Oxidative Gold Catalysis Research Articles

Enantioselective oxidative gold catalysis enabled by a designed chiral P,N-bidentate ligand.

A newly developed P,N-bidentate ligand enables enantioselective intramolecular cyclopropanation by a reactive α-oxo gold carbene intermediate generated in situ. The ligand design is based on our previously proposed structure (with a well-organized triscoordinated gold center) of the carbene intermediate in the presence of a P,N-bidentate ligand. A C2-symmetric piperidine ring was incorporated in the ligand as the nitrogen-containing moiety. A range of racemic transformations of α-oxo gold carbene intermediates have been developed recently, and this new class of chiral ligands could enable their modification for asymmetric synthesis, as demonstrated in this study.

Oxidative Gold Catalysis Meets Photochemistry – Synthesis of Benzo[a]fluorenones from Diynes

AbstractDiynes bearing one terminal and one triarylmethyl‐substituted alkyne were converted into complex benzofluorenone derivatives via a one‐pot process involving a gold‐catalyzed step followed by a photocyclization/oxidation. In the first step an N‐oxide was used to position‐selectively generate an α‐oxo carbenoid at the terminal alkyne which after a regioselective 1,6‐carbene transfer along the tethered tritylalkyne and a subsequent aryl 1,2‐shift furnished tetraphenylethylene‐like derivatives. These intermediates were successfully transformed to fluorenones via oxidative photocyclization.magnified image

ChemInform Abstract: Optimizing P,N‐Bidentate Ligands for Oxidative Gold Catalysis: Efficient Intermolecular Trapping of α‐Oxo Gold Carbenes by Carboxylic Acids.

AbstractA broadly applicable synthesis of carboxymethyl ketones from carboxylic acids and terminal alkynes under mild reaction conditions is developed.

Optimizing P,N-bidentate ligands for oxidative gold catalysis: efficient intermolecular trapping of α-oxo gold carbenes by carboxylic acids.

Steric Bulk or Conformation Control? Optimization of P,N-bidentate ligands reveals the importance of conformation control in the development of highly efficient intermolecular trapping of reactive α-oxo gold carbene intermediates. While a pendant piperidine ring offers suitable steric bulk, fixing its conformation to provide better shielding to the highly electrophilic carbene center turned out to be crucial for the excellent reaction efficiency. A generally highly efficient and broadly applicable synthesis of carboxymethyl ketones from readily available carboxylic acids and terminal alkynes is developed under exceptionally mild reaction conditions.

Optimizing P,N‐Bidentate Ligands for Oxidative Gold Catalysis: Efficient Intermolecular Trapping of α‐Oxo Gold Carbenes by Carboxylic Acids

Alles im Griff: Optimierungsstudien an zweizähnigen P,N-Liganden L offenbaren die Bedeutung einer festgelegten Konformation für das intermolekulare Abfangen reaktiver α-Oxogoldcarben-Zwischenstufen. Das Resultat ist eine hoch effiziente und breit anwendbare Synthese von Carboxymethylketonen aus leicht zugänglichen Carbonsäuren und endständigen Alkinen unter milden Reaktionsbedingungen.

Tempering the reactivities of postulated α-oxo gold carbenes using bidentate ligands: implication of tricoordinated gold intermediates and the development of an expedient bimolecular assembly of 2,4-disubstituted oxazoles.

2,4-Oxazole is an important structural motif in various natural products. An efficient modular synthesis of this structure has been achieved via a [3 + 2] annulation between a terminal alkyne and a carboxamide using a gold-catalyzed oxidation strategy. The postulated reactive intermediate, a terminal α-oxo gold carbene, previously known to be highly electrophilic and hence unlikely to be trapped by stoichiometric external nucleophiles, is coerced to react smoothly with the carboxamide en route to the oxazole ring by a P,N- or P,S-bidentate ligand such as Mor-DalPhos; in stark contrast, often-used ligands such as monodentate phosphines and N-heterocyclic carbenes are totally ineffective. The role of these bidentate phosphines in this reaction is attributed to the formation of a tricoordinated gold carbene intermediate, which is less electrophilic and hence more chemoselective when reacting with nucleophiles. The success in using bidentate phosphine ligands to temper the reactivities of in situ-generated gold carbenes is likely to open many new opportunities to apply oxidative gold catalysis to the development of novel methods, and the implication of tricoordinated gold intermediates in homogeneous gold catalysis should stimulate further advances in gold catalysis.

Homogeneous Gold-Catalyzed Oxidative Carboheterofunctionalization of Alkenes

Homogeneous carboamination, carboalkoxylation and carbolactonization of terminal alkenes are realized via oxidative gold catalysis, providing expedient access to various substituted N- or O-heterocycles. Deuterium-labeling studies established the anti nature of the alkene functionalization and the indispensible role of Au(I)/Au(III) catalysis. This study constitutes the first example of catalytically converting C(sp(3))-Au bonds into C(sp(3))--C(sp(2)) bonds in a cross-coupling manner and opens new opportunities to study gold alkene catalysis where alkylgold intermediates can be readily functionalized intermolecularly.