The syntheses of N-methyl and N-carboethoxy-7-B-phenoxyacetamido-.DELTA.3-N-2-isocephem-4-carboxylic acids 17a and 17b are reported. Treatment of the aldehyde with methylamine followed by reduction of the Schiff base gave a compound which was converted to its trifluoroacetamide 5c. Acid catalyzed elimination of 1 mol of ethanol from 5c gave a compound which was converted to the enol via the vinylogous pyrrolidino amide. Reductive removal of the trifluoroacetamide function led to spontaneous ring closure to give another intermediate. Alternatively, treatment of bis-mesylate derivative of the next intermediate 11b with ammonia or methylamine gave 2 compounds in which the treatment of 1 with sodium hydride in DMSO [dimethylsalfoxide] gave 11b. Attempted acylation of a previous compound which after reduction of the azido functions followed by coupling of the amines to phenoxyacetic acid and reductive removal of the benzyl esters gave 17a and 17b respectively. Structural assignments are discussed.