Synthetic Communications New Route to Synthesis of Unexpected

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New Route to Synthesis of Unexpected Pyridoin Derivatives: TheirStructure Determination with Spectroscopic and X-Ray MethodsAlaaddin Cukurovali a

a Chemistry Department, Faculty of Arts and Sciences, Firat University, Elazig, Turkey

Online publication date: 12 November 2009

To cite this Article Cukurovali, Alaaddin(2009) 'New Route to Synthesis of Unexpected Pyridoin Derivatives: TheirStructure Determination with Spectroscopic and X-Ray Methods', Synthetic Communications, 39: 24, 4396 — 4406To link to this Article: DOI: 10.1080/00397910902906537URL: http://dx.doi.org/10.1080/00397910902906537

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New Route to Synthesis of Unexpected PyridoinDerivatives: Their Structure Determination with

Spectroscopic and X-Ray Methods

Alaaddin CukurovaliChemistry Department, Faculty of Arts and Sciences,

Firat University, Elazig, Turkey

Abstract: The new 1,2,4-triazine-3-thione derivatives were obtained by a newroute using a one-step process. The structure of the compounds was determinedwith infrared (IR), 1H NMR, and 13C NMR spectroscopic methods and elemen-tal analysis. A representative x-ray crystallographic analysis of 3 was given, andits x-ray data are discussed in detail. This is a facile procedure and shorter thanearlier methods.

Keywords: Cyclization, pyridoin, triazine-3-thione

INTRODUCTION

The 1,2,4-triazine-thiones are well-known compounds, and a variety ofsynthetic methods for the preparation of substituted derivatives are avail-able. In the reported methods, the ring closures for as-triazine-3-thioneswere mainly started with a-diketone or a-dialdehyde.[1,2] Some closelyrelated compounds have also been synthesized starting from benzil andappropriate thiosemicarbazides,[3–6] and the most significant work onthese has been done by Gianturco and Romeo.[6]

The sustained interest in coordination chemistry of mercury withsulfur-containing ligands is related to the environmental consequences of

Received November 22, 2008.Address correspondence to Alaaddin Cukurovali, Chemistry Department,

Faculty of Arts and Sciences, Firat University, 23119 Elazig, Turkey. E-mail:[email protected]

Synthetic Communications1, 39: 4396–4406, 2009

Copyright # Taylor & Francis Group, LLC

ISSN: 0039-7911 print=1532-2432 online

DOI: 10.1080/00397910902906537

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the high toxicity of the metal to living systems.[7,8] Schiff base macroligandsderived from thiosemicarbazide are of significant interest not only for theirpharmacological properties as antibacterial and anticancer agents[9–11] butalso for their capacity for chemical recognition of metals of environmentalimportance.[12–16] The accidental liberation of mercury in the environmentposes dreadful toxicity problems, but recent studies have considered thereactivity of macroligands containing sulfur to entrap this metal.[17,18]

In the present work, for the first time, a facile and one-step processhas been developed for the preparation of 1,2,4-triazine-3-thionesstarting from nondiketone or nondialdehyde compounds as shown inScheme 1. These compounds (containing as-triazine ring, azomethinegroup, pyridine ring, second amine, and thione functions) seem to be sui-table candidates for further modifications and may be pharmacologicallyactive and useful as ligands in coordination chemistry. As far as I know,this is the first report on these molecules.

RESULTS AND DISCUSSION

The new 1,2,4-triazine-3-thiones, which also contain an azomethinegroup, B, were prepared by the reaction of pyridoin with 4-substitutedthiosemicarbazides in ethanol as a solvent in the presence of p-toluene-sulfonic acid (p-TsOH) as catalyst. In generaly, it is expected that thereaction of the thiosemicarbazide itself or 4-substituted thiosemicarbazidewith an acyloin (benzoin, pyridoin, etc.) must give carbazone type A com-pounds in the same reaction conditions as shown in Scheme 1. This expec-tation is not realized if acyloin is pyridoin; an unexpected ring closureoccurs. On the contrary, in the same reaction conditions, the reactionof thiosemicarbazide or 4-substituted thiosemicarbazide with benzoin

Scheme 1. Synthesis and the structures of the compounds.

