This journal is c The Royal Society of Chemistry 2011 Chem. Commun., 2011, 47, 2967–2969 2967 Cite this: Chem. Commun., 2011, 47, 2967–2969 A facile noncatalytic pathway for the nitrene transfer process: expeditious access to aziridinesw Indranirekha Saikia, Bishwapran Kashyap and Prodeep Phukan* Received 6th December 2010, Accepted 5th January 2011 DOI: 10.1039/c0cc05387b A fast and efficient method has been developed for generation of sulfonyl nitrene from N,N-dibromo-p-toluenesulfonamide (TsNBr 2 ) in the presence of a base without any catalyst. This method was applied to produce aziridines from different kinds of olefins within a short time in high yields. Nitrenes are among the most fundamental reactive intermediates in organic synthesis. 1 Nitrene transfer reaction provides an effective route for the construction of biologically important molecules such as drugs and natural products. 2 Consequently, development of new synthetic methods for this reactive inter- mediate is considered as the frontiers of organic synthesis. Classical methods for generation of nitrenes are: thermal or photochemical decomposition of hydrazoic acid, alkyl and aryl azides, sulfonyl azides, azidoformates and cyanogen azide. 1,3 In the recent past, several nitrene sources were reported. The most commonly employed nitrene source is PhI Q NR that can also be formed in situ by oxidizing sulfonamides or other amines with PhI(OAc) 2 or PhIO. 2 However, due to some limitations in the use of these iminoiodinanes, alternative nitrogen sources such as chloramine-T (TsN(Cl)Na), bromamine-T (TsN(Br)Na) and organic azides (RN 3 ) were more recently investigated. 2 A very common and widely utilized nitrene insertion reaction as a synthetic tool for achieving nitrogeneous molecules is the synthesis of aziridines. 2,4 Aziridines exhibit highly regio- and stereoselective ring opening reactions which provide a convenient entry to the stereoselective preparation of functionalized amino compounds, heterocycles, and alkaloids. 5 Among several approaches, metal-catalyzed aziridination of alkenes with proper nitrene sources is the most widely utilized method for the synthesis of the three-membered ring structure. 2 Iminoiodinane derivatives such as [N-(p-tolylsulfonyl)imino]- phenyliodinane (PhI Q NTs) 6 and its variants have been extensively used as the nitrene source in the presence of several transition metal catalysts including those based on Cu, 7 Mn, 8 Fe, 9 Rh, 10 Ru, 11 Ag, 12 and Au. 13 Alternative nitrene sources such as N-halo-sulfonamides, 14 organic azides, 15 etc. were also used in the presence of a catalyst. Recently, we have found that TsNBr 2 is a very reactive and efficient reagent for various organic transformations. 16 In this communication, we wish to report an expeditious, noncatalytic route for the synthesis of aziridines directly from olefins using TsNBr 2 as a nitrene source (Scheme 1). During the course of our investigation, we found that TsNBr 2 is a strong source of the bromonium ion and liberation of the bromonium ion from TsNBr 2 is very facile. It is well known that carbene can be generated by a-dehalogenation of gem-dihalo compounds. 17 We presumed that, analogous to carbene formation, it should be possible to generate nitrene from N,N-dibromo-p-toluenesulfonamide by debromination in the presence of a base. With this view in mind, we have carried out a reaction by adding a solution of TsNBr 2 (1.2 equiv.) in dichloromethane to a mixture of K 2 CO 3 (2.5 equiv.) and styrene (1 equiv.) in dichloromethane at room temperature. The process was carried out under inert atmosphere and the progress of the reaction was monitored by TLC. We observed that the reaction is very fast and the corresponding aziridine was isolated in 63% yield after 10 minutes of reaction. In order to find out the best reaction condition, we have investigated the effect of various solvents on the product yield (Table 1). When acetonitrile was used as a solvent the reaction did not produce the expected product after 10 minutes of reaction. Further investigation on the reaction using ethyl acetate as a solvent gave the best result of 84% isolated yield of the corresponding aziridine. The reaction was also studied with Scheme 1 Synthesis of aziridines using TsNBr 2 . Table 1 Influence of solvent and K 2 CO 3 amount on the synthesis of aziridine from styrene a Entry Solvent K 2 CO 3 /mmol Yield b (%) 1 DCM 2.5 63 2 CH 3 CN 2.5 Trace 3 EtOAc 2.5 84 4. EtOAc 1 25 5 EtOAc 1.5 40 6 EtOAc 3.5 84 a Reaction conditions: styrene (1 mmol), TsNBr 2 (1.2 mmol), solvent (10 mL), rt, 10 min. b Isolated yield. Department of Chemistry, Gauhati University, Guwahati-781014, Assam, India. E-mail: pphukan@yahoo.com w Electronic supplementary information (ESI) available: NMR spectral data. See DOI: 10.1039/c0cc05387b ChemComm Dynamic Article Links www.rsc.org/chemcomm COMMUNICATION