Department of Chemistry, Colby College, 5765 Mayflower Hill, Waterville, ME, 04901, USA.
Angew Chem Int Ed Engl. 2017 Apr 10;56(16):4499-4501. doi: 10.1002/anie.201701275. Epub 2017 Mar 21.
The hydrocarbons 1-cyclopentylidene-1a,9b-dihydro-1H-cyclopropa[l]phenanthrene and 1-cyclobutylidene-1a,9b-dihydro-1H-cyclopropa[l]phenanthrene undergo photolysis in solution at ambient temperature to produce cyclohexyne and cyclopentyne, respectively. These strained cycloalkynes, formed via the putative cycloalkylidenecarbenes, were intercepted as Diels-Alder adducts. Calculations at the CCSD(T)/cc-pVTZ//B3LYP/6-31+G* level of theory show that singlet cyclopentylidenecarbene has to overcome a barrier of 9.1 kcal mol to rearrange into cyclohexyne (with ΔE for ring expansion=-15.1 kcal mol ). By contrast, cyclobutylidenecarbene only needs to surmount a barrier of 1.6 kcal mol to rearrange into cyclopentyne (with ΔE for ring expansion=-6.2 kcal mol ).
在环境温度下，烃 1-环戊基-1a,9b-二氢-1H-环丙[a]菲和 1-环丁基-1a,9b-二氢-1H-环丙[a]菲在溶液中经历光解，分别产生环己炔和环戊炔。这些通过假定的环烷基卡宾形成的应变环炔被作为 Diels-Alder 加合物捕获。在 CCSD(T)/cc-pVTZ//B3LYP/6-31+G*理论水平的计算表明，单线态环戊基卡宾需要克服 9.1 kcal/mol 的能垒才能重排为环己炔（环扩展的ΔE=-15.1 kcal/mol）。相比之下，环丁基卡宾只需克服 1.6 kcal/mol 的能垒即可重排为环戊炔（环扩展的ΔE=-6.2 kcal/mol）。
