Transition states of strain-promoted metal-free click chemistry: 1,3-dipolar cycloadditions of phenyl azide and cyclooctynes
Transition states of strain-promoted metal-free click chemistry: 1,3-dipolar cycloadditions of phenyl azide and cyclooctynes
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DOI：
10.1021/ol8003657
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发表时间：
2008-04-17
期刊：
影响因子：
5.2
通讯作者：
Houk, K. N.
中科院分区：
文献类型：
--
作者：
Ess, Daniel H.;Jones, Gavin O.;Houk, K. N.
采用密度泛函理论（B3 LYP）对叠氮苯与乙炔、环辛炔和二氟环辛炔的Huisgen 1，3-偶极环加成反应的过渡态进行了研究。环辛炔“应变促进”环加成反应的低活化能（Δ E-双刃= 8.0）与无应变乙炔环加成相比（Δ E-双刃剑= 16.2）是由于减少了扭曲能量（Delta E-d（double dagger））环辛炔（Δ Δ E-d（双匕首）= 4.6）和苯基叠氮化物（Δ Δ E-d（双匕首）= 4.5）以实现该环加成过渡态。环辛炔上的电负性氟取代基通过增加相互作用能进一步增加环加成的速率。
Density functional theory (B3LYP) calculations on the transition states for the Huisgen 1,3-dipolar cycloadditions of phenyl azide with acetylene, cyclooctyne, and difluorocyclooctyne are reported. The low activation energy of the cyclooctyne "strain-promoted" cycloaddition (Delta E-double dagger = 8.0) compared to the strain-free acetylene cycloaddition (Delta E-double dagger = 16.2) is due to decreased distortion energy (Delta E-d(double dagger)) of cyclooctyne (Delta Delta E-d(double dagger)= 4.6) and phenyl azide (Delta Delta E-d(double dagger) = 4.5) to achieve that cycloaddition transition state. Electronegative fluorine substituents on cyclooctyne further increase the rate of cycloaddition by increasing interaction energies.