One-pot gold(I)-catalyzed synthesis of 2-pyridonyl alcohols

A highly efficient method for the synthesis of 2-pyridonyl alcohols via gold(I) catalyst was developed. The effect of methanesulfonic acid on the reaction progression with the gold catalyst was determined. The proposed mechanism involves intramolecular cyclization product formation derived from 5-exo-dig and 6-exo-dig addition of the nitrogen for 2-propargyloxypyridine and 2-(but-3-yn-1-yloxy)pyridine, respectively. The pyridinium salt formed by the gold(I) catalyst and methanesulfonic acid undergoes a rearrangement reaction in a weakly basic medium (5% aq. Na₂CO₃) to form N-alkenyl pyridonyl alcohols. N-alkenyl pyridonyl alcohols can be obtained in moderate to excellent yields using this method.

Catalytic Gold Chemistry: From Simple Salts to Complexes for Regioselective C-H Bond Functionalization

Gold coordinated to neutral phosphines (R₃ P), N-heterocyclic carbenes (NHCs) or anionic ligands is catalytically active in functionalizing various C-H bonds with high selectivity. The sterics/electronic nature of the studied C-H bond, oxidation state of gold and stereoelectronic capacity of the coordinated auxiliary ligand are some of the associated selectivity factors in gold-catalyzed C-H bond functionalization reactions. Hence, in this review a comprehensive update about the action of different types of gold catalysts, from simple to sophisticated ones, on C-H bond reactions and their regiochemical outcome is disclosed. This review also highlights the catalytic applications of Au(I)- and Au(III)-species in creating new opportunities for the regio- and site-selective activation of challenging C-H bonds. Finally, it also intends to stress the potential applications in selective C-H bond activation associated with a variety of heterocycles recently described in the literature.

Dinuclear gold(i) complexes: from bonding to applications

The last two decades have seen a veritable explosion in the use of gold(i) complexes bearing N-heterocyclic carbene (NHC) and phosphine (PR₃) ligands.

Dual gold catalysis - an update

This review summarizes the recent developments in the field of dual gold activation chemistry. New developments including synthetic strategies, latest mechanistic insights, computational studies and the identification and isolation of key intermediates, are discussed.

Different Selectivities in the Insertions into C(sp2 )-H Bonds: Benzofulvenes by Dual Gold Catalysis Competition Experiments

An unprecedented, often almost quantitative access to tricyclic aromatic compounds by dual gold catalysis was developed. This synthetic route expands the scope of benzofulvene derivatives through a C(sp² )-H bond insertion in easily available starting materials. The insertion takes place with an exclusive chemoselectivity with respect to the competing aromatic C-H positions. A bidirectional synthesis with two competing ortho-aryl C-H bonds in the selectivity-determining step also shows perfect selectivity; this result is explained by a computational investigation of the two conceivable intermediates. The intramolecular competition of two non-equivalent aryl C-H bonds with a benzylic methyl group also showed perfect selectivity.

Divergent access to N-hydroxypyrroles and isoxazoles via the gold(i)- or Brønsted acid-catalysed regioselective cyclization of N-(2-trifluoromethyl-3-alkynyl) oximes

The divergent regioselective cyclization of N-(2-trifluoromethyl-3-alkynyl) oximes by a suitable choice of a gold(i) or a Brønsted acid catalyst, leading to 4-trifluoromethyl-N-hydroxypyrroles or 4-trifluoromethyl-5-alkylisoxazoles was developed. In order to avoid the tedious separation of unstable N-(2-trifluoromethyl-3-alkynyl) oximes, an easy two-step, one-pot synthesis of 4-trifluoromethyl-5-alkylisoxazoles was realized via the sequential oxidation of the corresponding hydroxylamines and subsequent treatment with the reductant, sodium thiosulfate (Na₂S₂O₃)_. This two-step, one-pot procedure is a complementary method for the synthesis of 4-trifluoromethyl-5-alkylisoxazole from those unstable N-(2-trifluoromethyl-3-alkynyl) oximes.