Reversing the Stereoselectivity of a Palladium-Catalyzed O-Glycosylation through an Inner-Sphere or Outer-Sphere Pathway
作者:Shaohua Xiang、Kim Le Mai Hoang、Jingxi He、Yu Jia Tan、Xue-Wei Liu
DOI:10.1002/anie.201408739
日期:2014.11.3
An efficient and concise method for the construction of various O‐glycosidic bonds by a palladium‐catalyzed reaction with a 3‐O‐picoloyl glucal has been developed. The stereochemistry of the anomeric center derives from either an inner‐sphere or outer‐sphere pathway. Harder nucleophiles, such as aliphatic alcohols and sodium phenoxides give β‐products, and α products result from using softer nucleophiles
A stereodivergent synthesis of β- and α-O-glycosides using 3-O-quinaldoyl glucals was developed by palladium catalysis at 60 and 110 °C respectively. Various alcohols, monosaccharides, and aminoacid were glycosylated to form β- and α- products in good yields with high stereoselectivity. Mechanistic studies indicated no classic Pd–N (quinoline) coordination, but π–π stacking interactions promoted the