Palladium-catalyzed direct oxidative vinylation of thiophenes and furans under weakly basic conditions

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

“…Subsequently to the reports by Kasahara's and Fujiwara's teams on the cross-coupling of furans with activated alkenes mediated by stoichiometric amounts of Pd(OAc) 2 in refluxing AcOH [63] or AcOH/dioxane [29], Kozhevnikov disclosed catalytic conditions with Cu(OAc) 2 to regenerate active Pd species [30]. Increased catalyst turnovers were subsequently reported with Cu(OAc) 2 /O 2 [31,64], Cu(OAc) 2 /air [32], benzoquinone (BQ), Cu(OAc) 2 /BQ/O 2 [65], H 6 PMo 9 V 3 O 40 /air [33], HPMo 11 V/air [34], BQ/t-BuOOH [66], AgOAc [35], or PhCO 3 t-Bu [67] as oxidants with various additives and solvents [10].…”

C–H Bond Alkenylation

“…As in the examples described earlier, the alkenylations are usually performed in acidic solvents such as acetic and propionic acids, which limits coexisting functional groups in substrates. In contrast, the authors developed a reaction system, Pd(OAc) 2 /Cu(OAc) 2 /LiOAc/dimethylformamide (DMF), which is applicable to the reaction of thiophenes and furans possessing acid-sensitive substituents [42]. For example, the diphenyl(hydroxy)methyl function in diphenyl(2-thienyl)methanol is tolerable under the weakly basic conditions, as shown in Scheme 18.41.…”

Alkenylation Reactions of Heteroarenes by Transition-Metal Catalysts

“…Because palladium(II) acetate is expensive, several studies since 1979 have focused on the development of effective protocols for alkenylation of heteroarenes via oxidative cross-couplings that involve the use of only catalytic amounts of palladium(II) acetate 51c, or bis(acetonitrile)dichloropalladium(II) 79 and stoichiometric or suprastoichiometric quantities of reoxidants. These include compounds such as copper(II) acetate, 51c, 56,58,59,63,65,71,72,74,75,78 tert-butyl peroxybenzoate, 57,65,66,70 sodium persulfate, 58,59 sodium nitrite, 58,61 manganese(IV) oxide, 60,61 and tert-butyl hydroperoxide, 60 but, unfortunately, also expensive derivatives such as silver(I) acetate, 58,59,73 silver fluoride, 69 silver oxide, 69,76 and silver carbonate. 69,77 Thus…”