Gold-Catalysed Oxidative Cycloisomerisation of 1,6-Diyne Acetates to 1-Naphthyl Ketones

An emerging synthetic tool in organic synthesis to rapidly achieve molecular complexity and diversity is homogeneous gold catalysis.^[1–54] In recent years, the field has witnessed a myriad of elegant methods to assemble an array of compounds of potential synthetic value, such as carbocycles and heterocycles, from readily accessible propargyl substrates in a single step.^[18,30] An example of this is the gold(i)-catalysed preparation of 2,4a-dihydro-1H-fluorenes from 1,6-diyne esters in which computational studies revealed the likely involvement of the cyclopropene adduct I and gold carbenoid species II (Scheme 1a).^[28] Closely following this work, the participation of these type of intermediates was proposed in the cycloisomerisation of 1,6-diyne esters to vinyl-substituted β-napthols (Scheme 1b).^[29] Building on these initial studies, we were drawn to the potential reactivity of aryl-substituted 1,6-diyne esters containing a benzene tether (Scheme 1c). We anticipated that such substrates would form the corresponding cyclopropene intermediate I in the presence of a gold(i) complex.^[47] Cycloreversion might then give the gold carbenoid species II. In the absence of a pronucleophilic motif or external reagent, this newly formed organogold species might then be susceptible to hydrolysis and autoxidation to give the 1-naphthyl ketone derivative 6. Herein, we describe the details of this chemistry, which provides an expedient route to the aromatic carbonyl compound under reaction conditions that did not require an external oxidant.

Scheme 1.  Gold(i)-catalysed reactivities of 1,6-diyne esters.

We began our investigations by examining the gold-catalysed cycloisomerisations of 1,6-diyne ester 5a to establish the optimum reaction conditions (Table 1). This initially revealed subjecting the substrate to 5 mol-% of gold(i) phosphine complex A in dichloromethane at room temperature for 24 h gave the best result (entry 1). Under these conditions, the desired 1-naphthyl ketone 6a was afforded in 62 % yield. Lower product yields of 7–45 % were obtained on repeating the reaction with the gold(i) phosphine complexes B, C, and PPh₃PAuNTf₂ (Tf = triflate) in place of A as the catalyst (entries 2–4). Control experiments with the NHC-Au^I (NHC = N-heterocyclic carbene) complex D or gold(iii) complex E were found to result in incomplete consumption of the starting material, which was obtained along with 6a in respective yields of 48 and 23 %, and 45 and 37 % (entries 5 and 6). In contrast, the use of the gold(i) phosphite complex F as the catalyst was found to lead to no reaction and the near-quantitative recovery of the substrate (entry 7). Although the analogous reaction mediated by AuCl was initially found to give a product yield of 90 %, unfortunately this could not be consistently replicated (entry 8). A survey of other solvents such as 1,2-dichloroethane, chloroform, 1,3-dioxane or acetonitrile in place of dichloromethane was shown to give product yields of 25–43 % (entry 9–12). Likewise, comparable product yields of 31–58 % were afforded in control reactions in dichloromethane with 3 or 10 equiv. of water or only the latter as the solvent (entries 13–15). In a final set of control experiments, the introduction of 4-Å molecular sieves (MS) was observed to result in no reaction and near-quantitative recovery of the substrate (entry 16). On the other hand, conducting the reaction at reflux temperature in dichloromethane or the chlorinated solvent containing 10 equiv. of H₂O was found to provide product yields of 40 and 37 %, respectively (entries 17 and 18).

Table 1.  Optimisation of the reaction conditions
All reactions were performed at 0.05-mmol scale with catalyst : 5a ratio = 1 : 20 in given solvent at room temperature (rt) for 24 h

The generality of the transformation was next investigated with a variety of 1,6-diyne esters (Table 2). With gold(i) phosphine complex A as the catalyst, the reaction conditions were found to be broad, and a range of 1-naphthyl ketones with a variety of substitution patterns were furnished in 21–67 % yield from the corresponding substrates 5b–t. Reactions of substrates where the ester carbon centre contained a phenyl motif with an electron-withdrawing (5b and 5c) or donating (5d–f) group at either the o-, m- or p-position of the ring were shown to be well tolerated and gave 6b–f in 41–53 % yield. Likewise, 1,6-diyne acetates with a 1-naphthyl (5g), methyl (5h) or benzyl (5i) substituent at the R position were found to proceed well and give 6g–i in 24–47 % yield. Reactions with the introduction of other phenyl-substituted motifs (5j–n) or a 1-naphthyl group (5q) at the Ar¹ position of the starting acetate were also found to proceed well, affording the corresponding products 6j–n and 6q in 21–67 % yield. The reactions of substrates containing a p-anisyl (5o) or 2-Me-4-MeO-substituted phenyl (5p) group at the Ar¹ position were observed to be the only exceptions. In the case of the former, an inseparable mixture of 6o and the starting material in a ratio of 4 : 3 and 44 % overall yield was observed. For the latter, no reaction was found and the starting material was recovered in near-quantitative yield. In contrast, reaction of a substrate containing both a p-CF₃ and p-Me substituent on the phenyl rings at the respective R and Ar¹ positions (5r) was found to give corresponding ketone 6r in 39 % yield. Similarly, reactions of substrates in which the Ar² of the substrate is a p-anisyl (5s) or 2-naphthyl (5t) moiety were found to proceed well. Under the gold(i)-catalysed standard reaction conditions, these experiments gave the anticipated aryl ketone adducts 6s and 6t in respective yields of 35 and 41 %.

Table 2.  Cycloisomerisation of 1,6-diyne esters 5b–t catalysed by A
All reactions were performed at the 0.018–0.23-mmol scale with A : 5 = 1 : 20 in CH₂Cl₂ at room temperature (rt) for 24 h. Values in parentheses denote isolated yields

A tentative mechanism for the present gold(i)-catalysed 1-naphthyl ketone forming reaction is outlined in Scheme 2. With 5a as a representative example, this may initially involve activation of the propargyl moiety of the substrate by the Au^I catalyst to give the gold(i)-coordinated complex IIIa. This results in the [2,3]-sigmatropic rearrangement of the acetyl functional group to produce the gold carbenoid species Va via the 1,3-dioxin-1-ium intermediate IVa. Trapping of this newly formed organogold species by the remaining alkyne motif may then provide the putative cyclopropene adduct VIa.^[47,55] Further coordination of the Group 11 metal complex to the C=C bond of the tricyclic intermediate may next provide the gold(i)-activated species Ia. Ensuing electrophilic ring-opening of the gold(i)-activated three-membered ring in Ia would deliver the dibenzyl-stabilised gold carbenoid species IIa and its gold-stabilised allylic carbocation isomer IIa′. This is the active species that is prone to intermolecular nucleophilic attack by a molecule of water to form the hydrated organogold intermediate VIIa.^[59] A sequential deprotonation and protodeauration process may then be anticipated to give the benzylic alcohol species VIIIa, which undergoes autoxidation to yield the 1-naphthyl ketone 6a. The proposed role of water in providing the oxygen source for the carbonyl functional group formation through addition to the gold carbenoid species IIa would be in good agreement with our earlier findings described in Table 1, entry 16 showing no reaction when 4-Å MS were added to the reaction conditions. It is also supported by the following control experiment (Scheme 3). Treatment of 5a with 3 equiv. of H₂¹⁸O in distilled dichloromethane predried using 4-Å MS yielded the desired 1-naphthyl ketones 6a and 6a′ as an inseparable mixture of isotopic isomers in an overall yield of 45 %. The incorporation of ¹⁸O-content in 6a′ was detected by mass spectrometric measurements.

