Synthesis, Characterization, and Catalytic Activity of Alcohol

Article pubs.acs.org/Organometallics

Synthesis, Characterization, and Catalytic Activity of Alcohol-Functionalized NHC Gold(I/III) Complexes Béatrice Jacques,† Damien Hueber,‡ Sophie Hameury,† Pierre Braunstein,† Patrick Pale,‡ Aurélien Blanc,*,‡ and Pierre de Frémont*,† †

Laboratoire de Chimie de Coordination, Institut de Chimie (UMR 7177 CNRS), Université de Strasbourg, 4 rue Blaise Pascal, CS 90032, 67081 Strasbourg, France ‡ Laboratoire de Synthèse, Réactivité Organique et Catalyse, Institut de Chimie (UMR 7177 CNRS), Université de Strasbourg, 4 rue Blaise Pascal, CS 90032, 67081 Strasbourg, France S Supporting Information *

ABSTRACT: A series of alcohol-functionalized NHC gold(I/III) complexes of the types [(L)Au(Cl or NTf2)] and [(L)AuCl3] (L = IPrEtOH, (1, 4, 5), IMesEtOH (2, 6), IMeEtOH (3, 7)) was readily synthesized and characterized by NMR spectroscopy and single-crystal X-ray diffraction. The catalytic activity of the new complexes was assessed and compared with that of other gold catalysts, in the tandem 3,3-rearrangement−Nazarov reactions of enynyl acetate and the rearrangement reaction of alkynyloxirane. The new complexes appeared to be dual-site catalysts in both transformations, thanks to the presence of the primary alcohol function tethered to the NHC ligands.

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INTRODUCTION The N-heterocyclic carbene (NHC) story started with the pioneering work of Ö fele and Wanzlick, half a century ago, and the isolation of two complexes.1 In 1991, Arduengo set a milestone by isolating a stable imidazolylidene, launching the NHC chemistry rush.2 Today, 23 years later, carbenes have emerged from being laboratory curiosity to serving as versatile ligands in organometallic chemistry.3 Their electronic properties as strong two-electron σ-donor ligands, coupled with a weak π acidity, allow for the formation of complexes with all metals, including electropositive d0 metals.4 With late transition metals, they usually give rise to complexes with enhanced thermal and air/moisture stability. NHCs also provide excellent framework flexibility, where the steric environment around the carbene center can be adjusted with various N,N-aryl/alkyl substituents.5 Such groups also allow a fine tuning of the electronic properties of the carbene or the introduction of chirality elements.6 NHCs have become valuable alternatives to phosphines and allow access to complexes with outstanding activity in the homogeneous catalysis of organic transformations.7 Furthermore, the functionalization of NHCs with an additional donor moiety can provide a route to NHC pincertype ligands or to chelates with hemilabile properties.8 This is usually achieved by the introduction of a second NHC center5a,9 or a pnictogen- or chalcogen-based organic function such as an alcohol or ether,10 acetate,11 thiol or thioether,12 selenoether,13 amine,14 amide,15 enolate,16 imine,17 pyridine,18 phosphine,19 etc. The introduction of a chelating alcohol or alcoholate group has proven to be beneficial e.g. (i) to stabilize © 2014 American Chemical Society

some NHC complexes with late transition metals in high oxidation states (e.g., Cu(II)20 NHC complexes) or with electrophilic and oxophilic early transition or lanthanide/ actinide metals,21 (ii) to form bimetallic catalytic systems;22 (iii) to anchor the carbene ligand to a resin via a silyl ether bridge;23 and (iv) to efficiently perform asymmetric catalysis by bringing a chiral environment close to the metal site.24 Organogold chemistry takes advantage of the good stabilizing properties brought about by the NHC ligands,25 and NHC gold(I/III) complexes often lead to excellent results in homogeneous catalysis owing to their thermal stability and air/ moisture inertness, although turnover numbers are often modest.26 A few of these results include oxidative cyclization of dienynes, protodecarboxylation of aromatic carboxylic acids, condensation of dicarbonyl compounds with primary amines, C−C coupling, etc. Reactions were carried out very efficiently under mild and friendly conditions (room temperature, under air, nondry solvent, etc.), with low catalyst loading.27 The fate of the gold(I) precatalyst is not always fully established, and the reasons for their deactivation remain of current interest.28 In addition, recent works more focused on pharmacology and oncology have confirmed the promising anticancer activities of some NHC gold(I/III) complexes.29 In this contribution, we report the straightforward synthesis and characterization of a series of gold(I/III) complexes bearing different alcoholfunctionalized NHC ligands. The catalytic activity of the gold Received: March 7, 2014 Published: April 24, 2014 2326

dx.doi.org/10.1021/om500240h | Organometallics 2014, 33, 2326−2335

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signals appear between 173.0 and 171.0 ppm and correspond to an upfield shift of 10 ppm in comparison to the signals of the silver-bound carbene in the precursor complexes.33 IR spectroscopy evidences the characteristic ν(Au−Cl) and ν(O−H) absorption bands around 323−327 and 3412− 3482 cm−1, respectively.34 The clean formation of the gold complexes was further confirmed by elemental analysis. Complexes 1−3 were crystallized by slow diffusion of pentane or n-hexane into saturated CH2Cl2 solutions, and their structures were determined by single-crystal X-ray diffraction. They crystallize respectively with the P21/c, P21/c, and Pbca space groups. The gold(I) centers are in a nearly linear coordination environment with C−Au−Cl angles between 177.8(2) and 178.8(2)° (Figure 1). The C−Au bond lengths are in the range 1.976(6)−1.997(10) Å, similar to those in related neutral [(NHC)AuCl] complexes.35 The Au−Cl bond lengths, between 2.288(1) and 2.298(2) Å, are in the range of values found for other gold(I) complexes with chloride ligands.35 The packing of 3 exhibits noticeable aurophilic interactions with Au···Au distances equal to 3.3391(6) Å, leading to the formation of [(IMeEtOH)AuCl]2 dimers in the crystal lattice. There is no interaction between the hydroxyl groups and the gold(I) centers. Following a protocol described by Gagosz in 2007,36 the complex [(IPrEtOH)AuCl] (1) was reacted in CH2Cl2 with 1 equiv of silver triflimidate (AgNTf2), at room temperature, to afford the new complex [(IPrEtOH)AuNTf2] (4) in good yield (74%), after crystallization by slow diffusion of pentane into a saturated CH2Cl2 solution (Scheme 2).

complexes was evaluated toward tandem 3,3-rearrangement− Nazarov reactions of enynyl acetate and the rearrangement of alkynyloxiranes.

