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Selective derivatization of 2,4,6-triazidopyridines by the Staudinger reaction

 

作者: Sergei V. Chapyshev,  

 

期刊: Mendeleev Communications  (RSC Available online 1999)
卷期: Volume 9, issue 4  

页码: 166-167

 

ISSN:0959-9436

 

年代: 1999

 

出版商: RSC

 

数据来源: RSC

 

摘要:

Mendeleev Communications Electronic Version, Issue 4, 1999 (pp. 129–170) Selective derivatization of 2,4,6-triazidopyridines by the Staudinger reaction Sergei V. Chapyshev Institute of Problems of Chemical Physics, Russian Academy of Sciences, 142432 Chernogolovka, Moscow Region, Russian Federation. Fax: +7 096 515 3588; e-mail: chap@icp.ac.ru The selective addition of triphenylphosphine to the g-azido group of 2,4,6-triazidopyridines has been developed.Selective derivatization of the azide groups in polyazides is of considerable interest. Recently we have shown1–3 that 2,4,6-triazidopyridines 1a–c add electron-rich dipolarophiles to the azido group at the 4-position of the pyridine ring, whereas in reactions with electron-deficient dipolarophiles cycloadducts are formed at the azido groups in the 2- and 6-positions.To extend the synthetic methods of selective derivatization of the azido groups in 2,4,6-triazidopyridines, the nucleophilic additions of triphenylphosphine (Staudinger reaction4) to the azido groups of 1a–c were studied. In the reactions† of 1a–c with an equimolar amount of PPh3 in diethyl ether at 0 °C, only iminophosphoranes 3a–c were formed as the final products in quantitative yields.The structures of 3a–c are supported by the data of elemental analysis and spectroscopic investigations.‡ Thus, for instance, the presence of only three signals at d 111.5 (d, 3JPC 10.2 Hz), 147.0 (s) and 155.2 (d, 2JPC 3.6 Hz) ppm for the carbon atoms of the pyridine ring in the 13C NMR spectrum of 3a unambiguously indicates that the addition of a molecule of PPh3 to triazide 1a occurs regioselectively at the g-azido group.Based on literature analogies, 4 it seems reasonable to assume that the mechanism of the reactions involves initial nucleophilic attack by a molecule of PPh3 on the azide terminus in the g-azido group of 1a–c and formation of phosphazides 2a–c as intermediate products.Compounds 2a–c are obviously unstable at 0 °C and readily lose a molecule of nitrogen to form 3a–c. The reason for the selective nucleophilic addition of PPh3 to the g-azido groups of 1a–c can be rationalised from the analysis of the charge distribution in the azido groups of starting triazides. Thus, as can be seen in Table 1, the g-azido groups of 1a–c have the † A typical procedure for the synthesis of 2,6-diazido-4-iminophosphoranopyridines 3a–c.A diethyl ether solution of triphenylphosphine (2 mmol, 50 ml) was added dropwise to a solution, cooled at 0 °C, of triazide 1a–c (2 mmol) in 100 ml of the ether with stirring. The mixture was kept at 0 °C for 1 h and then warmed to room temperature. The solvent was evaporated under reduced pressure, and the solid residue was recrystallised from hexane. Yields (%): 3a, 93; 3b, 95 and 3c, 97.‡ Characteristic data for 3a: mp 151–152 °C (decomp.). 1HNMR (CDCl3) d: 7.47 (m, 6H, C3'–H), 7.55 (m, 3H, C4'–H), 7.77 (m, 6H, C2'–H). 13C NMR (CDCl3) d: 111.5 (d, C-3, C-5, 3JPC 10.2 Hz), 128.5 (d, C-3', 3JPC 13.1 Hz), 131.4 (d, C-1', 1JPC 106.1 Hz), 131.9 (d, C-4', 4JPC 2.2 Hz), 132.4 (d, C-2', 2JPC 10.2 Hz), 147.0 (s, C-2, C-6), 154.5 (d, C-4, 2JPC 3.6 Hz).IR (KBr, n/cm–1): 2140 (N3), 1630 and 1570 (C=N, C=C). Found (%): C, 54.86; H, 3.17; N, 22.01; P 5.88. Calc. for C23H15Cl2N8P (%): C, 54.68; H, 2.99; N 22.17; P, 6.13. 3b: mp 176–177 °C (decomp.). 1H NMR (CDCl3) d: 7.46 (m, 6H, C3'–H), 7.53 (m, 3H, C4'–H), 7.75 (m, 6H, C2'–H). 