2,3-Didehydrocephams: 5-thia-1-azabicyclo[4.2.0]oct-2-en-8-ones.
See: cephalosporins, cephams
Source:
PAC, 1995, 67, 1307. 'Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)' on page 1327 (https://doi.org/10.1351/pac199567081307)