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RESULTS AND DISCUSSION Synthesis of the Au(I) Complexes. The previously reported silver(I) complexes30 [(IPrEtOH)2AgCl] (IPrEtOH = bis(1-(2,6-diisopropylphenyl)-3-(2-hydroxyethyl)-1H-imidazol-2(3H)-ylidene), [(IMesEtOH)2AgCl] (IMesEtOH = bis(1-(2-hydroxyethyl)-3-mesityl-1H-imidazol-2(3H)-ylidene), and [(IMeEtOH)2AgCl] (IMeEtOH = bis(1-(2-hydroxyethyl)3-methyl-1H-imidazol-2(3H)-ylidene) were reacted with a slight excess of gold(I) dimethyl sulfide chloride [(Me2S)AuCl] (1.02 equiv of Au per NHC function) in CH2Cl2 to afford the corresponding new gold(I) complexes [(IPrEtOH)AuCl] (1), [(IMesEtOH)AuCl] (2), and [(IMeEtOH)AuCl] (3), respectively. In contrast with recent findings in nickel chemistry,30 the transmetalation of the NHC ligands from silver to gold is not hampered by the presence of the hydroxyl groups; the reaction proceeds smoothly at room temperature to afford good yields above 84%, as previously reported by Gosh et al. (Scheme 1).31 Scheme 1. Synthesis of Complexes 1−3 by Transmetalation

Scheme 2. Synthesis of the Complex [(IPrEtOH)Au(NTf2)] (4) An alternative synthesis strategy was recently reported by Hemmert et al. with the synthesis of bis(alcohol-functionalized NHC)gold(I) complexes, in moderate yields, by deprotonation of the starting imidazolium salts by sodium acetate in hot DMF, in the presence of [(Me2S)AuCl].32 The 1H NMR spectra of 1−3 are very similar to those of the silver(I) complex precursors. For 1 and 2, there is a slight overall shift downfield (between +0.03 and +0.28 ppm) for all signals, as well as the loss of 4J(1H−109/107Ag) couplings, due to the replacement of silver by gold. The spectrum of 3 remains virtually identical with that of the silver precursor, for which no 1H−109/107Ag coupling was visible, with signal shifts below 0.09 ppm. The 13C NMR spectra are more diagnostic to confirm the transmetalation. For 1−3, the different carbenic

The 1H NMR spectra of 1 and 4 appear virtually identical; all signal shifts are less than 0.09 ppm. The 13C NMR spectrum of 4 displays a carbenic signal at 165.4 ppm, shifted upfield by 7.6 ppm in comparison to that of 1. IR spectroscopy evidence the characteristic ν(Au−N) and ν(O−H) absorption bands around 511 and 3462 cm−1, respectively. No side products such as NHC gold(I) alcoholate adducts were detected during the

Figure 1. Ball and stick representations of (left) [(IPrEtOH)AuCl] (1), (middle) [(IMesEtOH)AuCl] (2), and (right) [(IMeEtOH)AuCl] (3). Hydrogen atoms have been omitted for clarity, except for the OH protons. 2327


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respectively with the P21/c, P21/c and P1̅ space groups. The asymmetric unit building the crystal network of 6 is composed of three distinct [(IPrEtOH)AuCl3] moieties. The unit cell of 6 exhibits an uncommonly long b axis of 41.4732(10) Å. All of the gold(III) centers are found with the expected square-planar coordination environment with C−Au−Cltrans angles between 176.52(7) and 179.6(3)°. All other interligand angles are very close to 90° with maximum deviations of −2.2 and +2.3° (Figure 3). The Au−C bond lengths, ranging from 1.985(9) to 2.018(8) Å, are in good agreement with those reported for similar NHC gold(III) complexes.39,40 The Au−Cltrans distances, in the range 2.312(3)−2.333(2) Å, are slightly longer than the Au−Clcis distances, in the range 2.233(3)−2.293(2) Å, due to the larger trans influence of the NHC ligands in comparison to that of chloride. All Au−Cl distances are in good agreement with those reported for similar NHC gold(III) trichloride complexes.17b,39 There is no interaction between the Au(III) centers and the alkoxy groups. Crystals of [(IPrEtOH)AuCl3] (5) were obtained with two very closely related unit cells, in the P21/c space group. In one case, the asymmetric unit appears disordered with strong thermal motion associated with one diisopropyl fragment from the NHC ligand (see the Supporting Information). Catalytic Properties. All new complexes proved to be stable toward light and air/moisture. The gold(III) complexes 5−7 did not show any propensity for reduction, even in boiling methanol.41 The influence of the hydroxyl group was assessed toward the tandem 3,3-rearrangement-Nazarov reactions (T1) of enynyl acetate and the alkynyloxirane rearrangement (T2) (Scheme 4).42 For T1, the reaction conditions, upon activation of the gold catalyst (1 mol %), were set at room temperature, lasting for 30 or 45 min, with 1 mol % of silver hexafluoroantimonate (AgSbF6), in dry CH2Cl2. The yields given correspond to isolated products. For the gold(I) complexes 1−3, no activity is observed without the presence of the silver salt (Table 1, entries 1−3). Upon activation, the three complexes display similar reactivities with yields ranging from 75 to 78% for the formation of 3-hexyl-5-methylcyclopenten-2-one (11) (Table 1, entries 4−6), a product obtained exclusively under wet CH2Cl2 conditions with the [(Ph3P)AuCl]/AgSbF6 system (Table 1, entry 7).43 As expected, the alcohol-functionalized substituent of the NHC ligand likely promotes a final hydrolysis/ alcoholysis step of the 5-acetyl-5-methyl-3-phenylcyclopent-2enone (10) intermediate (Table 1, entry 8), similarly to the hydrolysis step proposed by Zhang et al. in their reaction mechanism (Scheme 5). A control experiment performed with [(IPr)AuCl]/AgSbF6 supports this hypothesis, with a reaction outcome leading to 91% isolated yield of the acetoxylated product 10 (Table 1, entries 4 vs 10 and 9 vs 10). Moreover, the reaction conducted in a 9/1 mixture of CH2Cl2 and methanol afforded a 50/50 mixture of 10 and 11 (entry 11). Running the reaction in the presence of methanol clearly decreased the kinetics of the hydrolysis step, probably owing to the competition between the hydroxylated NHC arm and external alcohols. Water is nevertheless a better nucleophile, since the reaction performed in wet CH2Cl2, with complex 1, afforded 11 efficiently with a yield of 79% (Table 1, entry 12). These results demonstrate that the high local concentration of alcohol favors the hydrolysis of 10. They also clearly highlight the accelerating effect of our new ligands for this step. It is also worth mentioning that the alcohol function in our ligands may facilitate the key proton transfer step (Scheme 5).44

course of the reaction, highlighting the high preference of gold(I) for a nitrogen donor and the low basicity of the triflimidate anion.37 The complex 4 crystallizes in the P21/c space group. The gold center is in a nearly linear coordination environment with a C−Au−N angle equal to 176.3(2)° (Figure 2). The C−Au

