Efficient synthesis of karrikinolide via Cu(II)-catalyzed lactonization

The efficient total synthesis of karrikinolide (KAR1), a potent plant growth regulator discovered in smoke from burning plant material, is described. 3-Hydroxy-4-pyranone, prepared from d-xylose, was subjected to a Cu(II)-catalyzed transesterification–Wittig lactonization to afford the dihydrofuropyran in good yield. Finally, radical bromination, followed by olefin formation, provided KAR1 in acceptable yield.