Pyridinedithioesters as heterodienophiles: Application to the synthesis of aprikalim

Pyridinedithioesters can be used as efficient heterodienophiles when activated by complexation with BF3, by protonation, or by oxidation of the nitrogen atom of the pyridine moiety. The hetero-Diels-Alder reaction using 3-pyridinedithioester as a heterodienophile was the key step in a new synthesis of Aprikalim in racemic form. The methodology can be reliably extended to prepare new analogues of Aprikalim.