Gold-catalyzed regioselective oxidation of propargylic carboxylates: a reliable access to α-carboxy-α,β-unsaturated ketones/aldehydes

• Kegong Ji,
• Jonathan Nelson and
• Liming Zhang

Beilstein J. Org. Chem. 2013, 9, 1925–1930, doi:10.3762/bjoc.9.227

• ratio of 5a-OAc and 5a-H in the gold-catalyzed oxidation of 4a (reaction conditions: 5 mol % gold catalyst, 1.5 equiv of 3, DCE, rt, 3 h). Natural charges at and the 13C chemical shifts of the alkynyl carbons in 4a. Generation of α-oxo gold carbenes via intermolecular oxidation of alkynes: a non-diazo

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

• Eloi Coutant,
• Paul C. Young,
• Graeme Barker and
• Ai-Lan Lee

Beilstein J. Org. Chem. 2013, 9, 1797–1806, doi:10.3762/bjoc.9.209

• chroman 8 (Scheme 2) [13][15][16]. Chan and co-workers have previously proposed that the Friedel–Crafts mechanism could involve the activation of the allylic alcohol by the gold catalyst to turn the hydroxy group into a better leaving group [73]. The observed regioselectivities is then due to the

Gold(I)-catalyzed formation of furans from γ-acyloxyalkynyl ketones

• Marie Hoffmann,
• Solène Miaskiewicz,
• Jean-Marc Weibel,
• Patrick Pale and
• Aurélien Blanc

Beilstein J. Org. Chem. 2013, 9, 1774–1780, doi:10.3762/bjoc.9.206

• , 3-benzyloxypropyl (Table 2, entries 9–12), were fully compatible with our gold-catalysis giving furans 2i–l in good yields. Two different mechanistic hypotheses could be envisaged in the rearrangement of γ-acyloxyalkynyl ketones into furans based on multifaceted gold-catalyst properties, i.e. the

Zinc–gold cooperative catalysis for the direct alkynylation of benzofurans

• Yifan Li and
• Jérôme Waser

Beilstein J. Org. Chem. 2013, 9, 1763–1767, doi:10.3762/bjoc.9.204

• reagent 1-[(triisopropylsilyl)ethynyl]-1,2-benziodoxol-3(1H)-one (TIPS-EBX) based on the cooperative effect between a gold catalyst and a zinc Lewis acid. High selectivity was observed for C2-alkynylation of benzofurans substituted with alkyl, aryl, halogen and ether groups. The reaction was also

• based on a cooperative effect between a gold catalyst and a zinc Lewis acid using 1-[(triisopropylsilyl)ethynyl]-1,2-benziodoxol-3(1H)-one (TIPS-EBX, 8) as reagent (Scheme 1). The reaction proceeded under mild conditions (60 °C under air) and could also be used to alkynylate the more complex polycyclic

• reaction could proceed either via π-activation of the triple bond by the gold catalyst followed by conjugate addition of the benzofuran, α-elimination and 1,2-shift, or oxidative addition of TIPS-EBX (8) onto the gold catalyst (either at the Au(I) or Au(0) oxidation level) followed by electrophilic

Gold-catalyzed cyclization of allenyl acetal derivatives

• Dhananjayan Vasu,
• Samir Kundlik Pawar and
• Rai-Shung Liu

Beilstein J. Org. Chem. 2013, 9, 1751–1756, doi:10.3762/bjoc.9.202

• %), which was shown to be an active catalyst in the two cascade reactions, as depicted in Scheme 1 [17][18]. As shown in Table 1, the treatment of compound 1a with this gold catalyst (5 mol %) in dichloromethane (DCM, 28 °C, 0.5 h) afforded 5-isopropylidenecyclopent-2-en-1-one derivative 4a in 65% yield

• transferred to the allenyl acetate 5a’ by a gold catalyst [23][24]. As shown in Scheme 4, the treatment of species 5a with PPh3AuOTf (5 mol %) in dichloromethane (28 °C, 5 min) gave 4-methoxy-5-isopropylidenecyclopent-2-en-1-one 6a in 76% yield. The structure of compound 6a was determined by an X-ray

Gold-catalyzed intermolecular coupling of sulfonylacetylene with allyl ethers: [3,3]- and [1,3]-rearrangements

• Jungho Jun,
• Hyu-Suk Yeom,
• Jun-Hyun An and
• Seunghoon Shin

Beilstein J. Org. Chem. 2013, 9, 1724–1729, doi:10.3762/bjoc.9.198

• polarization of alkynes both by a gold catalyst and a sulfonyl substituent resulted in an efficient intermolecular tandem carboalkoxylation. Reactions of linear allyl ethers are consistent with the [3,3]-sigmatropic rearrangement mechanism, while those of branched allyl ethers provided [3,3]- and [1,3

