Gold(I)-catalyzed synthesis of γ-vinylbutyrolactones by intramolecular oxaallylic alkylation with alcohols

• Michel Chiarucci,
• Mirko Locritani,
• Gianpiero Cera and
• Marco Bandini

Beilstein J. Org. Chem. 2011, 7, 1198–1204, doi:10.3762/bjoc.7.139

• confirms the allylic SN1 mechanism for the present methodology [44]. The high chemoselectivity guaranteed by the gold catalysts is worthy of note, as it channels the reaction toward the allylic alkylation mechanism without any contamination deriving from transesterification reactions. This evidence is

Efficient gold(I)/silver(I)-cocatalyzed cascade intermolecular N-Michael addition/intramolecular hydroalkylation of unactivated alkenes with α-ketones

• Ya-Ping Xiao,
• Xin-Yuan Liu and
• Chi-Ming Che

Beilstein J. Org. Chem. 2011, 7, 1100–1107, doi:10.3762/bjoc.7.126

• -cocatalysis see [39] and for Au/Rh-cocatalysis see [40]). However, the use of homogeneous gold catalysts in cooperation with other metal catalysts has been reported only in a few cases [30][31][32][33][34][35][36][37][38][39][40]. In this work, we describe a highly efficient gold(I)/silver(I)-cocatalyzed

Recent developments in gold-catalyzed cycloaddition reactions

• Fernando López and
• José L. Mascareñas

Beilstein J. Org. Chem. 2011, 7, 1075–1094, doi:10.3762/bjoc.7.124

• nitriles in the presence of cationic gold catalysts, such as Et3PAuCl/AgSbF6, to give tetrasubstituted pyridines 30 in good yields (Scheme 18) [72]. Cycloadditions initiated by gold-activation of propargyl esters These cycloadditions are a special case of those based on the activation of alkynes and

• deserve a separate discussion due to their relevance, wide versatility, and mechanistic peculiarities. Propargyl esters, usually acetates, are prone to undergo 1,2- or 1,3-acyloxy migrations in the presence of gold catalysts. The migration process begins with the nucleophilic intramolecular attack of the

• a 3C-atom component in the annulation. A precise explanation for this dichotomy has not been specifically addressed. Cycloadditions initiated by gold-activation of allenes Several gold catalysts can activate allenes in a very chemoselective way, triggering different types of cycloaddition processes

Asymmetric Au-catalyzed cycloisomerization of 1,6-enynes: An entry to bicyclo[4.1.0]heptene

• Alexandre Pradal,
• Chung-Meng Chao,
• Patrick Y. Toullec and
• Véronique Michelet

Beilstein J. Org. Chem. 2011, 7, 1021–1029, doi:10.3762/bjoc.7.116

• chiral iridium catalyst [41] (Scheme 1, reaction 2). We and others recently pursued the improvement and development of this enantioselective process, by employing platinum [42][43][44], rhodium [45] or gold [46][47][48] complexes. Following our previous work with chiral gold catalysts [46], we report a

Triazole–Au(I) complex as chemoselective catalyst in promoting propargyl ester rearrangements

• Dawei Wang,
• Yanwei Zhang,
• Rong Cai and
• Xiaodong Shi

Beilstein J. Org. Chem. 2011, 7, 1014–1020, doi:10.3762/bjoc.7.115

• reactivity of gold catalysts greatly depends on the nature of the ligands coordinating with the metal cations [10][11][12][13][14][15]. Of the two typical oxidation states, Au(I) and Au(III), more studies have been focused on the former cation due to the easier preparation of the catalyst and better pre

Recent advances in the gold-catalyzed additions to C–C multiple bonds

• He Huang,
• Yu Zhou and
• Hong Liu

Beilstein J. Org. Chem. 2011, 7, 897–936, doi:10.3762/bjoc.7.103

• range of chiral gold catalysts (or gold combined with chiral ligands) has been developed and screened. However, only limited success has been achieved. The most notable example is the chiral BIPHEP-based catalyst, which has been successfully employed in several asymmetric cycloadditions. Several early

• 139 were obtained via gold(I)-catalyzed intramolecular dihydroamination of allenes with N,N′-disubstituted ureas 138. Iglesias et al. reported a complimentary diamination of alkenes 140 with homogeneous gold catalysts [66]. The key step is an intramolecular alkyl–nitrogen bond formation from a gold

Gold-catalyzed propargylic substitutions: Scope and synthetic developments

• Olivier Debleds,
• Eric Gayon,
• Emmanuel Vrancken and
• Jean-Marc Campagne

Beilstein J. Org. Chem. 2011, 7, 866–877, doi:10.3762/bjoc.7.99

• [46][47][48], gold catalysts may also act as propargylic alcohol-activating agents in propargylic substitutions (Scheme 1). To validate this hypothesis, the reactivity of 1-phenyloct-2-yn-1-ol (1a, R1 = Ph, R2 = H, R3 = n-pentyl) with allyltrimethylsilane in the presence of various gold catalysts at

