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Updated: Jun 7, 2025

Characterizing Lewis Pairs Using Titration Coupled with In Situ Infrared Spectroscopy
Published on: February 20, 2020
Mechanistic insight into benzylidene-directed glycosylation reactions using cryogenic infrared spectroscopy
Chun-Wei Chang1,2, Kim Greis1,2,3, Gurpur Rakesh D Prabhu1,2
1Freie Universität Berlin, Institute of Chemistry and Biochemistry, Berlin, Germany.
Abstract:
The stereoselective formation of 1,2-cis glycosidic linkages is challenging. The currently most widely used strategy for their installation uses 4,6-O-benzylidene-protected building blocks. The stereoselectivity of this reaction is thought to be driven by a covalent intermediate, which reacts via an SN2 mechanism. However, the role of cationic SN1-type intermediates in this reaction is unclear. Here we elucidate the structure of glycosyl cations carrying 4,6-O-benzylidene groups using cryogenic infrared ion spectroscopy and computational methods. The data reveal that the intermediates form anhydro cations, which correlates well with the stereoselective outcome of SN1-type glycosylations. The study highlights how cryogenic infrared spectroscopy can elucidate the role of intermediates in sugar chemistry and how these structural data can be linked to reactions in solution.
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