Efforts are reported in asymmetric synthesis of halo carbonyls through organocatalysis. In one study an acid chloride is converted into an α-halo ester with a strong base (sodium hydride), a bromine donor and an organocatalyst based on proline and quinine:
In the proposed reaction mechanism the base first converts the acid chloride to the ketene, the organocatalyst then introduces chirality through its quinonoid tertiary amine, forming a ketene adduct.