Selective cross-couplings. Sequential Stille-Liebeskind/Srogl reactions of 3-chloro-4-arylthiocyclobutene-1,2-dione

The synthesis and initial reactivity studies of 2 are described. It was found that it participates in Stille couplings exclusively at the C-Cl site with a number of organostannanes (58-71% yield) in the absence of Cu(I). Then, these new derivatives were functionalized at the C-S site with boronic acids by switching to the Liebeskind-Srogl reaction conditions (in the presence of a Cu(I) carboxylate) to yield the bifunctionalized cyclobutenediones (44-90% yield).