Figure 2. Ball and stick representation of [(IPrEtOH)Au(NTf2)] (4). Hydrogen atoms have been omitted for clarity, except for the OH proton.

and N−Au bond lengths are equal to 1.960(6) and 2.098(4) Å; they are similar to those reported for other [(NHC)Au(NTf2)] complexes.36,38 One trifluoromethyl group is severely disordered. The alkoxy group interacts with the NTf2 anion rather than with the gold(I) center via intermolecular H bonds. Synthesis of the Au(III) Complexes. Complexes 1−3 were reacted with a slight excess of dichloroiodobenzene (1.10 equiv) in CH2Cl2 to afford the corresponding new gold(III) complexes [(IPrEtOH)AuCl3] (5), [(IMesEtOH)AuCl3] (6), and [(IMeEtOH)AuCl3] (7), respectively. The oxidation proceeds smoothly at room temperature, and the yields are above 96% (Scheme 3). Scheme 3. Synthesis of Complexes 5−7 by Oxidative Chloride Transfer

The 1H NMR spectra of 5−7 are very similar to those of 1− 3 with a noticeable and anticipated downfield shift (+0.2 ppm) for the signals associated with the imidazole backbones. The 13 C NMR spectra further confirm the oxidation reactions and exhibit significant upfield shifts (between −26.2 and −30.0 ppm) for the carbenic carbon signals. Their values range from 140.9 to 146.8 ppm and are very close to those reported for the related [(NHC)AuCl3] complexes.39 IR spectroscopy exhibits the characteristic ν(O−H) absorption bands around 3463−3508 cm−1 and the ν(Au−Cltrans) and ν(Au−Clcis) absorptions around 314−324 and 359−373 cm−1, respectively.38 The clean formation of 5−7 was further confirmed by elemental analysis. Complexes 5−7 were crystallized by layering saturated CH2Cl2 solutions with pentane, and their structures were determined by single-crystal X-ray diffraction. They crystallize 2328


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Figure 3. Ball and stick representation of (left) [(IPrEtOH)AuCl3] (5), (middle) [(IMesEtOH)AuCl3] (6), and (right) [(IMeEtOH)AuCl3] (7). Hydrogen atoms have been omitted for clarity, except for the OH protons.

Scheme 4. Products Formed during Reactions T1 and T2

For the gold(III) complexes 5−7 and [(IPr)AuCl3], no activity is observed in the absence of AgSbF6 (Table 2, entries 1−4). A preliminary reaction with [(IPr)AuCl3]/AgSbF6 gives a 69% yield of the nonhydrolyzed cyclopentenone 10 (Table 2, entry 5). Upon activation with AgSbF6, complexes 5 and 7 display a similar reactivity with yields of 11 of 68 and 67%, while [(IMesEtOH)AuCl3] (6) leads to a reduced yield of 31% (Table 2, entries 6−8). Once again, the alcohol group seems to be an efficient alternative to water to afford the final cyclopentenone 11. In comparison to AuCl3 used in dry CH2Cl2 by Zhang et al., giving a 31% yield of 10, the incorporation of a NHC ligand bound to gold appears beneficial (Table 2, entry 9). Interestingly, [(IPr)AuCl3] and 5−7 lead to a mixture of products, not reported for AuCl3, corresponding to the expected 3-hexyl-5-methylcyclopenten-2-one (11) and also 5-acetyl-5-methyl-3-phenylcyclopent-2-enone (12) (Table 2, entries 5−8). The ratios were determined by 1H NMR spectroscopy and range from 76/24 to 100/0. The less active catalyst 6 is selective toward the clean formation of 11 (Table 2, entry 7). When the catalysts 5−7 were used in wet CH2Cl2, the formation of the second product 12 was not observed, hinting at a reaction pathway possibly different from that with AuCl3. Gratifyingly, in comparison to 5 mol % of AuCl3 in wet CH2Cl2, giving a 64% yield (Table 2, entry 10), complexes 5−7 display an interesting activity. For reaction T2, no activity, at 45 °C after 18 h, is observed prior to activation of the gold(I/III) complexes 1 and 5 with silver triflimidate (Table 3, entries 1 and 2). Consequently, the other reactions were set at 25 °C, with 5 mol % of gold catalyst and 5 mol % of silver salt, in dry CH2Cl2, with reaction times ranging from 0.5 to 1 h. The yields were determined by 1H NMR spectroscopy. Preliminary reactions performed with the Au(I) precursors [(IPr)AuCl]/AgOTf and [(IPr)AuCl]/ AgNTf2 (Table 3, entries 3 and 4) provide respectively 68 and

Table 1. Screening of the Gold(I) Catalysts for the Tandem 3,3-Rearrangement−Nazarov Reactions of Enynyl Acetate (T1)

yield (%) entry 1 2 3 4 5 6 7 8 9 10 11e 12

catalyst [(IPrEtOH)AuCl] (1) [(IMesEtOH)AuCl] (2) [(IMeEtOH)AuCl] (3) [(IPrEtOH)AuCl] (1) [(IMesEtOH)AuCl] (2) [(IMeEtOH)AuCl] (3) [(PPh3)AuCl] (wet CH2Cl2)d [(PPh3)AuCl]d [(IPr)AuCl] [(IPr)AuCl] [(IPrEtOH)AuCl] (1) (CH2Cl2/MeOH (9/1)) [(IPrEtOH)AuCl] (1) (wet CH2Cl2)

AgX

T (°C)

t (h)

10b

11c

4 4 4 0.5 0.5 0.5 0.5

0 0 0

AgSbF6 AgSbF6 AgSbF6 AgSbF6

45 45 45 25 25 25 25

0 0 0 75 75 78 92

0.5 4 0.5 0.75

65 0 91 41

8 0

AgSbF6 AgSbF6

25 45 25 25

AgSbF6

25

0.5

AgSbF6

39 79

a

Reactions run under argon, 1 mol % of [AuI], 1 mol % of [AgI], dry CH2Cl2 except for entries 7 and 11−12. Yields are based on isolated products. bIsolated yield. cIsolated yield of in situ hydrolyzed/alcoholyzed product. dComparison with known gold systems, as reported by Zhang et al.43 eIncomplete conversion (10% of 8 remaining).

