A periselective cross-Diels–Alder reaction

Due to predictable regioselectivity and stereoselectivity, the Diels–Alder reaction is one of the most widely used reactions in modern organic synthesis. However, Diels–Alder reactions involving two different conjugated dienes, named the cross-Diels–Alder reaction, often proceeds without periselectivity to form a mixture of [4+2]/[2+4] adducts. Recently, our group has developed a Cu(II)-catalyzed periselective and stereoselective cross-Diels–Alder reaction between 2-pyrones and 1,3-cyclodienes, which gives [2+4] adducts as sole products.