Aziridine conversion

The oxirane to aziridine conversion method was also utilized for the successful synthesis of naturally occurring (-i-)-(2S,3S)-aziridine-2,3-dicarboxylic acid 5 as is shown in Scheme 2 [9]. 

Mendlik, M.T., Tao, P., Hadad, C.M., Coleman, R.S., and Lowary, T.L. (2006) Synthesis of L-daunosamine and L-ristosamine glycosides via photo-induced aziridination. Conversion to thioglycosides for use in glycosylation reactions. Journal of Organic Chemistry, 71 (21), 8059-8070. 

The most useful reactions combine carbanion nucleophiles with activated aziridines. For example, the ring expansion which occurs on treatment of aziridines (219) with malonate salts typifies the heterocyclic synthesis possible. The conversion is quite general since many analogous transformations have been observed in which different carbanion stabilizing substituents were employed (73S546). 

The mechanism for the Wenker aziridine synthesis is very straightforward. As depicted by conversion 2—>3, the transformation is a simple case of intramolecular Sn2 displacement process, in which the sulfate ester is the leaving group. 

The Gabriel-Cromwell reaction is a convenient strategy for the synthesis of vinylaziridines. Treatment of 4,5-dibromopent-2-enoate 50 with primary amines 51 in the presence of DBU afforded the corresponding conjugated aziridines 52 in 63-80% yields (Scheme 2.16) [28]. The use of DBU has proven to be essential for the successful conversion. 

When a better leaving group than LiNSC R (e.g., OMe) is present at the a-position, retention of the potentially useful sulfonamide moiety occurs (e. g., in the conversion of aziridine 271 into the highly functionalized amino ether 272 Scheme 5.69) [98]. It should be noted that the analogous chemistry with epoxides of allylic diethers failed this could again (see above) be possibly due to the higher pKa of the epoxide proton relative to the aziridine proton. 

This conversion has been used as a key step in the preparation of optically active aziridines from optically active 1,2-diols (prepared by 15-46). ° Even hydrogen can be the leaving group. Benzylic hydrogens have been replaced by N3 by treatment with HN3 in CHCI3 in the presence of DDQ (p. 1511). °°... 

The overall pathway for the conversion of the unsaturated azido ether 281 to 2,5-dihydrooxazoles 282 involves first formation of the dipolar cycloaddition product 287, which thermolyzes to oxazoline 282 or is converted by silica gel to oxazolinoaziridine 288. While thermolysis or acid-catalyzed decomposition of triazolines to a mixture of imine and aziridine is well-documented [71,73], this chemoselective decomposition, depending on whether thermolysis or exposure to silica gel is used, is unprecedented. It is postulated that acidic surface sites on silica catalyze the triazoline decomposition via an intermediate resembling 289, which prefers to close to an aziridine 288. On the other hand, thermolysis of 287 may proceed via 290 (or the corresponding diradical) in which hydrogen migration is favored over ring closure. 

Tanner [3,10] used essentially the same methodology for the conversion of a monobenzyl derivative of a C2-symmetric epoxy bis-alcohol into the corresponding derivative 6 of a C2-symmetric aziridine bis-alcohol (Scheme 3). 

It may be concluded that the conversion of functionalized oxiranes into the corresponding aziridines by an azide ring opening followed by a Staudinger ring closure with triphenylphosphine constitutes a general method for the preparation of aziridines with high enantiopurity. 

A highly remarkable and entirely unexpected conversion of aziridine esters 21 into azirine esters 22 was accomplished by subjecting the aziridine to a Swern oxidation (Scheme 11). 

An intramolecular ring expansion of aziridine esters can be accomplished by installing an appropriate nucleophilic entity in these substrates. Conversion of the ester moiety into carboxamides derived from aminomalonate ester gives compounds 44 containing the requisite nucleophilic site in the malonate moiety (Scheme 35). 

In the case of the Diels-Alder reaction [68] (Scheme 12), several soUds (AlSBA-15, MCM-41, MSU-2 and zeolite HY) were tested as supports for the bis(oxazoline)-copper complexes. The best enantioselectivity results were obtained with the zeolite HY, although the yield was the poorest (16% yield, 41% ee). As happened with the aziridination reaction, the enantioselectivity changed with time. Short reaction times led to the same major enantiomer as observed in homogeneous reactions. However, at higher conversions, i.e., longer reaction times, the opposite major enantiomer was obtained. 

Intramolecular hydrogen abstraction leading to the aziridine 344 has been proposed to account for the unexpected conversion of the /f-amino vinyl phenyl ketones 345 into the pyrroles 346.286... 

Photoelimination of nitrogen from 1,2,3-triazolines has been widely used as a synthetic route to aziridines the reaction has been reviewed.355 Recent applications include the formation of a new valence isomer (425) of azepine from the triazoline 426,356 and conversion of the triazoline 427 into the aziridine 428, a process with potential as a synthetic route to mitomycins.357... 

Intermolecular addition of photochemically generated nitrenes and in particular acylnitrenes to alkenes provides a useful and widely applied route to aziridines.385 An analogous intramolecular photoreaction is thought to be involved in the conversion of the o-azidophenylethylfuran 461 into the pyrrolo[l,2-a]quinoline 462 as outlined in Scheme 13,386 and intramolecular addition to an azo group has been observed in the 8-azido-1-arylazonaphthalenes 463.387... 

The conversion of azidoformates to fused-ring aziridines via the thermal generation of a nitrene has previously been reported. More recently, the photolytic conversion of a sugar-derived azidoformate has been used to prepare fused-ring aziridines <06JOC8059>. Photolysis of azidoformate 66 at 254 nm provides aziridine 67 in excellent yield. The resulting bicyclic aziridine was reduced to provide oxazolidinone 68 in 95% yield. Oxazolidinone 68 was subsequently converted to L-daunosamine. 

Diethyl azidomethanephosphonate 228 reacts with norbornadiene at room temperature to give triazoline 229 in 86% yield. When heated at 60°C, derivative 229 decomposes with elimination of cyclopentadiene to provide (1,2,3-triazol-l-yl)methanephosphonate 230 in 74% yield. However, when it is left at room temperature for an extended period of time, triazoline 229 undergoes slow conversion to aziridine 231 with elimination of nitrogen (Scheme 30)... 

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