Synthesis of a novel thiabicyclo[3.2.0]heptan-6-one analogue of penicillin

Synthesis of (1SR, 4SR, 5SR, 7RS)-7-(tert-butoxycarbonylamino)-2-thiabicyclo[3.2.0]heptan-6-one-4-carboxylic acid ethyl ester, a novel cyclobutanone analogue of a β-lactam antibiotic is described. This was achieved by [2+2] cycloaddition of a 2,3-dihydrothiophene with dichloroketene, followed by conversion to a cyclobutanol and use of an intramolecular nitrene insertion strategy to install nitrogen functionality at C-7 with endo stereochemistry.