Scheme 2.  Proposed mechanism for Au^I-catalysed cycloisomerisation of 1,6-diyne esters represented by 1a.

Scheme 3.  Control experiment conducted with 5a and H₂¹⁸O.

In summary, we have demonstrated that propargyl esters containing a benzene-tethered alkyne undergo a 1,2-acyloxy migration–cyclopropenation–ring-opening sequence to access a dibenzyl-stabilised gold-carbenoid intermediate. In the absence of a pronucleophilic group or external reagent, addition of a molecule of water is followed by a deprotonation–protodeauration–autoxidation cascade to give access to a range of 1-naphthyl ketones. This successful utilisation of stabilised gold-carbenoid intermediates of this type should potentially lead to further useful transformations to compounds of synthetic value.

Unless specified, all reagents, solvents, and starting materials were purchased from commercial sources and used as received. The propargyl alcohol precursor to substrate 5 was prepared following literature procedures.^[28] Analytical thin-layer chromatography (TLC) was performed using precoated silica gel plates and visualisation was achieved with UV light (254 nm). Flash chromatography was performed using silica gel and a gradient solvent system (toluene or EtOAc/n-hexane as eluent). ¹H and ¹³C spectra were measured on 400 and 600 MHz spectrometers. Chemical shifts (ppm) were recorded with respect to TMS in CD₂Cl₂ and CDCl₃. Multiplicities are given as: s (singlet), brs (broad singlet), d (doublet), dd (doublet of doublets), ddd (doublet of doublets of doublets), t (triplet), dt (doublet of triplets), q (quartet) or m (multiplet). The number of protons (n) for a given resonance is indicated by nH. Coupling constants are reported as a J value in hertz. Infrared spectra were recorded on an IR spectrometer. Low- and high-resolution mass spectra (electrospray ionisation, ESI) were obtained using a liquid chromatography/high resolution mass spectrometry-time-of-flight (LC/HRMS TOF) spectrometer fitted with an analytical electrospray source using NaI for accurate mass calibration. Mass spectral data are reported in units of mass to charge ratio (m/z).

To a solution of the propargyl alcohol (1equiv.) and 4-dimethylaminopyridine (DMAP, 0.6 equiv.) in distilled CH₂Cl₂ (1 mL per 0.1 mmol) were sequentially added N,N-diisopropylethylamine (DIPEA, 4 equiv.) and acetic anhydride (3 equiv.). The reaction mixture was stirred at room temperature for 18 h. On completion, the reaction mixture was quenched by adding saturated aqueous NH₄Cl (10 mL) and extracted with CH₂Cl₂ (2 × 20 mL). The combined organic layers were washed with saturated aqueous NH₄Cl (2 × 20 mL), H₂O (15 mL), and brine (15 mL), dried over Na₂SO₄, and concentrated under reduced pressure. Purification of the crude mixture by flash column chromatography on silica gel (eluent: n-hexanes/EtOAc, gradient 14 : 1 to 9 : 1) gave the 1,6-diyne acetate substrate.

Orange solid (438 mg, 98 % yield); mp 155.5–156.3°C. δ_H (600 MHz, CD₂Cl₂) 7.99 (s, 1H), 7.56–7.51 (m, 3H), 7.42 (td, J 7.7, 1.5, 1H), 7.39–7.25 (m, 9H), 3.05 (s, 1H), 2.12 (s, 3H). δ_C (151 MHz, CD₂Cl₂) 168.44, 142.49, 142.48, 141.67, 141.66, 134.94, 134.93, 131.48, 131.46, 128.80, 128.78, 128.77, 128.55, 128.41, 128.30, 128.29, 127.08, 123.67, 121.12, 95.78, 88.46, 82.32, 79.14, 78.59, 21.65. ν_max (NaCl, neat)/cm⁻¹ 3252, 2113, 1745, 1491, 1442, 1364, 1226. m/z (HRMS ESI) 351.1277 [M + H]⁺; calc. for C₂₅H₁₈O₂: 351.1385.

Yellow solid (386 mg, 96 % yield); mp 114.0–116.0°C. δ_H (600 MHz, CD₂Cl₂) 7.99 (dd, J 8.0, 0.9, 1H), 7.53 (dd, J 7.6, 1.5, 1H), 7.50–7.47 (m, 2H), 7.43 (td, J 7.7, 1.5, 1H), 7.38–7.34 (m, 6H), 7.30–7.26 (m, 2H), 3.06 (s, 1H), 2.12 (s, 3H). δ_C (151 MHz, CDCl₃) 168.26, 141.66, 139.87, 134.86, 134.02, 131.20, 128.54, 128.53, 128.45, 128.42, 128.24, 127.88, 123.41, 120.94, 95.85, 88.21, 81.62, 78.71, 78.52, 21.63. ν_max (NaCl, neat)/cm⁻¹ 3267, 2221, 2113, 1740, 1490, 1442, 1228. m/z (HRMS ESI) 385.0963 [M + H]⁺; calc. for C₂₅H₁₇ClO₂: 385.0995.

Beige solid (275 mg, 81 % yield); mp 146.7–148.2°C. δ_H (600 MHz, CD₂Cl₂) 8.03–8.00 (m, 1H), 7.54 (dd, J 7.6, 1.1, 1H), 7.45 (td, J 7.7, 1.5, 1H), 7.41–7.33 (m, 7H), 7.31–7.27 (m, 2H), 7.03–6.96 (m, 1H), 3.08 (s, 1H), 2.14 (s, 3H). δ_C (151 MHz, CDCl₃) 168.30, 163.59, 161.97, 144.32, 141.88, 135.01, 131.46, 129.91, 128.84, 128.77, 128.50, 128.34, 123.54, 122.94, 121.12, 115.25, 115.10, 114.52, 114.36, 95.96, 88.25, 81.79, 78.95, 78.53, 21.60. ν_max (NaCl, neat)/cm⁻¹ 3250, 1742, 1592, 1491, 1441, 1368, 1223. m/z (HRMS ESI) 369.1285 [M + H]⁺ calc. for C₂₅H₁₇FO₂: 369.1291.

