Selective ring expansion and C-H functionalization of azulenes.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 38040685.
- Also identified by DOI 10.1038/s41467-023-43200-7 and PMC identifier 10692195.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
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)<sub>2</sub> (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.