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organic papers
Acta Crystallographica Section E

Structure Reports Online
ISSN 1600-5368

Unexpected formation of a thiazolo[3,2-a]pyridinium methide: a novel subclass of mesoionic compounds

Victor B. Rybakov,a* Alexander A. Bush,a Sergei I. Troyanov,a Eugene V. Babaeva and Erhard Kemnitzb
a Department of Chemistry, Moscow State University, 119992 Moscow, Russian Federation, and bHumboldt-Universitat zu Berlin. Math. Nat. Fakultat - Institut, fur Chemie, D-12489, Berlin, Germany

While trying to prepare mesoionic thiazolo[3,2-a]pyridinium2-thiolate by reaction of 2-bromo-1-(ethoxycarbonylmethyl)pyridinium bromide with CS2, an unexpected product was formed, namely (ethoxycarbonyl)[3-(ethoxycarbonyl)-1,3thiazolo[3,2-a]pyridin-4-ium-2-yl](2-thioxo-1,2-dihydropyridin-1-yl)methanide, C19H18N2O4S2. The structure of the product corresponds to a previously unknown subclass of mesoionic thiazolo[3,2-a]pyridinium-2-methylides.

Received 17 February 2006 Accepted 27 March 2006.

Comment
We have previously described the successful synthesis of previously unknown mesoionic thiazolo[3,2-a]pyridinium-2thiolates by the reaction of 2-halogen-N-phenacylpyridinium salts with CS2 (Babaev et al., 2004). An analogous reaction between 2-bromo-1-(2-ethoxy-2-oxoethyl)pyridinium bromide and CS2 unexpectedly formed the title compound, (2), instead of the desired thiolate, (3) (see first scheme below).

Correspondence e-mail: rybakov20021@yandex.ru

Key indicators Single-crystal X-ray study T = 100 K ° Mean (C­C) = 0.002 A R factor = 0.032 wR factor = 0.077 Data-to-parameter ratio = 17.5 For details of how these key indicators were automatically derived from the article, see http://journals.iucr.org/e.

The structure of (2) is shown in Fig. 1. The main structural feature of the molecule is the difference in the lengths of the two C S bonds (C3 S4 and C5 S4) in the thiazole ring (Table 1). Additionally, the N1 C2 bond is longer than the other two C N bonds of the bicyclic system. These observations may reflect the separation of charges in the mesoionic system into two parts: a positively charged 2-thiopyridinium fragment and a negatively charged C2 C3 C10 unit. Interestingly, the ester groups C11 O11 and C15 O15 seem to make a smaller contribution to the delocalization of the negative charge, since the C10 C11 and C2 C15 distances are relatively long.

# 2006 International Union of Crystallography All rights reserved

A possible rationalization of the formation of (2) is shown in the second scheme. Initial reaction of CS2 with the ylide
doi:10.1107/S1600536806011135 Rybakov et al.


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Data collection
Stoe IPDS diffractometer ! scans Absorption correction: none 6851 measured reflections 4380 independent reflections 3810 reflections with I > 2 (I) Rint max h= k= l= = 0.020 = 29.1 8!9 12 ! 12 20 ! 20

Refinement
Refinement on F 2 R[F 2 > 2 (F 2)] = 0.032 wR(F 2) = 0.077 S = 1.03 4308 reflections 246 parameters H-atom parameters constrained w = 1/[ 2(Fo2) + (0.0359P)2 + 0.5422P] where P = (Fo2 + 2Fc2)/3 (а/ )max = 0.002 ° аmax = 0.46 e A 3 ° аmin = 0.29 e A 3

Table 1

° Selected geometric parameters (A, ).
N1--C5 N1--C9 N1--C2 C2--C3 C2--C15 C3--C10 C3--S4 S4--C5 C5--C6 C6--C7 C7--C8 C8--C9 C10--C11 C10--N19 C11--O11 C5--N1--C9 C5--N1--C2 C9--N1--C2 C3--C2--N1 C3--C2--C15 N1--C2--C15 C10--C3--C2 C10--C3--S4 C2--C3--S4 C5--S4--C3 N1--C5--C6 N1--C5--S4 C6--C5--S4 C7--C6--C5 C6--C7--C8 C9--C8--C7 C8--C9--N1 C3--C10--C11 C3--C10--N19 C11--C10--N19 1.3677 (16) 1.3758 (16) 1.4143 (17) 1.4082 (17) 1.4636 (17) 1.3928 (17) 1.7675 (13) 1.7237 (14) 1.3983 (18) 1.3793 (19) 1.395 (2) 1.373 (2) 1.4337 (17) 1.4381 (15) 1.2295 (15) 119.24 113.37 127.35 112.66 128.68 118.38 131.70 118.39 109.70 91.55 121.32 112.47 126.20 119.50 118.49 121.33 120.12 119.18 122.55 117.51 (11) (11) (11) (11) (12) (11) (11) (9) (9) (7) (12) (10) (10) (12) (13) (13) (12) (11) (11) (11) C11--O12 O12--C13 C13--C14 C15--O15 C15--O16 O16--C17 C17--C18 N19--C24 N19--C20 C20--C21 C20--S20 C21--C22 C22--C23 C23--C24 O11--C11--O12 O11--C11--C10 O12--C11--C10 C11--O12--C13 O12--C13--C14 O15--C15--O16 O15--C15--C2 O16--C15--C2 C15--O16--C17 O16--C17--C18 C24--N19--C20 C24--N19--C10 C20--N19--C10 N19--C20--C21 N19--C20--S20 C21--C20--S20 C22--C21--C20 C21--C22--C23 C24--C23--C22 C23--C24--N19 1.3557 (15) 1.4581 (14) 1.5081 (18) 1.2160 (17) 1.3356 (18) 1.4567 (16) 1.504 (2) 1.3717 (18) 1.3852 (17) 1.4268 (17) 1.6897 (15) 1.366 (2) 1.406 (2) 1.3626 (19) 122.22 122.90 114.87 114.42 107.74 124.07 124.55 111.28 118.33 107.97 122.52 116.97 120.35 115.31 122.81 121.88 122.31 119.75 118.59 121.43 (11) (12) (10) (9) (10) (12) (13) (11) (11) (12) (11) (11) (11) (12) (9) (11) (13) (12) (13) (13)