Yellow oil (85 mg, 84 % yield). δ_H (600 MHz, CD₂Cl₂) 7.90–7.86 (m, 1H), 7.71 (dd, J 8.0, 1.4, 1H), 7.60–7.54 (m, 1H), 7.41–7.35 (m, 2H), 7.22 (td, J 7.4, 1.3, 1H), 7.19–7.15 (m, 1H), 7.15–7.10 (m, 1H), 3.09 (s, 1H), 2.23 (s, 3H), 2.09 (s, 3H). δ_C (151 MHz, CD₂Cl₂) 168.22, 141.75, 138.45, 136.55, 134.99, 132.73, 131.51, 129.52, 129.22, 128.71, 128.66, 128.59, 128.05, 125.47, 123.75, 121.76, 96.01, 88.61, 81.39, 79.77, 78.94, 21.66, 21.60. ν_max (NaCl, neat)/cm⁻¹ 3284, 2931, 2114, 1750, 1598, 1570, 1492, 1442, 1365, 1223. m/z (HRMS ESI) 365.1520 [M + H]⁺; calc. for C₂₆H₂₀O₂: 365.1542.

White oil (132 mg, 97 % yield). δ_H (400 MHz, CDCl₃) 7.94 (dd, J 7.9, 1.3, 1H), 7.52 (dt, J 7.6, 1.0, 1H), 7.47–7.42 (m, 2H), 7.41–7.28 (m, 7H), 7.14–7.09 (m, 2H), 2.99 (d, J 0.9, 1H), 2.32 (s, 3H), 2.13 (d, J 0.8, 3H). δ_C (101 MHz, CDCl₃) 168.44, 142.35, 138.36, 137.83, 134.77, 131.27, 128.81, 128.44, 128.33, 128.13, 128.11, 127.96, 126.81, 123.71, 120.99, 95.55, 88.56, 82.24, 79.08, 78.22, 77.48, 77.36, 77.16, 76.84, 21.67, 21.25, 1.17. ν_max (NaCl, neat)/cm⁻¹ 3283, 2923, 2113, 1751, 1492, 1365, 1224. m/z (HRMS ESI) 365.1532 [M + H]⁺; calc. for C₂₆H₂₀O₂: 365.1542.

Yellow oil (70.5 mg, 97 % yield). δ_H (600 MHz, CDCl₃) 7.93 (d, J 8.0, 1H), 7.53 (dd, J 7.6, 1.1, 1H), 7.49–7.46 (m, 2H), 7.40–7.35 (m, 3H), 7.34–7.29 (m, 4H), 6.85–6.81 (m, 2H), 3.76 (s, 3H), 3.00 (s, 1H), 2.13 (s, 3H). δ_C (151 MHz, CDCl₃) 168.41, 159.26, 142.38, 134.71, 133.39, 131.23, 128.41, 128.32, 128.27, 128.10, 128.07, 127.76, 123.61, 120.96, 113.37, 95.60, 88.47, 82.16, 78.87, 78.12, 77.38, 77.17, 76.96, 55.31, 55.27, 29.81, 21.66. ν_max (NaCl, neat)/cm⁻¹ 3286, 2927, 1752, 1608, 1510, 1494, 1443, 1368, 1229, 1176. m/z (HRMS ESI) 381.1481 [M + H]⁺; calc. for C₂₆H₂₀O₃: 381.1491.

Yellow oil (87 mg, 87 % yield). δ_H (400 MHz, CDCl₃) 8.11 (s, 1H), 8.01 (dt, J 8.0, 1.6, 1H), 7.80–7.68 (m, 3H), 7.57 (dt, J 8.7, 2.0, 1H), 7.50 (dt, J 7.6, 1.6, 1H), 7.46–7.36 (m, 3H), 7.33–7.18 (m, 7H), 3.04 (d, J 1.6, 1H), 2.17 (d, J 1.2, 3H). δ_C (101 MHz, CDCl₃) 168.32, 141.95, 138.12, 134.72, 132.89, 132.72, 131.18, 128.53, 128.32, 128.27, 128.23, 128.11, 127.97, 127.89, 127.58, 126.42, 126.21, 126.03, 124.51, 123.41, 120.96, 95.67, 88.34, 81.92, 79.11, 78.62, 77.42, 77.10, 76.78, 21.60, 21.11, 14.26, 1.10. ν_max (NaCl, neat)/cm⁻¹ 3286, 2169, 1751, 1600, 1494, 1226. m/z (HRMS ESI) 401.1523 [M + H]⁺; calc. for C₂₉H₂₀O₂: 401.1542.

Yellow oil (211 mg, 86 % yield). δ_H (600 MHz, CDCl₃) 7.64–7.58 (m, 3H), 7.43–7.36 (m, 3H), 7.28 (dd, J 7.5, 1.4, 1H), 7.24–7.22 (m, 1H), 7.21–7.15 (m, 4H), 7.11–7.07 (m, 2H), 3.79 (d, J 13.2, 1H), 3.67 (d, J 13.3, 1H), 2.85 (s, 1H), 2.08 (s, 3H). δ_C (101 MHz, CDCl₃) 168.57, 140.70, 134.83, 134.55, 131.26, 131.15, 128.58, 128.53, 128.50, 128.12, 127.82, 127.55, 126.91, 123.49, 119.01, 95.13, 88.54, 81.39, 79.43, 77.93, 77.34, 77.03, 76.71, 46.61, 21.27. ν_max (NaCl, neat)/cm⁻¹ 2184, 2162, 2140, 1750, 1559, 1540, 1522, 1507, 1496, 1457, 1437, 1419, 1225. m/z (HRMS ESI) 365.1532 [M + H]⁺; calc. for C₂₆H₂₀O₂: 365.1541.

Yellow oil (121 mg, 71 % yield). δ_H (600 MHz, CD₂Cl₂) 7.90 (dd, J 7.9, 0.9, 1H), 7.58–7.53 (m, 3H), 7.42–7.35 (m, 4H), 7.31 (td, J 7.5, 1.2, 1H), 2.89 (s, 1H), 2.10 (s, 3H), 2.02 (s, 3H). δ_C (151 MHz, CD₂Cl₂) 168.95, 142.97, 134.74, 131.58, 128.92, 128.87, 128.66, 128.12, 127.44, 123.81, 119.45, 95.36, 88.52, 83.45, 76.14, 75.82, 29.93, 21.37. ν_max (NaCl, neat)/cm⁻¹ 3283, 2933, 2116, 1744, 1598, 1570, 1493, 1441, 1224. m/z (HRMS ESI) 289.1211 [M + H]⁺; calc. for C₂₀H₁₆O₂: 289.1229.

