Synthesis of unsaturated lactone moieties by asymmetric hetero Diels–Alder reactions with binaphthol-titanium complexes

Natural products like ratjadone and callystatin A contain an α,β-unsaturated lactone moiety which adds to the biological activity of these compounds. Here we report a rapid and practical access to lactone precursor 3 by an asymmetric hetero Diels–Alder reaction as the key step and its subsequent transformation into a suitable building block 4.