New 1,2,3-selenadiazole and 1,2,3-thiadiazole Derivatives

New 1,2,3-thiadiazole and 1,2,3-selenadiazole derivatives, 14-23, were prepared from the ketones 1-5 via the corresponding semicarbazones or hydrazones 6-12. The Hurd-Mori and Lalezari methods were used, respectively, for the preparation of these 1,2,3-thiadiazole and 1,2,3-selenadiazole derivatives. The intermediate 13 was also trapped, separated and fully characterized. These derivatives are important for photocrosslinking processes and due to their potential biological activity.


Introduction:
Interest in the synthesis of selenium and sulfur containing compounds and the further utilization of these compounds in organic synthesis has been steadily increasing recently [1].Particular interest in 1,2,3-selenadiazole and 1,2,3-thiadiazole derivatives stems from the fact that they can undergo a wide variety of reactions where they act as 1,3-dipoles or as a source of selenium or sulfur and hence they have attracted much attention for the synthesis of different organoselenium and organosulfur compounds [2] in both the acyclic and cyclic series [3].In spite of the obvious attraction of Se and Sheterocycles, only a few preparative routes have been described.Lalezari et al. [4][5][6] were the first to report the synthesis of a 1,2,3-selenadiazole ring by analogy with the 1,2,3-thiadiazole system, which had been prepared previously by Hurd and Mori [7].We report herein the synthesis of new compounds containing 1,2,3-selenadiazole and 1,2,3-thiadiazole rings using the Lalezari et

Scheme 2
Table 1 shows the structures of the newly prepared compounds, melting point ranges and the percentage yields of these compounds.Table 1.Compound 13 was of particular interest as it represents the isolable and stable intermediate in the mechanism for 1,2,3-selenadiazole ring cyclization.Scheme 3 shows the proposed mechanism for the formation of compound 13.Its structure was confirmed by IR, 1 H-NMR, 13 C-NMR, mass spectrometry and elemental analysis.

General
The solvents used were purified by standard procedures.The melting points (m.p) were determined on an Electrothermal digital melting point apparatus and uncorrected.Infrared (IR) spectra of pure substances were recorded for KBr pellets using a NICOLET 410 FT-IR spectrometer (ν in cm -1 ).The 1 H-and 13 C-NMR spectra were recorded on Bruker AM 400 and AC200 spectrometers in CDCl 3 or DMSO-d 6 .The spectral data are reported in delta (δ) units relative to the TMS reference peak.The mass spectra were registered using MAT CH7A (Varian, EI: 70eV Ionizing energy, electron ionization) and MAT95 (Finnigan, FD: 5kV Ionizing energy, field desorption) instruments.The signals are given as m/z with the relative intensity between brackets.Elemental analyses were performed in the analytical laboratory of the Institute of Organic Chemistry of University of Mainz, Germany.D-(+)-camphor, acetyl ferrocene, diacetyl ferrocene, p-hydroxyacetophenone, acetophenone, ethyl hydrazine carboxylate, semicarbazide hydrochloride and sodium acetate were obtained from Aldrich.

Scheme 3 .
Scheme 3. Mechanism for the formation of compound 13
al. and Hurd and Mori methods.