Yellow solid (480 mg, 78 % yield); mp 133.2–135.2°C. δ_H (600 MHz, CD₂Cl₂) 7.98 (dd, J 9.2, 0.4, 1H), 7.53–7.49 (m, 3H), 7.49–7.47 (m, 2H), 7.44 (td, J 7.7, 1.5, 1H), 7.35 (td, J 7.5, 1.3, 1H), 7.33–7.26 (m, 3H), 7.24–7.20 (m, 2H), 3.05 (s, 1H), 2.11 (s, 3H). δ_C (151 MHz, CD₂Cl₂) 168.40, 142.58, 141.63, 134.88, 132.93, 132.04, 128.64, 128.59, 128.38, 128.32, 127.08, 122.87, 122.70, 120.84, 94.67, 89.62, 82.21, 79.08, 78.69, 21.66. ν_max (NaCl, neat)/cm⁻¹ 3269, 211, 1742, 1491, 1441, 1235, 1192. m/z (HRMS ESI) 429.0479 [M + H]⁺; calc. for C₂₅H₁₇BrO₂: 429.0490.

Yellow oil (87 mg, 86 % yield). δ_H (400 MHz, CDCl₃) 7.94 (ddd, J 8.0, 1.3, 0.5, 1H), 7.59 (ddd, J 7.5, 1.5, 0.5, 1H), 7.56–7.52 (m, 2H), 7.44–7.34 (m, 3H), 7.33–7.27 (m, 4H), 7.25–7.17 (m, 2H), 3.01 (s, 1H), 2.14 (s, 3H). δ_C (101 MHz, CD₂Cl₂) 168.55, 142.50, 141.58, 135.74, 135.34, 133.34, 129.84, 129.67, 128.80, 128.56, 128.41, 128.37, 128.34, 127.10, 126.96, 123.51, 120.74, 93.43, 92.48, 82.30, 79.11, 78.75, 21.67. ν_max (NaCl, neat)/cm⁻¹ 3288, 2921, 1752, 1487, 1227. m/z (HRMS ESI) 325.0767 [M – OAc]⁻; calc. for C₂₅H₁₇ClO₂: 325.0784.

White oil (98 mg, 87 % yield). δ_H (600 MHz, CD₂Cl₂) 7.99 (d, J 8.0, 1H), 7.65–7.58 (m, 4H), 7.58–7.52 (m, 3H), 7.49–7.41 (m, 5H), 7.40–7.26 (m, 5H), 3.07 (s, 1H), 2.14 (s, 3H). δ_C (151 MHz, CD₂Cl₂) 168.47, 142.49, 141.68, 141.39, 140.56, 134.93, 131.92, 129.29, 128.56, 128.42, 128.36, 128.32, 128.12, 127.40, 127.31, 127.11, 122.60, 121.16, 95.73, 89.21, 82.34, 79.16, 78.61, 21.70. ν_max (NaCl, neat)/cm⁻¹ 3284, 2925, 1725, 1599, 1489, 1448, 1226. m/z (HRMS ESI) 367.1471 [M – OAc]⁻; calc. for C₃₁H₂₂O₂: 367.1487.

Yellow solid (211 mg, 83 % yield); mp 142.0–143.2°C. δ_H (600 MHz, CD₂Cl₂) 7.97 (dd, J 8.0, 1.3, 1H), 7.55–7.52 (m, 2H), 7.50 (dd, J 7.6, 1.5, 1H), 7.41 (td, J 7.7, 1.5, 1H), 7.35–7.24 (m, 6H), 7.18–7.14 (m, 2H), 3.05 (s, 1H), 2.36 (s, 3H), 2.12 (s, 3H). δ_C (151 MHz, CD₂Cl₂) 168.46, 142.35, 141.68, 139.16, 134.84, 131.34, 129.54, 128.50, 128.29, 128.27, 128.24, 128.20, 127.08, 121.32, 120.59, 96.04, 87.84, 82.37, 79.15, 78.51, 21.66, 21.62. ν_max (NaCl, neat)/cm⁻¹ 3269, 2920, 2855, 2213, 2116, 1743, 1509, 1440, 1363, 1238. m/z (HRMS ESI) 365.1519 [M + H]⁺; calc. For C₂₆H₂₀O₂: 365.1542.

Yellow oil (498 mg, 73 % yield). δ_H (600 MHz, CD₂Cl₂) 7.99 (d, J 8.0, 1H), 7.59–7.55 (m, 2H), 7.55–7.51 (m, 1H), 7.42 (td, J 7.8, 1.5, 1H), 7.37–7.27 (m, 6H), 7.18 (d, J 8.2, 2H), 3.06 (s, 1H), 2.67–2.61 (m, 2H), 2.14 (s, 3H), 1.65–1.58 (m, 2H), 1.38 (h, J 7.4, 2H), 0.96 (t, J 7.4, 3H). δ_C (151 MHz, CD₂Cl₂) 168.46, 144.16, 142.35, 141.69, 134.88, 131.37, 128.92, 128.72, 128.51, 128.30, 128.29, 128.25, 128.20, 127.10, 126.29, 121.36, 120.80, 96.12, 87.87, 82.39, 79.18, 78.54, 35.95, 33.85, 22.77, 21.68, 14.12. ν_max (NaCl, neat)/cm⁻¹ 3283, 2955, 2927, 2215, 2117, 1725, 1509 1449, 1225. m/z (HRMS ESI) 407.1992 [M + H]⁺; calc. for C₂₉H₂₆O₂: 407.2011.

Yellow solid (134 mg, 98 % yield); mp 121.0–122.0°C. δ_H (600 MHz, CD₂Cl₂) 7.96 (dd, J 8.0, 0.9, 1H), 7.55–7.52 (m, 2H), 7.49 (dd, J 7.6, 1.1, 1H), 7.39 (td, J 7.7, 1.5, 1H), 7.35–7.25 (m, 6H), 6.90–6.84 (m, 2H), 3.82 (s, 3H), 3.04 (s, 1H), 2.12 (s, 3H). δ_C (151 MHz, CD₂Cl₂) 168.18, 159.95, 141.91, 141.43, 134.42, 132.65, 128.22, 128.02, 127.99, 127.95, 127.74, 126.81, 121.21, 115.46, 114.15, 95.68, 86.94, 82.11, 78.90, 78.21, 55.44, 21.39. ν_max (NaCl, neat)/cm⁻¹ 3271, 2935, 2842, 2218, 2113, 1741, 1508, 1442, 1363, 1247, 1224, 1181. m/z (HRMS ESI) 380.1441 [M]⁺; calc. for C₂₆H₂₀O₃: 380.1413.

