General Papers ARKIVOC 2006 (x) 42-54 ISSN 1424-6376 Page 42 © ARKAT Rearrangement of a 3-acyloxyamino-1,5-diketone into enamine and pyrrole: a mechanistic study Cornelia Uncuta,* a Emeric Bartha, a Catalin I. Tanase, a Anca Tanase, a Oana Costan, a Mihaela Ciuca, a Nicolas Vanthuyne, b and Christian Roussel b a Center of Organic Chemistry “C.D. Nenitzescu”,Spl. Independentei 202B, 35-108, 060023 Bucharest, Romania b University Paul Cézanne-Aix-Marseille III, Ave. Escadrille Normandie Niemen, 13397 Marseille Cedex 20, France E-mail : christian.roussel@univ.u-3mrs.fr ; cuncuta@cco.ro Dedicated to Professor Alexandru T. Balaban on the occasion of his 75 th birthday Abstract The paper reports on the diversity of products obtained from a 3-acyloxyamino-1,5 diketone in reaction with bases, the distribution of products being correlated with the nature of the base and the solvent. Like other derivatives of β-hydroxyamino ketones, this compound reacts to form a 2- acylaziridine. Unusually, however, the aziridine undergoes ring-opening with carbon-carbon bond breaking to yield a β-ketoenaminone as isolable product. A minor path occurring with carbon-nitrogen bond breaking gives an α-acylpyrrole. In a further reaction the ketoenaminone forms a dimer which is characterized by X-ray crystallography. Keywords: Aziridine rearrangement, aziridine-ring enlargement, captodative radical, dimerization, heterocycles Introduction We reported recently on a new synthon generated in several steps from 2,6-di-tert-butyl-4- methylpyrylium perchlorate and hydroxylamine, namely 5-isoxazolidinol 1. The occurrence of ring-chain tautomers of 1 has been demonstrated by regioselective acylation with carboxylic anhydrides which gave 1,3,5-trisubstituted 3-acyloxyamino-1,5-diketones 2. 1 This present paper reports on the rearrangement of the derivatives 2, under basic conditions, into the enamino-diketone 4 and the α-keto pyrrole derivative 5. We found that the reaction occurred through the intermediate aziridine diketone 3 (Scheme 1).