Synthesis of Pyridoin Derivatives 4397


gave hydrazone-type compounds such as A.[19] The structures of 1–3 wereclearly identified by infrared (IR), 1H NMR, and 13C NMR spectroscopictechniques.

The cyclocondenzation reaction of pyridoin with appropriate thiose-micarbazides in absolute ethanol and in the presence of p-TsOH as catalystafforded compounds 1–3 in moderate yields (52–74%). IR spectra ofcompounds 1–3 exhibited characteristic �OH stretching vibration, �NH�stretching vibration, C=S stretching vibration (thioamide I), �N�H bend-ing vibration (thioamide II), and C�N stretching vibration (thioamide III).Aliphatic and other related absorptions are given in the experimentalsection. As expected, IR spectra of compound 1 do not contain any aliphaticabsorption band. These facts confirm the formation of the proposed com-pounds 1–3, which is also in agreement with elemental analysis results.

Further evidence for the formation of 1–3 was obtained by 1H and13C NMR spectroscopies. Their 1H NMR and 13C NMR data are givenin the experimental section. The 1H NMR spectra of 3 indicates that theethylenic protons HA and HB are nonequivalent geminal protons. In the1H NMR spectra of 3, two different sextets, assigned to the �CH2� pro-tons, appear at d 3.54 ppm (centered) for HA and d 3.69 ppm (centered)for HB due to vicinal and geminal couplings. These two peaks are a con-sequence of the chirality on the N3 atom (see the ORTEP drawing,Fig. 1), which bound to the ethyl group in the triazine-thione ring. Eachone of these peaks must contain eight signals, but because of the overlapping

Figure 1. ORTEP-3[27] drawing of the title compound, 3, showing the atomicnumbering scheme. Displacement ellipsoids of non-H atoms are drawn at the30% probability level, and H atoms are shown as small spheres of arbitrary radii.The intramolecular O�H . . .N hydrogen bond is represented by dashed lines.

4398 A. Cukurovali


signals, these two peaks appear as sextets in the 1H NMR spectra. The�CH3 protons unexpectedly appeared as triplets at d 0.73 (centered) ppmas a result of vicinal coupling with two nonequivalent geminal protons.Probably, �CH3 protons coupled with two different geminal �CH2� pro-tons with the same coupling constants. If the compound were in theA struc-ture (see Scheme 1), it would have contained 17 relative proton equivalentsin the 1H NMR spectra, but the 1H NMR spectra of the compound showedthat the relative number of protons is equal to 15, which also implies ringclosure. Its NMR spectra and especially x-ray data definitely identified theunexpected new compound as the B structure shown in Fig. 1.

As mentioned in the introduction, similar compounds have beensynthesized. However, none of the published molecules contain the pyr-idine moiety, and in all these publications, one of the starting substancesis a-diketone. In the work performed by Gianturco and Romeo,[6] in spiteof benzoin is a starting substance, the method used is not the same as themethod reported in this article, and the product does not contain pyri-doin and hydroxyl groups. Unlike earlier work, in this study pyridineand hydroxyl containing 1,2,4-triazine-3-thiones have been synthesizedby a new one-pot method starting from pyridoin.

As in the first stage of the osazone synthesis from theD-glucose,[20] in thefirst step of these syntheses, pyridoin both condenses and oxidizeswith 4-sub-stituted thiosemicarbazides, and in the second step of the reaction cyclizationoccurs. It has been thought that the pyridine ring makes the carbonyl groupmore positive, which is effective on the cyclization part of the reaction. Atentative reaction mechanism for the cyclization of A to B is proposed inScheme 2.

Scheme 2. Tentative reaction mechanism.



The molecular structure of 3, together with the atom-numberingscheme and the intramolecular hydrogen bonding, is presented in Fig. 1,and a summary of crystallographic data for the compound is given inTable 1. Selected bond lengths and angles are listed in Table 2.