Yellow solid (155 mg, 81 % yield); mp 131.7–132.7°C. δ_H (600 MHz, CD₂Cl₂) 7.96 (dd, J 7.9, 1.0, 1H), 7.54–7.50 (m, 3H), 7.40 (td, J 7.7, 1.5, 1H), 7.35 (dd, J 7.5, 1.4, 1H), 7.33–7.26 (m, 3H), 7.25 (d, J 8.4, 1H), 6.74 (d, J 2.6, 1H), 6.71 (dd, J 8.4, 2.6, 1H), 3.79 (s, 3H), 3.05 (s, 1H), 2.29 (s, 3H), 2.11 (s, 3H). δ_C (151 MHz, CD₂Cl₂) 168.54, 160.14, 142.28, 141.72, 141.64, 134.93, 133.19, 128.48, 128.34, 128.30, 127.93, 127.17, 121.82, 115.66, 115.37, 111.67, 95.04, 90.89, 82.55, 79.32, 78.59, 55.62, 21.65, 20.97. ν_max (NaCl, neat)/cm⁻¹ 3283, 2936, 2837, 2207, 1751, 1604, 1501, 1449, 1237. m/z (HRMS ESI) 395.1660 [M + H]⁺; calc. for C₂₇H₂₂O₃: 395.1647.

White oil (40.2 mg, 77 % yield). δ_H (600 MHz, CDCl₃) 8.14–8.10 (m, 1H), 8.02 (ddd, J 7.9, 1.3, 0.5, 1H), 7.83 (ddt, J 12.4, 8.6, 0.9, 2H), 7.70 (ddd, J 7.6, 1.5, 0.5, 1H), 7.61–7.56 (m, 3H), 7.53–7.47 (m, 2H), 7.47–7.42 (m, 2H), 7.39 (td, J 7.5, 1.3, 1H), 7.36–7.28 (m, 3H), 3.05 (s, 1H), 2.10 (s, 3H). δ_C (151 MHz, CDCl₃) 168.65, 141.62, 141.57, 141.30, 135.10, 133.27, 130.13, 128.82, 128.60, 128.38, 128.27, 128.23, 128.20, 128.18, 127.78, 127.67, 127.03, 126.71, 126.60, 126.55, 125.37, 29.86. ν_max (NaCl, neat)/cm⁻¹ 3234, 2918, 1749, 1558, 1506, 1228. m/z (HRMS ESI) 341.1316 [M – OAc]⁻; calc. for C₂₉H₂₀O₂: 341.13303.

Orange oil (43 mg, 39 % yield). δ_H (600 MHz, CDCl₃) 7.99 (dd, J 8.0, 1.0, 1H), 7.63 (d, J 8.2, 2H), 7.51 (d, J 8.3, 2H), 7.47 (ddd, J 7.6, 1.5, 0.5, 1H), 7.38 (td, J 7.7, 1.5, 1H), 7.30 (td, J 7.5, 1.3, 1H), 7.16–7.13 (m, 2H), 7.10 (d, J 7.9, 2H), 3.00 (s, 1H), 2.34 (s, 3H), 2.13 (s, 3H). δ_C (151 MHz, CDCl₃) 168.20, 145.12, 141.18, 138.82, 134.83, 131.06, 129.32, 128.61, 128.14, 128.03, 127.34, 125.08, 125.06, 121.13, 120.20, 96.21, 87.42, 81.42, 79.05, 29.86, 22.34, 21.67, 21.60. ν_max (NaCl, neat)/cm⁻¹ 3297, 2921, 2210, 2182, 1755, 1326, 1226. m/z (HRMS ESI) 373.1187 [M – OAc]⁻; calc. for C₂₇H₁₉F₃O₂: 373.1204.

Brown solid (83 mg, 74 % yield); mp 116.6–117.1°C. δ_H (600 MHz, CDCl₃) 7.79 (dd, J 8.8, 1.4, 1H), 7.49 (dt, J 8.2, 1.6, 2H), 7.30–7.24 (m, 7H), 7.23–7.19 (m, 1H), 7.00 (dd, J 2.6, 1.1, 1H), 6.86 (dd, J 8.8, 2.7, 1H), 3.76 (s, 3H), 2.95 (s, 1H), 2.07 (s, 3H). δ_C (151 MHz, CDCl₃) 168.47, 159.05, 141.65, 134.51, 131.23, 129.76, 128.39, 128.04, 127.95, 126.71, 123.40, 122.11, 119.31, 114.01, 95.22, 88.23, 82.29, 78.81, 78.37, 55.49, 29.80, 21.65. ν_max (NaCl, neat)/cm⁻¹ 3283, 2925, 1752, 1601, 1569, 1225. m/z (HRMS ESI) 381.1448 [M + H]⁺; calc. for C₂₆H₂₀O₃: 381.1491.

White oil (10 mg, 42 % yield). δ_H (600 MHz, CDCl₃) 8.40 (s, 1H), 8.06 (s, 1H), 7.90 (dd, J 6.3, 2.9, 1H), 7.78 (dd, J 6.3, 2.7, 1H), 7.60–7.56 (m, 2H), 7.56–7.50 (m, 2H), 7.39–7.27 (m, 8H), 3.08 (d, J 0.7, 1H), 2.17 (d, J 0.8, 3H). δ_C (151 MHz, CDCl₃) 168.55, 141.15, 138.12, 135.16, 132.66, 132.17, 131.29, 128.72, 128.46, 128.32, 128.17, 128.13, 127.87, 127.38, 127.36, 127.28, 127.03, 123.68, 118.55, 94.58, 88.84, 82.18, 79.24, 78.84, 77.37, 77.16, 76.95, 21.82. ν_max (NaCl, neat)/cm⁻¹ 3286, 2225, 1752, 1598, 1495, 1449, 1226. m/z (HRMS ESI) 401.1528 [M + H]⁺; calc. for C₂₉H₂₀O_2: 401.1542.

To a reaction vessel containing the 1,6-diyne acetate substrate 5 (0.1 mmol) and gold(i) phosphine complex A (5 mol-%) under atmospheric conditions was added CH₂Cl₂ (2 mL) and the resulting reaction mixture was stirred for 24 h. The crude reaction mixture was purified by flash column chromatography on silica gel (eluent: n-hexane/EtOAc 14 : 1) to give the 1-naphthyl ketone product 6.

