Selective ring expansion and C−H functionalization of azulenes

Sangjune Park, Cheol-Eui Kim, Jinhoon Jeong, Ho Ryu, Chanyoung Maeng, Dongwook Kim, Mu-Hyun Baik () and Phil Ho Lee ()
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Sangjune Park: Kangwon National University
Cheol-Eui Kim: Kangwon National University
Jinhoon Jeong: Korea Advanced Institute of Science and Technology (KAIST)
Ho Ryu: Korea Advanced Institute of Science and Technology (KAIST)
Chanyoung Maeng: Kangwon National University
Dongwook Kim: Korea Advanced Institute of Science and Technology (KAIST)
Mu-Hyun Baik: Korea Advanced Institute of Science and Technology (KAIST)
Phil Ho Lee: Kangwon National University

Nature Communications, 2023, vol. 14, issue 1, 1-9

Abstract: Abstract We report a transition metal-catalyzed ring expansion of azulene that can be contrasted with C–H functionalization. This study represents the first example of the successful ring expansion of azulene using Cu(hfacac)2 (hfacac: hexafluoroacetylacetonate) with a diazo reagent. This result is notable for extending the Buchner reaction, previously limited to benzenoid aromatics, to nonbenzenoid compounds. The chemoselectivity of the reaction can be directed towards C–H functionalization by substituting the Cu catalyst with AgOTf. This approach does not require the addition of phosphine, NHC, or related ligands, and prefunctionalization of azulenes is unnecessary. Furthermore, the method exhibits excellent functional group tolerance, allowing for the synthesis of a wide range of 6,7-bicyclic compounds and C–H functionalized azulenes. We also present a theoretical study that explains the experimental observations, explaining why copper afford the ring expansion product while silver forms the C–H alkylation product.

Date: 2023
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DOI: 10.1038/s41467-023-43200-7

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