A stable N-oxyl radical, 2,2,6,6-tetramethyl-4-oxopiperidine-1-oxyl (I), afforded 1-hydroxy-2,2,6,6-tetramethyl-3-(2,2,6,6-tetramethyl-4-oxopiperidinoxy)-4-oxopiperidine (IX) by hydrogen-abstraction followed by the coupling reaction of the N-oxyl radical I with the C radical III derived from I. The product IX was characterized as the monoacetate (X), monobenzoate (XI), urethane (XII), semicarbazone (XIII), triol (XIV), triacetate (XV), and a new N-oxyl radical (XVI). It has been confirmed that i) the extremely stable N-oxyl radical abstracts the α-methylene-hydrogen of the ketone which affords a thermodynamically stable conjugated ketone, ii) radical I acts as a scavenger toward a C-radical intermediate and iii) the decomposition of radical I proceeds via the C-radical to give phorone (V).
Durch Reaktion von Mesityloxid mit Cyclohexanon (VIII) in Na ‐äthylat/Tolucl bei ‐55°C unter Stickstoff wird das Ketol (I) erhalten, dessen Dehydratisierung in siedendem Benzol in Gegenwart von p‐Toluolsulfonsäure die Ketone (II) und (III) liefert.
Das Oxyl (I) bildet bei ömonatigem Stehen bei Raumtemperatur das Dipiperidyloxid (III), das durch H‐Elirninierung und nachfolgende Kupplung von (I) mit dem aus (I) erhaltenen C‐Radikal (II) entsteht.
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