Nuclear analogs of β-lactam antibiotics. XIV. Synthesis of penems via (4-tritylthio-2-azetidinon-1-yl)triphenylphosphoranylideneacetates

The preparation of (4-tritylthio-2-azetidinon-l-yl)triphenylphosphoranylideneacetates from 4-acetoxyazetidin-2-one is described. They are easily converted to mercuric or silver mercaptides. These mercaptides are acylated with a wide variety of acylating agents and cyclized to 2-substituted penem-3-carboxylates.