Too Short-Lived Or Not Existing Species: N-Azidoamines

Article Cite This: J. Org. Chem. 2019, 84, 4033−4039 pubs.acs.org/joc Too Short-Lived or Not Existing Species: N‑Azidoamines Reinvestigated Klaus Banert* and Tom Pester Chemnitz University of Technology, Organic Chemistry, Strasse der Nationen 62, 09111 Chemnitz, Germany *S Supporting Information ABSTRACT: Treatment of N-chlorodimethylamine with sodium azide in dichloromethane does not lead to N-azidodimethylamine, as thought for more than 50 years. Instead, surprisingly, (azidomethyl)dimethylamine is generated with good reproducibility. A plausible reaction mechanism to explain the formation of this product is presented. The reaction of lithium dibenzylhy- drazide with tosyl azide does not result in the creation of an N-azidoamine, which can be detected by IR spectroscopy at ambient temperature, as it was claimed previously. Additional experiments with diazo group transfer to lithium hydrazides show that intermediate N-azidoamines are very short-lived or their formation is bypassed by direct generation of 1,1-diazenes via synchronous cleavage of two N−N bonds. 1. INTRODUCTION Scheme 1. Attempts To Generate N-Azidoamines The azido unit belongs to the most important functional groups in chemistry because of a variety of applications, particularly in the case of organic azides.1 Not only carbon but also most elements in the periodic table form a bond to azide;2 however, only a few of the corresponding covalent compounds are of general interest, for example, as reagents in synthetic chemistry, such as hydrazoic acid,3 silyl azides,4 phosphoryl azides,5 and sulfonyl azides.5b,6 In particular, azides attached to − another nitrogen atom have only rarely been reported.7a d Such azides, in which the azide-bearing additional nitrogen atom is always connected with at least one strongly electron- withdrawing group, turned out to be very unstable. On the Downloaded via TU CHEMNITZ on May 8, 2019 at 10:17:33 (UTC). other hand, N-azidoamines, particularly those derived from − nitrogen heterocycles,7e o attracted attention in numerous the trapping product 5 was isolated in 65% yield.10b The quantum chemical studies because these compounds are authors postulated the formation of 4c via intermediate 2c, discussed as high energy density compounds (HEDCs). which was generated from 3c and tosyl azide by diazo group See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles. In the case of N-azidoamines, four groups published their transfer. Whereas interception of 4c with the help of PTAD − results when they tried to generate such azides.8 11 In 1962, was successful, the stability of N-azidoamine 2c remained − Wiberg and Gieren presented the almost quantitative synthesis unclear. At first an IR band at 2060 cm 1, which was detected of azide 2a using the reaction of N-chloro compound 1a with with reduced intensity after workup at room temperature, was lithium azide in tetrahydrofuran (Scheme 1).8a Later, it turned assigned to azide 2c.10a Later, it was stated that liberation of out, however, that a mixture of hexamethyldisilazane and 2-azi- dinitrogen already occurred at about −20 °C, and this pointed 10b dotetrahydrofuran had been isolated instead of the supposed to lower stability of 2c. product 2a.8b Bock and Kompa reported on the treatment of N-Azidoamines 2b and 2c showed slightly divergent azido N-chlorodimethylamine (1b) with sodium azide in dichloro- bands in the IR spectra and quite different thermal stability. methane, which was claimed to afford, after workup by vacuum Thus, it is not easy to understand that 2b can be isolated at 2c distillation, a 25% yield of N-azidoamine 2b that showed an IR ambient temperature and cannot. Attempts to generate − 9,12 signal at 2110 cm 1. Anselme and co-workers reacted 1,1- nitrogen triazide (N10) from nitrogen trichloride and sodium, 3c lithium, or silver azide resulted in the formation of dinitrogen dibenzylhydrazine ( ) with butyllithium (1.0 equiv) and then 9b,11,13 with tosyl azide to obtain products that were most probably as the only product. To the best of our knowledge, the derived from the short-lived 1,1-diazene (aminonitrene) 4c.10 When the transformation was performed at low temperatures Received: January 4, 2019 in the presence of 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD), Published: February 19, 2019 © 2019 American Chemical Society 4033 DOI: 10.1021/acs.joc.9b00034 J. Org. Chem. 2019, 84, 4033−4039 The Journal of Organic Chemistry Article Scheme 2. Reaction of 1b with Sodium Azide in Dichloromethanea aYields based on weighed 1b and weighed 1H NMR standard. existence of simple N-azidoamines has not been further Scheme 3. Reaction of 1b with Sodium Azide in investigated. The wariness of experimenters is possibly based Dichloromethane Followed by Treatment with Cyclooctyne on the explosive properties of 2b. Bock and Kompa reported on a spontaneous explosion of 2b (50 mg), which led to a serious injury of a laboratory technician.9b Herein, we describe a corrigendum to the structure of the covalent azide that is formed from 1b and sodium azide in dichloromethane. Furthermore, we present experiments that indicate that N-azidoamines are very short-lived and cannot be isolated and characterized at room temperature. 