Site-Selective and Stereoselective C–H Alkylations of Carbohydrates via Combined Diarylborinic Acid and Photoredox Catalysis

Diphenylborinic acid serves as a
cocatalyst for site- and stereoselective
C–H alkylation reactions of carbohydrates under photoredox
conditions using quinuclidine as the hydrogen atom transfer mediator.
Products arising from selective abstraction of the equatorial hydrogens
of cis-1,2-diol moieties, followed by C–C
bond formation with net retention of configuration, are obtained.
Computational modeling supports a mechanism involving formation of
a tetracoordinate borinic ester, which accelerates hydrogen atom transfer
with the quinuclidine-derived radical cation through polarity-matching
and/or ion-pairing effects.