Photosensitized Diradical Rearrangement of Alkenyl Oxime Ethers towards Amino-Featured Oxiranes: Reaction, Mechanism, and Structural Prediction

Abstract

A novel diradical rearrangement protocol of alkenyl ketoxime ethers for the synthesis of amino-featured epoxides under energy transfer photocatalysis is developed. Mechanism studies reveal that this reaction is triggered by a specific diradical afforded by the second triplet excitation state T2 resulting from the π-π* excited transition of the alkene moiety of the substrate, followed by a cascade radical remote amino group translocation and intramolecular singlet O-, C-diradical cross-coupling after intersystem crossing. As a result, a series of amino-featured epoxides that were previously inaccessible, are easily and efficiently synthesized. Notably, this approach features mild conditions, good functional group tolerance, excellent stereoselectivity, and is well compatible with complex scaffolds such as steroids, amino acids and alkaloids. Detailed DFT calculations provide in-depth insights into the understanding of reaction as well as the structural standards and predictions. This strategy not only enriches the reaction mode of the oxime ethers, but also provides a facile synthetic method towards the valuable epoxides.