The triazine ring adopts a twist-boat ring conformation,[21] asis evident from the ring-puckering parameters[22] [h¼ 107.85 (36)�,

Table 1. Crystal data for 3

Parameter Value

Color=Shape Prism=YellowChemical formula C15H15N5OSFormula weight 313.38Temperature (K) 296Wavelength (A) 0.71073 Mo KaCrystal system TriclinicSpace group P� 1a (A) 8.5768 (7)b (A) 10.1150 (8)c (A) 10.6064 (8)a (�) 62.582 (6)b (�) 76.055 (6)c (�) 67.206 (6)Volume (A3) 750.80 (10)Z 2Calculated density (Mg=m3) 1.386m (mm�1) 0.225Absorption correction Integration (X-RED32)Tmin, Tmax 0.8690, 0.9445F000 328Crystal size (mm) 0.80� 0.58� 0.32Diffractometer=measurementmethod

STOE IPDS II=rotation (x scan)

Index ranges �10� h� 10, �12� k� 12, �13� l� 13Theta range for data collection (�) 2.17� h� 26.00Measured reflections 10833Independent=observed reflections 2942=2636Rint 0.1041Refinement method Full-matrix least-squares on F2

Data=restraints=parameters 2942=0=199Goodness-of-fit on F2 1.042R indices [I> 2r(I)] R1¼ 0.0354, wR2¼ 0.0967R indices (all data) R1¼ 0.0422, wR2¼ 0.1004Dqmax, Dqmin (e=A3) 0.21, �0.18

4400 A. Cukurovali


u¼ 103.90 (43)�, and Q¼ 0.2261 (15) A]. The C�S bond distance of1.6817 (14) A agrees well with similar bonds in related compounds,[23]

being intermediate between 1.82 A for a C�S single bond and 1.56 Afor a C�S double bond.[24] The corresponding C2�N2 and C2�N3 bonddistances of 1.3509 (19) and 1.3392 (17) A, respectively, are indicative ofsome double-bond character, suggesting extensive electron delocalizationin the whole molecule. In the structure, the C1�C9 bond [1.4827 (19) A]

Table 2. Selected geometric parameters (A, �)

Parameter Value Parameter Value

O1�C3 1.4011 (15) N3�C14 1.4742 (17)N1�C1 1.2801 (17) C1�C3 1.5174 (19)N1�N2 1.3585 (16) C14�C15 1.509 (2)N3�C3 1.4719 (16)C1�N1�N2 (12) 117.21 (12) O1�C3�N3 105.67 (10)C2�N2�N1 125.99 (11) O1�C3�C1 111.73 (11)C2�N3�C3 122.10 (11) N3�C3�C1 109.03 (10)C2�N3�C14 120.89 (11) O1�C3�C4 112.31 (11)C3�N3�C14 116.21 (11) N3�C3�C4 109.04 (11)N1�C1�C9 117.31 (13) C1�C3�C4 108.95 (10)N1�C1�C3 123.76 (12) N4�C4�C3 113.52 (11)C9�C1�C3 118.83 (11) C5�C4�C3 123.44 (13)N3�C2�N2 116.76 (12) N5�C9�C1 116.01 (13)N3�C2�S1 124.14 (11) C10�C9�C1 122.00 (13)N2�C2�S1 119.09 (10)

Figure 2. Molecular packing of the title compound, 3, showing the formation ofchains of rings running along [11 �11]. For clarity, only H atoms involved inhydrogen bonding have been included.



is shorter than the C3�C4 bond [1.5307 (19) A]. This difference is prob-ably a consequence of a stronger conjugation of C1�N1 double bondwith the pyridine p system.

The potential donors N5 and O1 are found in a syn disposition, as aresult of intramolecular hydrogen bond leading to the formation of asix-membered ring. The crystal structure is stabilized by C�H . . .O,N�H . . . S, and C�H . . . p(pyridine) intermolecular interactions (Fig. 2).In addition, weak intermolecular p–p stacking interactions are observedbetween (C9�C13=N5) ring and its symmetry partner at position (1� x,1� y, 1� z), with a distance of 3.9478 (15) A between the ring centroidsand a perpendicular distance of 3.636 (3) A. Full details of thehydrogen-bonding geometry are given in Table 3.

