2-Azabicyclo [2.2.0] hexane-3,5-dione, a new building block for carbapenem nuclei

2-Azabicyclo[2.2.0]hexane-3,5-dione is synthesized via photopyridone formation from 4-(t-butyldimethylsilyloxy)- or 4-alkoxy-2-pyridone followed by mild acid hydrolysis and reacts with a variety of alcohols or thiols to give 4-alkoxycarbonyl- or 4-alkylthiocarbonyl-methylazetidin-2-ones.