Selective Formation of β-<i>O</i>-Aryl Glycosides in the Absence of the C(2)-Ester Neighboring Group
作者:Matthew J. McKay、Benjamin D. Naab、Gregory J. Mercer、Hien M. Nguyen
DOI:10.1021/jo9002807
日期:2009.7.3
electron-withdrawing, and hindered phenols. The reaction is likely to proceed through a seven-membered ring intermediate, wherein the palladium catalyst coordinates to both C(1)-trichloroacetimidate nitrogen and C(2)-oxygen of the donor, blocking the α-face. As a result, the phenol nucleophile preferentially approaches to the top face of the activated donor, leading to formation of the β-O-aryl glycoside.
立体选择性合成β- O-芳基糖苷的通用方法的开发,该方法利用阳离子钯(II)催化剂的性质代替C(2)-酯导向基团的性质来控制β-选择性描述。这种β-糖基化反应具有很高的非对映选择性,并且需要2–3 mol%的Pd(CH 3 CN)4(BF 4)2在室温下活化糖基三氯乙酰亚氨酸酯供体。目前的方法已应用于具有在C(2)位置掺入非定向基团的d-葡萄糖,d-半乳糖和d-木糖供体,以提供O芳基糖苷具有良好至极好的β选择性。另外,它的应用广泛用于给电子,吸电子和受阻酚。该反应可能通过七元环中间体进行,其中钯催化剂与给体的C(1)-三氯乙亚氨酸氮和C(2)-氧均配位,从而阻断了α-面。结果,苯酚亲核试剂优先接近活化的供体的顶面,导致β- O-芳基糖苷的形成。