Abstract: A useful intermediate, glutaconic acid ester derivative (III), is prepared by Michael-type condensation of thiazoleacetic acid derivative (I) with alkoxyacrylic acid derivative (II) in the presence of base. ##STR1## (wherein, R is amino or protected amino;R.sup.1 is an ester forming group;R.sup.2 is hydrogen, cyano, or esterified carboxy;R.sup.3 is hydrogen, cyano, or esterified carboxy; andR.sup.4 is lower alkyl or aralkyl).

Abstract: Intermediates of the following formula are useful for the synthesis of 1-oxacephalosporins. Their preparation from penicillins and the transformation process to make 1-oxacephalosporins are disclosed. The compounds are of the formula: ##STR1## wherein A is amino or a selected acylamino;COB is carboxy or a selected protected-carboxy;X is halogen or the group ORin which R is a group represented by following formulas: ##STR2## wherein Nu is a selected nucleophilic group; R.sup.1 is a group of the following formula: ##STR3## in which Hal is halogen or alkylsulfonyloxy and R.sup.2 is alkyl or aryl; andY is hydrogen or methoxy; with the proviso that when R is propargyl or 2-oxopropyl andR.sup.1 is ##STR4## A is in the 3.alpha.-configuration and Y is 3.beta.-hydrogen or A is in the 3.beta.-configuration and Y is 3.alpha.-methoxy.

Abstract: A compound represented by the formula (II) epimerizes by the action of a base and the product is precipitated for shifting the equilibrium to yield the corresponding epimer represented by the formula (I). ##STR1## wherein Ar is an optionally substituted aryl or heterocyclic group;Tet is an optionally substituted tetrazolyl group andB.sup.1 and B.sup.2 are each ester forming group in the field of penicillin or cephalosporin chemistry.

Abstract: Potent antibacterial cephalosporin analogues of the following formula in forms of free acids, pharmaceutically acceptable salts, or esters preparable from penicillins through azetidinone derivatives by way of a new process, and utilizable as active ingredients in bactericidal compositions for pharmaceutical and veterinary use: ##STR1## (wherein Acyl is selected from phenylacetyl, D-mandeloyl, .alpha.-phenylmalonyl, D-.alpha.-(3-methanesulfonyl-2-oxoimidazolidin-l-yl)carbonamido-.alpha.-ph enylacetyl, and 2-thienylacetyl).