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Introduction
Hashmi, Toste, Echavarren, and Haruta, among others, have fueled the advance of gold into the forefront of transition metal catalysis.1,2 Phosphine ligated gold(I) complexes
have risen as powerful C–C, C–N, and C–O bond forming catalysts due to the ease with which they can activate C=C and C=C bonds thus allowing for unique
rearrangements or reactions with various nucleophiles. Gold catalysis provides an excellent method to construct complex chemical architectures in a mild manner that
would be difficult to achieve using other reaction paradigms. As illustrated below, the active catalysts are typically prepared by the addition of a silver activator to a gold
halide precatalyst, although there are examples of isolable gold catalysts.
Sigma-Aldrich is proud to offer a treasure-trove of gold precatalysts and silver salts, as well as an extensive portfolio of unsaturated building blocks to accelerate your
research success in this exciting field.
References:
(1) For recent examples, see: (a) Shapiro, N. D.; Toste, F. D. J. Am. Chem. Soc., 2007, 129, 4160. (b) Jiménez-Núñez, E.; Echavarren, A. M. Chem. Commun. 2007, 333. (c) Echavarren, A. M. et al. Angew. Chem., Int. Ed. 2006, 45, 5452. (d) Haruta, M. Nature
2005, 437, 1098. (e) Luzung, M. R et al. J. Am. Chem. Soc. 2004, 126, 10858. (f) Hashmi, A. S. K. Gold. Bull. 2004,
37, 51.
(2) For recent reviews, see: (a) Hashmi, A. S. K.; Hutchings, G. J. Angew. Chem., Int. Ed.
2006, 45, 7896. (b) Widenhoefer, R. A.; Han, X. Eur. J. Org. Chem.
2006, 4555.
(c) Zhang, L. et al. Adv. Synth. Catal. 2006, 348, 2271. (d) Hashmi, A. S. K.
Angew. Chem., Int. Ed., 2005, 44, 6990.
Advantages
- Catalysts readily activate alkenes, alkynes, and alkenes in a myriad of transformations
- Promote regio-, diastereo-, and enantioselective processes
- Catalysts are typically air- and water-stable and reactions can be performed in an “open flask”
- Exceptional functional group tolerance
- Market exclusivity for selected gold catalysts
Representative Applications
Cyclopropanation
The Toste group demonstrated that olefins undergo stereoselective cyclopropanation (cis) with propargyl esters in the presence of in situ generated
Ph3PAuSbF6 and is thus a complement to the trans selectivity observed in transition metal catalyzed cyclopropanation of olefins using
α-diazoacetates.
Isomerization of 1,6-Enynes
Echavarren and others have studied a variety of gold catalyzed cyclizations of 1,6-enynes with or without the presence of nucleophiles. A variety of gold(I) catalysts are
active, including Ph3PAuCH3, Ph3PAuSbF6, and Au[P(t-Bu)2(o-biphenyl)]SbF6
complexes. The reactions can tolerate heteroatoms located between the olefin and alkyne moieties.
Isomerization of 1,5-Enynes
Under gold(I) catalysis, 1,5-enynes of varying substitution patterns rearrange to give bicyclo[3.1.0]-hexenes in a high yielding, stereocontrolled fashion. For optically active
substrates, the reaction can occur with efficient chirality transfer. The catalyst system utilizes Ph3PAuCl in combination with AgBF4,
AgPF6, or AgSbF6 activators.
Isomerization of 1,4-Enynes (Rautenstrauch Rearrangement)
The Rautenstrauch rearrangement of 1,4-enynes provides an expeditious route to a diverse portfolio of functionalized cyclopentanones. Chiral 1-ethynyl-2-propenyl pivalates
efficiently rearrange enantioselectively under mild conditions. Either Ph3PAuSbF6 or Ph3PAuOTf (both generated in situ) can be
used, depending on the identity of the substrates.
Cyclization of ε-Acetylenic Carbonyls (Conia-Ene Reaction)
The non-catalyzed Conia-ene reaction provides access to methylenecyclopentanes without the need for deprotonation, however, the high temperatures required often result
in diminished yields. Toste and co-workers reported a mild catalytic version of this reaction that proceeds under neutral conditions at ambient temperatures.
5-Endo-dig Carbocyclizations
While the gold(I)-catalyzed Conia-ene cycloisomerization is limited to terminal γ-alkynes, the related 5-endo-dig reaction allows for cyclization onto non-terminal
δ-alkynes providing access to cyclopentene derivatives. This synthetic methodology can be applied to the preparation of simple bicyclic molecules, as well as in
heterocycle synthesis (below) and halogenated cyclopentenes via alkynyl halide precursors.