Yellow solid (33 mg, 62 % yield); mp 126.1–127.8°C. δ_H (400 MHz, CDCl₃) 8.19–8.13 (m, 1H), 8.00–7.95 (m, 2H), 7.70–7.60 (m, 2H), 7.55–7.42 (m, 8H), 7.41–7.35 (m, 3H), 1.97 (s, 3H). δ_C (151 MHz, CD₂Cl₂) 196.83, 169.86, 144.57, 138.33, 137.51, 135.01, 134.46, 134.28, 133.88, 130.75, 130.48, 129.80, 128.97, 128.72, 128.42, 127.42, 127.06, 126.14, 123.88, 20.69. ν_max (NaCl, neat)/cm⁻¹ 2923, 1761, 1494, 1197, 1176. m/z (HRMS ESI) 367.1333 [M + H]⁺; calc. for C₂₅H₁₈O₃: 367.1334.

Yellow oil (24 mg, 45 % yield). δ_H (600 MHz, CD₂Cl₂) 8.13–8.09 (m, 1H), 7.95–7.90 (m, 2H), 7.67–7.62 (m, 2H), 7.54–7.47 (m, 6H), 7.38 (s, 1H), 7.35–7.32 (m, 2H), 2.00 (s, 3H). δ_C (151 MHz, CD₂Cl₂) 196.74, 169.75, 144.62, 138.22, 137.92, 134.44, 134.08, 133.95, 133.58, 133.10, 132.02, 130.74, 129.76, 129.01, 127.63, 127.17, 126.73, 126.23, 123.69, 20.74. ν_max (NaCl, neat)/cm⁻¹ 2924, 1763, 1661, 1491, 1197, 1176. m/z (HRMS ESI) 401.0930 [M + H]⁺; calc. for C₂₅H₁₇ClO₃: 401.0945.

White oil (28.5 mg, 53 % yield). δ_H (400 MHz, CD₂Cl₂) 8.12–8.06 (m, 1H), 7.95–7.89 (m, 2H), 7.68–7.60 (m, 2H), 7.55–7.44 (m, 5H), 7.38 (s, 1H), 7.25–7.08 (m, 4H), 1.99 (s, 3H). δ_C (101 MHz, CD₂Cl₂) 196.73, 169.73, 164.30, 161.85, 144.58, 138.22, 138.02, 137.29, 137.21, 133.99, 133.97, 132.96, 132.94, 130.75, 130.49, 130.41, 129.74, 129.01, 127.66, 127.19, 126.74, 126.49, 126.46, 126.22, 123.69, 117.66, 117.44, 115.47, 115.26, 54.24, 20.70. ν_max (NaCl, neat)/cm⁻¹ 1764, 1582, 1489, 1449, 1437, 1369, 1338, 1269, 1242, 1201, 1172, 1123, 1020. m/z (HRMS ESI) 385.1233 [M + H]⁺; calc. for C₂₅H₁₇FO₃: 385.1240.

White oil (17 mg, 51 % yield). δ_H (400 MHz, CDCl₃) 8.18 (dt, J 8.4, 1.1, 1H), 8.00–7.95 (m, 2H), 7.63 (ddt, J 7.9, 6.9, 1.3, 1H), 7.54–7.36 (m, 8H), 7.34–7.28 (m, 1H), 7.20 (dd, J 7.2, 1.2, 1H), 2.02 (s, 3H), 1.92 (s, 3H). δ_C (151 MHz, CDCl₃) 196.87, 169.58, 144.74, 138.37, 137.70, 137.37, 134.48, 134.10, 134.04, 133.85, 130.78, 130.44, 129.71, 128.96, 128.68, 127.54, 127.09, 126.78, 126.26, 126.03, 124.06, 30.09, 20.61, 19.86. ν_max (NaCl, neat)/cm⁻¹ 2920, 2851, 1765, 1663, 1449, 1201. m/z (HRMS ESI) 381.1467 [M + H]⁺; calc. for C₂₆H₂₀O₃: 381.1491.

Yellow oil (18 mg, 41 % yield). δ_H (400 MHz, CDCl₃) 8.15 (dd, J 8.3, 1.6, 1H), 7.96 (dt, J 7.1, 1.4, 2H), 7.72–7.58 (m, 2H), 7.53–7.40 (m, 4H), 7.37 (s, 1H), 7.32 (d, J 7.8, 2H), 7.28–7.22 (m, 2H), 2.46 (s, 3H), 1.99 (s, 3H). δ_C (101 MHz, CDCl₃) 196.63, 169.55, 144.09, 137.95, 137.70, 136.86, 134.23, 134.10, 133.42, 131.56, 130.53, 129.96, 129.57, 129.02, 128.57, 126.92, 126.79, 126.71, 125.81, 123.58, 77.33, 77.01, 76.69, 21.36, 20.57, 1.02. ν_max (NaCl, neat)/cm⁻¹ 2957, 2923, 1763, 1661, 1595, 1579, 1508, 1449, 1231, 1200. m/z (HRMS ESI) 381.1487 [M + H]⁺; calc. for C₂₆H₂₀O₃: 381.1491.

White oil (32.3 mg, 44 % yield). δ_H (600 MHz, CDCl₃) 8.16 (d, J 8.4, 1H), 7.96 (d, J 8.2, 2H), 7.71 (d, J 8.4, 1H), 7.64–7.60 (m, 1H), 7.53–7.42 (m, 4H), 7.37 (s, 1H), 7.32–7.28 (m, 2H), 7.08–7.03 (m, 2H), 3.91 (s, 3H), 2.01 (s, 3H). δ_C (151 MHz, CDCl₃) 196.78, 169.71, 159.47, 144.37, 138.07, 136.95, 134.38, 134.11, 133.58, 131.44, 130.67, 129.73, 128.72, 127.09, 126.89, 126.87, 126.78, 125.97, 123.71, 55.46, 20.74. ν_max (NaCl, neat)/cm⁻¹ 2927, 1759, 1578, 1507, 1448, 1366, 1244, 1196, 1172. m/z (HRMS ESI) 397.1412 [M + H]⁺; calc. for C₂₆H₂₀O₄: 397.1440.

White oil (20 mg, 36 % yield). δ_H (600 MHz, CD₂Cl₂) 8.14 (d, J 8.1, 1H), 8.02 (d, J 8.4, 1H), 7.99–7.91 (m, 4H), 7.87 (s, 1H), 7.71–7.68 (m, 1H), 7.66 (tt, J 7.8, 1.3, 1H), 7.61–7.56 (m, 2H), 7.55–7.48 (m, 4H), 7.47–7.42 (m, 2H), 1.91 (s, 3H). δ_C (151 MHz, CD₂Cl₂) 196.84, 169.87, 144.78, 138.34, 137.62, 134.39, 134.30, 133.90, 133.60, 133.32, 132.55, 130.77, 129.83, 129.67, 128.99, 128.49, 128.36, 128.31, 128.16, 127.49, 127.13, 127.11, 126.89, 126.82, 126.19, 123.93, 54.02, 20.72. ν_max (NaCl, neat)/cm⁻¹ 2925, 1763, 1662, 1200, 1175. m/z (HRMS ESI) 417.1451 [M + H]⁺; calc. for C₂₉H₂₀O₃: 417.1491.

