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Direct Stereospecific Synthesis of Unprotected N-H and N-Me Aziridines from Olefins

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Science  03 Jan 2014:
Vol. 343, Issue 6166, pp. 61-65
DOI: 10.1126/science.1245727

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Unadorned Aziridines

Multiple catalytic methods have been developed to make aziridines—strained triangular carbon-nitrogen-carbon rings that function as versatile synthetic intermediates. However, the majority require protection of the nitrogen precursor with a sulfonyl group that is subsequently inconvenient to remove. Jat et al. (p. 61; see the Perspective by Türkmen and Aggarwal) used a hydroxylamine derivative as the nitrogen source together with an established rhodium catalyst to prepare a wide range of unprotected aziridines, with nitrogen bonded simply to hydrogen or a methyl group.

Abstract

Despite the prevalence of the N-H aziridine motif in bioactive natural products and the clear advantages of this unprotected parent structure over N-protected derivatives as a synthetic building block, no practical methods have emerged for direct synthesis of this compound class from unfunctionalized olefins. Here, we present a mild, versatile method for the direct stereospecific conversion of structurally diverse mono-, di-, tri-, and tetrasubstituted olefins to N-H aziridines using O-(2,4-dinitrophenyl)hydroxylamine (DPH) via homogeneous rhodium catalysis with no external oxidants. This method is operationally simple (i.e., one-pot), scalable, and fast at ambient temperature, furnishing N-H aziridines in good-to-excellent yields. Likewise, N-alkyl aziridines are prepared from N-alkylated DPH derivatives. Quantum-mechanical calculations suggest a plausible Rh-nitrene pathway.

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