Novel CuX2-mediated cyclization of acid–base salts of (l)-cinchonidine or (d)-/(l)-α-methylbenzylamine and 2,3-allenoic acids in an aqueous medium. An efficient entry to optically active β-halobutenolides

Abstract

The treatment of 1∶1 salts of 2,3-allenoic acid–chiral base with CuX₂ (4 equiv.) in an aqueous medium, i.e. acetone–H₂O (2∶1), at 60–65 °C afforded β-halobutenolides with high enantiopurities in good to excellent yields.