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

• Benito Alcaide,
• Pedro Almendros,
• M. Teresa Quirós and
• Israel Fernández

Beilstein J. Org. Chem. 2013, 9, 818–826, doi:10.3762/bjoc.9.93

• -2-ones 3 with concurrent regeneration of the gold catalyst (Scheme 4, left catalytic cycle). In line with the above mechanistic proposal, the easy breakage of the tert-butyl group at species 7 is essential for the formation of 1,3-oxazinan-2-ones 3. Besides, the replacement of the tert-butyl group

• ) have been carried out at the PCM-M06/def2-SVP//B3LYP/def2-SVP level to gain more insight into the reaction mechanism of the above discussed gold-catalyzed divergent oxycyclization reaction. The corresponding computed reaction profiles of the model allene 1M with the model gold catalyst AuPMe3(OTf) are

• , respectively). Again, the data in Figure 1 indicate that the final product 4M is thermodynamically more stable than 3M, which is in line with the experimentally observed conversion of 3a into 4a by heating in the presence and also in the absence of the gold-catalyst. From the computed reaction profile, it can

Combination of gold catalysis and Selectfluor for the synthesis of fluorinated nitrogen heterocycles

• Antoine Simonneau,
• Pierre Garcia,
• Jean-Philippe Goddard,
• Virginie Mouriès-Mansuy,
• Max Malacria and
• Louis Fensterbank

Beilstein J. Org. Chem. 2011, 7, 1379–1386, doi:10.3762/bjoc.7.162

• absence of either the gold catalyst or Selectfluor, the starting material was recovered. The homologue of 1a, compound 1b, was treated with Ph3PAuCl (5 mol %) and Selectfluor (1.1 equiv) in acetonitrile at rt. As expected, the 6-exo-dig cyclization occurred and only led to one compound, 3b, which was

• %, respectively. In the absence of a gold catalyst, a similar result was obtained (Scheme 5) confirming that Selectfluor itself can react with 6 and 7 to give 3a and 5a, which is consistent with Shreeve’s study on the fluorination of enamines [29]. However, the formation of 5a may also be ascribed to the

• Into an oven-dried Schlenk apparatus, the Selectfluor (0.33 mmol, 117 mg, 1.1 equiv) and the gold catalyst (16 µmol, 0.05 equiv) were loaded under a flow of argon. These solids were dried under vacuum at 70–80 °C for 2 h. The aminoalkyne (0.30 mmol, 1 equiv) was then added, followed by anhydrous MeCN

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

• mixture was observed with concomitant decomposition of the starting material. The mechanistic proposal for the formation of γ-vinylbutyrolactones 2 is depicted in Scheme 2. As previously mentioned, the formation of an allylic cationic species (II) is assumed, upon coordination of the gold catalyst to the

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

• the coordinated Cl− ligand, to give a reactive gold catalyst, and secondly to act as an efficient catalyst for the intermolecular N-Michael addition. On the basis of these observations and our previous work on gold(I)-catalyzed intramolecular hydroalkylation of unactivated alkenes with α-ketones [24

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

• highly stereoselective (4 + 2) cycloaddition with the vinyl ether to yield, after the elimination of the gold catalyst, highly substituted oxacyclic systems 7 in good yields and with notable diastereoselectivities. Importantly, this reaction tolerates a wide range of vinyl ethers, and different

• activation of the alkyne group of 10 by the carbophilic gold catalyst (Ph3PAuCl/AgOTf), followed by an intramolecular cyclization that generates the furanyl–gold complex IX. This intermediate is then trapped by the nucleophilic oxygen atom of the nitrone to afford X, which eventually evolves to the final

• furanyl intermediate featuring an iminium ion (XI). This species undergoes an intramolecular cyclization to yield the observed azepine product, and regenerates the gold catalyst. Very recently, the same group reported a related gold-triggered formal (4 + 3) cycloaddition between nitrones and 1-(1-alkynyl

Intramolecular hydroamination of alkynic sulfonamides catalyzed by a gold–triethynylphosphine complex: Construction of azepine frameworks by 7-exo-dig cyclization

• Hideto Ito,
• Tomoya Harada,
• Hirohisa Ohmiya and
• Masaya Sawamura

Beilstein J. Org. Chem. 2011, 7, 951–959, doi:10.3762/bjoc.7.106

• cyclization to afford the nitrogen-containing heterocyclic seven-membered rings, such as tetrahydroazepine and dihydrobenzazepine, in good yields. Keywords: azepine; cyclization; gold catalyst; hydroamination; triethynylphosphine; Introduction Nitrogen-containing heterocyclic seven-membered rings are found

