Abstract: Broadly applicable and stereoselective formation of glycosidic linkage remains challenging yet of critical importance in giycoscience. By developing an SN2 glycosylation, this work advances a general solution to this challenge via stereoinversion at the anomeric position of glycosyl ester donors. This SN2 process is enabled by a basic directing-group in the leaving-group, which is activated by a cationic gold catalyst or any other electrophilic reagent. Unlike all the reported directing group approaches, this strategy is applicable to any glycosyl donors—a long sought-after yet unmet goal in carbohydrate chemistry; moreover, the basic directing-group upon glycosylation is lost as part of the leaving-group and hence traceless in the glycoside products, therefore avoiding potential complications in downstream transformations. Highly selective construction of glycosidic bonds including challenging 1,2-cis glycosidic bonds is achieved in excellent yields.

Abstract: An outdoor electric cabinet and an air duct structure thereof are provided. The air duct structure is used to guide airflow to an air inlet side of a fan. The air duct structure includes an air inlet port, a flow-guiding cavity and an air distribution assembly. The air inlet port is configured to introduce external airflow into the air duct structure. The flow-guiding cavity is formed between the air inlet port and the air inlet side of the fan. The air distribution assembly is arranged in the flow-guiding cavity to uniformly distribute an air suction force of the air inlet port. The airflow suction force at the air inlet port is distributed more uniformly by the air distribution assembly, which effectively weakens the maximum wind speed on the shortest path.