Abstract: An improved process for preparing 4-thia-2,6-diazabicyclo[3,2,0]hept-2-ene-7-ones such as methyl 3-phenoxy-4-thia-2,6-diazabicyclo[3,2,0]hept-2-ene-7-one-6-isopropenylacet ate which comprises extruding sulfur from dithiazeneazetidinones such as methyl 3-phenoxymethyl-4,5-dithia-2,7-diazabicyclo[4,2,0]-oct-2-ene-8-one-7-isopr openylacetate. The compounds obtained are useful intermediates in the preparation of certain 3-cephems.

Abstract: The invention relates to compounds of the formula: ##STR1## wherein R stands forBenzyl,Phenoxymethyl,4-amino-4-carboxy-1-butyl,R.sup.3 o--, r.sup.3 s--, r.sup.3 r.sup.4 n-- whereinR.sup.3 is loweralkyl, aryl or arylloweralkyl,R.sup.4 is hydrogen or R.sup.3, andR.sup.2 is hydrogen or methoxy, andR.sup.1 is hydrogen or a cleavable radical such as--CH.sub.2 OCH.sub.3, loweralkyl, 2,2,2-trichloroethyl, benzyl, p-nitrobenzyl, benzhydryl, phenacyl or trimethylsilyl. The novel compounds are useful intermediates in the preparation of known penicillin and cephalosporin derivatives.

Abstract: The invention relates to compounds of the formula: ##STR1## wherein R stands for benzyl, phenoxymethyl, 4-amino-4-carboxy-1-butyl, R.sup.3 O--, R.sup.3 S--, R.sup.3 R.sup.4 N-- wherein R.sup.3 is loweralkyl, aryl or arylloweralkyl, R.sup.4 is hydrogen or R.sup.3, and OH when the radicals R.sup.3 O--, R.sup.3 S-- and R.sup.3 R.sup.4 N--are hydrolyzed; R.sup. 2 is hydrogen or methoxy, and R.sup.1 is hydrogen or a cleavable radical such as --CH.sub.2 OCH.sub.3, loweralkyl, 2,2,2-trichloroethyl, benzyl, p-nitrobenzyl, benzhydryl, phenoxyethyl or trimethylsilyl. The novel compounds are useful intermediates in the preparation of known penicillin and cephalosporin derivatives.