A General Strategy for the Synthesis of Functionalised Benzo[b]furans via Copper-Catalysed Domino C-H Activation/Carbocyclisation
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A General Strategy for the Synthesis of Functionalised Benzo[b]furans via Copper-Catalysed Domino C-H Activation/Carbocyclisation of Alkynes with ortho-Substituted Aryl Iodides
Jian Zhang,† Huanfeng Jiang,* and Wanqing Wu*
Key Laboratory of Functional Molecular Engineering of Guangdong Province, School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou 510640, P. R. China
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ABSTRACT:
A general strategy for the synthesis of functionalized benzo[b]furans has been developed through copper-catalyzed domino C-H activation/carbocyclization of alkynes with ortho-substituted aryl iodides. This protocol features a broad substrate scope and good functional group tolerance. The reaction proceeds smoothly under mild conditions to afford various substituted benzo[b]furans in moderate to excellent yields.
Scheme 1. Previous Work on the Synthesis of Benzo[b]furans
Scheme 2. Our Strategy for the Synthesis of Benzo[b]furans
Table 1. Optimization of Reaction Conditions
| Entry | Cu Source | Ligand | Additive | Solvent | Yield (%) |
| 1 | CuI | PPh3 | K2CO3 | DMSO | 85 |
| 2 | CuBr | PPh3 | K2CO3 | DMSO | 78 |
| 3 | CuCl | PPh3 | K2CO3 | DMSO | 72 |
| 4 | CuI | dppp | K2CO3 | DMSO | 65 |
| 5 | CuI | PPh3 | Na2CO3 | DMSO | 80 |
| 6 | CuI | PPh3 | Cs2CO3 | DMSO | 88 |
| 7 | CuI | PPh3 | K2CO3 | DMF | 75 |
| 8 | CuI | PPh3 | K2CO3 | Toluene | Trace |
| 9 | CuI | PPh3 | K2CO3 | DCE | 60 |
| 10 | CuI | PPh3 | K2CO3 | DMSO | 92[a] |
[a] Reaction conditions: 1a (0.2 mmol), 2a (0.4 mmol), Cu source (10 mol%), ligand (20 mol%), additive (2.0 equiv), solvent (2.0 mL), 100 °C, 12 h. Isolated yield.
With the optimized conditions in hand, we next explored the scope of this transformation with respect to the alkyne component.
As shown in Scheme 3, a variety of terminal alkynes bearing different substituents were well tolerated.
Scheme 3. Scope of Terminal Alkynes
Subsequently, we investigated the scope of aryl iodides.
Scheme 4. Scope of Aryl Iodides