Three-Component Coupling Reactions of Arynes for the Synthesis of Benzofurans and Coumarins

摘要

The domino three-component coupling reaction of arynes with DMF and active methylenes or methines was studied as a highly efficient method for preparing heterocycles. Coumarin derivative >5 was formed when diethyl malonate (>2) or α-bromomalonate (>3) were used as a C2-unit. In contrast, dihydrobenzofurans >7a and >7b were obtained by using α-chloroenolates generated from α-chloromalonates >4a and >4b and Et2Zn. The benzofuran >15a could be obtained by using ethyl iodoacetate (>14) as a C1-unit. The one-pot conversion of dihydrobenzofurans >7a, >7b and >8a into benzofurans >15a and >15b was also studied. The direct synthesis of benzofuran >15b was achieved by using the active methine >18 having ketone and ester groups.