Process for producing thiophene compound and intermediate thereof

A dihydrothiophene compound represented by the formula (6):

• wherein:
• R1 represents a C6-10 aryl group or a C1-5 heteroaryl group, unsubstituted or substituted with one or more halogen atoms, one or more carboxy groups, one or more nitro groups, one or more formyl groups, one or more cyano groups, one or more hydroxy groups, one or more protected hydroxy groups, one or more thiol groups, one or more amino groups, one or more C1-10 alkyl groups, one or more C2-6 alkenyl groups, one or more C2-6 alkynyl groups, one or more C1-10 alkoxy groups, one or more C1-10 alkylcarbonyl groups, one or more C1-10 alkylcarbonyloxy groups, one or more C1-10 alkoxycarbonyl groups or one or more C6-10 aryl groups, such that the C1-10 alkyl groups, the C2-6 alkenyl groups, the C2-6 alkynyl groups, the C1-10 alkoxy groups, the C1-10 alkylcarbonyl groups, the C1-10 alkylcarbonyloxy groups, the C1-10 alkoxycarbonyl groups and the C6-10 aryl groups are unsubstituted or substituted with one or more halogen atoms;
• R2 and R3 independent represent a hydrogen atom, a C1-6 alkyl group or a C6-10 aryl group, unsubstituted or substituted with one or more halogen atoms, one or more nitro groups, one or more cyano groups, one or more hydroxy groups, one or more protected hydroxy groups, one or more thiol groups, one or more amino groups, one or more C1-10 alkyl groups, one or more C2-6 alkenyl groups, one or more C2-6 alkynyl groups, one or more C1-10 alkoxy groups or one or more C6-10 aryl groups, such that the C1-10 alkyl groups, the C2-6 alkenyl groups, the C2-6 alkynyl groups, the C1-10 alkoxy groups and the C6-10 aryl groups are unsubstituted or substituted with one or more halogen atoms.