Expanding the substrate scope in palladium-catalyzed C-N and C-C bond-forming reactions

Abstract

Chapter 1. The first detailed study of the palladium-catalyzed amination of aryl nonaflates is reported. Use of bulky electron-rich monophosphinobiaryl ligands or BINAP allow for the catalytic amination of electron-rich and -neutral aryl nonaflates with both primary and secondary amines. Using XantPhos, the catalytic amination of a variety of functionalized aryl nonaflates resulted in excellent yields of anilines; even 2-carboxymethyl aryl nonaflate is effectively coupled with a primary alkyl amine. Moderate yields were obtained when coupling halo-aryl nonaflates with a variety of amines, where in most cases the aryl nonaflate reacted in preference to the aryl halide. Overall, aryl nonaflates are an effective alternative to aryl triflates in palladium-catalyzed C-N bond-forming processes due to their increased stability under the reaction conditions. Chapter 2. A catalyst comprised of a Pd precatalyst and 2-dicyclohexylphosphino-2',4',6'-triisopropylbiphenyl is explored in C-N bond-forming processes. This catalyst displayed unprecedented stability and scope allowing, for the first time, the coupling of substrates bearing a carboxylic acid or a primary amide.

(cont.) Also, the more bulky catalyst system Pd/2-tert-butylphosphino-2',4',6'-triisopropylbiphenyl was found to be effective for the Narylation of 2-aminoheterocycles and weakly basic HN-heterocycles: pyrazole and indazole. The chemoselectivity for amination using these catalysts was explored where the rough order of reactivity for amines is: aryl amines >> primary and secondary alkyl amines > 2-aminoheterocycles > primary amides - HN-heterocycles. Chapter 3. The palladium-catalyzed Suzuki-Miyaura coupling of haloaminoheterocycles and functionalized organoboronic acids using a highly active and stable monophosphinobiaryl ligand, 2-dicyclohexylphosphino-2',6'-dimethoxybiphenyl, efficiently produced aminoheterocyclic biaryl derivatives. This same catalyst was effective in coupling 2-haloaminoaryl compounds with 2-formyl or 2-acetylphenyl boronic acids, providing the fused heterocyclic compounds phenanthridine, benzo[c][1 ,8]naphthridine and benzo[c][1,5]naphthridine in excellent yields. Chapter 4. A water-soluble monophosphinobiaryl ligand, sodium -dicyclohexylphosphino-2',6'-dimethoxybiphenyl-3'-sulfonate, was synthesized by electrophilic sulfonation of the lower-aromatic ring of 2-dicyclohexylphosphino-2',6'- dimethoxybiphenyl.

(cont.) This ligand was utilized in the palladium-catalyzed Suzuki-Miyaura reaction of water-soluble aryl/heteroaryl halides and organoboronic acids. The catalyst displays unprecedented reactivity and stability for Suzuki-Miyaura reactions conducted in water. Chapter 5. A water-soluble monophosphinobiaryl ligand, sodium 2'-(dicyclohexyl-osphanyl)-2,6-diisopropyl-biphenyl-4-sulfonate, was synthesized by a proposed electrophilic ipso-substitution/reverse Friedel-Crafts alkylation of the lower-aromatic ring on 2-dicyclohexylphosphino-2',4',6'-triisopropylbiphenyl. This ligand was utilized in the palladium-catalyzed Heck alkynylation (copper-free Sonogashira coupling) of hydrophobic and hydrophilic aryl halides and terminal alkynes conducted in an aqueous acetonitrile solvent system. For the first time, an electron-deficient terminal alkyne, propiolic acid, was successfully coupled with aryl bromides. We also demonstrated that this catalyst is useful in the reaction of benzyl chlorides and terminal alkynes to provide benzyl alkynes in good yields. We show that by using an excess amount of base (> 1.0 equiv.) and higher reaction temperatures ( 80 °C), base-catalyzed isomerization to the corresponding aryl allenes can be achieved in a one-pot process.