Nevertheless, complexes 1−3 are overall less efficient than the [(Ph3P)AuCl]/AgSbF6 system, which yielded 92% of 11 with the same catalyst loading in wet CH2Cl243 (Table 1, entry 7). 2329


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Scheme 5. Mechanistic Hypothesis for the Hydrolysis Step

Table 2. Screening of the Gold(III) Catalysts for the Tandem 3,3-Rearrangement−Nazarov Reactions of Enynyl Acetate (T1)

Table 3. Screening of the Gold(I/III) Catalysts for the Rearrangement Reaction of Alkynyloxirane (T2)

yield (%) entry 1 2 3 4 5 6 7 8 9 10 a

catalyst [(IPr)AuCl3] [(IPrEtOH) AuCl3] (5) [(IMesEtOH) AuCl3] (6) [(IMeEtOH) AuCl3] (7) [(IPr)AuCl3] [(IPrEtOH) AuCl3] (5) [(IMesEtOH) AuCl3] (6) [(IMeEtOH) AuCl3] (7) AuCl3d AuCl3 (wet CH2Cl2)d

AgX

AgSbF6 AgSbF6

T (°C)

t (h)

b

10

entry

catalyst [(IPrEtOH)AuCl] (1) [(IPrEtOH)AuCl3] (5) [(IPr)AuCl] [(IPr)AuCl] [(PPh3)AuCl]b [(IPrEtOH)AuCl] (1) [(IPrEtOH)AuCl] (1) [(IPrEtOH)AuCl] (1) [(IMesEtOH)AuCl] (2) [(IMeEtOH)AuCl] (3) [(IPrEtOH)Au(NTf2)] (4) [(PPh3)AuCl] (CH2Cl2/ MeOH)b [(IPrEtOH)AuCl3] (5) AuCl3c AuCl3 (CH2Cl2/MeOH)c

68

76/24

1 2 3 4 5 6 7 8 9 10 11

e

100/0

12

88/12

13 14 15

c

11

45 45

4 4

0 0

0 0

45

4

0

0

45

4

0

0

25 25

0.5 0.5

ratio 11/12

69

AgSbF6

25

0.75

AgSbF6

25

0.75

25 25

0.5 0.5

31

67 31 64

I

T (°C)

t (h)

yield of 13 (%)b

45 45 25 25 25 25 25 25 25 25 25

18 18 0.75 1 1 0.75 1 1 0.5 0.5 0.5

0 0 68 55 51 51 50 50 53 54 57

AgOTf

25

0.1

90

AgNTf2

25 25 25

0.5 1 24

50 36 10

AgX

AgOTf AgNTf2 AgOTf AgOTf AgSbF6 AgNTf2 AgNTf2 AgNTf2

a

Reactions run under argon, 5 mol % of [AuI/III], 5 mol % of [AgI], dry CH2Cl2 except for entries 12 and 15. Yields are calculated by 1H NMR relative to an internal standard (hexamethylbenzene). bPrior to hydrolysis/alcoholysis. cComparison with known gold systems as reported by Pale et al.42b

I

Reactions run under argon, 1 mol % [Au ], 1 mol % [Ag ], dry CH2Cl2 except entry 10. Yields are based on isolated products. bPrior hydrolysis/alcoholysis. cAfter hydrolysis/alcoholysis. dComparison with known gold systems (5 mol %) as reported by Zhang et al.43 e No complete conversion.

no clear correlation between the catalyst activity and the size of the different NHC ligands employed (Table 3, entries 9−11). Since the results obtained with 5−7/AgNTf2 were similar to those reported with [(PPh3)AuCl]/AgOTf in dry CH2Cl2, in the presence of a small amount of adventitious water catalyzing reaction T2 (arising from the silver triflate),42b a control experiment was performed using presynthesized and crystallized [(IPrEtOH)Au(NTf2)] (4). Gratifyingly, the reaction proceeded efficiently with 57% yield of furan 13 after 30 min (Table 3, entry 11). Even though complex 4 is less efficient than [(PPh3)AuCl]/AgOTf in CH2Cl2/methanol (9/1), with a 90% yield of 13 in 10 min (Table 3, entry 12), such disparity in activity might be explained by the difference in concentrations

55% yields of the desired 2-butyl-5,6,7,8-tetrahydro-4Hcyclohepta[b]furan (13) after 0.75 h; a result that is better than the 51% NMR yield obtained with (PPh3)AuCl/AgOTf in dry CH2Cl2 after 1 h (Table 3, entry 5). The reaction performed with [(IPrEtOH)AuCl] (1)/AgOTf provides a similar NMR yield (51%) of 13 (Table 3, entry 6).42b The use of different silver salts such as AgSbF6 and AgNTf2 did not affect the reaction, thus minimizing the effect of the noncoordinating anion on the catalytic system, with yields lying between 50 and 51% (Table 3, entries 6−8). The systems based on 5−7/ AgNTf2, with NHC ligands of different steric hindrance, were tested and provided yields of 13 between 50 and 54%. There is 2330