Propargyl Claisen Rearrangement
The gold catalyst [(Ph3PAu)3O]BF4 provides access to a variety of homoallenic alcohols via a rapid two-step, one-pot sequence of
a Claisen rearrangement of a propargyl vinyl ether followed by reduction of the aldehyde functionality. The reactions are generally high yielding and the robust catalyst
system also shows superb ability to relay resident chirality into the allene products.
Stereoselective Synthesis of Dihydropyrans
Using gold(I) catalysis, 2-substituted dihydropyrans are readily prepared from propargyl vinyl ethers in a stereocontrolled fashion.
Hydroamination of Alkenes and Alkynes
Widenhoefer and He have explored a variety of gold catalyzed hydroamination reactions with alkenes and alkynes, and both intra- and intermolecular variants were studied.
Using either Au(I) or Au(III) catalysts, amines, pyrrolidines, imines, and indoles can be easily accessed.
Hydrofunctionalization of Allenes with C, N, and O Nucleophiles
Vinylated tetrahydrofurans, tetrahydropyrans, pyrrolidines, and piperidines can be readily prepared from the corresponding heteroatom functionalized allenes using
Au[P(t-Bu)2(o-biphenyl)]Cl and one of several silver activators. Alternatively, allene tethered indoles can be used in the preparation of carbazole
derivatives.
Stereoselective Synthesis of Functionalized Dihydrofurans
Gagosz and co-workers have prepared a variety of 2,5-dihydrofurans via formation of an allene intermediate followed by cycloisomerization. The rapid reactions occur in the
presence of Ph3PAuNTf2, and complete chirality transfer is observed.
Ring Expansions of Alkynylcycloalkanols
1-Alkynylcycloalkanols rapidly rearrange to the corresponding 2-alkylidenecycloalkanones in the presence of several gold catalysts. The high yielding reactions provide a
single olefin isomer when internal alkynes are employed.
Acetylenic Schmidt Reaction
In the presence of a gold catalyst, pyrroles of varying substitution patterns can be prepared by an intramolecular acetylenic Schmidt reaction of homopropargyl azides.
Product Information
| Product | Product Name |
Structure | Add to Cart |
| 404217 |
Chloro(trimethylphosphine)gold(I), 99%
|
 | |
| 288225 | Chloro(triethylphosphine)gold(I), 97%
|
 | |
| 254037 | Chloro(triphenylphosphine)gold(I), 99.9+%
|
 | |
|
677922 |
Bis(trifluoromethanesulfonyl)imidate-(triphenylphosphinegold(I) 0.5 toluene adduct
|
 | |
| 665177 |
Chloro(tris(4-trifluoromethylphenyl)phosphinegold(I), 99%
|
 | |
|
679771 |
[1,1'-biphenyl-2-yl(di-tert-butyl)phosphine]chlorogold(I), 98%
|
 | |
| 665185 |
Bis(diphenylphosphinomethane)dichlorodigold(I), 97%
|
 | |
|
665142 |
Tris(triphenylphosphinegold)oxonium tetrafluoroborate
|
 | |
| 677876 |
Trichloro(pyridine)gold(III), 97%
|
 | |
|
481130 |
Gold(I) chloride, 99.9% (metals basis)
|
AuCl | |
| 379948 |
Gold(III) chloride, 99.99+%
|
AuCl3 | |
| G4022 |
Gold(III) chloride trihydrate, ≥49.0% as Au
|
HAuCl4 • 3H2O | |
| 298174 |
Sodium tetrachloroaurate(III) dihydrate, 99%
| NaAuCl4 • 2H2O | |
|
398470 |
Gold(III) bromide hydrate, 99.9%
|
AuBr4 • xH2O | |
| 674583 |
Silver perchlorate, 97% |
AgClO4 | |
|
176427 |
Silver p-toluenesulfonate, ≥99%
|
Ag(OSO2C6H4CH3) | |
| 176435 |
Silver trifluoromethanesulfonate, ≥99%
|
Ag(OSO2CF3) | |
|
550256 |
Silver methanesulfonate
|
Ag(OSO2CH3) | |
| T62405 |
Silver trifluoroacetate, 98%
|
Ag(CO2CF3) | |
|
208361 |
Silver tetrafluoroborate, 98%
|
AgBF4 | |
| 227722 |
Silver hexafluorophosphate, 98%
|
AgPF6 | |
|
227730 |
Silver hexafluoroantimonate(V), 98%
|
AgSbF6 | |
| 668001 |
Silver bis(trifluoromethanesulfonyl)imide, 97%
|
AgN(OSO2CF3)2 |
|
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