Yellow oil (5.8 mg, 47 % yield). δ_H (600 MHz, CDCl₃) 8.17–8.12 (m, 1H), 8.06–8.02 (m, 1H), 7.96–7.91 (m, 2H), 7.62 (ddt, J 7.7, 7.1, 1.3, 1H), 7.52–7.44 (m, 4H), 7.38 (s, 1H), 7.28–7.23 (m, 2H), 7.21–7.16 (m, 3H), 4.45 (s, 2H), 2.27 (s, 3H). δ_C (125 MHz, CDCl₃) 194.83, 170.61, 142.99, 139.17, 136.56, 133.85, 132.69, 130.42, 129.99, 128.51, 126.78, 126.37, 125.43, 33.51, 20.02. ν_max (NaCl, neat)/cm⁻¹ 3062, 3028, 2922, 2853, 2360, 2341, 2250, 1761, 1659, 1594, 1515, 1495, 1449, 1368, 1339, 1281, 1255, 1199, 1176, 1082, 1011, 907. m/z (HRMS ESI) 381.1483 [M + H]⁺; calc. for C₂₆H₂₀O₃: 380.1412.

White oil (15 mg, 24 % yield). δ_H (400 MHz, CDCl₃) 8.16 (ddd, J 8.5, 1.4, 0.7, 1H), 8.09 (ddd, J 8.6, 1.3, 0.7, 1H), 7.91–7.87 (m, 2H), 7.63–7.57 (m, 2H), 7.53–7.44 (m, 3H), 7.30 (s, 1H), 2.58 (s, 3H), 2.37 (s, 3H). δ_C (151 MHz, CD₂Cl₂) 169.68, 145.17, 143.66, 138.55, 135.72, 134.22, 133.67, 130.68, 129.57, 128.97, 128.87, 127.33, 126.88, 126.61, 124.94, 124.03, 100.40, 30.09, 21.04, 12.27. ν_max (NaCl, neat)/cm⁻¹ 2922, 2853, 1759, 1594, 1199. m/z (HRMS ESI) 305.1170 [M + H]⁺; calc. for C₂₀H₁₆O₃: 305.1178.

Yellow oil (20 mg, 32 % yield). δ_H (400 MHz, CDCl₃) 8.14 (ddd, J 8.4, 1.5, 0.7, 1H), 7.86–7.79 (m, 2H), 7.69–7.63 (m, 3H), 7.55–7.42 (m, 6H), 7.39–7.34 (m, 3H), 1.98 (s, 3H). δ_C (151 MHz, CD₂Cl₂) 195.78, 169.86, 144.53, 137.19, 136.81, 134.90, 134.80, 134.31, 132.30, 132.26, 130.44, 129.69, 129.01, 128.74, 128.47, 127.51, 127.21, 127.11, 126.02, 124.08, 70.87, 20.68. ν_max (NaCl, neat)/cm⁻¹ 2865, 1763, 1583, 1201. m/z (HRMS ESI) 445.0431 [M + H]⁺; calc. for C₂₅H₁₇BrO₃: 445.0440.

Brown solid (24 mg, 31 % yield); mp 137.0–138.0°C. δ_H (400 MHz, CDCl₃) 8.87 (d, J 8.6, 1H), 7.70–7.61 (m, 2H), 7.58 (d, J 7.2, 1H), 7.55–7.44 (m, 6H), 7.43–7.32 (m, 4H), 1.93 (s, 3H). δ_C (151 MHz, CD₂Cl₂) 196.09, 169.70, 144.59, 139.65, 136.89, 135.76, 134.83, 134.54, 132.45, 132.40, 130.84, 130.34, 129.78, 128.69, 128.53, 128.07, 127.59, 127.33, 127.18, 127.15, 126.33, 20.63. ν_max (NaCl, neat)/cm⁻¹ 2926, 1751, 1674, 1582, 1197. m/z (HRMS ESI) 401.0938 [M + H]⁺; calc. for C₂₅H₁₇ClO₃: 401.0945.

Yellow solid (20 mg, 67 % yield); mp 126.4–127.2°C. δ_H (600 MHz, CDCl₃) 8.18 (d, J 8.4, 1H), 8.08–8.03 (m, 2H), 7.73 (d, J 8.2, 2H), 7.69–7.64 (m, 3H), 7.54–7.37 (m, 11H), 1.99 (s, 3H). δ_C (151 MHz, CDCl₃) 196.34, 169.72, 146.37, 144.22, 139.96, 137.32, 136.67, 134.80, 134.23, 134.10, 131.30, 130.24, 129.67, 129.14, 128.48, 128.15, 127.48, 127.40, 127.20, 126.94, 126.86, 126.00, 123.56, 20.67. ν_max (NaCl, neat)/cm⁻¹ 2923, 1761, 1655, 1600, 1260, 1198, 1176. m/z (HRMS ESI) 443.1641 [M + H]⁺; calc. for C₃₁H₂₂O₃: 443.1647.

Yellow oil (14.9 mg, 28 % yield). δ_H (400 MHz, CDCl₃) 8.16–8.10 (m, 1H), 7.92–7.85 (m, 2H), 7.68–7.63 (m, 1H), 7.54–7.41 (m, 5H), 7.39–7.35 (m, 3H), 7.32–7.28 (m, 2H), 2.45 (s, 3H), 1.98 (s, 3H). δ_C (101 MHz, CDCl₃) 196.42, 169.64, 144.63, 144.19, 137.56, 135.43, 134.81, 134.01, 133.94, 130.82, 130.22, 129.62, 129.42, 128.42, 128.08, 127.08, 126.77, 125.97, 123.28, 77.45, 77.33, 77.13, 76.81, 21.88, 20.62, 1.14. ν_max (NaCl, neat)/cm⁻¹ 2926, 1763, 1604, 1495, 1201. m/z (HRMS ESI) 381.1461 [M + H]⁺; calc. for C₂₆H₂₀O₃: 381.1491.

Orange oil (12.7 mg, 21 % yield). δ_H (400 MHz, CDCl₃) 8.05 (d, J 8.1, 1H), 7.82 (d, J 8.3, 2H), 7.61–7.54 (m, 1H), 7.46–7.34 (m, 5H), 7.32–7.28 (m, 3H), 7.26–7.20 (m, 2H), 2.66–2.59 (m, 2H), 1.90 (s, 3H), 1.63–1.53 (m, 2H), 1.31 (dq, J 14.7, 7.3, 3H), 0.87 (t, J 7.3, 3H). δ_C (151 MHz, CD₂Cl₂) 168.47, 145.15, 144.45, 144.15, 142.33, 141.67, 134.88, 134.47, 131.46, 131.35, 128.92, 128.86, 128.72, 128.51, 128.49, 128.39, 128.32, 128.28, 128.18, 127.08, 126.91, 126.27, 35.93, 33.81, 22.75, 21.67, 14.09. ν_max (NaCl, neat)/cm⁻¹ 2925, 2859, 1765, 1605, 1456, 1201. m/z (HRMS ESI) 423.1929 [M + H]⁺; calc. for C₂₉H₂₆O₃: 423.19604.

