Palladium-Catalyzed Reactions Using Water as a Solvent

Abstract

Part I. Pd-catalyzed reaction using water-soluble NHC ligand in water

Chapter 2. Synthesis of water-soluble NHC containing quaternary ammonium salts: Application to a Pd-catalyzed alcohol oxidation in water Water-soluble imidazolium salts containing a quaternary ammonium salt were easily synthesized and formation of aggregates in the presence of Pd(OAc)2 and a base in water was observed. The effect of the formation of micelles (or vesicles) on the catalytic activity in the palladium-catalyzed oxidation of 1-heptanol in water was examined.

Part II. Pd-Catalyzed C-H activation reactions on water under mild conditions

Chapter 3. Room-Temperature, On Water, Phosphine-Free Palladium-Catalyzed, Site-Selective C-2 Arylation of Indoles via Direct C-H Activation The efficient phosphine-free Pd(OAc)2 catalyzed direct C2-arylation of N-alkyl and N-arylindoles with aryl iodides in the presence of Ag2CO3 and PivOH has been developed. Reactions are performed at room temperature on water in yields up to 99%.

Chapter 4. Phosphine-Free Palladium-Catalyzed Direct Bis-arylation of Pyrroles with Aryl Iodide on Water The Pd-catalyzed bis-arylation of pyrroles with aryl iodides on water is described. The reaction proceeds under mild conditions, i. e. relatively low temperature (40 oC) and phosphine-free.

Chapter 5. Palladium-Catalyzed Bisarylation of 3-Alkylbenzofurans to 3-Arylalkyl-2-arylbenzofurans on Water: Tandem C(sp3)-H Activations of 3-Alkylbenzofurans A protocol involving facile sequential C(sp3)-H activation of 3-alkylbenzofurans catalyzed by Pd(OAc)2 in the presence of pivalic acid, silver salt, and tricyclohexylphosphine oxide on water was developed. Aryl iodides were used as substrates in a tandem bisarylation reaction to generate 3-arylalkyl-2-arylbenzofurans in moderate to high yields at room temperature. The reaction revealed in this study is a rare example of consecutive C(sp3)-H bonds activations under mild reaction conditions.

Chapter 6. Palladium-Catalyzed Bisarylation of 2,3-Dialkylbenzofurans Using an Enantiopure BINOL-Phosphoric Acid Ligand on Water: Tandem C(sp3)-H Activation and Heck Reaction The facile construction of quaternary 3-benzylidene-2,3-dihydrobenzofurans via the palladium-catalyzed arylation of C(sp3)-H bonds of 2,3-alkylbenzofurans and Heck reaction on water is enabled by a chiral BINOL phosphate ligand. Ag2CO3, chiral phosphoric acid, and water as a solvent are essential for high yields. A nonlinear relationship is found to exist between the enantiomeric excess of the phosphate ligand and the reactivity.

Part III. Pd-catalyzed oxidative dimerization reaction via activation of C-H Bond in HFIP Solvent

Chapter 7. Palladium(II)-Catalyzed Transformation of 3-Alkylbenzofurans to [2,3-Bibenzofuran]-2(3H)-ones: Oxidative Dimerization of 3-Alkylbenzofurans An unprecedented oxidative dimerization by palladium catalysis has been developed using PhI(OPiv)2 as a by-standing oxidant. This provides a facile method for the synthesis of quaternary 2,3-bibenzofuran-2(3)-ones from readily accessible substrates. A plausible mechanism involving a Pd(II)-Pd(IV) catalytic cycle is proposed

a trace amount of water is required for subsequent oxidation.