Atomic positional parameters and all bond distances and angles arelisted in the supplementary material. CCDC 711959 contains the supple-mental crystallographic data for this article. These data can be obtainedfree of charge from the Cambridge Crystallographic Data Centre viawww.ccdc.cam.ac.uk/data_request/cif.

The software used in this research is as follows: for compound datacollection, X-AREA[25]; cell refinement, X-AREA[25]; data reduction,XRED[25]; solving structures, SHELXS97[26]; refining structures,SHELXL97[26]; molecular graphics, ORTEP3 for Windows[27]; andpreparation material for publication, WinGX.[28]

EXPERIMENTAL

Chemicals were purchased from Aldrich and Merck chemical companies.Melting point was determined on a Gallenkamp melting-point apparatusand is uncorrected. The elemental analyses were determined on a LecoCHNSO-932 elemental analysis apparatus. The IR spectra were measuredwith Mattson 1000 Fourier transform (FT)-IR spectrophotometer usingKBr pellets. The 1H NMR and 13C NMR spectra was recorded on a VarianMercury spectrometer using tetramethylsilane (TMS) as internal reference.

Table 3. Hydrogen-bonding geometry (A, �)

D�H . . .A D�H H . . .A D . . .A D�H . . .A

O1�H1 . . .N5 0.82 2.00 2.6328 (17) 133.2C5�H5 . . .O1i 0.93 2.45 3.3574 (19) 165.5N2�H2 . . . S1ii 0.86 2.51 3.3247 (12) 158.1C12�H12 . . .Cg1iii 0.93 2.86 3.676 (2) 144.99

Symmetry codes: (i) 1� x, 1� y,�z; (ii) �x,�y, 1� z; (iii) 1� x, 1� y, 1� z.

4402 A. Cukurovali


General Method for the Synthesis of the Compounds (1–3)

A solution of 10mmol of 2-hydroxy-1,2-di-pyridin-2-yl-ethanone(pyridoin) and 20mmol of appropriate thiosemicarbazide in 50mLabsolute ethanol was refluxed (4 h for 1, 7 h for 2, and 20 h for 3) inthe presence of 0.005 g p-TsOH as catalyst, with continuous stirring.The course of the reaction was monitored by IR spectroscopy. Whencooling to room temperature, the target product was precipitated withthe slow addition of water, filtered, washed with copious cold ethanol,and dried in air. The shiny crystals of 1–3, suitable for x-ray analysis,were obtained by slow evaporation from their ethanol solutions.

Data

5-Hydroxy-5,6-di-pyridin-2-yl-4,5-dihydro-2H-[1,2,4]triazine-3-thione (1)

Yield: 1.82 g, 64%; mp 221�C; FT-IR (KBr, cm�1): 3159 (�OH), 3089(�NH�), 1568 (thioamide I), 1247 (thioamide II), 1086 (thioamide III),631 (thioamide IV); 1H NMR (400MHz, DMSO-d6): d 7.15–7.19 (m,2H, aromatics), 7.54 (s, 1H, �OH, D2O exchangeable), 7.68–7.80 (m,4H, aromatics), 8.15–8.17 (m, 1H, aromatics), 8.30–8.31 (m, 1H, aro-matics), 9.96 (s, 1H, �NH�, D2O exchangeable), 11.91 (s, 1H, �NH�,D2O exchangeable); 13C NMR (400MHz, DMSO-d6): d 169.04, 162.04,153.40, 148.58, 148.45, 145.30, 137.27, 137.02, 123.99, 123.30, 122.20,121.08, 79.23. Anal. calcd. for C13H11N5OS: C, 54.72; H, 3.89; N,24.55; S, 11.24. Found: C, 54.63; H, 3.68; N, 25.00; S, 11.35.

