Summing up the results of the reactions of derivatives of Ȗ-bromodypnone with azoles, one can conclude
that the rate of formation of the quaternary salts of the azoles is determined by the basicity of the azole and decreases
in the series: 1-alkyl-1H-imidazoles > 1-alkyl-1H-benzimidazoles > 1-alkyl-1H-1,2,4-triazoles > 5-chloro-1-methyl-
1H-imidazole > 4-methyl-1,3-thiazole > 1,3-benzothiazole > N-phenyl-1,3,4-thiadiazole-2-amine. The influence of
the structure of the azole and the nature of the substituents in the benzene rings of the dypnone unit on the rate
of cyclization of the quaternary salts is nonexistent, but results in the lower stability of the intermediate hydroxy
derivatives of dihydroazolo[a]pyridines with increasing acceptor properties of the substituents on the pyridine
ring [6].
EXPERIMENTAL
1
IR spectra (KBr tablets) were recorded on a Perkin-Elmer Spectrum BX instrument. H NMR spectra
were recorded in DMSO-d6 with TMS as internal standard on a Bruker AVANCE DRX-500 (500 MHz)
instrument. Two-dimensional correlation experiments were carried out with Varian Mercury 400 (1H and 13C,
400 and 100 MHz respectively), with TMS as internal standard, chemical shifts on the į scale. Control of the
purity of the compounds synthesized was by TLC on Silufol UV-254 plates and HPLC mass-spectroscopic
method with an Agilent 1100 series instrument with an Agilent LC/MSD SL selective detector (samples were
introduced in a CF3CO2H matrix, EI ionization).
(Z)-4-Bromo-1,3-diphenyl-2-buten-1-one 3a was prepared by method [7], (Z)-1,3-diaryl-4-bromo-
2-buten-1-ones 3b-d were made by method [8].
5-Chloro-1-methyl-1H-imidazole, 4-methyl-1,3-thiazole, 1,3-benzothiazole, N-phenyl-1,3,4-thiadiazole-
2-amine, and 1-methyl-1H-1,2,4-triazole were commercial products of the "Enamine" company.
(Z)-3-[2,4-diaryl-4-oxo-2-butenyl]-5-chloro-1-methyl-1H-imidazol-3-ium Bromides 4a-c. 5-Chloro-
1-methyl-1H-imidazole (0.41 g, 3.55 mmol) was added to a solution of Ȗ-bromodypnone 3 (1.07 g, 3.55 mmol)
in benzene (30 ml). The mixture was kept for 1-2 d at room temperature. The precipitate was filtered off, washed
with acetone, and recrystallized from nitromethane.
6,8-Diaryl-2-chloro-1-methyl-1H-imidazo[1,2-a]pyridine-4-ium Bromides 5a-c. A mixture of salt
4a-c (1.15 mmol) and morpholine (2 ml) in acetone (10 ml) was heated for 2h. After cooling, the precipitate was
filtered off and washed with acetone.
(Z)-3-[2,4-Diaryl-4-oxo-2-butenyl]-4-methyl-1,3-thiazol-3-ium Bromides 6a-d and (Z)-3-[2,4-Di-
aryl-4-oxo-2-butenyl]-1,3-benzothiazol-3-ium Bromides 7a,b were prepared by the method used to synthesize
products 4a-c. Reaction time 2-3 d.
6,8-Diaryl-3-methyl[1,3]thiazolo[3,2-a]pyridine-4-ium Bromides 8a-d and 2,4-Diarylpyrido-
[2,1-b][1,3]benzothiazol-10-ium Bromides 9a,b. A mixture of salts 6a-d or 7a,b (1.15 mmol) and
triethylamine (2 ml) in acetone (10 ml) was heated for 2 h. After cooling, the precipitate was filtered off and
washed with acetone.
2-Anilino-6,8-diphenyl[1,3,4]thiadiazolo[3,2-a]pyridin-4-ium Bromide (10). N-phenyl-1,3,4-thia-
diazole-2-amine (0.63 g, 3.55 mmol) was added to a solution of Ȗ-bromodypnone 3a (1.07 g, 3.55 mmol) in
benzene (30 ml). The mixture was kept for 4 d at room temperature. The precipitate formed was filtered off and
washed with acetone. Triethylamine (2 ml) was added to a suspension of the solid substance in acetone (15 ml)
and the mixture was heated for 2 h. After cooling, the precipitate was filtered off and washed with acetone.
(Z)-4-[2,4-diaryl-4-oxo-2-butenyl]-1-methyl-1H-1,2,4-triazol-4-ium Bromides 12b-d were prepared
by the method used for the synthesis of products 4a-c. Reaction time 24 h.
1-Methyl-6,8-diphenyl-1H-[1,2,4]triazolo[4,3-a]pyridin-4-ium Bromide (14a). 1-Methyl-1H-1,2,4-
triazole (0.3 g, 3.55 mmol) was added to a solution of Ȗ-bromodypnone 3a (1.07 g, 3.55 mmol) in benzene
(30 ml). The mixture was kept at room temperature for 24 h, the precipitate was filtered off and washed with
230