Cycloadditions in syntheses. Part 27. rel-(1R,4R,5S)-5-hydroxy-2-azabicyclo[2.2.0]hexan-3-one and its derivatives: synthesis and transformation to azetidin-2-ones

The title compound, a synthetic equivalent of 4-(2-oxoethyl)azetidin-2-one, has been synthesized as a stable crystalline compound from the 2-pyridone having an appropriately protected 4-hydroxy group via photopyridine formation, catalytic hydrogenation, and deblocking of the protecting group. Successful conversion of the title compound and its derivatives into azetidin-2-ones having a terminally oxygenated ethyl side chain at the 4-position is also described.