A facile noncatalytic pathway for the nitrene transfer process: expeditious access to aziridines (original) (raw)
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A Micellar Iodide-Catalyzed Synthesis of Unprotected Aziridines from Styrenes and Ammonia
Angewandte Chemie International Edition, 2008
Aziridines are useful intermediates and pharmaceuticals. Therefore there is a growing need for their environmentally benign production. [1] Many olefin aziridinations rely on the addition of nitrenes, which are generated by either thermal or photochemical azide decomposition or are formed in situ from tosylimino phenyliodinane, sulfonyl azides, or chloramine-T using metal catalysts. [2] Halogens have also been proposed as catalysts in combination with chloramine-T, which is both a strong nucleophile and an oxidant. [3] In this route, pioneered by Sharpless [3a] and Komatsu, [3b] reaction of the oxidized halogen ("Br + ", "I + ") with the double bond is followed by nucleophilic attack of chloramine-T and cyclization. The main drawback of all previous reactions is the use of complex nitrogen-containing sources, which lead to N-substituted aziridines that require a subsequent deprotection step. Direct routes from olefins to unprotected aziridines have only been described for a,b-unsaturated carbonyl compounds and often require complex NH donors. Ammonia, which is the most obvious nucleophilic nitrogen source, has barely been considered in aziridinations. Only the Gabriel-Cromwell aziridination uses NH 3 , but the scope of this reaction is restricted to a,b-unsaturated a-halocarbonyl compounds. [5a,b] The direct incorporation of ammonia into olefins is therefore justly recognized as a top priority for catalysis. [6] Herein we describe the first successful catalytic synthesis of unprotected aziridines from NH 3 and simple olefins. Our method resembles a halide-assisted epoxidation, in which the olefin is attacked by "Br + " cation, which is formed in situ by oxidation of bromide, and then by water as the oxygen source. The resulting bromohydrin is then cyclized to the epoxide. As will be shown, a similar concept can be applied for the N-functionalization of styrenes by replacing water with ammonia as the nucleophile: unprotected aziridines are formed in a one-pot, micellar system using iodide as a catalyst, aqueous bleach as an oxidant, and ammonia as the nitrogen source [Eq. (1)].
Direct Stereospecific Synthesis of Unprotected N-H and N-Me Aziridines from Olefins
Science, 2014
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.
Tetrahedron Letters, 1997
The preparation of different lN-(arenesulfonyl)iminolphenyliodinanes is described along with an evaluation of their utility as nitrene precursors for the copper-catalyzed aziridination of different olefins. The best results were obtained with p-NO2-Cr, H, flO~=IPh and p-MeO-Ce~I4SO2N=IPh, both of which were found superior to Phl=NTs, which previously has been the reagent of choice for this type of reaction. The corresponding aziridine derivatives were obtained in good to excellent yields (60-99%) using 1.0 equivalent of olefin and 1.5 equivalents of the nitrene precursor.
The Journal of Organic Chemistry, 2008
We have developed an efficient protocol for copper-catalyzed olefin aziridination using 5-methyl-2pyridinesulfonamide or 2-pyridinesulfonyl azide as the nitrenoid source. The presence of a 2-pyridyl group significantly facilitates aziridination, suggesting that the reaction is driven by the favorable formation of a pyridyl-coordinated nitrenoid intermediate. Using this chelation-assisted strategy, synthetically acceptable yields of aziridines could be obtained with a range of aryl olefins even in the absence of external ligands. Importantly, a large excess of olefin is not required. X-ray crystallography, ESI-MS, Hammett plot analysis, kinetic studies, and computational undertakings strongly support that the observed aziridination is driven by internal coordination.