Efficient Method for Cleavage of Aziridines with Aromatic Amines Govindasamy Sekar and Vinod K. Singh* Department of Chemistry, Indian Institute of Technology, Kanpur 208 016, India Received September 15, 1998 Ring opening of activated aziridines with several nucleophiles by means of Lewis acids has been studied. 1-4 If the nucleophiles are amines, the products become diamines, which synthetically are an important class of compounds. Recently, the ring opening reaction of mainly activated aziridines by amines has been reported in the presence of ytterbium triflate and other lanthanide triflates as catalysts. 5 Most of the amines used in the reaction were aliphatic, and there was only one entry where aniline was used as nucleophile. The reaction required higher concentration of the catalyst (20 mol %) and longer reaction time (1-3 d). While working on epoxide cleavage reactions with amines, 6 we discovered that aziridines were efficiently cleaved with less reactive aromatic amines and 5 mol % of Sn(OTf) 2 or Cu(OTf) 2 in a short time. The unusual feature of the reaction was that aliphatic amines did not open aziridines with these catalysts, in sharp contrast to the behavior of Yb(OTf) 3 and La(OTf) 3 . 5 This prompted us to look at the reaction, and we report our results in this paper. A variety of aziridines were synthesized from the corresponding amino alcohols in one step, using MsCl (1.1 equiv) and Et 3 N (2.5 equiv) in pyridine (as solvent) at room temperature. At the outset, the opening reaction was done using N-phenylcyclohexeneimine and aniline, with 5 mol % of Sn(OTf) 2 in ether at room temperature for 10 min, and product 1a was obtained in 91% yield (Table 1, entry 1). The reaction was studied in several solvents, such as CH 2 Cl 2 (90% yield), MeCN (88% yield), and THF (80% yield), and it was found that both ether and CH 2 Cl 2 were equally good solvents for the above reaction. Use of Cu(OTf) 2 as a catalyst facilitated the reaction equally well, but the reaction time was a little longer (1 h). The opening of N-phenylcyclohexeneimine was tried with a variety of aromatic amines, using both the catalysts (entries 1-12). In all the cases, a very clean reaction was observed and the trans stereochemistry of diamines was deduced from the relevant coupling con- stants. The aziridine opening reaction tolerated a varying degree of steric hindrance on aromatic amines such as R-naphthylamine (entry 9), diphenylamine (entry 10), and o,o′-diisopropylaniline (entry 11). To show the scope of the reaction, we extended it to a variety of cyclic and acyclic aziridines. In almost all cases, a high yield of the opened product was obtained. In the case of acyclic terminal aziridines, the reaction was highly regioselective. Only one product was isolated, and it was due to the attack of aromatic amines at the less hindered terminal carbon atoms (entries 20-22). 7 In the case of 2-phenyl aziridines (entries 24 and 25), the situation was the reverse; the product formed was the one due to the attack of aromatic amines at the benzylic carbon atom (internal attack). 8 The aziridine opening * Fax: 91-512-590007. E-mail: vinodks@iitk.ac.in. (1) (a) For a general review of aziridine chemistry, see: Pearson, W. H.; Lian, B. W.; Bergmeier, S. C. In Comprehensive Heterocylic Chemistry II; Katritzky, A. R., Rees, C. W., Scriven, E. F. V., Eds; Pergamon: New York, 1996; Vol 1a. (b) Dauben, P.; Dubois, L.; Dau, M. E. T. H.; Dodd, R. H. J. Org. Chem. 1995, 60, 2035. (c) da Zhang, Z.; Scheffold, R. Helv. Chim. Acta 1993, 76, 2602. (d) Bodenan, J.; Chanet-Ray, J.; Vessiere, R. Synthesis 1992, 288. (e) Sato, K.; Kozikowski, A. P. Tetrahedron Lett. 1989, 30, 4073. (f) Nakajima, K.; Neya, M.; Yamada, S.; Okawa, K. Bull. Chem. Soc. Jpn. 1982, 55, 3049. (2) For Cr complex catalyzed opening of aziridine with TMS azide, see: Leung, W.-H.; Yu, M.-T.; Wu, M.-C.; Yeung, L.-L. Tetrahedron Lett. 1996, 37, 891. (3) For opening of aziridine with TMSCN in the presence of lanthanoid tricyanide, see: (a) Matsubara, S.; Kodama, T.; Utimoto, K. Tetrahedron Lett. 1990, 31, 6379. (b) Osborn, H. M. I.; Sweeney, J. B. Synlett 1994, 145. (4) While this manuscript was being prepared, a paper appeared where acylaziridine is rearranged to oxazoline by means of orthogonal Lewis acids. For reference, see: Ferraris, D.; Drury, W. J., III; Cox, C.; Lectka, T. J. Org. Chem. 1998, 63, 4568. (5) (a) Meguro, M.; Asao, N.; Yamamoto, Y. Tetrahedron Lett. 1994, 35, 7395. (b). Meguro, M.; Yamamoto, Y. Heterocycles 1996, 43, 2473. (6) .Sekar, G.; Singh, V. K. J. Org. Chem. 1999, 64, 287. (7) This was ascertained by comparing the δ value of N-Me in products obtained from the opening of similar epoxide with N-methyl aniline. For details, see ref 6. Table 1. Sn(II) and Cu(II) Triflate Catalyzed Aziridine Opening with Aromatic Amines in Ether at Room Temperature 2537 J. Org. Chem. 1999, 64, 2537-2539 10.1021/jo981869r CCC: $18.00 © 1999 American Chemical Society Published on Web 03/09/1999