Highly Selective β‑Mannosylations and β‑Rhamnosylations Catalyzed by Bis-thiourea

We
report highly β-selective bis-thioureas-catalyzed 1,2-cis-O-pyranosylations employing easily accessible acetonide-protected
donors. A wide variety of alcohol nucleophiles, including complex
natural products, glycosides, and amino acids were β-mannosylated
and β-rhamnosylated successfully using an operationally simple
protocol under mild and neutral conditions. Less nucleophilic acceptors
such as phenols were also glycosylated efficiently in excellent yields
and with high β-selectivities.

本研究报道了一种双硫脲（bis-thioureas）催化的高β选择性1,2-顺式-O-吡喃糖基化反应（1,2-cis-O-pyranosylation），该反应以易得的丙酮叉保护糖基供体为原料。该方法可兼容多种醇亲核试剂，包括复杂天然产物、糖苷及氨基酸，可在温和中性且操作简便的反应条件下，高效完成β-甘露糖基化与β-鼠李糖基化修饰。对于亲核性较弱的受体（如苯酚类化合物），该催化体系同样可实现高效糖基化，获得优异产率与高β选择性。