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Information as well as their ORTEP representations (see S2 and S14 in the Supporting Information) Synthesis of the Gold Complexes. All reactions were carried out in air with nondried solvents, unless stated otherwise. The precursor functionalized NHC silver(I) complexes were synthesized by following a published protocol.30 PhICl2 was prepared following a procedure described by Kalyani and Sanford47 and stored at −30 °C. All other reagents were used as received from commercial suppliers. Synthesis of [(IPrEtOH)AuCl] (1). Solid [(Me2S)AuCl] (568 mg, 1.93 mmol, 2.04 equiv) was added to a solution of [(IPrEtOH)AgCl] (650 mg, 0.95 mmol, 1 equiv) in dichloromethane (30 mL). The reaction mixture was stirred at room temperature for 6 h. Activated coal was then added, and the reaction mixture was stirred at room temperature overnight. The solution was filtered through Celite. The filtrate was concentrated to ca. 5 mL and was then added to pentane (30 mL). The resulting white precipitate was filtered, washed with pentane (3 × 10 mL), and dried under vacuum to afford 1 as a white solid (881 mg, 1.75 mmol). Yield: 92%. 1H NMR (CD2Cl2, 300 MHz): δ 7.53 (t, J = 7.5 Hz, 1H, CHp‑Ar), 7.37 (d, J = 2.0 Hz, 1H, CHimidazole), 7.30 (d, J = 7.5 Hz, 2H, CHm‑Ar), 6.97 (d, J = 2.0 Hz, 1H, CHimidazole), 4.46 (t, J = 5.0 Hz, 2H, CH2), 4.08 (q, J = 5.0 Hz, 2H, CH2OH), 2.40 (sept, J = 7.0 Hz, 2H, CHiPr), 1.87 (t, J = 5.0 Hz, 1H, OH), 1.28 (d, J = 7.0 Hz, 6H, CH3iPr), 1.13 (d, J = 7.0 Hz, 6H, CH3iPr). 13C{1H} NMR (CD2Cl2, 125.7 MHz): δ 173.0 (Ccarbene), 146.4 (CAr), 134.8 (CAr), 130.9 (CHAr), 124.6 (CHAr), 123.6 (CHimidazole), 122.2 (CHimidazole), 62.5 (CH2OH), 53.9 (CH2), 28.8 (CH i Pr ), 24.5 (CH 3 i Pr ), 24.4 (CH 3 i P r ). Anal. Calcd for C17H24AuClN2O: C, 40.45; H, 4.79; N, 5.55. Found: C, 40.17; H, 4.85; N, 5.25. IR: ν (cm−1) 3457 (OH), 323 (Au−Cltrans). Synthesis of [(IMesEtOH)AuCl] (2). A procedure similar to that used for compound 1 with [(Me2S)AuCl] (978 mg, 3.32 mmol, 2.04 equiv) and [(IMesEtOH)AgCl] (944 mg, 1.66 mmol, 1 equiv) gave 2 as a white solid (1339 mg, 2.89 mmol). Yield: 87%. 1H NMR (CD2Cl2, 300 MHz): δ 7.36 (d, J = 2.0 Hz, 1H, CHimidazole), 7.03 (s, 2H, CHm‑Ar), 6.93 (d, J = 2.0 Hz, 1H, CHimidazole), 4.44 (t, J = 5.0 Hz, 2H, CH2), 4.07 (q, J = 5.0 Hz, 2H, CH2OH), 2.36 (s, 3H, p-CH3), 2.03 (s, 6H, o-CH3), 1.90 (t, J = 5.0 Hz, 1H, OH). 13C{1H} NMR (CD2Cl2, 100.6 MHz): δ 171.9 (Ccarbene), 140.2 (CAr), 135.4 (CAr), 135.4 (CAr), 129.6 (CHAr), 122.4 (CHimidazole), 122.3 (CHimidazole), 62.5 (CH2OH), 53.9 (CH2), 21.3 (p-CH3), 18.0 (o-CH3). Anal. Calcd for C14H18AuClN2O: C, 36.34; H, 3.92; N, 6.05. Found: C, 36.20; H, 4.06; N, 5.97. IR: ν (cm−1) 3412 (OH), 324 (Au−Cltrans). Synthesis of [(IMeEtOH)AuCl] (3). A procedure similar to that used for compound 1 with [(Me2S)AuCl] (457 mg, 1.55 mmol, 2.04 equiv) and [(IMeEtOH)AgCl] (275 mg, 0.76 mmol, 1 equiv) gave 3 as a white powder (459 mg, 1.28 mmol). Yield: 84%. 1H NMR (CD2Cl2, 500 MHz): δ 7.12 (d, J = 2.0 Hz, 1H, CHimidazole), 6.96 (d, J = 2.0 Hz, 1H, CHimidazole), 4.30 (t, J = 5.0 Hz, 2H, CH2), 4.00 (q, J = 5.0 Hz, 2H, CH2OH), 3.82 (s, 3H, CH3), 2.05 (t, J = 5.0 Hz, 1H, OH). 13C{1H} NMR (CD2Cl2, 125.7 MHz): δ 171.0 (Ccarbene), 122.2 (CHimidazole), 122.0 (CHimidazole), 62.4 (CH2OH), 53.8 (CH2), 38.6 (CH3). Anal. Calcd for C6H10AuClN2O: C, 20.10; H, 2.81; N, 7.81. Found: C, 20.09; H, 2.96; N, 7.69. IR: ν (cm−1) 3482 (OH), 327 (Au−Cltrans). Synthesis of [(IPrEtOH)Au(NTf2 )] (4). In a Schlenk flask, [(IPrEtOH)AuCl] (30.0 mg, 1 equiv, 0.059 mmol) was dissolved in 2 mL of dichloromethane. Then AgNTf2 was added (23.1 mg, 1 equiv, 0.059 mmol) and the solution was stirred at room temperature for 15 min. The reaction mixture remained pale yellow, and a white precipitate of AgCl formed. The solution was filtered through a canula capped with a filter paper. After its volume was reduced to 0.5 mL, 5 mL of pentane was added; this led to the appearance of a pale white precipitate. This precipitate was filtered, washed with 5 mL of cold pentane, and dried to afford the desired complex (33 mg, 0.044 mmol). Yield: 74%. 1H NMR (CD2Cl2, 500 MHz): δ 7.51 (t, J = 7.8 Hz, 1H, CHp‑Ar), 7.42 (d, J = 2.0 Hz, 1H, CHimidazole), 7.29 (d, J = 7.8 Hz, 2H, CHm‑Ar), 7.07 (d, J = 2.0 Hz, 1H, CHimidazole), 4.39 (t, J = 5.0 Hz, 2H, CH2), 4.08 (q, J = 5.0 Hz, 2H, CH2OH), 2.33 (sept, J = 7.0 Hz, 2H, CHiPr), 1.90 (t, J = 5.0 Hz, 1H, OH), 1.24 (d, J = 7.0 Hz, 6H, CH3iPr), 1.12 (d, J = 7.0 Hz, 6H, CH3iPr). 13C{1H} NMR (CD2Cl2, 125.7 MHz): δ 165.4 (Ccarbene), 146.2 (CAr), 134.2 (CAr),

between the hydroxyl arm (NHC) and free methanol (solvent) present in the two different reaction media. In this regard, the hydroxyl arm borne by the NHC ligand is likely involved in the oxirane opening step, thus providing a dual organo/organometallic catalyst-type system. With gold(III) precatalysts, a test reaction performed with [(IPrEtOH)AuCl3]/AgNTf2 provides a NMR yield of 50% after only 0.5 h. In comparison to AuCl3, which gave a 36% NMR yield after 1 h,45 the introduction of a NHC ligand to the gold(III) center appears beneficial (Table 3, entries 13 and 14). Interestingly, the presence of the alcohol moiety on the NHC ligand does not seem to hamper the reaction, since AuCl3 in CH2Cl2/methanol (9/1) gave only a 10% yield after 24 h (Table 3, entry 15).

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CONCLUSION A series of alcohol-functionalized NHC gold(I) complexes was readily prepared by transmetalation from the corresponding silver(I) complex precursors. The corresponding alcoholfunctionalized NHC gold(III) complexes were obtained by oxidation with PhICl2. The alcohol function is fully compatible with the trichloride gold(III) entity, and no gold(III) to gold(I) reduction with concomitant oxidation of the alcohol was observed, even in boiling methanol. The new complexes were tested in homogeneous catalysis. The introduction of an alcohol moiety on the NHC ligand facilitates the final hydrolysis step on the tandem 3,3-rearrangement−Nazarov reactions of enynyl acetate and provides a second catalytic site for the rearrangement reaction of alkynyloxiranes, thus emphasizing an interesting strategy consisting of the functionalization of NHC ligands with organic groups to access dual organometallic/ organo catalysts. Work is currently in progress to have a more accurate insight into the contribution(s) of the alkoxy group, including its possible interactions with the cationic gold(I/III) centers.

