The Structure of N-Benzylazoles from Pyrrole to Carbazole: Geometries and Energies Dionisia Sanz, Rosa M. Claramunt, Christian Roussel, Ibon Alkorta, José Elguero
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Dionisia Sanz, Rosa M. Claramunt, Christian Roussel, Ibon Alkorta, José Elguero. The Structure of N-Benzylazoles from Pyrrole to Carbazole: Geometries and Energies. Indian Journal of Heterocyclic Chemistry, 2018, 28 (1), pp.1-10. hal-02093199
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Dionisia Sanz1*, Rosa M. Claramunt1, Christian Roussel2, Ibon Alkorta3, José Elguero3 1Departamento de Química Orgánica y Bio-Orgánica, Facultad de Ciencias, UNED, Paseo Senda del Rey, 9, E-28040 Madrid, Spain 2Aix-Marseille Université, CentraleMarseille, CNRS, Institut des Sciences Moléculaires de Marseille UMR 7313, 13397 Marseille, France 3Instituto de Química Médica, Centro de Química Orgánica “Lora-Tamayo”, CSIC, Juan de la Cierva, 3, E-28006 Madrid, Spain
(Dedicated to Prof. S.P. Singh on his 80th Birthday)
ABSTRACT The complete series of 18 parents N-benzylazoles (10 azoles and 8 benzazoles) have been calculated at the B3LYP/6-311++G(d,p) level. The geometries have been compared with the X-ray structures reported in the literature for six derivatives (1H-imidazole, 1H-1,2,3-triazole, 1H-1,2,3,4-tetrazole, 1H-benzimidazole, 1H-benzotriazole, and 9H-carbazole). Only one minimum has been found for the 18 molecules, but several transition states connecting them have been located. The calculated geometries agree well with those reported by X-ray crystallography.
KEY WORDS N-Benzylazoles, N-Benzylbenzazoles, X-Ray geometries, DFT calculations, Enantiomerization.
INTRODUCTION phosphorus analogues), six-membered rings (azines and their oxygen, sulfur, and phosphorus analogues), and larger rings (seven-, eight-, and nine-membered rings).[1-3] Although this following one: Small rings (three- and four-membered rings), not covers all heterocycles, it shows the importance of azoles, between one-third and one-fourth of all heterocycles.[4] Systematic exploration of the whole family of azoles verify that the structures obtained correspond to energetic (including azoles and benzazoles) is almost impossible minima (0) or to TSs (1). All the calculations have been because there are several thousands of them, thus, some carried out with the Gaussian-09 package.[11] restriction must be applied. We have restricted the present study to parent compounds (no C-substituents) bearing RESULTS AND DISCUSSION on the nitrogen atom a benzyl group. The resulting 18 derivatives were calculated to determine their minimum X-ray structures energy conformations (rotations about two single bonds) and geometries. Furthermore, the transition states (TSs) A search in the Cambridge Structural Database[12] of connecting the minima have been calculated. Note that even N-benzylazoles afforded six hits that are represented in Figure 1. in the case of a unique minimum, there are several TSs in the The refcodes, from EYIRIN to NUPSIG, are also reported.[12] path from one minimum to an identical minimum. Calculated structures A total of 17 N-benzylazoles are known; only 1-benzyl- 1H-pentazole (10) has never been reported. Some of these Figure 2 summarizes the information concerning the compounds have been described in many papers, their optimized geometries (absolute minima). interest lies mainly as synthetic intermediates,[5] although To analyze these results, we have reported in Table 1 some interesting biological properties have been reported.[6] the four angles, the nature of the substituents at positions A commentary is necessary here. For comparative (P) 2, 3, 4, and 5 (P2-P5) assuming that the N-benzyl is at purposes, it is useful to the number the N atom bearing the position 1 and the absence-presence matrix[20,21] of the three benzyl group, N1; but, this is not the IUPAC numbering possible substituents at positions 2, 3, 4, and 5, C, N, and B rule; according to it, the N atoms must have the lowest (benzene). The CH substituents have been removed since numbers, this lead to N4 for 5 and N2 for 7, 9, 12, 15, and 17. they are used as reference to calculate the intercepts.[22,23] Finally, carbazole is an accepted exception and the N atom The results of the statistical analyses of Table 1 are given is numbered N9. When, in general, for the 18 compounds, in Table 2. ! ! "# "$ "% "&