Trimethylsilyl azide, aziridine

S,3S)-(+)-Aziridine-2,3-dicarboxylic acid (234 Scheme 3.86), an example of a naturally occurring aziridinecarboxylic acid, is a metabolite of Streptomyces MD398-A1. This aziridine was prepared by treatment of diethyl (2i ,3K)-(-)-oxir-ane-2,3-dicarboxylate (231) with trimethylsilyl azide in EtOH/DMF to produced azido alcohol 232 [137], and treatment of this alcohol with triphenylphosphine afforded the aziridine dicarboxylate 233 in 71 % yield. Hydrolysis of 233 afforded the natural product 234 in 69% yield. 

Alkenylsilanes react with silyl azide and other organic azides to give bissilylenamines and silylaziridines, respectively, via unstable triazoline intermediates.78 Heating trimethylsilyl azide with cyclohexene or vinyltrieth-ylsilane for 10 days affords a modest yield of the respective aziridine,178 but with carefully purified trimethylsilyl azide, even after 2 weeks of reflux, no olefin consumption is indicated.104 Unstable triazoline intermediates are also formed from the reaction of cyanogen azide,808 picryl azide,29 and arylsulfonyl azides808 with unactivated olefinic bonds. 

In another study, the reaction of trimethylsilyl azide, chloride, or iodide with /V-iosylaziridines in DMF opened the aziridine ring by attack at the least substituted carbon giving the trans product in high yield.47 However, when a phenyl group was on the aziridine ring, both possible products were obtained and attack at the benzyl carbon predominated. 

The p-amino-a-hydroxy esters have been converted to diamino acids [88, 89] and related compounds like the nitrogen-substituted azetidinone shown in Scheme 13, a key structure in the synthesis of the commercially available antibiotic loracarbef [90] by substitution of the alcohol moiety with an azide. Several approaches have been used to achieve this transformation. Mesylation of the alcohol followed by substitution with sodium or trimethylsilyl azide provided cis-diamino acids [88,89]. trans-Diamino acids were obtained by ring opening of the aziridine [88] or by inversion of the alcohol bearing carbon followed by substitution under Mitsunobo conditions [90]. 

Trimethylsilyl azide has low reactivity toward alkenes, low yields of aziridines were obtained23 and some results could later not be reproduced24. 

Aziridines react with nucleophiles other than carbon nucleophiles. In the presence of TBAF, trimethylsilyl azide react with V-tosylaziridines to give the azido A-tosylamine. A-Benzylic aziridines are opened by trimethylsilyl azide in the presence of a chromium catalyst. Acetic anhydride reacts with N-tosylaziridines, in the presence of PBU3, to give the A-tosylamino acetate. A-Tosylaziridines react with InCls to give the chloro A-tosylamine. ... 

A mixture of either lead tetra-acetate or phenyliodosoacetate with trimethylsilyl azide apparently acts as a source of electrophilic azide at —15 °C, although free-radical reactions predominate when lead tetra-acetate is used at higher temperatures (see p. 314). The ionic reaction seems best represented as in Scheme 9, probably giving the unstable IV-diazonium-aziridines (171) and (172). The isolated products from trisubstituted olefins (e.g. cholesteryl acetate) are... 

The chiral (salen)Co catalysts have also been applied to cyclization reaction and preparation of intermediates for natural product synthesis [85]. In addition, chiral (salen)Ru catalysts proved to be effective for kinetic resolution of racemic epoxides [86]. Tridentate Schiff base Cr(III) complex (201) derived l-amino-2-indanol acts as a potent catalyst for asymmetric ring-opening reaction of meso-aziridines with trimethylsilyl azide (Scheme 16.60) [87]. The aziridine (200) was readily converted at —30 °C to the corresponding amino-azide in 95% yield with 94% ee. 

Ring opening of aziridines catalyzed by In(III) salts was studied by Yadav et al. and the results showed the same trend as above. InBrs was used for addition of amines to N-tosyl aziridines [86], In(OTf)3 for carboxylic acids [87], and InCh for trimethylsilyl azide [88] (Figure 8.45). 

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