3-Silylated furfurals, readily prepared in three steps from biomass-derived furfural and 5-methylfurfural, are converted into 3-silylated 2-furyl carbinols upon condensation with organomagnesium or organolithium reagents. The hydroxy unit of the carbinol adducts can be exploited to promote C3(sp2)–Si bond functionalization through intramolecular activation. Two approaches were contemplated for this purpose. Activation by alkoxides of the C3–SiEt3 or C3–SiMe2t-Bu bonds was ineffective. Conversely, treatment of the C3-benzyldimethylsilyl-appended derivatives with tetrabutylammonium fluoride led to cyclic siloxanes, which revealed to be competent donors for copper-catalyzed cross-coupling reactions, such as arylation reactions catalyzed by Pd2(dba)3/CuI, as well as allylation and methylation reactions catalyzed by CuI⋅PPh3. C3-Benzyldimethylsilyl-appended furfurals are thus introduced as versatile platforms, providing a modular access to 3-substituted 2-furyl carbinols from renewable feedstock.
3
硅烷化
糠醛很容易通过三个步骤从
生物质衍生的
糠醛和 5-甲基
糠醛中制备出来,在与
有机镁或
有机锂试剂缩合后转化为 3
硅烷化 2-
糠醇。通过分子内活化作用,可利用这些烷醇加合物的羟基单元促进 C3(sp2)-Si 键官能化。为此考虑了两种方法。C3-SiEt3 或 C3-SiMe2t-Bu 键的烷氧基活化效果不佳。相反,用
四丁基氟化铵处理 C3-苄基二甲基
硅烷添加衍
生物会产生环状
硅氧烷,这些环状
硅氧烷是
铜催化的交叉偶联反应(如 Pd2(dba)3/CuI 催化的芳基化反应)以及 CuI⋅PPh3 催化的烯丙基化和甲基化反应的有效供体。因此,C3-苄基二甲基
硅基添加的
呋喃类化合物是一种多功能平台,为从可再生原料中获得 3-取代的 2-
呋喃基
甲醇提供了模块化途径。