Conversion to aziridines

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)... 

See, for example, Ittah Sasson Shahak Tsaroom Blum J. Org. Chem. 1978, 43, 4271. For the mechanism of the conversion to aziridines, see Pdchlauer Muller Peringer Helv. Chim. Acta 1984, 67, 1238. 

The results of the photochemical and chromium(II) chloride promoted reactions on steroid-5-enes are shown below. The tram stereochemistry of the prevalent adducts was shown by conversion to aziridines. No adduct was, however, isolated from progesterone and TV-chloro carbamate78. 

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. 

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]. 

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). 

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 reaction of 2 -benzyloxychalcone dibromides (605) with ammonia gives a chalcone aziridine (606). Following conversion to the (V-benzoyl derivative, acid hydrolysis removed the protecting group at C-2 and a 3-aminoflavanone results (Scheme 230) (73ACH(76>95). 

The fixation of C02 into a three-membered ring has also been promoted, under relatively severe conditions, by other catalytic systems such as tetrapheny-lantimony halides (333 K, 5 MPa) [68e] or the p-methoxyphenol/DMAP system (DMAP = 4,6-(dimethylamino)pyridine 393 K, 3.6MPa, 48h) [68f] or, under much milder conditions, by alkali [68g-k] or tetralkylammonium halides [68j], or by (Salen)Cr(III)(DMAP) [681]. It is worth noting that, with 2-alkyl or 2-aryl substituted aziridines, alkali or tetralkylammonium halides catalyze the formation of the 4-substituted regioisomer as the main or unique product, whereas the chromium(III) catalyst promoted the preferential conversion to the 5-subshtuted regioisomer with high selectivity and yield. 

Dichloroazetidines 83 are easily converted into aziridine derivatives 84 in excellent yields by sodium methox-ide in methanol (Equation 22). Conversion to the aziridine ring system has been explained by the intermediacy of a 2-azetine ring system <2002JOC2075>. 

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. 

Poly(ethylenimine) (PEI) has been examined extensively both in its classical, random branched topology [125] and in its linear form [126]. The various architectural and topological forms of PEI have been reviewed recently [127], Here we describe the first example of this polymer system as an ideal, hyper-branched molecular assembly. Synthesis of a tri-dendron poly(ethyleneimine) dendrimer derived from an ammonia core involved, first the selective alkylation of diethylenetriamine (DETA) with aziridine to produce a symmetrical core cell, namely tris-(-2-aminoethyl)amine. Subsequent exhaustive alkylations of the terminal amino moieties with activated aziridines [2, 127, 128], such as IV-tosyl- or N-mesylaziridine gave very good conversions to the first-generation protected... 

Consequently, for polymerization of N-substituted aziridines with small substituents like N-methylaziridine, limited conversions to relatively low molecular weight polymers were observed [165,166]. On the other hand, in the polymerization of N-f-butylaziridine chain transfer to polymer is practically eliminated [167]. No other transfer or termination reaction involving quaternary ammonium active species with, e.g., BF4-counterion has been detected ... 

The stereochemistry of the major adduct was elucidated by H NMR and by conversion to the known 3/i-nitrocholestane. The corresponding aziridine could not be prepared, since the reduction with lithium aluminum hydride or zinc gave 2-cholestene, and treatment with iron(II) sulfate and hydrochloric acid gave starting material only. 

Addition of cyclopentene to JV-chloro carbamates gives lower yields and a smaller cis/trans ratio than cyclohexene. The addition of ethyl chlorocarbamate to l-methylcyclohexene was efficient and had better diastereoselectivity than the comparable addition to cyclohexene, however, the reaction did not occur with complete regioselectivity giving 5 and 6 8. The stereochemistry of the minor trans-isomers was shown by conversion to the corresponding aziridines. Ethyl bromocarbamate and /V-halo amides are less selective. 

Unsaturated amides are easily converted to imidates by 0-alky la ting reagents such as trimethyl-oxonium telrafluoroborate or trimethylsilyl triflate. Nucleophilic attack by the thus formed imino group on an halonium ion followed by hydrolysis gives a lactam. Thus an unsaturated dimethyl imidate was treated with bromine in dichloromethane at 0 °C and cyclized with total regio- and stereoselectivity to give 1, since the tertiary cation forces the cyclization towards the formation of a six-membered ring. The trans addition to the double bond was shown by successive conversion to a m-aziridine 2126. 

Starting from the Diels-Alder adduct 13, dihydrotriazoles were prepared by cycloaddition with /m-butyloxycarbonyl azide and successively converted to aziridines 14 and 15 and trans-aminolactone 1653. Although dihydrotriazoles generally gave mixtures of products by acidic treatment, it is possible to achieve the clean conversion to ring-opened products without the preliminary decomposition to aziridines. 

A chiral, nonracemic oxirane, (3 )-2-[(R)-fluoro(phenyl)methyl]oxirane, can react with (chiral) amines under the influence of lithium perchlorate using either heat or microwave irradiation. This reaction sequence provides a material from which the ee of chiral a-branched amines can be determined <2005OL3829>. Guanidines serve as a useful nitrogen nucleophile for the direct conversion of epoxides to aziridines <2004JOC8504>. 

---