Described herein is a process for the preparation of 6.alpha.-fluorosteroids of formula (I), in which R is chosen from H, OH and an alkyl group with from 1 to 4 carbon atoms and R' is a carboxyalkyl group with from 1 to 4 carbon atoms in the alkyl chain, comprising the selective fluorination at the 6.alpha.-position ##STR1## by treatment of the compound of formula (III), wherein R and R' are as defined above, with an electrophilic fluorinating agent.

Described herein is the isomerisation process of 6.beta.-fluorosteroids into the corresponding pharmacologically active 6.alpha.-fluoro derivatives, comprising the reaction of 6.beta.-fluorosteroids, or 6.alpha./6.beta. isomeric mixtures, with an organic base containing a diazoimino group in a suitable organic solvent.

The present invention refers to process for the preparation of a tiazoline-azetidinone of formula I ##STR1## which comprises N-protecting in position 1 of (3S,4S)-3-phenylace tamido-4-acetoxy-azetidin-2-one, converting the product thus obtained into the corresponding thioamide and subsequently ciclyzing and deprotecting.

The preparation of a novel crystalline cefaclor and the conversion of such a product to cefaclor monohydrate are described. The new intermediate cefaclor is a particular crystalline form and possesses the same antibiotic properties as cefaclor monohydrate.

The preparation of a novel crystalline cefaclor and the conversion of such a product to cefaclor monohydrate are described. The new intermediate cefaclor is a particular crystalline form and possesses the same antibiotic properties as cefaclor monohydrate.