Abstract: Intermediates for preparaing an antibacterial 1-dethia-1-oxacephalosporins which are represented by the following formula: ##STR1## wherein R is a monovalent group (minus the carbonyl) from an acyl derived from a carboxylic or carbonic acid;Y.sup.1 is a divalent group of the following formula: ##STR2## wherein COB is carboxy or protected carboxy;X is hydrogen or a nucleophilic group; andZ is a leaving groupare prepared from a compound of the following formula: ##STR3## wherein R and Y.sup.1 are as defined aboveby the action of an acid.The new compounds of this invention shown by the following formula: ##STR4## wherein A is amino or substituted amino;E is hydrogen or methoxy; andY is a divalent group of the following formula: ##STR5## in which COB, X, and Z are as defined above are convertible into other compounds of the same formula by applying conventional methods in .beta.-lactam chemistry.

Abstract: Intermediates for preparing an antibacterial 1-dethia-1-oxacephalosporins which are represented by the following formula: ##STR1## wherein R is a monovalent group (minus the carbonyl) from an acyl derived from a carboxylic or carbonic acid;Y.sup.1 is a divalent group of the following formula: ##STR2## wherein COB is carboxy or protected carboxy;X is hydrogen or a nucleophilic group; andZ is a leaving groupare prepared from a compound of the following formula; ##STR3## wherein R and Y.sup.1 are as defined above by the action of an acid. The new compounds of this invention shown by the following formula: ##STR4## wherein A is amino or substituted amino;E is hydrogen or methoxy; andY is a divalent group of the following formula: ##STR5## in which COB, X, and Z are as defined above are convertible into other compounds of the same formula by applying conventional methods in .beta.-lactam chemistry.

Abstract: Intermediates for preparing an antibacterial 1-dethia-1-oxacephalosporins which are represented by the following formula: ##STR1## wherein R is a monovalent group (minus the carbonyl) from an acyl derived from a carboxylic or carbonic acid;Y.sup.1 is a divalent group of the following formula: ##STR2## wherein COB is carboxy or protected carboxy;X is hydrogen or a nucleophilic group; andZ is a leaving groupare prepared from a compound of the following formula: ##STR3## wherein R and Y.sup.1 are as defined above by the action of an acid.

Abstract: Intermediates for preparing an antibacterial 1-dethia-1-oxa-cephalosporins which are represented by the following formula: ##STR1## wherein R is a monovalent group (minus the carbonyl) from an acyl derived from a carboxylic or carbonic acid;Y.sup.1 is a divalent group of the following formula: ##STR2## wherein COB is carboxy or protected carboxy;X is hydrogen or a nucleophilic group; andZ is a leaving groupare prepared from a compound of the following formula: ##STR3## wherein R and Y.sup.1 are as defined above by the action of an acid.

Abstract: Intermediates for preparing an antibacterial 1-dethia-1-oxacephalosporins which are represented by the following formula: ##STR1## wherein R is a monovalent group (minus the carbonyl) from an acyl derived from a carboxylic or carbonic acid;Y.sup.1 is a divalent group of the following formula: ##STR2## wherein COB is carboxy or protected carboxy;X is hydrogen or a nucleophilic group; andZ is a leaving groupare prepared from a compound of the following formula: ##STR3## wherein R and Y.sup.1 are as defined above by the action of an acid. The new compounds of this invention shown by the following formula: ##STR4## wherein A is amino or substituted amino;E is hydrogen or methoxy; andY is a divalent group of the following formula: ##STR5## in which COB, X, and Z are as defined above are convertible into other compounds of the same formula by applying conventional methods in .beta.-lactam chemistry.

Abstract: Intermediates for preparing an antibacterial 1-dethia-1-oxacephalosporins which are represented by the following formula: ##STR1## wherein R is a monovalent group (minus the carbonyl) from an acyl group derived from a carboxylic or carbonic acid;Y.sup.1 is a divalent group of the following formula: ##STR2## wherein COB is carboxy or protected carboxy;X is hydrogen or a nucleophilic group; andZ is a leaving group are prepared from a compound of the following formula: ##STR3## wherein R and Y.sup.1 are as defined above by the action of an acid. The new compounds of this invention shown by the following formula: ##STR4## wherein A is amino or substituted amino;E is hydrogen or methoxy; andY is a divalent group of the following formula: ##STR5## in which COB, X, and Z are as defined above are convertible into other compounds of the same formula by applying conventional methods in .beta.-lactam chemistry.

Abstract: Useful intermediates for preparing a 1-dethia-1-oxacephalosporin and represented by the following formula: ##STR1## (wherein R is a monovalent group resulting from the elimination of the carbonyl function of an acyl group derived from a carboxylic or carbonic acid;COB is carboxy or protected carboxy; andX is hydrogen or a nucleophilic group)are prepared from the corresponding penicillin 1-oxides of the following formula: ##STR2## (wherein R, COB, and X are as defined above) by heating, if required in the presence of a desulfurizing reagent, or by exchanging the X group with another one under the condition of an appropriate nucleophilic substitution.

Abstract: Useful intermediates for preparing a 1-dethia-1-oxacephalosporin and represented by the following formula: ##STR1## (wherein R is a monovalent group resulting from the elimination of the carbonyl function of an acyl group derived from a carboxylic or carbonic acid;COB is carboxy or protected carboxy; andX is hydrogen or a nucleophilic group)are prepared from the corresponding penicillin 1-oxides of the following formula: ##STR2## (wherein R, COB, and X are as defined above) by heating, if required in the presence of a desulfurizing reagent, or by exchanging the X group with another one under the condition of an appropriate nucleophilic substitution.

Abstract: .alpha.-[3(R)-Substituted amino-4(R)-substituted alkoxy-2-oxo-azetidin-1-yl]-.alpha.-isopropenylacetate (Ia) and .alpha.-[3(R)-substituted amino-4(R)-substituted alkoxy-2-oxo-azetidin-1-yl]-.alpha.-isopropylideneacetate (Ib) prepared from (1R,5S)-.alpha.-(3-substituted-7-oxo-4-oxa-2,6-diazabicyclo[3.2.0]hept-2-e n-6-yl)-.alpha.-isopropenylacetate or (1R,5S)-.alpha.-(3-substituted-7-oxo-4-oxa-2,6-diazabicyclo-[3.2.0]hept-2- en-6-yl)-.alpha.-isopropylideneacetate with a primary alcohol in the presence of an acid. The products are useful intermediates for preparing oxadethiacephalosporins.

Abstract: Useful intermediates for preparing a 1-dethia-1-oxacephalosporin and represented by the following formula: ##STR1## (wherein R is a monovalent group resulting from the elimination of the carbonyl function of an acyl group derived from a carboxylic or carbonic acid;COB is carboxy or protected carboxy; andX is hydrogen or a nucleophilic group)are prepared from the corresponding penicillin 1-oxides of the following formula: ##STR2## (wherein R, COB, and X are as defined above) by heating, if required in the presence of the desulfurizing reagent, or by exchanging the X group with another one under the condition of an appropriate nucleophilic substitution.

Abstract: Intermediates (I) for preparing a potent antibacterial, 1-oxadethiacephalosporin, are shown by the following formula ##STR1## (wherein R is a group of acyl-minus-carbonyl derived from a carboxylic or carbonic acid;COB is carboxy or protected carboxy;X is hydrogen or a nucleophilic group;Y is a nucleophilic group; andZ is a leaving group)and prepared from the corresponding exomethylene compound (II) by addition of a compound of formula: Y-Z (in which Y and Z are as defined above).