Cyclic thiosulfinates and thiosulfonates from oxidation of the 2-thiacephem ring system. Synthesis of (5R)-penems by stereospecific sulfur dioxide extrusion
Displacement of leaving groups from a number of 2-oxo-azetidin-4-ylthio derivatives with sulphide or hydrosulphide salts conveniently affords 2-thiacephem, whose desulphurisation gives penems.