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 was developed. Mechanism studies revealed that this reaction was 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, were synthesized easily and efficiently. Notably, this approach featured mild conditions, good functional group tolerance, excellent stereoselectivity and was very compatible with complex scaffolds (steroids, amino acids, alkaloids). Detailed density functional theory (DFT) calculations provided in-depth insights into the understanding of the reaction as well as structural standards and predictions. This strategy not only enriches the reaction mode of the oxime ethers but also provides a facile synthetic method towards valuable epoxides.