Highly Stereoselective, One-Pot Synthesis of Azetidines and 2,4-Dioxo-1,3-diazabicyclo[3.2.0] Compounds Mediated by I2

We report here a convenient method to construct polysubstituted azetidines and 2,4-dioxo-1,3-diazabicyclo[3.2.0] compounds with high stereoselectivities in a one-pot reaction mediated by I2. The tetramethylguanidine (TMG)/I2-mediated formal [2 + 2] cycloaddition reaction of α-amidomalonate 1 with enones 2 affords functionalized azetidine derivatives 4 in moderate to good yields with high diastereoselectivity. When the α-ureidomalonate 5 is used instead of 1, 2,4-dioxo-1,3-diazabicyclo[3.2.0]­heptanes 8 and 2,4-dioxo-1,3-diazabicyclo[3.2.0]­heptenes 9 can be prepared selectively through the control of solvent and temperature. 2,4-Dioxo-1,3-diazabicyclo[3.2.0]­heptanes 8 can further undergo ring-opening reactions with different nucleophilic reagents to afford the corresponding polyfunctionalized azetidine derivatives 13–16 with high steroselectivities.