Thioester derivatives of thiazolyl acetic acid and their use in the preparation of cephalosporin compounds

A process for preparing thiazolyl acetic acid derivative represented by formula (I),

• comprising, reacting a thiazolyl acetic acid represented by formula (IV),
• wherein,
• R1 represents H, trityl, CH3, or CRaRbCOOR3, in which Ra and Rb, independently of one another, represents hydrogen or methyl and R3 represents H or C1-C7 alkyl;
• with thio-oxadiazole of formula (VI),
• wherein, R2 represents C1-C4 alkyl or phenyl;
• in the presence of an organic solvent base and a condensation agent, at a temperature being maintained in the range −10° C. to +30° C.

A process for preparing a compound of formula (II),

• wherein,
• R1 represents H, trityl, CH3, or CRaRbCOOR3, in which Ra and Rb, independently of one another, represents hydrogen or methyl and R3 represents H or C1-C7 alkyl;
• R4 is CH3, —CH═CH2, CH2OCH3, CH2OCOCH3,
• R5 is H or a salt or a carboxylic protecting group;
• or,
• comprising, acylating a compound of formula (III),
• wherein, R4 and R5 are defined as above, and R6 is H or trimethylsilyl;
• with a compound of formula (I),
• wherein, R1 and R2 are as defined above;
• in the presence of an organic solvent, organic base and a silylating agent at a temperature in the range of −10° C. to +30° C.