Tetrahedron Vol. 51, No. 4, pp. 1277-1284, 1995 Pergamon Copyright © 1995 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0040-4020/95 $9.50+0.00 0040-4020(94)01006-4 Selenium-Induced Cyclization of O-Allyl Oximes as a Synthetic Route to N-Alkyl Isoxazolidines Marcello Tnecco, Lorenzo Testafern, Marco Tingoli, Luana Bagnoli and Claudio Santi lstituto di Chimica Organica, Facoltcl di Farmacia, UniversiKl di Perugia, 06100 - Perugia, Italy Abstract: Phenylselenenyl bromide easily reacts with O-allyl oximes to afford cyclic iminium bromides which can be reduced in situ with sodium borohydride to produce substituted N-alkyl isoxazolidines in good yield. Ring-closure reactions which take place by the formation of a carbon-nitrogen bond can be easily effected starting from alkenes containing internal nitrogen nucleophiles under the influence of electrophilic reagents, including metals, iodine, bromine and several phenylselenenyl derivatives. This synthetic process is very useful since it offers an easy access to a wide range of substituted nitrogen heterocycles.l-3 Much attention has been recently devoted to the cyclization reactions of alkenes in which the nitrogen internal nucleophile is that of an imidate, 4 oxime, 5-7 an O-allyl oxime 8,9 or an imine.10,11 In these compounds the imino nitrogen atom is sufficiently nucleophilic to attack the carbon atom of the intermediate formed from the interaction of the electrophilic reagent with the olefinic double bond, e. g. 2 (Scheme 1). Thus, lactams and cyclic nitrones are formed from imidates and oximes, respectively, and cyclic iminium salts, which can evolve in different ways, are produced from O-allyl oximes and from imines. Scheme 1 PhSe R /" " / ~ + R2 PhSe R ~,~"~. N~ R2 L~O~=rf'a2 gl ..... ,,,~ • ~ - u / ----" 1 R1 2 R1 3 /'~'O"~1"~ R2 / 5 R1 1277