Pd(II)-Catalyzed Direct Dehydrogenative Mono- and Diolefination of Selenophenes

Abstract

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.

Palladium‐Catalyzed Direct Cross‐Dehydrogenative Alkynylation of Selenophenes

“…Similarly, 3,3′‐dibromo‐2,2′‐biselenophene ( 8 ) was converted to 8 a in a 43% yield by using Pd(OAc) 2 as the catalyst. Olefinated selenophene derivatives 9 and 10 were used as the coupling partners to generate 9 g and 10 g in 71% and 69% yields [16] . In order to enhance the applicability of the alkynylated selenophenes, we introduced the electron‐withdrawing dicyanovinyl group at C 2 ‐position of selenophene.…”

Pd-Catalyzed Intermolecular Dehydrogenative Heck Reactions of Five-Membered Heteroarenes

“…Pd(OAc) 2 -catalyzed DHR of selenophenes with Ag 2 CO 3 as oxidant in the presence of t-BuCO 2 H provided the α-mono or α,α'-diolefination products depending on the olefinating agent/selenophene ratio (Equations (71) and (72)) [109]. Although Fujiwara's team disclosed, in 1973, the synthesis of 2-styrylselenophene and 2,5distyrylselenophene from stoichiometric amounts of selenophene, styrene, and Pd(OAc)2 in refluxing AcOH/dioxane [29], the DHRs of Se-arenes under catalytic conditions have been seldom reported.…”

“…Pd(OAc)2-catalyzed DHR of selenophenes with Ag2CO3 as oxidant in the presence of t-BuCO2H provided the α-mono or α,α'-diolefination products depending on the olefinating agent/selenophene ratio (Equations (71) and (72)) [109].…”

“…Benzoselenophene reacted under conditions of selenophene to yield the C2 substituted product (Equation (73))[109].…”

Recent Advances in the Synthesis of Selenophenes and Their Derivatives

“…After a pre-activation with a halide or an organometallic (B, Li, Mg, Sn or Zn), these compounds can be employed as reagents in the formation of new C-C [98][99][100][101][102][103][104][105][106][107], C-N [108][109][110] and C-S [111] bonds under Pd or Cu catalysis, through Heck, Stille, Negish, Kumada, Suzuki and Sonogashira coupling reactions. In recent years, unactivated selenophenes have been used as reagents in several synthetic transformations by palladium-catalyzed direct C-H bond activation [112][113][114][115][116]. The traditional methods for the synthesis of selenophenes involve the addition of a seleniumbased nucleophile or electrophile to an appropriate acyclic precursor containing a π-system, followed by an intramolecular cyclization (type A precursor).…”