Mechanism of asymmetric photocyclization of alpha-oxoamides

The molecules of N,N-diisopropylarylglyoxylamides, 1, are converted into the corresponding beta-lactams, 2, on exposure to UV light in the solid state, However, the chemical and optical yields of the photocyclization are quite different among the crystals, The crystal structures of the three positional isomers 1a-c as reactants and the photoproduct 2b derived from 1b are determined by X-ray structure analysis: (1a) o-chlorophenyl-N,N-diisopropylglyoxylamide; (1b) m-chlorophenyl-N,N-diisopropylglyoxylamide; (1c) p-chlorophenyl-N,N-diisopropylglyoxylamide; (2b) 3-(m-chlorophenyl)-3-hydroxy-N-isopropyl-4,4-dimethylazetidin-2-one. The reactivity and enantioselectivity of the reactions are discussed on the basis of the structures and the packing potential energy calculated.