Arylation tris dipalladium

Buchwald has shown that, in combination with palladium(II) acetate or Pd2(dba)3 [tris(dibenzylideneacetone)dipalladium], the Merrifield resin-bound electron-rich dialkylphosphinobiphenyl ligand (45) (Scheme 4.29) forms the active polymer-supported catalysts for amination and Suzuki reactions [121]. Inactivated aryl iodides, bromides, or even chlorides can be employed as substrates in these reactions. The catalyst derived from ligand (45) and a palladium source can be recycled for both amination and Suzuki reactions without addition of palladium. 

Cyclocarbonylation of o-iodophenols 503 with isocyanates or carbodiimides and carbon monoxide in the presence of a catalytic amount of a palladium catalyst (tris(dibenzylideneacetone)dipalladium(O) Pd2(DBA)3) and l,4-bis(di-phenylphosphino)butane (dppb) resulted in formation of l,3-benzoxazine-2,4-diones 504 or 2-imino-l,3-benzoxazin-4-ones 505 (Scheme 94). The product yields were dependent on the nature of the substrate, the catalyst, the solvent, the base, and the phosphine ligand. The reactions of o-iodophenols with unsymmetrical carbodiimides bearing an alkyl and an aryl substituent afforded 2-alkylimino-3-aryl-l,3-benzoxazin-4-ones 505 in a completely regioselective manner <1999JOC9194>. On the palladium-catalyzed cyclocarbonylation of o-iodoanilines with acyl chlorides and carbon monoxide, 2-substituted-4f/-3,l-benzoxazin-4-ones were obtained <19990L1619>. 

Palladium can also catalyze cross-coupling between aryl halides and aryl or vinylstannanes and there are examples of application of this reaction in the synthesis of pyrroles and indoles. 1-Tosyl-3-(tri-n-butylstannyl)indole gives good yields of coupling products with vinyl and aryl iodides and triflates. The recommended catalyst is tris-(dibenzylideneacetone)-dipalladium (5 mol%) used with triphenylarsine (10 mol%) (Equation (121)) <94TL2405>. 

Oxidative addition of palladium(O) species into unsaturated halides or triflates provides a popular method for the formation of the a-bound organopalladium(II) species. It is important to use an unsaturated (e.g. aryl or alkenyl) halide or tri-flate, as (3-hydride elimination of alkyl palladium species can take place readily. Oxidative addition of palladium(0) into alkenyl halides (or triflates) occurs stere-ospecifically with retention of configuration. The palladium is typically derived from tetrakis(triphenylphosphine)palladium(0), [Pd(PPh3)4], or tris(dibenzylidene-acetone)dipalladium(O), [Pd2(dba)3], or by in situ reduction of a palladium(II) species such as [Pd(OAc)2] or pd(PPh3)2Cl2]. 

A reaction tube was charged with 2-dicyclohexylphosphino-2, 4, 6 -triisopropylbiphenyl (XPhos) (19.1 mg, 4.00 pmol, 4 mol%), tris(dibenzylidene-acetone)dipalladium(O) (9.16 mg, 5.00 pmol, 1 mol%), lithium rer/-butoxide (202 mg, 2.40 mmol), the tosylhydrazone (1.1 mmol), and dioxane (4 mL). After 1 min, the aryl halide (1 mmol) was added. The system was heated at 110°C with stirring and reflux. When the reaction was completed, the crude reaction mixture was allowed to cool to ambient temperature, taken up in dry pentane, hexanes or dichloromethane (15 mL), and filtered through celite. The solvents were evaporated under reduced pressure, and the residue was purified by flash chromatography on silica gel. ... 

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