• the catalyst. Although it was reported that Au(NTf2)(IPr) was somewhat unstable in the gold-catalyzed intermolecular hydroamination of alkyne under heating conditions [59], the deactivation of the gold catalyst with IPr and X-Phos was not significant under the present reaction conditions: The

• unstable at room temperature even in the absence of the gold-catalyst. According to these results, the formation of exomethylene compound 6 and subsequent alkene isomerisation should not be a major pathway to 5. Instead, a possible reaction pathway from 4a to 5a is illustrated in Figure 4. First, the

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

• tetrahydropyran 24 were produced by an efficient gold(I) chloride catalyzed cycloisomerization of 2-alkynyl-1,5-diol 22 [28]. A plausible mechanism for the gold-catalyzed transformation of dioxabicyclo[4.2.1]ketal 25 to tetrahydropyran 31 is outlined in Scheme 5. The gold catalyst activates one of the oxygen

• in high yields [77]. However, in some cases, aryl-substituted N-tosyl alkynyl aziridines 169 undergo a gold-catalyzed ring expansion to afford 2,5-substituted or 2,4-substituted pyrrole products [78]. Interestingly, the reaction pathway is determined by the counter ion of the gold catalyst. The

• )phenylacetamides 178 could be achieved with AuPPh3Cl/AgSbF6 as the catalyst and gave 3-benzazepin-2-ones 180 via 7-endo-dig pathway [82]. Moreover, a AuBr3-mediated transformation of 2-(1-alkynyl)phenylacetamides 178 to 5-bromo-3-benzazepin-2-ones 179 was discovered, which indicated that the gold catalyst not only

The role of silver additives in gold-mediated C–H functionalisation

• Scott R. Patrick,
• Ine I. F. Boogaerts,
• Sylvain Gaillard,
• Alexandra M. Z. Slawin and
• Steven P. Nolan

Beilstein J. Org. Chem. 2011, 7, 892–896, doi:10.3762/bjoc.7.102

• functionalisation of aromatic C–H bonds. Doubt is cast on the commonly cited route of halide abstraction from gold and evidence of substrate activation is given. Keywords: C–H functionalisation; gold catalyst; halide abstraction; N-heterocyclic carbene; silver salt; substrate activation; Introduction The use of

Gold(I)-catalyzed formation of furans by a Claisen-type rearrangement of ynenyl allyl ethers

• Florin M. Istrate and
• Fabien Gagosz

Beilstein J. Org. Chem. 2011, 7, 878–885, doi:10.3762/bjoc.7.100

• ). Thus, a wide range of ynenyl allyl ethers 6a–s was synthesized (see Supporting Information File 1) and reacted under the conditions that were found to be optimal for the analogous formation of pyrroles from ynenyl allyl tosylamides, that is, 2 mol % of the gold catalyst {[(p-CF3-C6H4)3P]-Au-NTf2} [66

• ] in dichloromethane at room temperature (Table 1). Under these conditions, we observed the rapid formation (usually less than 10 minutes) of the expected furans. The allyl (6a), crotyl (6b), prenyl (6c) and geranyl (6d) derivatives were readily cycloisomerized in the presence of the gold catalyst, but

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

• ) and a lower amount of gold catalyst should slow down the Meyer–Schuster process. It also suggests that, not only the OH group but also the OEt group can act as a good leaving group in these reactions. Indeed, when isolated compound 10 was subjected to Au(III) catalyst in the presence of water, 11 was

• in the presence of chiral gold catalyst, through coordination to the triple bond (Scheme 1), enantioselective transformations could be obtained. We also found that with chiral gold(III) complexes very deceiving results can be obtained. It is worth noting that, recently, Bandini described very

• Scheme 16, the reaction proved restricted to alcohols and no reaction occurred with TsNH2 or electron-rich aromatic compounds such as 1,3-dimethoxybenzene. Some contradictions arose from these experiments. On one hand, when propargylic alcohols 1 and protected hydroxylamines were treated with gold

Isotopic labelling studies for a gold-catalysed skeletal rearrangement of alkynyl aziridines

• Paul W. Davies,
• Nicolas Martin and
• Neil Spencer

Beilstein J. Org. Chem. 2011, 7, 839–846, doi:10.3762/bjoc.7.96

• reaction conditions resulted in selective cycloisomerisation to produce either the 2,5-disubstituted pyrrole 2 or the skeletally rearranged 2,4-disubstituted pyrrole 3 (Scheme 1) [18]. The nature of both the solvent, and the counter ion to the cationic gold catalyst, proved crucial to the reaction outcome

High chemoselectivity in the phenol synthesis

• Matthias Rudolph,
• Melissa Q. McCreery,
• Wolfgang Frey and
• A. Stephen K. Hashmi

