Transition metal-catalyzed C–H activation and annulation involving vinyl acetate remains a significant challenge, and the mechanistic process following vinyl insertion is ambiguous. Herein, we report the Rh(III)-catalyzed two-fold C–H activation and [4 + 2] annulation of N-aryl cyclic hydrazides with vinyl acetate to build 3,4-unsubstituted, 1,2-phthaloyl-protected cinnolines. Using prop-1-en-2-yl acetate as the C2 source, the tandem [4 + 2] annulation and methyl C(sp³)–H oxidation occurred to give 3-formyl cinnolines. Furthermore, The unusual K₂CO₃/O₂-mediated C4(sp²)–H oxidation/deprotection of the resulting 1,2-phthaloyl cinnolines enables an access to cinnolin-4(1H)-ones for the first time. The combination of control experiments, ESI-MS, and DFT calculations indicates there are two possible pathways after vinyl insertion: a thermodynamically preferred syn-OAc/H β-H elimination and a kinetically favored syn-Rh/H β-H elimination.

中文翻译：

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使用醋酸乙烯酯获得肉桂碱和肉桂素-4（1H）-酮的铑催化 C-H 活化和环化的机理见解


涉及醋酸乙烯基的过渡金属催化的 C-H 活化和环化仍然是一个重大挑战，乙烯基插入后的机理过程尚不清楚。在此，我们报道了 Rh（III） 催化的两重 C-H 活化和 N-芳基环酰肼与醋酸乙烯酯的环状酰肼的 [4 + 2] 环状，以构建 3,4-未取代的 1,2-酞酰基保护的肉桂啉。使用丙-1-烯-2-乙酸酯作为 C2 源，串联 [4 + 2] 环化和甲基 C（sp³）-H 氧化发生，得到 3-甲酰基辛诺林。此外，不寻常的 K₂CO₃/O₂ 介导的 C4（sp²）-H 氧化/脱保护所得的 1,2-酞酰桂醇首次使肉桂素-4（1H）-酮成为可能。对照实验、ESI-MS 和 DFT 计算的组合表明，乙烯基插入后有两种可能的途径：热力学上优选的 syn-OAc/H β-H 消除和动力学上优β-H 消除。