Xu, Bin
Troian-Gautier, Ludovic
[UCL]
Dykstra, Ryan
Martin, Robert T.
Gutierrez, Osvaldo
Tambar, Uttam K.
Endergonic isomerizations are thermodynamically unfavored processes that are difficult to realize under thermal conditions. We report a photocatalytic and diastereoselective isomerization of acyclic cinnamyl chlorides to strained cyclopropanes. Quantum mechanical calculations (uM06-2X and DLPNO), including TD-DFT calculations, and experimental studies provide evidence for the energy transfer from an iridium photocatalyst to the allylic chloride substrate followed by C–Cl homolytic cleavage. Subsequent Cl• radical migration forms a localized triplet 1,3-diradical intermediate that, after intersystem crossing, undergoes ring-closing to form the desired product. The mild reaction conditions are compatible with a broad range of functional groups to generate chlorocyclopropanes in high yields and diastereoselectivities. A more efficient process is developed by addition of a catalytic amount of a nickel complex, and we propose a novel role for this cocatalyst to recycle an allyl chloride byproduct generated in the course of the reaction. The reaction is also shown to be stereoconvergent, as an E/Z mixture of cinnamyl chlorides furnish the anti-chlorocyclopropane product in high diastereoselectivity. We anticipate that the use of a visible light activated photocatalyst to transform substrates in combination with a transition metal catalyst to recycle byproducts back into the catalytic cycle will provide unique opportunities for the discovery of new reactivity.
Bibliographic reference |
Xu, Bin ; Troian-Gautier, Ludovic ; Dykstra, Ryan ; Martin, Robert T. ; Gutierrez, Osvaldo ; et. al. Photocatalyzed Diastereoselective Isomerization of Cinnamyl Chlorides to Cyclopropanes. In: Journal of the American Chemical Society, Vol. 142, no.13, p. 6206-6215 (2020) |
Permanent URL |
http://hdl.handle.net/2078.1/255034 |