Orange oil (42 mg, 25 % yield, obtained as inseparable mixture of 5o and 6o in a ratio 4 : 1). δ_H (400 MHz, CD₂Cl₂) 8.07–8.02 (m, 1H), 7.95–7.91 (m, 2H), 7.73–7.65 (m, 2H), 7.57–7.27 (m, 7H), 7.02–6.97 (m, 2H), 3.89 (s, 3H), 1.98 (s, 3H). δ_C (101 MHz, CD₂Cl₂) 169.89, 164.50, 156.57, 144.62, 142.18, 134.69, 133.12, 132.92, 131.29, 131.04, 130.51, 128.26, 128.22, 128.01, 126.98, 126.84, 126.17, 123.00, 87.21, 82.38, 79.16, 78.50, 56.01, 55.69, 21.67. ν_max (NaCl, neat)/cm⁻¹ 3282, 2959, 2934, 2214, 2114, 1751, 1511, 1247, 1226. m/z (HRMS ESI) 397.1417 [M + H]⁺; calc. for C₂₆H₂₀O₄: 397.1440.

Yellow oil (12.9 mg, 31 % yield). δ_H (600 MHz, CDCl₃) 8.69 (d, J 8.4, 1H), 8.54 (d, J 8.5, 1H), 8.06 (d, J 8.2, 1H), 7.96 (d, J 7.6, 1H), 7.74 (dd, J 7.1, 1.1, 1H), 7.68 (d, J 8.5, 2H), 7.60 (ddd, J 8.1, 6.8, 1.3, 1H), 7.55 (ddd, J 8.4, 6.8, 1.4, 1H), 7.53–7.45 (m, 5H), 7.40 (s, 1H), 7.38–7.33 (m, 2H), 1.91 (s, 3H). δ_C (151 MHz, CDCl₃) 198.48, 169.59, 144.25, 138.36, 136.49, 135.37, 134.76, 134.19, 134.08, 133.14, 131.38, 130.18, 130.00, 128.66, 128.46, 128.29, 128.19, 127.39, 127.25, 126.90, 126.84, 126.17, 126.04, 125.74, 124.57, 14.27. ν_max (NaCl, neat)/cm⁻¹ 2920, 1745, 1653, 1578, 1173. m/z (HRMS ESI) 417.1489 [M + H]⁺; calc. for C₂₉H₂₀O₃: 417.1491.

Orange solid (20 mg, 35 % yield); mp 75.0–76.0°C. δ_H (600 MHz, CDCl₃) 8.12 (d, J 8.6, 1H), 7.87 (d, J 8.2, 2H), 7.79 (d, J 8.0, 2H), 7.56–7.44 (m, 6H), 7.37 (s, 1H), 7.32–7.29 (m, 2H), 2.45 (s, 3H), 2.00 (s, 3H). δ_C (151 MHz, CDCl₃) 196.25, 169.50, 144.88, 144.22, 138.85, 138.41, 135.26, 133.57, 132.25, 130.84, 130.82, 129.59, 129.52, 127.53, 127.03, 126.27, 126.20, 125.51, 125.48, 125.45, 125.43, 123.38, 123.02, 21.94, 20.67. ν_max (NaCl, neat)/cm⁻¹ 2918, 1766, 1574, 1323, 1176. m/z (HRMS ESI) 365.1159 [M + H]⁺; calc. for C₂₃H₁₅F₃O: 365.1153.

Orange oil (30 mg, 35 % yield). δ_H (600 MHz, CDCl₃) 7.96 (d, J 7.2, 2H), 7.67 (d, J 2.5, 1H), 7.65–7.61 (m, 1H), 7.57–7.44 (m, 7H), 7.39 (s, 1H), 7.37–7.33 (m, 2H), 7.11 (dd, J 9.3, 2.6, 1H), 3.83 (s, 3H), 1.96 (s, 3H). δ_C (151 MHz, CDCl₃) 197.08, 169.83, 158.65, 142.43, 138.43, 134.93, 134.91, 134.89, 133.39, 131.28, 130.65, 130.15, 129.44, 128.70, 128.43, 128.31, 128.13, 125.15, 120.03, 104.28, 55.46, 20.63. ν_max (NaCl, neat)/cm⁻¹ 2931, 1765, 1513, 1471, 1203. m/z (HRMS ESI) 397.1418 [M + H]⁺; calc. for C₂₆H₂₀O₄: 397.1440.

White oil (3 mg, 41 % yield). δ_H (600 MHz, CDCl₃) 8.84 (s, 1H), 8.19 (s, 1H), 8.04 (s, 2H), 7.96–7.92 (m, 1H), 7.84–7.80 (m, 1H), 7.67–7.62 (m, 1H), 7.60–7.56 (m, 2H), 7.55–7.51 (m, 3H), 7.48–7.42 (m, 4H), 7.40 (s, 1H), 2.00 (s, 3H). δ_C (151 MHz, CDCl₃) 196.81, 169.77, 143.27, 138.21, 137.08, 134.95, 133.80, 133.64, 132.13, 132.04, 131.93, 130.75, 130.31, 128.78, 128.71, 128.61, 128.28, 127.56, 126.52, 126.31, 125.95, 125.48, 124.85, 29.90, 20.70, 14.28. ν_max (NaCl, neat)/cm⁻¹ 1758, 1655, 1459, 1258. m/z (HRMS ESI) 417.1468 [M + H]⁺; calc. for C₂₉H₂₀O₃: 417.1491.

To a reaction vessel containing the 1,6-diyne acetate substrate 5a (41.2 mg, 0.1 mmol), H₂¹⁸O (6.4 μL, 0.3 mmol), and gold(i) phosphine complex A (4.5 mg, 5 mol-%) under atmospheric conditions was added CH₂Cl₂ (2 mL) and the resulting reaction mixture was stirred for 24 h. The crude reaction mixture was purified by flash column chromatography on silica gel (eluent: n-hexane/EtOAc 14 : 1) to give an inseparable mixture of the 1-naphthyl ketone products 6a and 6a′ (19.6 mg, 45 % yield).

¹H and ¹³C NMR spectra for all starting materials and products are available on the Journal’s website.

The authors declare no conflicts of interest.