AbstractTransition‐metal‐catalyzed oxidative C−H amination reactions are among the most attractive topics in organic synthesis to construct nitrogen‐containing motifs. The challenge is that most of these reactions employed stoichiometric oxidants to achieve satisfied catalytic efficiencies. Herein, we report a Pd(II)/LA‐catalyzed (LA: Lewis acid) oxidative C−H amination reaction of 2‐acetaminobiphenyls to construct carbazoles by using dioxygen balloon as the sole oxidant source, and the presence of LA sharply improved the catalytic efficiency of Pd(OAc)2. Remarkably, in certain cases, the deacetylation of the annulation product happened under standard conditions to afford free carbazoles as the final product. The H/D exchange studies confirmed the reversibility of C−H activation and also disclosed multiple C−H activation sites by using −NAc and −NTs as the directing groups. In addition, the palladacycle compound was identified through 1H NMR characterizations and proved to be the intermediate prior to the carbazole formation.
摘要 过渡金属催化的氧化 C-H amination 反应是有机合成中构建含氮基团最有吸引力的课题之一。面临的挑战是,这些反应中的大多数都需要使用一定比例的氧化剂才能达到满意的催化效率。在此,我们报告了一种 Pd(II)/LA 催化(LA:路易斯酸)的 2-acetaminobiphenyls 氧化 C-H amination 反应,该反应以二氧气球作为唯一的氧化剂源来构建咔唑,LA 的存在极大地提高了 Pd(OAc)2 的催化效率。值得注意的是,在某些情况下,环化产物会在标准条件下发生脱乙酰化反应,从而得到游离的咔唑作为最终产物。H/D交换研究证实了C-H活化的可逆性,并通过使用-NAc和-NTs作为引导基团,发现了多个C-H活化位点。此外,通过 1H NMR 表征确定了帕拉代环化合物,并证明它是咔唑形成之前的中间体。