Catalyst-free 1,3-dipolar [3 + 2] cycloadditions of N,N′-cyclic azomethine imines with β-substituted-α,β-unsaturated carbonyls: Access to highly regioselective functionalized N,N′-bicyclic pyrazolidinones

We have developed a catalyst-free [3 + 2]-cycloaddition of N,N'-cyclic azomethine imines with γ-hydroxy-α,β-unsaturated ketones at 60 °C, producing N,N'-bicyclic pyrazolidinones with high yields and remarkable diastereoselectivity. This approach was also applied to the [3 + 2]-cycloaddition of β-substituted-α,β-unsaturated ketones and esters, making it a practical and efficient protocol for the synthesis of biologically relevant pyrazolidinone frameworks.