Synthesis of optically active beta-lactams using the photochemical reaction of 3-deazauridines

The photochemical reaction of 3-deazauridines was investigated with the intention of obtaining chiral beta-lactams. Irradiation of appropriately protected 3-deazauridines at greater than or equal to 300 nm gave 2-(protected D-ribofuranosyl)-3-oxo-2-azabicyclo[2.2.0]hex-5-enes as a mixture of diasteromers, which were chromatographically separable. Treatment of each isomer with acid, such as trifluoroacetic acid, afforded the 5-oxo derivatives which by methanolysis gave rise to the corresponding chiral 4-methoxy-carbonylmethyl-1-(protected D-ribofuranosyl)azetidin-2-ones in good yields.