Journal
ACS CATALYSIS
Volume 10, Issue 11, Pages 5990-6001Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acscatal.0c01470
Keywords
copper catalysis; visible light; C(sp(3))-O bond; cross-coupling; stereoselective
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Funding
- NIH [U01 GM120293]
- NSF [CHE1856437]
- NSF CAREER [CHE1943737]
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Copper-catalyzed cross-coupling reactions have become one of the most powerful methods for generating carbonheteroatom bonds, an important framework of many organic molecules. However, copper-catalyzed C(sp(3))-O cross-coupling of alkyl halides with alkyl alcohols remains elusive because of the sluggish nature of oxidative addition to copper. To address this challenge, we have developed a catalytic copper system, which overcomes the copper oxidative addition barrier with the aid of visible light and effectively facilitates the cross-couplings of glycosyl bromides with aliphatic alcohols to afford C(sp(3))-O bonds with high levels of diastereoselectivity. Importantly, this catalytic system leads to a mild and efficient method for stereoselective construction of alpha-1,2-cis glycosides, which are of paramount importance, but challenging. In general, stereochemical outcomes in alpha-1,2-cis glycosidic C-O bond-forming processes are unpredictable and dependent on the steric and electronic nature of protecting groups bound to carbohydrate coupling partners. Currently, the most reliable approaches rely on the use of a chiral auxiliary or hydrogen-bond directing group at the C2- and C4-position of carbohydrate electrophiles to control alpha-1,2-cis selectivity. In our approach, earthabundant copper not only acts as a photocatalyst and a bond-forming catalyst, but also enforces the stereocontrolled formation of anomeric C-O bonds. This cross-coupling protocol enables highly diastereoselective access to a wide variety of alpha-1,2-cis-glycosides and biologically relevant alpha-glycan oligosaccharides. Our work provides a foundation for developing new methods for the stereoselective construction of natural and unnatural anomeric carbon(sp(3))-heteroatom bonds.
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