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Imlirenla Pongener Dionissia A. Pepe Joseph J. Ruddy Eoghan M. McGarrigle 《Chemical science》2021,12(29):10070
Stereoselective β-mannosylation is one of the most challenging problems in the synthesis of oligosaccharides. Herein, a highly selective synthesis of β-mannosides and β-rhamnosides from glycosyl hemi-acetals is reported, following a one-pot chlorination, iodination, glycosylation sequence employing cheap oxalyl chloride, phosphine oxide and LiI. The present protocol works excellently with a wide range of glycosyl acceptors and with armed glycosyl donors. The method doesn''t require conformationally restricted donors or directing groups; it is proposed that the high β-selectivities observed are achieved via an SN2-type reaction of α-glycosyl iodide promoted by lithium iodide.Breaking from the current paradigm, a highly selective synthesis of hard-to-make β-mannosides and β-rhamnosides from simple glycosyl hemi-acetals has been achieved without using conformational restrictions. 相似文献
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