Journal, 15. pp. 876-891. ISSN 1861-471X

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Abstract

The photoinitiated thiol-ene addition reaction is a highly stereo- and regioselective, and environmentally friendly reaction proceeding under mild conditions, hence it is ideally suited for the synthesis of carbohydrate mimetics. A comprehensive study on UV-light-induced reactions of 2,3- unsaturated O-, C-, S- and N-glycosides with various thiols was performed. The effect of experimental parameters and structural variations of the alkenes and thiols on the efficacy and regio- and stereoselectivity of the reactions was systematically studied and optimized. The type of anomeric heteroatom was found to profoundly affect the reactivity of 2,3-unsaturated sugars in the thiol-ene couplings. Hydrothiolation of 2,3-dideoxy O-glycosyl enosides efficiently produced the axially C2-S-substituted addition products with high to complete regioselectivity. Moderate efficacy and varying regio- and stereoselectivity were observed with 2,3- unsaturated N-glycosides and no addition occurred onto the endocyclic double bond of C-glycosides. Upon hydrothiolation of 2,3-unsaturated S-glycosides, the addition of thiyl radicals was followed by elimination of the thiyl aglycone resulting in 3-S-substituted glycals.

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