Palladium-catalyzed three-component assembling of allenes, organic halides, and arylboronic acids

An efficient method for the construction of two carbon-carbon bonds in a regio- and stereoselective fashion via palladium-catalyzed assembling of allenes, organic halides, and arylboronic acids is described. Organic halides (RI = C6H5I, o-, m-, and p-CH3OC6H4I, p-C2H5OCOC6H4I, p-CH3COC6H4I, p-CH3C6H4I, p-CH3C6H4Br, p-CH3C6H4Cl, p-NO2C6H4I, p-NO2C6H4Br, p-NO2C6H4Cl, P-IC6H4Cl, 1-iodonaphthalene, 2-iodothiophene, 3-iodo-2-cyclopenten-1-one, 3-iodo-5,5-dimethyl-2-cyclohexen-1-one, C6H5(Br)C=CH2 and ICH2CO2C2H5), and arylboronic acids (ArB(OH)(2), Ar = C6H5, p-CH3OC6H4, m-NO2C6H4, p-FC6H4, 1-C10H7, and o-, m-, and p-CHOC6H4) undergo Suzuki-type three-component assembling with 1,1-dimethylallene to give the corresponding allylic derivatives, (CH3)(2)=CRCH2Ar, in DMF at 70degreesC in the presence of CsF using Pd(dba)(2) as the catalyst. Higher yields of products were obtained for aryl iodides than for the corresponding aryl bromides and chlorides. This three-component assembling is highly regioselective, with the organic group on halides adding to the middle carbon and the aryl group on arylboronic acids to the unsubstituted terminal carbon of allenes. Monosubstituted allenes 1b-e (cyclopentylallene, cyclohexylallene, tertbutylallene, and n-butylallene) also undergo similar assembling reaction with organic halides and arylboronic acids to afford the corresponding products 7a-i with high regio- and stereoselectivity. Based on the known palladium chemistry, a mechanism is proposed to account for the catalytic reaction and the stereochemistry.