Calix[4]pyrrole as a Promoter of the CuCl-Catalyzed Reaction of Styrene and Chloramine-T Héctor Martínez-García, † Dolores Morales, † Julio Pérez,* ,† Daniel J. Coady, ‡ Christopher W. Bielawski,* ,‡ Dustin E. Gross, ‡ Luciano Cuesta, ‡ Manuel Marquez, § and Jonathan L. Sessler* ,‡ Departamento de Química Orgánica e Inorgánica, IUQOEM, Facultad de Química, UniVersidad de OViedo-CSIC, Spain, Department of Chemistry and Biochemistry, UniVersity of Texas at Austin, Austin, Texas 78712, and Harrington Department of Bioengineering, Arizona State UniVersity, Tempe, Arizona 85287 ReceiVed September 27, 2007 Summary: Calix[4]pyrrole, an easy-to-prepare anion receptor, acts to promote the cuprous chloride-catalyzed aziridination of styrene by the nitrene source chloramine-T in acetonitrile. The mechanism of action is belieVed to inVolVe incipient anion- receptor interactions inVolVing the calix[4]pyrrole NH protons and the chlorine atom of the CuCl, rather than direct bonding to, and actiVation of, the chloramine-T. Consistent with this supposition were the findings that (1) the use of calix[4]pyrrole, in combination with CuCl, did promote enhanced reactiVity when PhIdNTs was used as the nitrene source and (2) the presence of calix[4]pyrrole had no effect on the reaction when CuI was used as a catalyst. Decreased yields were also seen with CuCl 2 , and no appreciable aziridination product was obserVed when the calix[4]pyrrole was replaced by an ap- propriately chosen dipyrromethane control compound. On the other hand, the enhancement effect proVided by calix[4]pyrrole proVed relatiVely insensitiVe to the presence of trace quantities of water. Introduction Anion recognition has emerged as an important subdiscipline within the rapidly expanding area of supramolecular chemistry. While a large number of elegant anion receptors have been reported in recent years, many of which have proved useful as sensors, carriers, and extractants, 1 little focus within the field has been devoted to the development of functional systems, namely, those that exploit anion-receptor interactions to modu- late or promote chemical reactivity. Although, a stoichiometric system capable of activating dichloromethane was recently described by Smith and co-workers 2 and the use of anion recognition to enhance phosphate ester hydrolysis was reported by Král et al. in 2006, 3 we are currently unaware of any examples where a simple anion receptor 4 is used to promote a bond-forming reaction. 5 In principle, the ability to polarize a bond through partial or complete complexation of an incipient anionic leaving group could serve to promote reactivity in transformations where weakening or rupture of an anion-substrate bond is critical to reactivity. 6 As a first demonstration of this potentially broad principle, we report here the use of calix[4]pyrrole 1 to promote the CuCl-catalyzed aziridination of styrene using chloramine-T as the nitrene source. Copper-catalyzed nitrene transfer to olefins as a route to aziridines has attracted considerable interest in recent years. 7 The most commonly employed nitrene source is the iminoio- dinane PhIdNTs; unfortunately, this compound is not com- mercially available, and its preparation suffers from variable yields. 8 Furthermore, PhIdNTs is hydrolytically unstable, and when it acts as a nitrene source, a byproduct of the reaction is iodobenzene. In contrast, chloramine-T (as the mono- or trihydrate, TsNClNa · (H 2 O) n ; n ) 1 or 3) is an inexpensive, commercially available source of nitrene that produces nontoxic and readily separable sodium chloride as a byproduct. 9 Thus, efforts have been made in recent years to exploit chloramine-T as an alternative to PhIdNTs. In 1998, Komatsu and co-workers reported the aziridination of olefins using chloramine-T as nitrene source and copper(I) triflate as a catalyst. 10 A drawback * Corresponding authors.: E-mail: japm@uniovi.es; sessler@mail.utexas.edu; bielawski@cm.utexas.edu † Universidad de Oviedo-CSIC. ‡ University of Texas at Austin. § Arizona State University. (1) (a) Sessler, J. L.; Gale, P. A.; Cho, W. S. Anion Receptor Chemistry; Royal Society of Chemistry: Cambridge, 2006. (b) Beer, P. D.; Gale, P. A. Angew. Chem., Int. Ed. 2001, 40, 486–516. (2) Lee, J.-J.; Stanger, K. J.; Noll, B. C.; Gonzalez, C.; Marquez, M.; Smith, B. D. J. Am. Chem. Soc. 2005, 127, 4184–4185. (3) Král, V.; Lang, K.; Králová, J.; Martásek, P.; Chin, K. O. A.; Andrievsky, A.; Lynch, V. M.; Sessler, J. L. J. Am. Chem. Soc. 2006, 128, 432–437. 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