Aryl to Aryl Palladium Migration in the Heck and Suzuki Coupling of o-Halobiaryls

Abstract

A novel 1,4-palladium migration between the o-and o'-positions of biaryls has been observed in organopalladium intermediates derived from o-halobiaryls. The organopalladium intermediates generated by this migration have been trapped either by a Heck reaction employing ethyl acrylate or by Suzuki cross-coupling using arylboronic acids. This palladium migration can be activated or deactivated by choosing the appropriate reaction conditions. Chemical and computational evidence supports the presence of an equilibrium that correlates with the C−H acidity of the available arene positions.

Catalytic C–C coupling through C–H arylation of arenes or heteroarenes

“…Recently the isomeric Pd intermediates have been trapped by Suzuki cross-coupling using arylboronic acids (Scheme 44) [134].…”

“…Pd migration from aryl to aryl, likely involving palladacycle formation [133,134], may be favored by oxidative addition of an acid to the palladacycle, thus forming Pd(IV), if migration is 1,3 and through Pd(II)-catalyzed C-H activation-assisted by proton abstraction, if migration is 1,5 or 1,6; however, these pathways can compete in the case of 1,4 migration. The results indicate that very subtle effects can influence the energy of the transition state.…”

From Chrysene to Double [5]Helicenes

“…This observed rearrangement is reminiscent of the migrations between aromatic substitution positions observed in Pd-catalyzed Heck and Suzuki reactions. [10] To obtain the target diimides, we treated esters 11 and 12 with excess 6-aminoundecane and imidazole in o-dichloroethane heated to reflux, and obtained the respectively red and orange diimides 14 and 15 in 74 and 61 % yield. Like the esters, these imides bearing four relatively short peripheral pentyl chains are soluble in chlorinated solvents at room temperature and dissolve in hot butanol, which was our solvent of choice for recrystallizations.…”

1,2-Bis(diphenylphosphino)methane

“…When a palladium/dppm complex was used as the catalyst, the O-allylated alcohol (7) was isolated in 85% yield as the only product. When both these vanadium and palladium/dppm catalysts were employed simultaneously, the desired allylated enone (8) Direct C-H Arylation of (NH)-Indoles. Pd(OAc) 2 /dppm mediates the site-selective C-H arylations of (NH)-indoles without the need for protecting or directing groups.…”