Gold-catalysed reactions of alcohols: isomerisation, inter- and intramolecular reactions leading to C–C and C–heteroatom bonds

Gold(I)-catalysed one-pot synthesis of chromans using allylic alcohols and phenols

A gold(I)-catalysed reaction of allylic alcohols and phenols produces chromans regioselectively via a one-pot Friedel-Crafts allylation/intramolecular hydroalkoxylation sequence. The reaction is mild, practical and tolerant of a wide variety of substituents on the phenol.

Gold-catalyzed oxycyclization of allenic carbamates: expeditious synthesis of 1,3-oxazin-2-ones

A combined experimental and computational study on regioselective gold-catalyzed synthetic routes to 1,3-oxazinan-2-ones (kinetically controlled products) and 1,3-oxazin-2-one derivatives (thermodynamically favored) from easily accessible allenic carbamates has been carried out.

Cu(II)-catalyzed aerobic hydroperoxidation of Meldrum's acid derivatives and application in intramolecular oxidation: a conceptual blueprint for O2/H2 dihydroxylation

Aerobic hydroperoxidation of Meldrum's acid derivatives via a Cu(II)-catalyzed process is presented. The mild reaction conditions are tolerant to pendant unsaturation allowing the formation of endoperoxides via electrophilic activation. Cleavage of the O-O bond provides 1,n-diols with differentiation of the hydroxy groups.

The tandem intermolecular hydroalkoxylation/Claisen rearrangement

The Au(I)-catalyzed intermolecular hydroalkoxylation of alkynes with allylic alcohols to provide allyl vinyl ethers that subsequently undergo Claisen rearrangement is reported. This new cascade reaction strategy facilitates the direct formation of γ,δ-unsaturated ketones from simple starting materials in a single step.

Coordination chemistry of gold catalysts in solution: a detailed NMR study

Coordination chemistry of gold catalysts bearing eight different ligands [L=PPh(3), JohnPhos (L2), Xphos (L3), DTBP, IMes, IPr, dppf, S-tolBINAP (L8)] has been studied by NMR spectroscopy in solution at room temperature. Cationic or neutral mononuclear complexes LAuX (L=L2, L3, IMes, IPr; X=charged or neutral ligand) underwent simple ligand exchange without giving any higher coordinate complexes. For L2AuX the following ligand strength series was determined: MeOH≪hex-3-yne <MeCN≈OTf(-) ≪Me(2)S<2,6-lutidine<4-picoline<CF(3)CO(2)(-) ≈DMAP<TMTU<PPh(3) <OH(-) ≈Cl(-). Some heteroligand complexes DTBPAuX exist in solution in equilibrium with the corresponding symmetrical species. Binuclear complexes dppf(AuOTf)(2) and S-tolBINAP(AuOTf)(2) showed different behavior in exchange reactions with ligands depending on the ligand strength. Thus, PPh(3) causes abstraction of one gold atom to give mononuclear complexes LLAuPPh(3)(+) and (Ph(3)P)(n)Au(+), but other N and S ligands give ordinary dicationic species LL(AuNu)(2)(2+). In reactions with different bases, LAu(+) provided new oxonium ions whose chemistry was also studied: (DTBPAu)(3)O(+), (L2Au)(2)OH(+), (L2Au)(3)O(+), (L3Au)(2)OH(+), and (IMesAu)(2)OH(+). Ultimately, formation of gold hydroxide LAuOH (L=L2, L3, IMes) was studied. Ligand- or base-assisted interconversions between (L2Au)(2)OH(+), (L2Au)(3)O(+), and L2AuOH are described. Reactions of dppf(AuOTf)(2) and S-tolBINAP(AuOTf)(2) with bases provided more interesting oxonium ions, whose molecular composition was found to be [dppf(Au)(2)](3)O(2)(2+), L8(Au)(2)OH(+), and [L8(Au)(2)](3)O(2)(2+), but their exact structure was not established. Several reactions between different oxonium species were conducted to observe mixed heteroligand oxonium species. Reaction of L2AuNCMe(+) with S(2-) was studied; several new complexes with sulfide are described. For many reversible reactions the corresponding equilibrium constants were determined.

