Palladium(II) mediated aziridination of olefins with bromamine-T as the nitrogen source: scope and mechanism Alexandra M. M. Antunes, Vasco D. B. Bonif acio, Susana C. C. Nascimento, Ana M. Lobo, Paula S. Branco * and Sundaresan Prabhakar REQUIMTE/CQFB, Departamento de Qu ımica, FCT, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal Received 3 January 2007; revised 3 May 2007; accepted 4 May 2007 Available online 22 May 2007 Abstract—The palladium(II)-promoted reaction of a variety of olefins and bromamine-T provided N-tosyl-2-substituted aziridines under mild conditions. Olefins bearing chiral appendages gave only a poor to modest diastereoselectivity. Appropriate deuterated olefins were selected to study the stereochemistry of the reaction. A Pd(IV) intermediate is proposed as the aziridinating species. Ó 2007 Elsevier Ltd. All rights reserved. 1. Introduction Aziridines are versatile substances for the synthesis of biologically important substances such as amino acids, b- lactam antibiotics, and alkaloids. 1,2 Of late there has been an increased interest in the catalytic use of copper, 3–8 rho- dium, 9,10 manganese, 11 and rhenium, 12 for the conversion of olefins to aziridines. Among these metals, copper in con- junction with tosylimino-phenyliodane 3–8,11,12 has been widely used as the nitrogen transfer reagent. Chloramine- T 13 or bromamine-T 14 extensively used to prepare epox- ides, 15 a-hydroxyamines 16,17 and a- chloroamines 18 have also been amply used in aziridination reactions. 13,14,17,19 A combination of bromamine-T with porphyrin complexes of transition metals such as Mn, Fe, Ru, and Co was also shown to yield aziridines. 20,21 Polymers incorporating Mn and Fe were found to be efficient in aziridination reactions with bromamine-T. 22 In spite of the extensive use of palladium in organic synthesis, 23 intermolecular amination of simple olefins involving Pd +2 and primary or secondary amine was found to be inefficient. 24 The poor yield was attributed to strong coordination of the amines with palladium(II) catalyst. 25,26 We had previously reported 27 a novel PdCl 2 -assisted aziri- dination of olefins with bromamine-T as the nitrogen transfer reagent. Full details of this method, its probable re- action mechanism, its scope, and limitations are described herein. Also briefly summarized are our efforts to achieve enantio- and diastereoselection by employing appropriate substrates. 2. Results and discussion A variety of acrylic acid derivatives and other simple allyl alcohols were subjected to the palladium(II) promoted aziridination with bromamine T as the nitrogen transfer re- agent under two different experimental conditions. Method A consisted of addition of bromamine T (0.18 mmol) to a previously stirred solution of olefin (0.45 mmol) and bis- (acetonitrile)dichloropalladium (0.075 mmol) in acetonitrile (1/2 h). Method B involved addition in portions, of brom- amine-T (0.06 mmol) to a previously stirred solution of olefin (0.15 mmol) and dichloropalladium (0.024 mmol) in acetonitrile (1/2 h), each addition being done only after a negative starch-iodide test for the oxidant was observed. Appropriate choice of the method led occasionally to a marked improvement in the yield. For example whilst method A gave 57% of aziridine for N,N-dimethylacryl- amide, method B furnished the same product in 81% (Table 1, entry c). The catalytic efficiency of other palladium(II) compounds, such as Pd(OAc) 2 , Pd(CF 3 COO) 2 , and PdBr 2 , bearing different leaving groups on the metal was also exam- ined. Palladium(II) chloride or bis(acetonitrile)dichloropal- ladium(II) was found to give best result. An examination of the Table 1 shows that a wide variety of olefins are aziri- dinated with varying degrees of efficiency. It can also be noted that the greater the deactivation of the double bond in acrylic acid derivatives the lower was the yield of aziri- dines (CN<COR<CO 2 R<CONMe 2 ). A b substituent caused a dramatic fall in the yield (81% for entry c; 16% for entry d). Irrespective of the electronic nature of the Keywords: Aziridination; Palladium(II); Catalysis; Bromamine-T. * Corresponding author. Tel.: +351 294 8300; fax: +351 294 8550; e-mail: psb@dq.fct.unl.pt 0040–4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.tet.2007.05.020 Tetrahedron 63 (2007) 7009–7017