• expected isoxazolines 23 could not be directly obtained but required a dual iron(III)/gold(III) catalysis to be effective. Nevertheless, gold catalysts exert interesting π- and σ-Lewis properties, allowing direct nucleophilic substitution of various di or tri-substituted alcohols and cyclization reactions

Gold-catalyzed oxidation of arylallenes: Synthesis of quinoxalines and benzimidazoles

• Dong-Mei Cui,
• Dan-Wen Zhuang,
• Ying Chen and
• Chen Zhang

Beilstein J. Org. Chem. 2011, 7, 860–865, doi:10.3762/bjoc.7.98

• –carbon triple bonds by homogeneous gold catalysts was reported recently [28][29][33]. To the best of our knowledge, gold and other transition metal-catalyzed oxidations of allenes have not been reported [37][38]. In the context of ongoing studies on metal-catalyzed atom-economical reactions, we have been

• tetrafluoroborate anion was demonstrated by a comparison with other weakly or non-coordinating counter anions. In addition, a change of the counter anion to OTf−, SbF6−, or NTf2− was also effective (Table 1, entries 2–4). The use of other gold catalysts, e.g., (Ph3P)AuNO3 and IMesAuCl, led to only to combined

When gold can do what iodine cannot do: A critical comparison

• Sara Hummel and
• Stefan F. Kirsch

Beilstein J. Org. Chem. 2011, 7, 847–859, doi:10.3762/bjoc.7.97

• reactions [41][42]. As a logical extension, one might speculate about analogous processes triggered by direct iodonium activation in the absence of gold catalysts (Scheme 1c). Since Barluenga, Larock, and others have shown over the last decades that various cyclizations of carbon and heteroatom nucleophiles

• analogous manner either by using gold-catalysts or electrophilic iodine sources. Typically, these processes are easily understood by postulating stabilized cationic intermediates. For example, aromatic 1,5-enynes can be cyclized to the corresponding naphthalenes in the presence of gold(I) catalysts as

• being solely anti. This reaction is an excellent example that underlines the great potential of the alkynophilicity of the gold metal center. While gold-catalysts make both carbon–carbon and carbon–heteroatom bond formation possible, the analogous process with iodine electrophiles was not realized

Solvent- and ligand-induced switch of selectivity in gold(I)-catalyzed tandem reactions of 3-propargylindoles

• Estela Álvarez,
• Delia Miguel,
• Patricia García-García,
• Manuel A. Fernández-Rodríguez,
• Félix Rodríguez and
• Roberto Sanz

Beilstein J. Org. Chem. 2011, 7, 786–793, doi:10.3762/bjoc.7.89

• -diphenylprop-2-ynyl)-1H-indole (1a) was selected as the model compound and was treated with several gold catalysts under different reaction conditions (Table 1). As expected, under our standard reported conditions ((Ph3P)AuCl/AgSbF6 in CH2Cl2 at room temperature), the 3-(inden-2-yl)indole 3a was obtained as

Highly efficient gold(I)-catalyzed Overman rearrangement in water

• Dong Xing and
• Dan Yang

Beilstein J. Org. Chem. 2011, 7, 781–785, doi:10.3762/bjoc.7.88

• have been used for different types of [3,3]-sigmatropic rearrangements [14][15], only Pd(II) and Hg(II) salts have found wide application in Overman rearrangements. In recent years, gold catalysts have been successfully applied to a series of [3,3]-sigmatropic rearrangements, such as the rearrangement

Synthetic applications of gold-catalyzed ring expansions

• David Garayalde and
• Cristina Nevado

Beilstein J. Org. Chem. 2011, 7, 767–780, doi:10.3762/bjoc.7.87

• early examples reported by Gassman and de Meijere, the field of gold-catalyzed ring expansions has experienced a continuous and sustained growth. Recently, the development of chiral gold catalysts, and the implementation of highly stereocontrolled transformations, has opened up the avenue for the

When cyclopropenes meet gold catalysts

• Frédéric Miege,
• Christophe Meyer and
• Janine Cossy

Beilstein J. Org. Chem. 2011, 7, 717–734, doi:10.3762/bjoc.7.82

• particularly active research area over the last decade. The ability of gold catalysts to act as potent carbophilic Lewis acids and hence to chemoselectively activate π bonds towards nucleophilic attack is now well-established and has found many impressive applications for the formation of C–C or C–heteroatom

• illustrates the different aspects of the reactivity of cyclopropenes in the presence of gold catalysts and covers the contributions in this field up to February 2011. Besides their implication in several gold-catalyzed reactions, cyclopropenes have also served as substrates in order to gain insight into the

• vinylidenecyclopropanes, Shi et al. investigated the behaviour of 1-(2,2-diarylvinyl)-2-phenylcyclopropenes in the presence of gold catalysts [20]. Upon treatment with [(Ph3P)AuOTf], vinylcyclopropene 18 was found to produce a mixture of regioisomeric indenes 19 and 20 in a 75:25 ratio (99%). The use of AgOTf alone led

