1,2‐Oxazine N‐Oxides as Catalyst Resting States in Michael Additions of Aldehydes to Nitro Olefins Organocatalyzed by α,α‐Diphenylprolinol Trimethylsilyl Ether |
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Authors: | Dieter Seebach Marc‐Olivier Ebert W Bernd Schweizer Albert K Beck |
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Institution: | 1. Laboratorium für Organische Chemie, Departement für Chemie und Angewandte Biowissenschaften, ETH‐Zürich, H?nggerberg HCI, Wolfgang‐Pauli‐Strasse 10, CH‐8093 Zürich, (phone: +41‐44‐632‐2990;2. fax: +41‐44‐632‐1144) |
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Abstract: | By combining enamines, derived from aldehydes and diphenylprolinol trimethylsilyl ether (the Hayashi catalyst), with nitroethenes ((D6)benzene, 4‐Å molecular sieves, room temperature) intermediates of the corresponding catalytic Michael‐addition cycles were formed and characterized (IR, NMR, X‐ray analysis; Schemes 3–6 and Fig. 1–3). Besides cyclobutanes 2 , 1,2‐oxazine N‐oxide derivatives 3 – 6 and 8 have been identified for the first time, some of which are very stable compounds. It may not be a lack of reactivity (between the intermediate enamines and nitro olefins) that leads to failure of the catalytic reactions (Schemes 3–5) but the high stability of catalyst resting states. The central role zwitterions play in these processes is discussed (Schemes 1 and 2). |
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Keywords: | 1 2‐Oxazine N‐oxides Enamines Nitro olefins Organocatalysis Hayashi catalyst Catalysis Michael addition X‐Ray crystallography |
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