The transition metal-catalyzed reductive cyclization of o-nitrostyrene in the presence of carbon monoxide (CO) has been developed to be a general synthetic route to an indole skeleton, wherein CO was used as a reductant to deoxidize nitroarene into nitrosoarene and/or nitrene with CO₂ release, but the selective insertion of CO into the heterocyclic product with higher atom economy has not yet been realized. Herein, the Pd-catalyzed reduction of o-nitrostyrene by CO and its regioselective insertion were efficiently achieved to produce synthetically useful five- and six-membered benzo-fused lactams. Detailed investigations revealed that the chemoselectivity to indole or lactam was sensitive to the nature of the counteranions of Pd²⁺ precursors, whereas ligands significantly decided the carbonylative regioselectivity by different reaction pathways. Using PdCl₂/PPh₃/B(OH)₃ (condition A), an olefin hydrocarboxylation was primarily initiated followed by partial reduction of the NO₂ moiety and cyclization reaction to give N-hydroxyl indolin-2-one, which was further catalytically reduced by CO to afford the indolin-2-one as the final product with up to 95% yield. When the reaction was conducted under the Pd(TFA)₂/BINAP/TsOH·H₂O system (condition B), complete deoxygenation and carbonylation of the NO₂ group occurred initially to yield the corresponding isocyanate followed by internal hydrocyclization to generate 3,4-dihydroquinolin-2-one with up to 98% yield. Importantly, the methodology could be efficiently applied in the synthesis of marketed drug Aripiprazole.

中文翻译：

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除还原外，还可以将CO插入邻硝基苯乙烯中，以选择性地获得吲哚-2-酮和二氢喹啉-2-酮衍生物

一氧化碳（CO）存在下过渡金属催化的邻硝基苯乙烯的还原环化反应已发展成为吲哚骨架的一般合成路线，其中CO被用作还原剂，将硝基芳烃还原为亚硝基芳烃和/或硝基苯。 CO ₂释放出来，但尚未实现将CO选择性插入具有更高原子经济性的杂环产物中。在本文中，有效地实现了Pd通过CO催化的邻硝基苯乙烯的还原及其区域选择性插入，以生产合成上有用的五元和六元苯并稠合的内酰胺。详细研究表明，对吲哚或内酰胺的化学选择性对Pd ²⁺的抗衡阴离子的性质敏感。前体，而配体则通过不同的反应途径显着决定了羰基的区域选择性。使用PdCl ₂ / PPh ₃ / B（OH）₃（条件A），首先引发烯烃加氢羧化，然后部分还原NO ₂部分并环化反应，得到N-羟基吲哚啉-2-酮，将其进一步催化用CO还原得到最终产物吲哚-2-酮，产率高达95％。当反应在Pd（TFA）₂ / BINAP / TsOH·H ₂ O系统下进行（条件B）时，NO ₂完全脱氧并羰基化最初发生的有机基团产生相应的异氰酸酯，然后进行内部氢环化以产生高达98％的产率的3,4-二氢喹啉-2-酮。重要的是，该方法可以有效地应用于市售药物阿立哌唑的合成。