Pd(II)-catalyzed dehydrogenative Heck olefination of selenophenes with a broad olefinic substrate scope and high functional group tolerance is demonstrated. Carbonyl-substituted and phenyl-substituted olefins with electron-donating (D) and electron-accepting (A) groups can be regioselectively installed at C2 of the selenophene. The 2-olefinated selenophenes can subsequently undergo a second oxidative olefination to rapidly produce a new class of symmetrical D−π−D or unsymmetrical D−π−A 2,5-diolefinated selenophene materials.
A series of new unsymmetrical benzotrichalcogenophenes (BTCs) were synthesized by the Pd-N-heterocyclic carbene catalyzed intramolecular C3-arylation of furan, thiophene, selenophene and tellurophene units. This is the first time that a C3-direct arylation of selenophene and tellurophene moieties has ever been demonstrated.
A palladium‐catalyzed (Pd(PPh3)4/Ag2O/PivOH) C2‐regioselective direct dehydrogenative alkynylation of unsubstituted selenophene was achieved. The selenophenes substituted with R1 groups at 2‐position can be C5‐alkynylated with a variety of 4‐substituted phenylacetylenes (R2 groups). The R1 and R2 can be either electron‐withdrawing or electron‐donating groups, demonstrating a wide range of substrate scope with various functional group tolerance. The mono/C2‐alkynylated selenophenes can subsequently undergo the second direct alkynylation at C5‐position to afford symmetrical or unsymmetrical donor‐π‐acceptor 2,5‐dialkynylated selenophenes.
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