l-Proline-Catalyzed Three-Component Reaction of 4-Chloro-3-formylcoumarin, Sodium Sulfide, and α-Halo Ketones: A Direct Approach to Thieno[3,2- c ]coumarins

Abstract

A new protocol for the synthesis of thieno[3,2-c]coumarins is disclosed. In this method, a 3-formyl-2-oxo-2H-chromene-4-thiolate anion is generated in situ by treatment of 4-chloro-3-formylcoumarin with sodium sulfide. This chromene-4-thiolate undergoes an L-prolinecatalyzed substitution/Knoevenagel cascade with various α-halo ketones to afford the desired thienocoumarins in moderate to good isolated yields. This protocol eliminates the need for stoichiometric amounts of inorganic bases and the use of foul-smelling thiols. The reaction conditions tolerate a variety of α-halo ketones.