Synthesis of β-Glucosides with 3-O-Picoloyl-Protected Glycosyl Donors in the Presence of Excess Triflic Acid: A Mechanistic Study
作者： Michael P. Mannino , Alexei V. Demchenko
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摘要: Our previous study showed that picoloylated donors are capable of providing excellent facial stereoselectivity through the H-bond-mediated aglycone delivery (HAD) pathway. Presented herein is a detailed mechanistic stereoselective glycosylation with 3-O-picoloylated glucosyl donors. While reactions glycosyl equipped 3-O-benzoyl group typically non-stereoselective because these proceed via oxacarbenium intermediate, enhanced, but somewhat relaxed, β-stereoselectivity by HAD In an attempt to refine this reaction, we noticed glycosylations highly β-stereoselective in presence NIS and stoichiometric TfOH. The pathway unlikely picoloyl nitrogen protonated under reaction conditions. protonation were studied low-temperature NMR, intermediacy triflate has been observed. This article dedicated broadening scope application variety substrates targets.
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