Multi-Auto-Tandem Reaction to Access Site-Specific Functionalized Tricyclic Furo[3,2-<i>c</i>]coumarins and Naphtho[2,3-<i>b</i>]furan-4,9-diones

A three-component multi-auto-tandem reaction for the construction of site-specific tricyclic furo[3,2-<i>c</i>]coumarins via the formation of C-C, C-O, and C-S bonds in one step from 4-hydroxycoumarins/4-hydroxy-2-pyrones, ynals, and sodium sulfinates is reported. This cascade reaction efficiently produces a variety of rare C-2-functionalized furo[3,2-<i>c</i>]coumarins in moderate to good yields under straightforward reaction conditions. Furthermore, this protocol can be extended to a three-component coupling involving 2-hydroxy-1,4-naphthoquinone, ynals, and sodium sulfinates, yielding tricyclic naphtho[2,3-<i>b</i>]furan-4,9-dione derivatives. Notably, the carbonyl group and the α-position of ynals act as C-2 synthons in the specific multi-auto-tandem reaction, enabling the two aforementioned types of multicomponent transformations.