-Butyl(2-oxo-2-pyran-5-yl)carbamate as the First Chameleon Diene Bearing an Electron-Donating Substituent.

The 2()-pyran-2-one bearing electron-donating -butylcarbamate (BocNH-) group at the 5- position is a "chameleon" diene and undergoes efficient Diels-Alder cycloadditions with alkene dienophiles with both electron-rich and electron-deficient substituents. Cycloadditions afford the 5-substituted bicyclic lactone cycloadducts regardless of the electronic nature of the dienophile. However, cycloadditions with electronically matched electron-deficient dienophiles proceed faster than those with electronically mismatched electron-rich dienophiles.