Synthesis of β-lactams by photolytic Wolff rearrangement

Abstract

3-Diazo-5-methylpyrrolidine-2,4-dione (5) undergoes a Wolff rearrangement when irradiated in the presence of t-butyl carbazate to give cis- and trans-β-lactam derivatives [(6) and (7)]. The (Z)-adduct (8) derived from the dione (5) by the addition of acetylenedicarboxylic esters gives both the (E)- and the (Z)-trans-β-lactams [(10) and (11)] when irradiated for a short time in the presence of t-butyl carbazate. but on prolonged irradiation the (E)-trans-β-lactam (10) is generated exclusively. Benzyl 6-diazo-5,7-dioxohexahydropyrrolizine-3-carboxylate (16; R = CH₂Ph). when irradiated at low temperature in the presence of β-methylphenethyl carbazate gives the 7-oxo-1-azabicyclo[3.2.0]heptane derivative (17; R = CH₂Ph), which, as expected, is a highly reactive system.