A highly efficient synthesis of oxygenated 5,5-spiroketals was performed towards the synthesis of the cephalosporolides. Gold(I) chloride in methanol induced the cycloisomerization of a protected alkyne triol with concomitant deprotection to give a strategically hydroxylated 5,5-spiroketal, despite the potential for regiochemical complications and elimination to furan. Other late transition metal Lewis acids were less effective. The use of methanol as solvent helped suppress the formation of the undesired furan by-product. This study provides yet another example of the advantages of gold catalysis in the activation of alkyne π-systems.
一种高效合成含氧5,5-螺环
缩酮的方法被用于
头孢菌素类化合物的合成。在
甲醇中,
氯化金(I)诱导了一种受保护的炔三醇的环异构化反应,并伴随去保护作用,形成了一种具有战略性羟基化的5,5-螺环
缩酮,尽管可能存在区域
化学复杂性和生成
呋喃的可能性。其他晚期过渡
金属Lewis酸的效果较差。
甲醇作为溶剂有助于抑制不良
呋喃副产物的生成。这项研究提供了另一个
金催化在激活炔π-体系中的优势的例子。