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 ...