A gold(I)-catalyzed route to α-sulfenylated carbonyl compounds from propargylic alcohols and aryl thiols

A one-step atom efficient gold(I)-catalyzed route to α-sulfenylated ketones and aldehydes from propargylic alcohols and aryl thiols is described.

Diastereoselective total synthesis of (±)-schindilactone A, Part 1: Construction of the ABC and FGH ring systems and initial attempts to construct the CDEF ring system

First-generation synthetic strategies for the diastereoselective total synthesis of schindilactone A (1) are presented and methods for the synthesis of the ABC, FGH, and CDEF moieties are explored. We have established a method for the synthesis of the ABC moiety, which included both a Diels-Alder reaction and a ring-closing metathesis as the key steps. We have also developed a method for the synthesis of the FGH moiety, which involved the use of a Pauson-Khand reaction and a carbonylative annulation reaction as the key steps. Furthermore, we have achieved the construction of the central 7-8 bicyclic ring system by using a [3,3]-rearrangement as the key step. However, unfortunately, when this rearrangement reaction was applied to the construction of the more advanced CDEF moiety, the anticipated annulation reaction did not occur and the development of an alternative synthetic strategy would be required for the construction of this central core.

N-heterocyclic carbene gold(I) and copper(I) complexes in C-H bond activation

Environmental concerns have and will continue to have a significant role in determining how chemistry is carried out. Chemists will be challenged to develop new, efficient synthetic processes that have the fewest possible steps leading to a target molecule, the goal being to decrease the amount of waste generated and reduce energy use. Along this path, chemists will need to develop highly selective reactions with atom-economical pathways producing nontoxic byproduct. In this context, C-H bond activation and functionalization is an extremely attractive method. Indeed, for most organic transformations, the presence of a reactive functionality is required. In Total Synthesis, the "protection and deprotection" approach with such reactive groups limits the overall yield of the synthesis, involves the generation of significant chemical waste, costs energy, and in the end is not as green as one would hope. In turn, if a C-H bond functionalization were possible, instead of the use of a prefunctionalized version of the said C-H bond, the number of steps in a synthesis would obviously be reduced. In this case, the C-H bond can be viewed as a dormant functional group that can be activated when necessary during the synthetic strategy. One issue increasing the challenge of such a desired reaction is selectivity. The cleavage of a C-H bond (bond dissociation requires between 85 and 105 kcal/mol) necessitates a high-energy species, which could quickly become a drawback for the control of chemo-, regio-, and stereoselectivity. Transition metal catalysts are useful reagents for surmounting this problem; they can decrease the kinetic barrier of the reaction yet retain control over selectivity. Transition metal complexes also offer important versatility in having distinct pathways that can lead to activation of the C-H bond. An oxidative addition of the metal in the C-H bond, and a base-assisted metal-carbon bond formation in which the base can be coordinated (or not) to the metal complexes are possible. These different C-H bond activation modes provide chemists with several synthetic options. In this Account, we discuss recent discoveries involving the versatile NHC-gold(I) and NHC-copper(I) hydroxide complexes (where NHC is N-heterocyclic carbene) showing interesting Brønsted basic properties for C-H bond activation or C-H bond functionalization purposes. The simple and easy synthesis of these two complexes involves their halide-bearing relatives reacting with simple alkali metal hydroxides. These complexes can react cleanly with organic compounds bearing protons with compatible pK(a) values, producing only water as byproduct. It is a very simple protocol indeed and may be sold as a C-H bond activation, although the less flashy "metalation reaction" also accurately describes the process. The synthesis of these complexes has led us to develop new organometallic chemistry and catalysis involving C-H bond activation (metalation) and subsequent C-H bond functionalization. We further highlight applications with these reactions, in areas such as photoluminescence and biological activities of NHC-gold(I) and NHC-copper(I) complexes.