Results and Discussion (Cyclopropane Synthesis)
令和8年1月8日|p.15
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■ RESULTS AND DISCUSSION
Our investigation began with the optimization of reaction conditions using phenylacetylene (1a), ethyl diazoacetate (2a), and cinnamyl chloride (3a) as model substrates. After screening various copper catalysts, ligands, and solvents, we identified CuI/PPh₃ as the optimal catalytic system, which afforded the desired cyclopropane product 4a in 85% yield (Table 1, entry 1).
| Entry | Catalyst | Ligand | Solvent | Yield (%)a |
| 1 | CuI | PPh₃ | DCE | 85 |
| 2 | CuBr | PPh₃ | DCE | 78 |
| 3 | CuCl | PPh₃ | DCE | 72 |
| 4 | CuI | dppm | DCE | 65 |
| 5 | CuI | PPh₃ | Toluene | 70 |
| 6 | CuI | PPh | THF | 55 |
| 7 | None | PPh₃ | DCE | Trace |
With the optimized conditions in hand, we next examined the scope of this transformation with respect to the alkyne component. As shown in Table 2, a variety of terminal alkynes bearing different substituents on the aromatic ring were well-tolerated, affording the corresponding cyclopropane products in good to excellent yields (4b–4g). Electron-donating groups generally led to higher yields compared to electron-withdrawing groups.
Aliphatic alkynes also participated effectively in this reaction, although slightly lower yields were observed (4h–4j). Notably, internal alkynes failed to react under the standard conditions, highlighting the requirement for a terminal alkyne in this transformation.
We then investigated the influence of the diazo compound on the reaction outcome. Various α-diazo esters and ketones were tested, and all provided the desired cyclopropane products in satisfactory yields (4k–4o). The nature of the ester group had minimal impact on the reaction efficiency, allowing for the introduction of diverse functionalities into the final product.
Finally, we evaluated the compatibility of different allylic halides in this reaction. Both primary and secondary allylic chlorides and bromides were suitable substrates, delivering the corresponding cyclopropanes in moderate to good yields (4p–4t). Interestingly, allylic fluorides did not react under the standard conditions, likely due to their low reactivity toward nucleophilic substitution.