Process for preparing 2,5-disubstituted 3-alkylthiophenes

Process for preparing 2,5-disubstituted 3-alkylthiophenes of formula

• in which
• A represents a CH3, R2CH2, HOCH2 or R2CH(OH)— group,
• B represents a CHOH or CH2 group,
• R1 represents H or a C1-C5 alkyl group,
• R2 represents a C1-C5 alkyl group,
• R3 represents H or a C1-C5 alkyl group or a C1-C5 haloalkyl group, or a halogen chosen from fluorine, chlorine and bromine,
• which comprises:
• (a) reaction of a compound of formula
• in which
• A represents a CHO, CH3, R2CH2 or R2—CO— group, and
• R1 and R2 have the meanings given above;
• with a compound of formula
• in which
• X represents OH, halogen or a group of formula
• or a group of formula
• —OCOOR4 (VI)
• in which
• R4 represents a C1-C5 alkyl, an optionally substituted benzyl or an option-ally substituted aryl, and
• R3 has the meanings given above;
• to give a compound of formula
• in which
• A, R1, R2 and R3 have the meanings given above;
• and
• (b) reduction of the compound of formula IV thus obtained to give the compound of formula I.