2. RESULTS AND DISCUSSION When we repeated the experiments with equimolar amounts of 1b and sodium azide in dichloromethane (rt, 24 h) several times,14 we were able to confirm all of the reported9b,c phenomena.15 But after removal of the insoluble sodium salts, we did not obtain any evidence about the formation of N- yield) that resulted from hydrazoic acid and cyclooctyne. For 16 azidoamine 2b. Instead, we detected the ammonium salt 8b, comparison, we also prepared 15 and 16 from an excess of 17 16,18 19 the amidinium salts 9 and 11, and the known azide 13, cyclooctyne and hydrazoic acid or 13, respectively. which were generated with good reproducibility and nearly Our results demonstrate that the structure of 2b was quantitatively (Scheme 2). The reaction of 1b with sodium erroneously assigned for the real product 13.9 In Scheme 2,we azide was also realized in deuterated dichloromethane to propose mechanisms to explain the formation of 8b, 9, 11, and exclude any incorporation of the solvent into one of the 13 from 1b and sodium azide.15 We assume that sodium azide 20 products, especially the surprising azide 13. Diazidomethane first acts as a base and induces 1,2-elimination24 of hydrogen was produced in very small traces only; however, a significant chloride from 1b, which leads to the imine 6, sodium chloride, proportion of this dangerous azide (22−26% 1H NMR yield and hydrazoic acid. The highly reactive species 6 is known25 to based on the azide salt) was formed besides 8b, 9, 11, and 13, reversibly trimerize, creating the cyclic aminal 7. Oxidation of when the experiments were performed with more soluble azide the latter compound with the help of 1b results in the salts such as hexadecyltributylphosphonium azide21 instead of generation of the final products 8b and 9. Equilibration of 8b sodium azide or in the presence of benzyltrimethylammonium with hydrazoic acid and dimethylamine facilitates the addition chloride. After recondensation22 of the reaction mixture of this secondary amine to imine 6, which furnishes the aminal resulting from 1b and sodium azide in dichloromethane, 13 10. Such a species is then oxidized with the aid of 1b to was the only (volatile) product. When such a reaction mixture produce 8b and amidinium salt 11.If10 is transformed into (without recondensation) was treated with cyclooctyne, we did the hydrogen azide salt 12, cleavage of the latter compound not obtain the trapping product 14b, although 1-amino-1H- and attack of the azide anion leads to N-(azidomethyl)- 1,2,3-triazoles are established as stable substances23 (Scheme dimethylamine (13). 3). Instead, we obtained the 2H-1,2,3-triazole 16 (11% isolated In control experiments, we treated commercially available 7 yield based on 1b), which was formed from 13 by with 1b in dichloromethane (rt, 24 h) and obtained the cycloaddition followed by rapid rearrangement of the known17,26 amidinium chloride, including the same cation as corresponding 1H-1,2,3-triazole, and the product 15 (9% amidinium azide 9, along with dimethylamine hydrochloride. 4034 DOI: 10.1021/acs.joc.9b00034 J. Org. Chem. 2019, 84, 4033−4039 The Journal of Organic Chemistry Article When 7 was similarly exposed to 8b, the covalent azide 13 was Scheme 4. Attempts To Generate and Trap the N- formed with 8% yield besides large amounts of unreacted 7.In Azidoamine 2d this case, 13 was most probably generated via the intermediates 6, 10, and 12. Even treatment of the extremely reactive imine 625a with 8b under the same reaction conditions led to the product 13 (7% yield) along with trimer 7 (82%). When we repeated the experiments with equimolar amounts of 3c and butyllithium followed by treatment with tosyl azide (Scheme 1), we were able to confirm all the phenomena, in particular, the IR data, reported by G. Koga and J.-P. Anselm.10a However, it turned out that the IR signal at 2060 cm−1 did not result from N-azidoamine 2c because it has to be assigned to lithium azide, which was formed as a byproduct after attack of the lithium hydrazide at the sulfur atom of tosyl azide. Consequently, we also detected known27,28 1,1-dibenzyl- 2-tosylhydrazine that originated from the same reaction. This unwanted side reaction was repressed by using the sterically shielded 2,4,6-triisopropylbenzenesulfonyl azide instead of tosyl azide; in this case, we observed an IR signal at 2060 cm−1 with significantly diminished intensity and thus a lower proportion of lithium azide.

Load more