Temperature-Controlled Chemoselective Synthesis of Multisubstituted 4-Alkynyl/ trans 4-Alkenyl Coumarins.

A temperature-controlled facile synthesis of multisubstituted 4-alkynyl/ trans 4-alkenyl coumarins with a metal salt cascade approach is reported. H 2 O serves both as a nucleophile and hydrogen source. The presence of metal salt facilitates the reduction of alkyne. The present protocol bypasses the structural shortcomings of the existing Sonogashira and Heck coupling reactions. In addition, the obtained 2,3-disubstituted coumarins are readily transformed into 2,3-disubstituted dihydrocoumarins, which serve as important building blocks in organic transformations.