Gold-catalyzed naphthalene functionalization

• Pedro J. Pérez,
• M. Mar Díaz-Requejo and
• Iván Rivilla

Beilstein J. Org. Chem. 2011, 7, 653–657, doi:10.3762/bjoc.7.77

• bond. In addition, no byproducts derived from carbene coupling were observed. Keywords: carbene insertion; copper catalysts; diazoacetates; gold catalysts; naphthalene functionalization; selective insertion; Introduction At the end of the nineteenth century, Buchner discovered [1] the thermal and

Gold-catalyzed alkylation of silyl enol ethers with ortho-alkynylbenzoic acid esters

• Haruo Aikawa,
• Tetsuro Kaneko,
• Naoki Asao and
• Yoshinori Yamamoto

Beilstein J. Org. Chem. 2011, 7, 648–652, doi:10.3762/bjoc.7.76

• reaction of silyl enol ethers with ortho-alkynylbenzoic acid esters which leads to the formation of α-alkylated silyl enol ethers (path b). We examined the reactions of silyl enol ether 1a with ortho-alkynylbenzoic acid benzyl esters 2 in the presence of gold catalysts under several reaction conditions and

Gold-catalyzed heterocyclizations in alkynyl- and allenyl-β-lactams

• Benito Alcaide and
• Pedro Almendros

Beilstein J. Org. Chem. 2011, 7, 622–630, doi:10.3762/bjoc.7.73

• oxycyclization/hydroxylation of 2-azetidinone-tethered alkynols for the synthesis of non-fused, spiro, and fused oxabicyclic β-lactams has been reported [65]. Attempts at a cyclization reaction of terminal alkynols using gold catalysts failed. However, under the appropriate reaction conditions was found that

Construction of cyclic enones via gold-catalyzed oxygen transfer reactions

• Leping Liu,
• Bo Xu and
• Gerald B. Hammond

Beilstein J. Org. Chem. 2011, 7, 606–614, doi:10.3762/bjoc.7.71

• increased substantially and gold catalysis has become one of the hottest research fields in synthetic organic chemistry [34][35][36][37][38][39][40][41][42]. Due to their unique alkynophilicity, gold catalysts are especially suited to the activation of carbon–carbon triple bonds. Gold-catalyzed formation of

• these transformations were also comparatively discussed. Similar Brønsted acid or other metal mediated transformations and their applications to cascade cyclizations were additionally described. Given gold’s strong π-electrophilicity, it is expected that novel applications of gold catalysts in reactions

Gold-catalyzed regioselective oxidation of terminal allenes: formation of α-methanesulfonyloxy methyl ketones

• Yingdong Luo,
• Guozhu Zhang,
• Erik S. Hwang,
• Thomas A. Wilcoxon and
• Liming Zhang

Beilstein J. Org. Chem. 2011, 7, 596–600, doi:10.3762/bjoc.7.69

• allenes could also be oxidized by these N-oxides in the presence of gold catalysts. As shown in Scheme 1B, intermediate C, likely formed via an initial nucleophilic attack of a gold-activated allene, cannot undergo elimination in the same way as intermediate A, hence gold carbene intermediate B would not

• bulky gold catalysts, such as IPrAuNTf2 (entry 6) and Cy-JohnPhosAuNTf2 (entry 7), did not fare as well as Ph3PAuNTf2, the more Lewis acidic (4-CF3Ph)3PAuNTf2 was better, and 2a was formed in 77% isolated yield (entry 8). A decrease in the amount of MsOH was counterproductive (entry 9), whilst no

A gold-catalyzed alkyne-diol cycloisomerization for the synthesis of oxygenated 5,5-spiroketals

• Sami F. Tlais and
• Gregory B. Dudley

Beilstein J. Org. Chem. 2011, 7, 570–577, doi:10.3762/bjoc.7.66

• encouraging results. Other gold catalysts and solvents were screened, with the best results being achieved with a higher catalyst loading of gold(I) chloride in methanol (Table 1, entry 10). The need for higher catalyst loading is tentatively ascribed to some form of instability of the gold catalyst in

One-pot gold-catalyzed synthesis of 3-silylethynyl indoles from unprotected o-alkynylanilines

• Jonathan P. Brand,
• Clara Chevalley and
• Jérôme Waser

Beilstein J. Org. Chem. 2011, 7, 565–569, doi:10.3762/bjoc.7.65

• capable of promoting nucleophilic attack on acetylenes, gold has recently attracted interest from the synthetic chemistry community [11][12][13][14]. Gold catalysts have also been used in domino sequences starting from o-alkynylanilines. Arcadi and Marinelli reported that gold-catalyzed cyclization of 2

Gold film- catalysed benzannulation by Microwave- Assisted, Continuous Flow Organic Synthesis (MACOS)

• Gjergji Shore,
• Michael Tsimerman and
• Michael G. Organ

Beilstein J. Org. Chem. 2009, 5, No. 35, doi:10.3762/bjoc.5.35

• homogeneous and heterogeneous gold catalysts, and indeed we found that a pure Au film provided good conversion for a short period (Table 1, entry 4), although the film had a short lifespan. Films of palladium (entry 2) and silver (entry 3) showed no conversion of starting materials at all. Surprisingly