Journal of Organic Chemistry
Journal of Organic Chemistry
5 years ago

Sequential Functionalizations of Carbohydrates Enabled by Boronic Esters as Switchable Protective/Activating Groups

Sequential Functionalizations of Carbohydrates Enabled by Boronic Esters as Switchable Protective/Activating Groups
Mark S. Taylor, Jessica B. Lee, Ross S. Mancini
Processes for site-selective, sequential functionalizations of carbohydrate derivatives are described. In these processes, a tricoordinate boronic ester initially serves as a protective group for a sugar-derived 1,2- or 1,3-diol motif, permitting functionalization of free OH groups. In a second step, addition of a Lewis base generates a tetracoordinate adduct, which serves as an activating group, enabling functionalization of one of the boron-bound oxygen atoms by a second electrophile. By combining an initial acylation, alkylation, or glycosylation step with an amine-mediated glycosylation of the boronic ester, a variety of selectively protected di- and trisaccharide derivatives can be accessed in an operationally simple fashion without purification of intermediates. This Lewis base-triggered switching of behavior from “latent” to “active” nucleophile is a unique feature of boronic esters relative to other protective groups for diol moieties in carbohydrate chemistry.

Publisher URL: http://dx.doi.org/10.1021/acs.joc.7b01605

DOI: 10.1021/acs.joc.7b01605

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