New cephalosporins of the formula: ##STR1## in which n=0 or 1, R.sub.1 is a radical of the formula: ##STR2## [in which R.sub.4 is a protective radical and R.sub.5 is hydrogen, alkyl, vinyl, cyanomethyl or a protective radical], or R.sub.1 is a protective radical and R.sub.2 is a protective radical or an enzymatically removable radical, or R.sub.1 is an acyl radical which may be substituted in various ways and R.sub.2 is a protective radical, in the 3-oxoethyl-bicyclooct-2-ene or -bicyclooct-3-ene or 3-oxoethylidene-bicyclooctane form if n=0, and in the 3-oxoethyl-bicyclooct-2-ene or 3-oxoethylidene-bicyclooctane form if n=1, are useful as intermediates for the preparation of 3-thiovinyl-cephalosporins useful as antibacterial agents.