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EXPERIMENTAL SECTION

General Considerations. Proton (1H NMR) and carbon (13C NMR) nuclear magnetic resonance spectra were recorded on the following instruments: AVANCE I, 300 MHz spectrometer; AVANCE III, 400 MHz spectrometer; AVANCE I, 500 MHz spectrometer, respectively. The chemical shifts are given in parts per million (ppm). Data are presented as follows: chemical shift, multiplicity (s = singlet, d = doublet, t = triplet, q = quartet, quint = quintet, sept = septet, m = multiplet, b = broad), coupling constants (J/Hz), and integration. Assignments were determined on the basis of either unambiguous chemical shifts or coupling patterns. The residual solvent proton (1H) or carbon (13C) resonances were used as reference values. For 1H NMR: CDCl3, 7.26 ppm; CD2Cl2, 5.32 ppm. For 13C{1H} NMR: CDCl3, 77.1 ppm; CD2Cl2, 53.8. IR and FIR spectra were recorded in the region 4000−200 cm−1 on a 6700 FT-IR spectrometer (ATR mode, diamond crystal). Elemental analyses were performed by the “Service de Microanalyses”, Université de Strasbourg. Mass spectrometry analyses (HR-MS) were performed by the “Service de spectrométrie de masse”, Université de Strasbourg. For the X-ray diffraction studies, the intensity data were collected at 173(2) K (graphite-monochromated Mo Kα radiation, λ = 0.71073 Å). The structures were solved by direct methods (SHELXS-97) and refined by full-matrix least-squares procedures (based on F2, SHELXL-97) with anisotropic thermal parameters for all of the non-hydrogen atoms.46 The hydrogen atoms were introduced into the geometrically calculated positions (SHELXL-97 procedures) and refined riding on the corresponding parent atoms. Crystallographic and experimental details for all the structures are summarized in the Supporting 2331


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warmed to −20 °C over 15 min. Heptanal (11.1 mmol) was then added at −78 °C. The reaction mixture was stirred for 30 min at −78 °C and was then warmed to room temperature and stirred for a further 1 h 30 min (monitored by TLC). The mixture was quenched with Ac2O (27.8 mmol) and stirred at 0 °C for 2 h. A saturated NH4Cl solution was then added, and the mixture was extracted with Et2O (2×). The combined organic extracts were dried over MgSO4 and evaporated. Flash column chromatography over silica gel (cyclohexane 95%/EA 5%) gave the desired product 8 (1.391 g, 6.26 mmol, 56%) as a yellowish oil: TLC Rf 0.58 (cyclohexane 80%/EA 20%); 1H NMR (300 MHz, CDCl3) δ 0.87 (t, J = 6.7 Hz, 3 H), 1.28−1.42 (m, 8 H), 1.72−1.80 (m, 2 H), 1.87 (s, 3 H), 2.07 (s, 3 H), 5.23 (m, 1 H), 5.30 (m, 1 H), 5.48 (t, J = 6.6 Hz, 1 H); 13C{1H} NMR (125 MHz, CDCl3) δ 14.1, 21.2, 22.6, 23.4, 25.0, 28.8, 31.7, 34.9, 64.5, 85.6, 86.4, 122.7, 126.1, 170.1. Three-Step Synthesis of the 1-(Hex-1-yn-1-yl)-8oxabicyclo[5.1.0]octane (9) Used for Reaction T2. 1-(Hex-1-yn-1yl)cycloheptanol.49

131.0 (CHAr), 124.5 (CHAr), 124.2 (CHimidazole), 122.8 (CHimidazole), 119.4 (q, J = 325 Hz, CF3), 62.3 (CH2OH), 54.3 (CH2), 28.8 (CHiPr), 24.6 (CH3iPr), 23.8 (CH3iPr). IR: ν (cm−1) 3462 (OH), 511 (Au−Ntrans). Synthesis of [(IPrEtOH)AuCl3] (5). PhICl2 (234 mg, 0.85 mmol, 1.1 equiv) was added to a solution of [(IPrEtOH)AuCl] (391 mg, 0.78 mmol, 1 equiv) in dichloromethane (10 mL). The reaction mixture was stirred at room temperature for 3 h and then filtered through Celite. The filtrate was added to a solution of pentane (30 mL). The resulting yellow precipitate was filtered, washed with pentane (3 × 10 mL), and dried under vacuum to afford 5 as a yellow solid (436 mg, 0.76 mmol). Yield: 98%. 1H NMR (CD2Cl2, 300 MHz): δ 7.61 (d, J = 2.0 Hz, 1H, CHimidazole), 7.58 (t, J = 8.0 Hz, 1H, CHp‑Ar), 7.36 (d, J = 8.0 Hz, 2H, CHm‑Ar), 7.19 (d, J = 2.0 Hz, 1H, CHimidazole), 4.62 (t, J = 5.0 Hz, 2H, CH2), 4.21 (q, J = 5.0 Hz, 2H, CH2OH), 2.63 (sept, J = 7.0 Hz, 2H, CHiPr), 2.06 (t, J = 5.0 Hz, 1H, OH), 1.32 (d, J = 7.0 Hz, 6H, CH3iPr), 1.05 (d, J = 7.0 Hz, 6H, CH3iPr). 13C{1H} NMR (CD2Cl2, 125.7 MHz): δ 146.8 (CAr), 142.8 (Ccarbene), 132.3 (CAr), 132.1 (CHAr), 127.1 (CHimidazole), 125.1 (CHAr), 125.0 (CHimidazole), 61.5 (CH2OH), 54.0 (CH2), 29.1 (CHiPr), 26.7 (CH3iPr), 22.8 (CH3iPr). Anal. Calcd for C17H24AuCl3N2O: C, 35.47; H, 4.20; N, 4.87. Found: C, 35.69; H, 4.45; N, 4.79. IR: ν (cm−1) 3463 (OH), 373 (Au−Clcis), 324 (Au−Cltrans). Synthesis of [(IMesEtOH)AuCl3] (6). A procedure similar to that used for compound 5 with PhICl2 (457 mg, 1.66 mmol, 1.1 equiv) and [(IMesEtOH)AuCl] (996 mg, 1.51 mmol, 1 equiv) gave 6 as a yellow solid (800 mg, 1.50 mmol). Yield: 99%. 1H NMR (CD2Cl2, 300 MHz): δ 7.59 (d, J = 2.0 Hz, 1H, CHimidazole), 7.16 (d, J = 2.0 Hz, 1H, CHimidazole), 7.05 (s, 2H, CHm‑Ar), 4.58 (t, J = 5.0 Hz, 2H, CH2), 4.19 (q, J = 5.0 Hz, 2H, CH2OH), 2.37 (s, 3H, p-CH3), 2.15 (s, 6H, o-CH3), 2.03 (t, J = 5.0 Hz, 1H, OH). 13C{1H} NMR (CD2Cl2, 125.7 MHz): δ 141.9 (Ccarbene), 141.4 (CAr), 135.9 (CAr), 132.7 (CAr), 130.1 (CHAr), 125.7 (CHimidazole), 125.6 (CHimidazole), 61.5 (CH2OH), 53.7 (CH 2 ), 21.3 (p-CH 3 ), 18.6 (o-CH3 ). Anal. Calcd for C14H18AuCl3N2O: C, 31.51; H, 3.40; N, 5.25. Found: C, 31.54; H, 3.34; N, 5.26. IR: ν (cm−1) 3504 (OH), 363 (Au−Clcis), 317 (Au−Cltrans). Synthesis of [(IMeEtOH)AuCl3] (7). A procedure similar to that used for compound 5 with PhICl2 (293 mg, 1.07 mmol, 1.1 equiv) and [(IMeEtOH)AuCl] (435 mg, 0.97 mmol, 1 equiv) gave 7 as a yellow solid (399 mg, 0.93 mmol). Yield: 96%. 1H NMR (CD2Cl2, 500 MHz): δ 7.37 (d, J = 2.0 Hz, 1H, CHimidazole), 7.17 (d, J = 2.0 Hz, 1H, CHimidazole), 4.43 (t, J = 5.0 Hz, 2H, CH2), 4.09 (q, J = 5.0 Hz, 2H, CH2OH), 3.96 (s, 3H, CH3), 1.94 (t, J = 5.0 Hz, 1H, OH). 13C{1H} NMR (CD2Cl2, 125.7 MHz): δ 140.9 (Ccarbene), 125.3 (CHimidazole), 124.9 (CHimidazole), 61.5 (CH2OH), 53.4 (CH2), 38.3 (CH3). Anal. Calcd for C6H10AuCl3N2O: C, 16.78; H, 2.35; N, 6.52. Found: C, 17.00; H, 2.51; N, 6.27. IR: ν (cm−1) 3508 (OH), 359 (Au−Clcis), 314 (Au−Cltrans). Homogenous Catalysis. Reagents and solvents were purified using standard methods. Dichloromethane and tetrahydrofuran (THF) were dried using a Glass Technology GTS100 device. Anhydrous reactions were carried out in flame-dried glassware and under an argon atmosphere. All extractive procedures were performed using nondistilled solvents. Analytical thin-layer chromatography (TLC) was carried out on silica gel 60 F254 plates with visualization by ultraviolet light, cerium ammonium molybdate (CAM), or potassium permanganate dip. Flash column chromatography was carried out using silica gel 60 (40−63 μm), and the procedure included the subsequent evaporation of solvents in vacuo. Synthesis of the 2-Methylundec-1-en-3-yn-5-yl Acetate (8) Used for Reaction T1.