5-Hydroxy-4-methyl-5,6-di-pyridin-2-yl-4,5-dihydro-2H-[1,2,4]triazine-3-thione (2)

Yield: 1.64 g, 52%; mp 202�C; FT-IR (KBr, cm�1): 3185 (�OH), 3133(�NH�), 2947 (aliphatics), 1529 (thioamide I), 1292 (thioamide II),1074 (thioamide III), 612 (thioamide IV); 1H NMR (400MHz,DMSO-d6): d 2.91 (s, 3H, �CH3), 7.15–7.18 (ddd, 1H, J1¼ 7.4Hz,J2¼ 4.9Hz, J3¼ 1.1Hz), 7.23–7.27 (ddd, 1H, J1¼ 6.7Hz, J2¼ 4.7Hz,J3¼ 1.1Hz), 7.68–7.97 (m, 4H, aromatics), 8.04 (s, 1H, �NH�, D2Oexchangeable), 8.17–8.19 (ddd, 1H, J1¼ could not be detected,J2¼ 4.8Hz, J3¼�1Hz), 8.37–8.40 (ddd, 1H, J1¼ could not be detected,J2¼ 4.4Hz, J3¼�1Hz), 12.00 (s, 1H, �OH, D2O exchangeable); 13CNMR (400MHz, DMSO-d6): d 171.22, 160.28, 153.42, 149.34, 148.43,143.48, 137.32, 136.96, 124.05, 123.78, 122.38, 122.28, 82.79, 33.71. Anal.



calcd. for C14H13N5OS: C, 56.17; H, 4.38; N, 23.40; S, 10.71. Found: C,55.90; H, 4.41; N, 22.97; S, 10.48.

5-Hydroxy-4-ethyl-5,6-di-pyridin-2-yl-4,5-dihydro-2H-[1,2,4]triazine-3-thione (3)

Yield: 1.75 g, 56%; mp 219�C; FT-IR (KBr, cm�1): 3175 (�OH), 3134(�NH�), 2986–2928 (aliphatics), 1519 (thioamide I), 1243 (thioamideII), 1079 (thioamide III), 634 (thioamide IV) cm�1. 1H NMR(400MHz, DMSO-d6): d 0.72 (t, J¼ 7.0Hz, 3H, �CH3), 3.54 (sextet,1H, J¼ 6.6Hz, �CH2A�), 3.69 (sextet, 1H, J¼ 6.7Hz, �CH2B�) (bothare centered), 7.15–7.18 (ddd, 1H, J1¼ 7.4Hz, J2¼ 4.9Hz, J3¼ 1.1Hz),7.23–7.27 (ddd, 1H, J1¼ 6.7Hz, J2¼ 4.7Hz, J3¼ 1.1Hz), 7.68–7.97 (m,4H, aromatics), 8.04 (s, 1H, �NH�, D2O exchangeable), 8.17–8.19(ddd, 1H, J1¼ could not be detected, J2¼ 4.8Hz, J3¼�1Hz),8.37–8.40 (ddd, 1H, J1¼ could not be detected, J2¼ 4.4Hz, J3¼�1Hz),11.92 (s, 1H, �OH, D2O exchangeable);13C NMR (400MHz,DMSO-d6): d 170.46, 160.93, 153.50, 149.15, 148.33, 143.73, 137.35,137.15, 123.98, 123.81, 122.30, 122.04, 82.94, 41.64, 14.25. Anal. calcd.for C15H15N5OS: C, 57.49; H, 4.82; N, 22.35; S, 10.23. Found: C,57.65; H, 5.03; N, 22.71; S, 9.96.

ACKNOWLEDGMENTS

I express my sincere thanks to Prof. Muharrem Dincer, Faculty of Artsand Sciences, Physics Department, Ondokuz Mayis University (Samsun,Turkey), for preparing the crystal structure analysis utilized in this article.I also express my sincere thanks to Prof. Emine Kilic, Faculty of Arts andSciences, Chemistry Department, Ankara University (Ankara, Turkey),and Assoc. Prof. Suleyman Servi, Faculty of Arts and Sciences, Chemis-try Department, Firat University (Elazig, Turkey), for preparing thereaction mechanism proposed in this article.

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