Figure 1
The structure of (2), showing the atom numbering scheme. Displacement ellipsoids are drawn at the 50% probability level, with H atoms shown as spheres of arbitrary radius.

from (1) leads to the formation of the adduct (4a). This could react with an additional molecule of (1) to give the intermediate (4b) and then (4c). The arylthio-group in (4c) could then undergo intramolecular substitution leading to the product (2). Substitution of an SR group in analogous 2-RSthiazolo[3,2-a]isoquinolinium salts in the presence of CH acids is well documented (Mizuyama et al., 1976).

Experimental
2 Bromo 1 (2 ethoxy 2 oxoethyl)pyridinium bromide, (1) (9.8 g, 30 mmol), was suspended in dichloromethane (70 ml). The mixture was cooled to 233 K and Et3N (13.9 ml, 10.1 g, 100 mmol, 3.3 equivalents) added dropwise. The resulting suspension was kept at 233 K for an additional 15 min and then CS2 (7.25 ml, 9.12 g, 120 mmol, 4 equivalents) was added. The reaction mixture turned yellow, then deep red as the temperature was increased to 283 K. After standing overnight, the mixture was diluted with water (200 300 ml), the organic layer separated and the aqueous layer extracted with dichloromethane (2 б 200 ml). The organic phases were combined, dried (Na2SO4) and evaporated. The resulting dark residue was dissolved in chloroform and purified using flash chro matography (SiO2, CHCl3). A crude dark brown solid (2.45 g) was obtained, which yielded dark red crystals of (2) (2.1 g, 34%, m.p. 463 466 K) after final recrystallization from acetone. Crystal data
C19H18N2O4S2 Mr = 402.47 Triclinic, P1 ° a = 6.8600 (14) A ° b = 9.0710 (18) A ° c = 14.634 (3) A = 82.66 (3)  = 80.06 (3) = 84.11 (3) ° V = 886.6 (3) A3 Z=2 Dx = 1.508 Mg m 3 Mo K radiation Cell parameters from 6851 reflections = 3.5 31 = 0.33 mm 1 T = 100 (2) K Plate, dark red 0.40 б 0.40 б 0.14 mm


° All H atoms were refined using a riding model, with C H 0.95 A ° and Uiso(H) 1.2Ueq(C) for aromatic, C H 0.99 A and Uiso(H) ° 1.2Ueq(C) for CH2, and C H 0.98 A and Uiso(H) 1.5Ueq(C) for CH3 atoms. Data collection: X AREA (Stoe & Cie, 2002); cell refinement: X AREA; data reduction: X RED32 (Stoe & Cie, 2002); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP 3 for Windows (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).

The authors are indebted to the Russian Foundation for Basic Research for covering the licence fee for use of the Cambridge Structural Database (Version 5.27; Allen, 2002).
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References
Allen, H. F. Babaev, E. Nasonov, Farrugia, L. (2002). Acta Cryst. B58, 380 388. V., Rybakov, V. B., Orlova, I. A., Bush, A. A., Maerle, K. V. & A. F. (2004). Russ. Chem. Bull. (Int. Ed. Engl.), 53, 176 180. J. (1997). J. Appl. Cryst. 30, 565. Farrugia, L. J. (1999). J. Appl. Cryst. 32, 837 838. Mizuyama, K., Matsuo, Y., Tominaga, Y., Matsuda, Y. & Kobayashi, G. (1976). Chem. Pharm. Bull. 24, 1299 1304. Sheldrick, G. M. (1997). SHELXS97 and SHELXL97. University of Ё Gottingen, Germany. Stoe & Cie (2002). X-AREA (Version 1.18) and X-RED32 (Version 1.04). Stoe & Cie, Darmstadt, Germany.

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