To a solution of n-BuLi (1.6 M in hexanes, 18.3 mmol) in THF (30 mL) was added 1-hexyne (18.3 mmol) at −78 °C under argon. The resulting mixture was stirred at the same temperature for 15 min and was then warmed to −20 °C over 15 min. Cycloheptanone (18.3 mmol) was then added at −78 °C. The reaction mixture was stirred for 30 min at −78 °C and was then warmed to room temperature and was stirred for a further 30 min (monitored by TLC). The mixture was quenched with a NH4Cl solution and extracted with Et2O (2×). The combined organic extracts were dried over MgSO4 and evaporated. Flash column chromatography over silica gel (cyclohexane 90%/EA 10%) gave the desired product (3.054 g, 15.72 mmol, 86%) as a colorless oil: TLC Rf 0.40 (cyclohexane 80%/ EA 20%); 1H NMR (300 MHz, CDCl3) δ 0.90 (t, J = 7.2 Hz, 3 H), 1.34−1.67 (m, 12 H), 1.72−1.84 (m, 3 H), 1.86−2.00 (m, 2 H), 2.20 (t, J = 7.0 Hz, 2 H); 13C{1H} NMR (125 MHz, CDCl3) δ 13.6, 18.3, 21.9, 22.3, 27.9, 30.9, 43.4, 71.9, 84.0, 82.9. 1-(Hex-1-yn-1-yl)cyclohept-1-ene.42b

To a solution of 1-(hex-1-yn-1-yl)cycloheptanol (15.70 mmol) in pyridine (40 mL) was added slowly at 0 °C phosphoryl trichloride (47.09 mmol). The resulting mixture was stirred at room temperature for 3.5 h. The mixture was then diluted with 200 mL of water and extracted with Et2O (3×). The combined organic extracts were washed with brine, dried over MgSO4, and evaporated at room temperature. The residue was then taken in Et2O and washed with HCl (1.5 N, 2 × 100 mL) and brine, dried over MgSO4, and evaporated at room temperature. Flash column chromatography over silica gel (n-pentane) gave the desired product (1.475 g, 8.37 mmol, 53%) as a colorless oil: TLC Rf 0.58 (n-pentane); 1H NMR (300 MHz, CDCl3) δ 0.91 (t, J = 7.1 Hz, 3H), 1.34−1.60 (m, 8H), 1.67−1.78 (m, 2H), 2.10−2.19 (m, 2H), 2.25−2.35 (m, 4H), 6.19 (t, J = 6.7 Hz, 1H); 13C{1H} NMR (125 MHz, CDCl3) δ 13.7, 19.1, 22.1, 26.6, 26.7, 29.0, 31.1, 32.3, 34.6, 83.9, 87.4, 127.3, 138.2; MS (EI) 176.2 [C13H20], calculated 176.2. 1-(Hex-1-yn-1-yl)-8-oxabicyclo[5.1.0]octane (9).42b

To a solution of 1-(hex-1-yn-1-yl)cyclohept-1-ene (8.37 mmol) in CH2Cl2 (25 mL) was added at room temperature m-CPBA (16.73 mmol). The resulting mixture was stirred for 15 min at room temperature and then quenched with NaOH (1 N). The layers were separated, and the aqueous layer was extracted with EA (3×).

2-Methylundec-1-en-3-yn-5-yl Acetate (8).48 To a solution of n-BuLi (1.6 M in hexanes, 11.7 mmol) in THF (22 mL) was added 2-methyl1-buten-3-yne (11.1 mmol) at −78 °C under argon. The resulting mixture was stirred at the same temperature for 15 min and then was 2332


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preactivated catalyst (5 mol %) in CH2Cl2 (1 mL). After completion of the reaction (TLC monitored), the mixture was evaporated. Flash column chromatography over silica gel (cyclohexane) gave the desired product 13 as a yellowish oil: TLC Rf 0.62 (cyclohexane 80%/EA 20%); 1H NMR (300 MHz, CDCl3) δ 0.93 (t, J = 7.3 Hz, 3H), 1.38 (sext, J = 7.4 Hz, 2H), 1.52−1.80 (m, 8H), 2.37−2.45 (m, 2H), 2.52 (t, J = 7.6 Hz, 2H), 2.67−2.76 (m, 2H), 5.73 (s, 1H); 13C{1H} NMR (75 MHz, CDCl3) δ 26.0, 107.5, 119.5, 125.0, 128.9, 129.3, 129.4, 151.9, 157.7, 186.5; HR-MS [M + Na] 237.0894 [C14H14O2Na], calculated 237.0886.

