An efficient and redox-neutral synthesis of 2H-chromene-3-carboxylic acids from N-phenoxyacetamides and methyleneoxetanones has been realized via a solvent-controlled and rhodium(III)-catalyzed C–H activation/unusual [3 + 3] annulation sequence. This transformation represents the first example of using an α-methylene-β-lactone unit as the three-carbon source in transition-metal-catalyzed C–H activations through selective alkyl C–O bond cleavage. Synthetic applications and mechanistic details, including further derivatization of 2H-chromene-3-carboxylic acids, the isolation and identification of a five-membered rhodacycle, as well as the theoretical studies for reasoning a plausible Rh(III)–Rh(V)–Rh(III) process, have also been discussed.

中文翻译：

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溶剂控制和铑（III）催化的氧化还原-中性CH活化/ [3 + 3]级联反应合成2 H-铬-3-羧酸

通过溶剂控制和铑（III）催化的C–H活化/不寻常的[3 + 3]环化反应，已经实现了由N-苯氧基乙酰胺和亚甲基氧杂环丁烷高效合成和氧化还原中性的2 H-苯甲基-3-羧酸顺序。这种转变代表了使用α-亚甲基-β-内酯单元作为过渡碳催化的CH活化（通过选择性烷基C-O键断裂）中的三碳源的第一个例子。合成应用和机理细节，包括2 H-苯并-3-羧酸的进一步衍生化，五元罗丹环的分离和鉴定以及合理的Rh（III）-Rh（V）的理论研究-Rh（III）过程，也已经讨论过。