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Communication | Special issue | Vol 101, No. 2, 2020, pp.423-428
Published online, 13th August, 2019
DOI: 10.3987/COM-19-S(F)39
Synthesis of Dibenzoxazonines by Domino [2+2] Cycloaddition—4π Electrocyclic Ring Opening Reaction of Cyclic Imines with Ynamides

Kiyosei Takasu,* Masaki Tsutsumi, Tomohiro Ito, Hiroshi Takikawa, and Yousuke Yamaoka

*Graduate School of Pharmaceutical Sciences, Kyoto University, 46-29 Yoshida-shimoadachi-machi, Sakyo-ku, Kyoto 606-8501, Japan

Abstract

Dibenzo[b,h][1,4]oxazonines and the thiazonine congener were synthesized from cyclic imines with ynamides by acid-mediated domino (2+2) cycloaddition—4π electrocyclic ring opening reaction. The reaction enables two carbon-enlargement of the cyclic imine substrates. The X-Ray crystallography made clear that the oxazonine skeleton has a unique bent-conformation.