The combined organic extracts were washed with brine, dried over MgSO4, and evaporated. Flash column chromatography over silica gel (cyclohexane 100−95%/EA 0−5%) gave the desired product 9 (1.468 g, 7.63 mmol, 91%) as a colorless oil: TLC Rf 0.56 (cyclohexane 95%/EA 5%); 1H NMR (300 MHz, CDCl3) δ 0.90 (t, J = 7.1 Hz, 3H), 1.31−1.60 (m, 10H), 1.67−1.81 (m, 1H), 1.87−2.07 (m, 2H), 2.08−2.15 (m, 1H), 2.18 (t, J = 6.9 Hz, 2H), 3.22 (dd, J = 7.0, 3.7 Hz, 1H); 13C{1H} NMR (125 MHz, CDCl3) δ 13.7, 18.4, 22.0, 24.3, 24.8, 29.3, 30.7, 31.2, 35.0, 54.6, 63.6, 81.5, 82.4. Gold(I/III)-Catalyzed Tandem 3,3-Rearrangement-Nazarov Reactions T1. 4-Hexyl-2-methylcyclopenta-1,4-dien-1-yl acetate (10) or 3-Hexyl-5-methylcyclopent-2-enone (11).43

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ASSOCIATED CONTENT

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AUTHOR INFORMATION

S Supporting Information *

Figures, tables, and CIF files giving NMR spectra and the crystal data and ORTEP representations of 1−7. This material is available free of charge via the Internet at http://pubs.acs.org. The CIF files have also been deposited with the CCDC, 12 Union Road, Cambridge CB2 1EZ, U.K., and can be obtained on request free of charge, by quoting the publication citation and deposition numbers 984396−984403.

A solution of 2-methylundec-1-en-3-yn-5-yl acetate (8; 0.270 mmol) in CH2Cl2 (2 mL) was added to a solution of catalyst (5 mol %) in CH2Cl2 (3 mL). The resulting mixture was stirred at 45 °C for 6 h. No conversion was observed using either AuI or AuIII catalyst (1H NMR analysis only showed the starting material). Activated Conditions. A solution of 2-methylundec-1-en-3-yn-5-yl acetate (8; 0.270 mmol) in CH2Cl2 (2 mL) was added to a solution of catalyst (1 mol %) activated with AgSbF6 (1 mol %). After 30 min, the mixture was evaporated. Flash column chromatography over silica gel (cyclohexane 95%/EA 5%) gave the desired product 10 as a colorless oil or 11 as a yellowish oil, depending upon the presence of water or alcohol in the reaction medium. 10: TLC Rf 0.57 (cyclohexane 80%/ EA 20%); 1H NMR (300 MHz, CDCl3): δ 0.88 (t, J = 6.5 Hz, 3H), 1.21−1.36 (m, 6H), 1.41−1.53 (m, 2H), 1.82 (s, 3H), 2.21 (s, 3H), 2.29 (td, J = 7.8, 1.5 Hz, 2H), 2.79 (s, 2H), 5.95 (m, 1H); 13C{1H} NMR (75 MHz, CDCl3) δ 11.4, 14.1, 20.8, 22.7, 29.2 (2C), 31.0, 31.8, 43.6, 121.5, 123.3, 145.6, 146.4, 169.1. 11: TLC Rf 0.45 (cyclohexane 80%/EA 20%); 1H NMR (300 MHz, CDCl3) δ 0.89 (t, J = 6.9 Hz, 3 H), 1.15 (d, J = 7.5 Hz, 3 H), 1.26−1.38 (m, 6 H), 1.52−1.62 (m, 2 H), 2.16 (d, JAB = 18.3 Hz, 1 H), 2.83 (t, J = 7.7 Hz, 2 H), 2.36−2.45 (m, 1 H), 2.81 (dd, JAB = 18.3 Hz, J = 6.7 Hz, 1 H), 5.90 (s, 1 H); 13 C{1H} NMR (75 MHz, CDCl3) δ 14.0, 16.5, 22.5, 27.0, 29.0, 31.6, 33.5, 40.4, 40.7, 128.2, 181.4, 212.7. The reaction gave the byproduct 12 with the NHC gold(III) catalysts. 5-Acetyl-5-methyl-3-phenylcyclopent-2-enone (12).

Corresponding Authors

*E-mail for A.B.: [email protected]. *E-mail for P.d.F.: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The Centre National de la Recherche Scientifique (CNRS) and the Ministère de la Recherche are gratefully acknowledged for financial support of this work. Johnson Matthey PLC is also gratefully acknowledged for a generous loan of gold metal. A.B. and D.H. thank the Agence Nationale de la Recherche (ANR) for financial support and a Ph.D. fellowship (Grant ANR-11JS07-001-01 Synt-Het-Au).

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12: TLC Rf 0.45 (cyclohexane 80%/EA 20%); 1H NMR (300 MHz, CDCl3) δ 0.87 (t, J = 6.9 Hz, 3 H), 1.23−1.37 (m, 6 H), 1.40 (s, 3H), 1.52−1.62 (m, 2 H), 2.18 (s, 3H), 2.23 (d, JAB = 18.6 Hz, 1 H), 2.42 (t, J = 7.7 Hz, 2 H), 3.27 (d, JAB = 18.6 Hz, 1 H), 5.83 (m, 1 H); 13C{1H} NMR (75 MHz, CDCl3) δ 14.0, 21.3, 22.5, 25.8, 26.9, 29.0, 31.5, 33.5, 42.7, 62.7, 126.3, 182.6, 204.9, 206.5. Gold(I/III)-Catalyzed Enynyl Acetate and the Rearrangement of Alkynyloxirane Reactions (T2). 2-Butyl-5,6,7,8-tetrahydro-4Hcyclohepta[b]furan (13).

To a solution of 1-(hex-1-yn-1-yl)-8-oxabicyclo[5.1.0]octane (9; 0.260 mmol) in CH2Cl2 (1.5 mL) was added the catalyst (5 mol %). The resulting mixture was stirred at 45 °C for 6 h. No conversion was observed using either AuI or AuIII catalyst (1H NMR analysis only showed the starting material). Activated Conditions. A solution of 1-(hex-1-yn-1-yl)-8oxabicyclo[5.1.0]octane (9; 0.260 mmol) in CH2Cl2 (0.5 mL) was added to a solution of catalyst (5 mol %) activated with AgX (X = NTf2, OTf, SbF6) (5 mol %) in CH2Cl2 (3 mL) or to a solution of 2333


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