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Reactivity and thermal behaviour of 7-methyl- 2h,3h,7h-imidazo[2,1-b]thiazol-4-ium chloride

Recently, in the course stability study of thyrostatic drug methimazole (1-methyl-1, 3-dihydro-1Himidazole-2-thione, 2) in DCE we reported synthesis and characterisation of 7-methyl-2H, 3H, 7Himidazo[2, 1-b]thiazol-4-ium chloride (1) as a novel and stable thiiranium ion isomer.[1] To gain more insight into its reactivity we performed reaction of 1 with 2 in boiling MeCN whichunexpectedly led to theformation of 2, 3-dihydro-3-methyl-1-[(1-methyl-1Himidazole-2-yl) thioethyl]-1H-imidazole-2-thione (3)in low yield. Furthermore, we found that 1underwent thermal ringopening isomerisation to1-chloroethyl-2, 3-dihydro-3 - methyl - 1H - imidazole-2-thione (4) in low yield (25 %) due to its equilibrium to 1. In addition, isolated, solid 4, after 20hours at room temperature, spontaneously and quantitively isomerized back to 1. Finally, inreaction of 4 with 2 in boiling MeCN, dimeric product 3 is obtained in 92 % yield. It, by heatingat 170°C during 10 hours, also underwent to thermal isomerization to its regio-isomer 1, 2-bis(2, 3-dihydro-3-methyl-1H-imidazole-2-thione-1yl)ethane (5) in 88% yield. Isomerization was studied using spectroscopic and computational methods as well. All products were characterized using spectroscopic and thermal methods, while structure of 3[C10H14N4S2], (Mr=254.37) was additionally determined by single crystal X-ray analysis. Itcrystallizes in centrosymmetric space group P21/c and its molecules consist of two methylimidazole rings separated with a thioether −CH2−CH2−S− spacer. The crystal data are as follows: a = 12.1442(5), b = 6.9640(3), c = 14.1111(6)Å, V = 1191.48(9) Å3, Z = 4, R = 0.0321, Rw = 0.0803, S = 1.076, 8232 reflexes with I>2(I).

Reactivity ; thermal behaviour ; 7-methyl- 2h, 3h, 7h-imidazo[2, 1-b]thiazol-4-ium chloride

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