Electrochemical trimethylsilylation of mono- and polyhalothiophenes (h
al = Cl, Br) has been examined. In order to predict the selectivity of
the reaction in accordance with the halogen position on the ring, the
reduction potentials of the commercially available halothiophenes hav
e been determined by cyclic voltammetry. Thus, as expected, the bromo
derivatives are more easily reduced than the chloro analogs, and the 2
-position is more reactive than the S-position. We obtained 2- and 3-(
trimethylsilyl)thiophenes, 2-(trimethylsilyl)-3 (or 5)-halothiophenes,
2-(trimethylsilyl)-3,4,5-trihalothiophenes, 2,5-bis(trimethylsilyl)th
iophene, 2,5-bis(trimethylsilyl)-3,4-dihalothiophenes and 2,3,5-tris(t
rimethylsilyl)-4-halothiophenes with an excellent selectivity. In cont
rast, the silylation of 2-(trimethylsilyl)3-halo- and 2,3,5-tris(trime
thylsilyl)-4-halothiophenes occurred with ring opening and afforded 1,
1,4,4-tetrakis(trimethylsilyl)-1,2-butadiene and hexakis(trimethylsily
l)-2-butyne, respectively. A coherent interpretation of the synthetic
results is proposed in correlation with the measured potential values.