Month 2014 Regio-controlled and Stereo-controlled Ring Expansion of N-Substituted-2 Benzoylaziridines Using Fe(NO 3 ) 3 Heshmat A. Samimi * and Zahra Shams Department of Chemistry, Faculty of Sciences, University of Shahrekord, PO Box 115, Shahrekord, Iran *E-mail: samimi-h@sci.sku.ac.ir Received April 8, 2012 DOI 10.1002/jhet.1773 Published online 00 Month 2014 in Wiley Online Library (wileyonlinelibrary.com). N R 1 O Ph R 2 O N O R 2 R 1 Ph O 2 3 H N R 1 O Ph 1 i i) RCOCl,Et 3 N,CH 2 Cl 2 , rt. ii) Fe(NO 3 ) 3 ,CH 3 CN,r.t. ii R 1 =C 6 H 5 , 3-NO 2 C 6 H 4 , 4-ClC 6 H 4 , 2,4-Cl 2 C 6 H 3 , 4-OMeC 6 H 4 ;R 2 =C 6 H 5 , 4-NO 2 C 6 H 4 O N R 2 R 1 Ph O not formed Several N-acyl-2-benzoylaziridines were previously prepared conveniently and used in the preparation of 5-benzoyl-2,4-diaryl oxazolines in the presence of NaI. In this work, synthesis of some trans-4-benzoyl- 2,5-diaryl oxazolines by a regio-controlled and stereo-controlled reaction in the presence of Iron (III) nitrate at room temperature is reported. A plausible mechanism has been proposed for ring expansion of N-acylaziridines to oxazolines. J. Heterocyclic Chem., 00, 00 (2014). INTRODUCTION Oxazolines have a wide variety of applications such as chiral auxiliaries [1], pharmaceutical and biological activi- ties, [2] synthetic intermediates [2], protecting groups [3], versatile intermediates in P–C bond formation [4], ligands in the asymmetric catalysis of organic reactions [5], and in the synthesis of b-substituted serines because of their util- ity in the synthesis of various antibiotics [4b]. For more than a century, considerable interest has been devoted to find a new methodology for the synthesis of oxazoline building blocks [6]. In most cases, they are prepared from amino alcohols [5b], carboxylic esters [5c], nitriles, or aldehydes as starting materials [7]. N-Acyl activated aziridines easily afford ring opening and can be transformed into the corresponding oxazolines through a ring expansion reaction in the presence of some different Lewis acids [8–12]. The majority of these ring enlargements proceed with full stereochemical control [9,10]. Despite few work reported on the reactivity of aziri- dines, further developments in utilization of aziridines derivatives as useful synthetic precursors is still required. In addition, so far, no example has been reported in the literature describing the synthesis of two regioisomers of oxazolines from the same N-acyl aziridines [8–12]. In continuation of our recent interest in the synthesis and using of heterocyclic compounds as well as the ring expansion of keto aziridines with NaI for the prepara- tion of some trans-5-benzoyloxazolines [11,13], herein we report the synthesis of their regioisomers, namely trans-4-benzoyloxazolines, in the presence of Iron(III) nitrate at room temperature in moderate to good yields (Scheme 1). RESULTS AND DISCUSSION Initially, we prepared trans-2-benzoylaziridines 1 via Gabriel–Cromwell procedure [13]. Then trans-2- Benzoylaziridines 1 were used for the preparation of N-acetyl-2-benzoylaziridines 2 in the presence of Et 3 N in CH 2 Cl 2 (Scheme 1). Some of N-acetyl-2-benzoylaziridines (2a,f) were characterized by their spectral data ( 13 C NMR, 1 H NMR, and IR) and melting points. In this study, as a model reaction, the effect of different catalysts on the efficiency of ring expansion of 1,2-dibenzoyl- 3-phenyl aziridine (2a) was investigated in acetonitrile (Scheme 2). The results of this study revealed that the ring expansion reaction in the presence of ZnCl 2 , ZnO, AlCl 3 , Zn (HSO 4 ) 2 , Co(HSO 4 ) 2 , and H 3 BO 3 gave a mixture of unknown products with a small amount of trans-4-benzoyloxazolines (10–56%) of the desired oxazoline (Scheme 2, Table 1). In the absence of catalyst, the reaction did not give any of oxazolines (entry 8). However, the best results for the conversion of 1,2-dibenzoyl-3-phenyl aziridine (2a) to trans-4-benzoyl- 2,5-diphenyl oxazoline (3a) achieved with Fe(NO 3 ) 3 in acetonitrile (81% yield; Table 1, entry 7). The effects of some solvents such as Et 2 O, CH 2 Cl 2 , EtOH, CHCl 3 , and CH 3 CN on the ring-expansion of 1,2-dibenzoyl-3-phenyl aziridine (2a) in the presence of Fe(NO 3 ) 3 were examined. Only acetonitrile was a suitable solvent for this isomerization. However, it is well known that N-acetyl aziridines can undergo ring expansion in the presence of catalysts such as BF 3 .OEt 2 or Sc(OTf) 3 in CH 3 CN with the formation of imidazoles, but it gives oxazolines in solvents such as CH 2 Cl 2 or CHCl 3 [8c–d]. Surprisingly, against that, our © 2014 HeteroCorporation