We here report glycosyl sulfoxides appended with an aryl iodide moiety as readily available,air and moisture stable precursors to glycosyl radicals.These glycosyl sulfoxides could be converted to glycosyl radicals by way of arapid and efficient intramolecular radical substitution event. The use of this type of precursors enabled the synthesis of various complex Clinked glycoconjugates under mild conditions.T his reaction could be performed in aqueous media and is amenable to the synthesis of glycopeptidomimetics and carbohydrate-DNA conjugates. Scheme 1. a) Glycosyl radicals as valuable intermediates in C-glycoside synthesis. b) Our strategy to generate glycosyl radicals.
Described here is
an enantioselective approach of making chiral,
β-substituted homoallylic organoboronic esters. In the presence
of LiO
t
Bu and a catalytic amount of silver
salt, commercial bis[(pinacolato)boryl]methane participated in the
iridium-catalyzed asymmetric allylation reactions, delivered a “CH2B(pin)” group, and yielded the title compounds from
allylic carbonates. The synthetic utility of the prepared chiral organoboronates
was demonstrated by their conversion to other important classes of
compounds.
Direct and site-selective O-arylation of carbohydrates has been a challenge in synthesis. Herein we report a method based on copper-catalyzed O-arylation to address this challenge. Proper choice of the ancillary ligand on copper is critical for the efficiency and site selectivity of this transformation. This method features mild conditions, tolerates various functional groups, and demonstrates broad substrate scope.
Here we report a general approach to make unnatural amino acids from readily available cysteine derivatives. This method capitalizes on an intramolecular radical substitution process that generates alkyl radicals through CÀS cleavage. The resulting alkyl radicals partook in diverse CÀC bond forming events. These reactions proceed under mild, photocatalytic conditions at room temperature, and can be performed open to air. The utility of these transformations is further demonstrated in the straightforward synthesis of various unnatural amino acids and peptides that are difficult to access previously.
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