13C NMR (CDCl3) d: 92.3 (d, C-5, 3JPC 15.2 Hz), 108.5 (d, C-3, 3JPC 7.3 Hz), 115.8 (CºN), 128.6 (d, C-3', 3JPC 13.1 Hz), 130.5 (d, C-1', 1JPC 106.1 Hz), 131.9 (d, C-4', 4JPC 2.2 Hz), 132.3 (d, C-2', 2JPC 10.2 Hz), 152.0 (s, C-6), 154.1 (s, C-2), 159.2 (d, C-4, 2JPC 2.2 Hz).IR (KBr, n/cm–1): 2225 (CºN), 2145 (N3), 1640 and 1565 (C=N, C=C). Found (%): C, 58.32; H, 3.28; N, 27.98; P 6.04. Calc. for C24H15ClN9P (%): C, 58.14; H, 3.05; N 28.24; P, 6.25. 3c: mp 190–191 °C (decomp.). 1H NMR (CDCl3) d: 7.56 (m, 6H, C3'–H), 7.67 (m, 3H, C4'–H), 7.80 (m, 6H, C2'–H). 13C NMR (CDCl3) d: 89.8 (d, C-3, C-5, 3JPC 12.4 Hz), 115.1 (CºN), 128.9 (d, C-3', 3JPC 13.1 Hz), 129.0 (d, C-1', 1JPC 106.1 Hz), 132.5 (d, C-2', 2JPC 10.9 Hz), 132.7 (d, C-4', 4JPC 2.2 Hz), 159.1 (s, C-2, C-6), 163.4 (d, C-4, 2JPC 2.2 Hz). IR (KBr, n/cm–1): 2230 (CºN), 2150 (N3), 1640 and 1565 (C=N, C=C).Found (%): C, 61.97; H, 3.32; N, 28.55; P 6.16. Calc. for C25H15N10P (%): C, 61.74; H, 3.11; N 28.78; P, 6.37. most electrophilic azide termini. By comparing the charges at the azido groups of 1a–c and their derivatives 3a–c (Table 1), one can also find that the transformation of the g-azido groups of 1a–c into a strong electron-donating N=PPh3 substituent leads to a decrease in the electrophilicity of azide termini in the a-azido groups of pyridines.Therefore, no surprise that the addition of PPh3 to all three azido groups of 1b has been achieved only on prolonged boiling of the reaction mixture in a benzene solution.7 To our knowledge, compounds 3a–c are the first representatives of azides containing an active phosphaza group in the molecule.According to PM3 computations, among three resonance forms 3, 4 and 5 the last one most closely fits the structure of such compounds. This conclusion is in full accord with the published data8,9 on the structure of aryliminophosphoranes. Taking into account the fact that azido and phosphaza groups can be easily modified in numerous fashions4,10 into other N-containing functions, compounds 3a–c can be considered as very promising synthons for the preparation of novel pyridine derivatives.Table 1 The charge distribution on the Ng atoms in azido groups of 1a–c and 3a–c computed by the PM3 and RHF/3-21 G* methods.5,6 Compound 2-N3 4-N3 6-N3 PM3 3-21 G* PM3 3-21 G* PM3 3-21 G* 1a –0.30 — –0.28 — –0.30 — 1b –0.28 0.10 –0.26 0.14 –0.28 0.10 1c –0.27 0.11 –0.24 0.15 –0.26 0.11 3a –0.34 — — — –0.33 — 3b –0.32 — — — –0.32 — 3c –0.31 — — — –0.31 — N R2 N3 N3 N3 R1 N R2 N N3 N3 R1 N N P Ph Ph Ph PPh3 1a–c 2a–c – N2 N R2 N3 N3 R1 N P Ph Ph Ph 3a–c N R2 N3 N3 R1 N P Ph Ph Ph 5a–c N R2 N3 N3 R1 N P Ph Ph Ph 4a–c a R1 = R2 = Cl b R1 = Cl, R2 = CN c R1 = R2 = CNMendeleev Communications Electronic Version, Issue 4, 1999 (pp. 129–170) References 1 S. V. Chapyshev, U. Bergstrasser and M. Regitz, Khim. Geterotsikl. Soedin., 1996, 67 [Chem. Heterocycl. Compd. (Engl. Transl.), 1996, 32, 59]. 2 S. V. Chapyshev and V. M. Anisimov, Khim. Geterotsikl. Soedin., 1997, 1521 [Chem. Heterocycl. Compd. (Engl. Transl.), 1997, 33, 1315]. 3 S. V. Chapyshev, Mendeleev Commun., 1999, 164. 4 (a) Yu. G. Gololobov, I.N. Zhmurova and L. F. Kazukhin, Tetrahedron, 1981, 37, 437; (b) Yu. G. Gololobov and L. F. Kazukhin, Tetrahedron, 1992, 48, 1353. 5 (a) J. J. P. Stewart, J. Comput. Chem., 1989, 10, 209; (b) Spartan version 4.0, Wavefunction, Inc., USA, 1995. 6 M. W. Schmidt, K. K. Baldrige, J. A. Boatz, S. T. Elbert, M. S. Gordon, J. H. Jensen, S. Koseki, N. Matsunaga, K. A. Nguyen, S. J. Su, T. L. Windus, M. Dupius, J. A. Montgomery, J. Comput. Chem., 1993, 14, 1347. 7 S. V. Chapyshev and T. Ibata, Heterocycles, 1993, 36, 2185. 8 M. Pomerantz, D. S. Marynick, K. Rajeshwar, W.-N. Chou, L. Throckmorton, E. W. Tsai, P. C. Y. Chen and T. Cain, J. Org. Chem., 1986, 51, 1223. 9 T. A. Albright, W. J. Freeman and E. E. Schweizer, J. Am. Chem. Soc., 1975, 97, 940. 10 E. Scriven and K. Turnbull, Chem. Rev., 1988, 88, 297. Received: 4th March 1999; Com. 99/1457

 



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