Role of Halide Ions in Divalent Palladium-Mediated Reactions:  Competition between β-Heteroatom Elimination and β-Hydride Elimination of a Carbon−Palladium Bond

Abstract

The integral role of halide ions as a ligand in the reactions of stoichiometric arylpalladium reagents and Pd(II)-catalyzed reaction of phenylmercuric acetate with various allylic compounds were studied. The halide ion was found to inhibit β-H elimination and promote β-heteroatom elimination in acidic media. In this reaction, a C-Pd intermediate with a β-heteroatom (including halogen, acetoxy, alkoxy, and hydroxyl groups) gives only β-heteroatom elimination product in the presence of halide ions, while β-H elimination is effectively blocked.

Formal anti‐Carbopalladation Reactions of Non‐Activated Alkynes: Requirements, Mechanistic Insights, and Applications

“…These allenes were formed by carbopalladation and subsequent b-hydroxy elimination. Such a b-heteroatom elimination is not a favored process [16] compared with the b-Scheme 2. Design of our system and anticipated sequence to intercept the formal anti-carbopalladation intermediate 4.…”

Control of the β-Hydride Elimination Making Palladium-Catalyzed Coupling Reactions more Diversified

“…Our previous work has shown that excess of halide ions can block the usual b-hydride elimination [21,40]. In the above catalytic cycle, the normal b-hydride elimination is also inhibited and b-acetoxy elimination takes place from the alkylpalladium intermediate III (scheme 9).…”

“…Catalytic reactions. Then, we turned our attention to Pd(II)-initiated reaction in which the carbon-palladium bond was quenched with b-heteroatom elimination (scheme 1) [40]. In the synthesis of a-haloalkylidene-b-vinyl-c-butyrolactone derivatives from the enyne-coupling of 4¢-halo-2¢-alkenyl alkynoates, excess halide salts were used to obtain high (Z)-stereoselectivity of the exocyclic double bond in the lactone products [15,16].…”

“…The result of the role of halide ions in protonolysis reactions also stimulated us to study the effect of halide ions in the b-heteroatom elimination processes. propenol (11) was conducted in HOAc at room temperature with different amounts of LiCl (scheme 5) [40].…”

“…The results of the reactions of complex 5 with allylic compounds (including halides, acetate, ether and alcohol) in HOAc in the presence of different amounts of LiCl (scheme 6) were given in table 2 [40].…”