Ligand-Free PdCl2-Catalyzed Heck Reaction of Arylboronic Acids and Olefins under Reusable TBAB/H2O Conditions

Abstract

A novel method was developed for Heck reaction of olefins and arylboronic acids using a ligand-free PdCl 2 catalyst to afford the coupling products with excellent regio-and stereoselectivity. It is noteworthy that the PdCl 2 /CuSO 4 /K 2 CO 3 /TBAB/H 2 O system can be recovered and used for three cycles directly.

Oxidative and Reductive Cross-Coupling Reactions Catalyzed by an Anionic “Ligandless” Palladium Complex

“…Among the most straightforward and well-established methods are palladium-catalyzed cross-coupling reactions. − While the Mizoroki–Heck reaction allows access to stilbenes (Scheme a), − the Suzuki–Miyaura reaction, among others, yields biphenyls (Scheme b). − However, most of these cross-coupling reactions suffer from low atom economy and the necessity to use toxic, air-sensitive organometallic reagents. − Among the required aryl halides, aryl chlorides are the reaction partners of choice since they are less expensive, but on the other side, they are also less reactive. One approach to attenuate these drawbacks is the development of the oxidative Heck reaction − of a boronic acid (as a surrogate for the aryl halide) and an alkene for the synthesis of stilbenes (Scheme a). − A viable alternative for the synthesis of symmetric biphenyls is the reductive homodimerization of aryl halides (Scheme b). − …”

Palladium-Catalyzed C–H Monoalkoxylation of α,β-Unsaturated Carbonyl Compounds

“…Recently, transition-metal-catalyzed C–H functionalizations have been in the spotlight in organic chemistry due to the elimination of the partial preactivation of substrates, such as the introduction of a leaving group . The palladium-catalyzed functionalization of a terminal C–H bond of monosubstituted alkenes using nucleophiles under oxidative conditions, which is the so-called Wacker-type reaction, has been applied for C–N and C–C − bond formations. However, no general methods for the mono C–O functionalization of α,β-unsaturated carbonyl compounds generating β-monoalkoxylated α,β-unsaturated carbonyl compounds have been developed in spite of their valuable utilities, while acetals could be effectively prepared through a further alkoxylation at the β-position (Scheme , eq 1). , Recently, the Pd/Cu-catalyzed 1,2-diacetoxylation of alkenes under aerobic oxidation conditions has been achieved by the addition of the nitrite anion to the acetic acid-acetic anhydride solution (Scheme , eq 2) .…”

“…The present oxidative conditions for the C­(sp 2 )–H β-monoalkoxylation of α,β-unsaturated carbonyl compounds could be applied to the C–H β-amination and β-arylation of benzyl acrylate. When 3 equiv of benzyl acrylate was used for the reaction with diphenylamine in 1,2-dichloroethane in the presence of Pd­(OAc) 2 , AgOAc, and NaNO 2 , the desired enamine was obtained in 84% yield (Scheme , eq 1).…”