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 <b>1</b> with enones <b>2</b> affords functionalized azetidine derivatives <b>4</b> in moderate to good yields with high diastereoselectivity. When the α-ureidomalonate <b>5</b> is used instead of <b>1</b>, 2,4-dioxo-1,3-diazabicyclo[3.2.0]­heptanes <b>8</b> and 2,4-dioxo-1,3-diazabicyclo[3.2.0]­heptenes <b>9</b> can be prepared selectively through the control of solvent and temperature. 2,4-Dioxo-1,3-diazabicyclo[3.2.0]­heptanes <b>8</b> can further undergo ring-opening reactions with different nucleophilic reagents to afford the corresponding polyfunctionalized azetidine derivatives <b>13</b>–<b>16</b> with high steroselectivities