Catalytic Regioselective Benzoylation of 1,2-trans-Diols in Carbohydrates with Benzoyl Cyanide: The Axial Oxy Group Effect and the Action of Achiral and Chiral Amine Catalysts
Catalytic Regioselective Benzoylation of 1,2-trans-Diols in Carbohydrates with Benzoyl Cyanide: The Axial Oxy Group Effect and the Action of Achiral and Chiral Amine Catalysts
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DOI：
10.1021/acscatal.0c02112
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发表时间：
2020-10-02
期刊：
影响因子：
12.9
通讯作者：
Peng, Peng
中科院分区：
文献类型：
--
作者：
Li, Tianlu;Li, Tong;Peng, Peng
在催化条件下用酰基对多官能碳水化合物进行区域选择性保护是通过糖苷化进行有效结构修饰和扩链的先决条件。一个普遍的，也很强的“轴向氧基效应”，现在观察到与苯甲酰氰作为酰化剂和4-二甲氨基吡啶作为催化剂，允许优选的O-酰化赤道羟基旁边的轴向氧基。这种作用通过具有邻位反式二醇部分的2，3-O-未保护的β-D-半乳糖和α-D-吡喃葡萄糖苷和3，4-O-未保护的吡喃甘露糖苷得到证实。此外，邻位反式二醇与轴向氧基旁边的每个羟基，具有与手性叔胺催化剂，可以区分。在这方面特别令人感兴趣的是双官能（S，S）-N-（N，N-二烷基氨基环己基）-硫脲作为催化剂的作用;它们有利于2，3-O-未保护的α-吡喃半乳糖苷的2-O-苯甲酰化，这也得到了密度泛函理论计算的支持。这种导向作用可以用奎尼丁作为催化剂或在异头位置用大体积取代基逆转。
Regioselective protection of the polyfunctional carbohydrates with acyl groups under catalytic conditions is a prerequisite for efficient structural modification and chain extension via glycosidation. A general and also strong "axial oxy group effect" was now observed with benzoyl cyanide as the acylating agent and 4-dimethylaminopyridine as the catalyst, permitting the preferred O-acylation of equatorial hydroxy groups next to axial oxy groups. This effect is substantiated with 2,3-O-unprotected beta-D-galacto- and alpha-D-glucopyranosides and 3,4-O-unprotected mannopyranosides possessing vicinal trans-diol moieties. Moreover, vicinal trans-diols with axial oxy groups next to each hydroxy group, possessing expectedly comparable reactivity, could be differentiated with chiral tertiary amine catalysts. Particularly interesting in this regard is the action of bifunctional (S,S)-N-(N,N-dialkylaminocyclohexyl)-thioureas as catalysts; they favor 2-O-benzoylation of 2,3-O-unprotected alpha-galactopyranosides, as is also supported by density functional theory calculations. This directing effect can be reversed with quinidine as the catalyst or with bulky substituents at the anomeric position.