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Photochemical Generation of Strained Cycloalkynes from Methylenecyclopropanes
Author(s) -
Maurer Daniel P.,
Fan Rui,
Thamattoor Dasan M.
Publication year - 2017
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.201701275
Subject(s) - phenanthrene , chemistry , ring (chemistry) , photochemistry , adduct , photodissociation , singlet state , activation barrier , computational chemistry , density functional theory , organic chemistry , excited state , physics , nuclear physics
The hydrocarbons 1‐cyclopentylidene‐1a,9b‐dihydro‐1 H ‐cyclopropa[ l ]phenanthrene and 1‐cyclobutylidene‐1a,9b‐dihydro‐1 H ‐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 −1 to rearrange into cyclohexyne (with Δ E for ring expansion=−15.1 kcal mol −1 ). By contrast, cyclobutylidenecarbene only needs to surmount a barrier of 1.6 kcal mol −1 to rearrange into cyclopentyne (with Δ E for ring expansion=−6.2 kcal mol −1 ).