Beilstein J. Org. Chem. 2011, 7, 794–801, doi:10.3762/bjoc.7.90

• gold(I) catalyst to [Mes3PAu]NTf2 [41], only 10 was again observed. Thus, neither of the two oxidation states of the gold catalyst gave any product derived from the intercepted intermediate (the solvent was changed to CDCl3 since the activity of gold(I) is significantly reduced by MeCN). Intramolecular

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

• containing electron-withdrawing, electron-donating, and sterically demanding substituents. This transformation is thought to proceed through activation of the substituted cyclopropylmethanol by the gold catalyst, which leads to the ionization of the alcohol followed by the subsequent cyclopropyl ring opening

A racemic formal total synthesis of clavukerin A using gold(I)-catalyzed cycloisomerization of 3-methoxy-1,6-enynes as the key strategy

• Jae Youp Cheong and
• Young Ho Rhee

Beilstein J. Org. Chem. 2011, 7, 740–743, doi:10.3762/bjoc.7.84

• -catalyzed cycloisomerization of a 3-methoxy-1,6-enyne 5 as the key strategy followed by Rh-catalyzed stereoselective hydrogenation of the cycloheptenone 4. Keywords: clavukerin A; cycloisomerization; gold catalyst; hydrogenation; stereoselectivity; Findings Clavukerin A is a member of marine trinorguaiane

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

• with traces of water) should favour the formation of the more stable cyclopropyl cation 23. Afterwards, ring-opening and intramolecular Friedel–Crafts reactions should enable the formation of indene 20 or naphthalene 21. With the gold catalyst, the formation of indene 19 indicated that electrophilic

• cyclopropene for coordination to the gold catalyst (Scheme 13) [21][26]. The rearrangement of 27a to 28a (95%) had been previously reported by Müller et al. using rhodium(II) perfluorobutyrate as a catalyst (1 mol %, C6H6, reflux, 48 h) [32], whereas Padwa et al. showed that the isomerization of 27b to 28b was

• -deficient olefins, via charged intermediates, under simple thermal conditions [37]. In contrast to the behaviour of cyclopropenone acetal 3, Toste et al. observed that the reaction of the 3,3-disubstituted cyclopropene 47 and (Z)-stilbene in the presence of a cationic gold catalyst could effectively provide

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

• formed, identified as ethyl 1a,7b-dihydro-1H-cyclopropa[a]naphthalene-1-carboxylate (2a), i.e., the product derived from the direct cyclopropanation of the naphthalene C–C double bond (Scheme 4a). By contrast, the use of the gold catalyst IPrAuCl (1b) under the same reaction conditions gave a mixture of

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

• Research, Tohoku University, Sendai 980-8578, Japan 10.3762/bjoc.7.76 Abstract Unprecedented alkylation of silyl enol ethers has been developed by the use of ortho-alkynylbenzoic acid alkyl esters as alkylating agents in the presence of a gold catalyst. The reaction probably proceeds through the gold

• the results are summarized in Table 1 [18][19][20][21]. With a cationic gold catalyst, derived from Ph3PAuCl and AgClO4, the reaction of 1a with 2a proceeded at 80 °C over 2 h and the benzylated silyl enol ether 3a was obtained in 35% yield, along with the eliminated isocoumarin 4a and recovered 2a in

• , this is the first example of the introduction of simple alkyl groups through a substitution-type reaction [37][38][39][40]. The chemical yield was increased to 55% by use of sterically hindered (o-Tol)3PAuCl as the gold catalyst (entry 2). Besides benzene, (CH2Cl)2 and 1,4-dioxane were also suitable

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

• oxyauration to form the zwitterionic species 10. Loss of HCl followed by protonolysis of the carbon–gold bond of 11 affords products 9 and regenerates the gold catalyst (Scheme 5). Having found a solution for the 5-exo selective hydroalkoxylation, attention was turned to the more intricate heterocyclization

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

• case, the gold catalyst exhibited a dual role, namely the activation of alkyne and carbonyl moieties. Yamamoto and co-workers attempted to utilize their protocol to build five-membered cyclic enones, however, when they employed alkynyl ketone 9 as the substrate, the gold catalyst did not show good

• reported gold-catalyzed cyclizations to cyclohexenones 17, employing terminal 1,6-diynes 16 as substrates in the presence of a Brønsted acid and 1 equiv of water (Scheme 12) [48]. None of the desired products were obtained in the absence of the gold catalyst, the Brønsted acid or water. Interestingly, when

• the diacid 1,6-diyne (R1 = R2 = COOH) was employed in the reaction, only the esterified product (R1 = R2 = COOMe) was isolated, albeit in low yield. The authors also carried out this gold-catalyzed transformation in an ionic liquid [49]. This modification enabled the separation of the gold catalyst