The present invention relates to a process for preparing a 3-substituted thiophene represented by the formula (2):
wherein R represents a cyano group, a formyl group, a carboxyl group, a hydrocarbyloxycarbonyl group which may have a substituent(s) or an acyl group which may have a substituent(s),
which comprises reacting a vinyl compound represented by the formula (1):
RCH═CHY (1)
wherein R has the same meaning as defined above, and
Y represents a leaving group,
and an α-mercaptoacetaldehyde or a multimer thereof.