English

• 1.   Introduction

  The transition metal-catalyzed ring-opening reaction of oxa- and aza-bicyclic alkenes is a useful method to construct carbon-carbon and carbon-heteroatom bonds.^[1] It is well known that 1, 2-dihydronaphthalene skeleton was found in a wide range of naturally occurring compounds which exhibited a variety of biological activities.^[2] In addition, this transformation is valuable because multiple stereocenters can be established in a single step. In this regard, numerous metal catalysts, including Ir, ^[3] Ni, ^[4] Pd, ^[5] Cu, ^[6] Rh, ^[7] Pt, ^[8] Ru, ^[9] Fe, ^[10] and so forth, ^[11] have been investigated for the ring-opening reaction of heterobicyclic alkenes with various carbon and heteroatom nucleophiles.

  Since the seminal work of Lautens, ^{[1b, 1d]} many research groups have been working on the transition metal-catalyzed asymmetric ring-opening (ARO) reactions of oxa(aza)bicyclic alkenes and make some considerable progress. Our group has long-term interest in the ARO reactions of oxa- and aza-bicyclic alkenes with various nucleophiles. The nucleophiles, such as amines, ^{[3a, 3c, 3e, 12]} phenols, ^{[8a, 13]} alcohols, ^{[3f, 14]} carboxylic acids, ^{[3b, 3d]} Grignard reagents^[15] and organic zincs^[16] have been found as feasible nucleophiles used in the ring-opening reaction. In recent years, arylboronic acids and arylsulfinate salts, because of their stability and low toxicity, also have been employed as effective carbanion nucleophiles in ring-opening reactions of oxabicyclic alkenes to afford the corresponding product 2-aryl-1, 2-dihydronaphthalen-1-ols in high yields. For instance, our group demonstrated platinum-catalyzed ring-opening of oxabenzonorbornadienes with sodium sulfinates^[17] and arylboronic acids^[18], which generated cis-1, 2-ring-opening products in high yields.

  Arylsulfonyl hydrazides are generally stable in the air. They can be prepared in one step from readily available arylsulfonyl chlorides and hydrazine hydrates, ^[19] and increasing attention has recently been paid to the construction of C—C bonds through the extrusion of N₂ and SO₂ in situ.^[20] Recently, our group^[21] has reported palladium-catalyzed syn-stereocontrolled ring-opening reactions of oxabenzonorbornadienes with arylsulfonyl hydrazides, affording the desired products in good to excellent yields (up to 96%) under an air atmosphere. To the best of our knowledge, there is no literature reported about platinum-catalyzed syn-stereocontrolled ring-opening of oxabicyclic alkenes with arylsulfonyl hydrazides till now. Our continuous interest in this type of reactions promotes us to further explore and expand the possibility of this reaction in the presence of platinum catalyst. Herein, we reported platinum-catalyzed ring-opening of oxabicyclic alkenes with arylsulfonyl hydrazides to afford the corresponding products of cis-2-aryl-1, 2-dihydronapthalene-1-ols and 2-aryl-napthalenes in good to excellent yields.

  2.   Results and discussion

  Oxabenzonorbornadiene (1a) and phenylsulfonyl hydrazide (2a) were initially chosen as model substrates to identify the feasibility of our process. When 2a reacted with 1a in 1, 2-dichloroethane (DCE) at 80 ℃ in the presence of PtCl₂ (10 mol%), PPh₃ (20 mol%) and Cu(OAc)₂ (3 equiv.), the desired ring-opening product 3aa was obtained in 62% yield after 4 h (Table 1, Entry 1). Other two platinum catalysts were then screened, and PtCl₂ was the best one (Entries 1~3). It was worth mentioning that the ring-opening reaction did not take place in the absence of PtCl₂ (Entry 4). When the catalyst loading was 5 mol% and 20 mol%, the ring-opening product 3aa could be obtained with yields of 39% and 60%, respectively (Entries 5, 6). In order to further improve the yield of 3aa, series achiral phosphine ligands, including 1, 3-bis(diphenylphosphino)-propane (DPPP), 1, 2-bis(diphenylphosphino)ethane (DPPE) and 1, 1'-bis(diphenylphosphino)ferrocene (DPPF) were examined for the ring-opening reaction (Entries 7~9) (yields up to 62%). Moreover, chiral phosphine ligands, including (S)-SEGPHOS, (R, S)-PPF-^tBu₂, (R)-BINAP, (S)-DM-SEGPHOS, (4S, 5S)-DIOP and (2S, 4S)-BDPP were also tested. Unfortunately, the product 3aa was obtained only in moderate yield and low enantioselectivity (up to 53% yield and 43% ee) (Entries 10~15). Therefore, among the ligands screened, achiral ligand PPh₃ was the most effective in terms of yield (Entries 1~15). Next, several cupric salts, such as CuO, CuCl₂ and Cu(acac)₂ were also investigated. Unfortunately, all of them gave low yields (Entries 16~18). The effect of solvent was then examined (Entries 1, 19~21). The results indicated that solvents played an important role in the ring-opening reaction. The solvent DCE was the optimal solvent. Furthermore, the impact of reaction temperature on the reaction efficiency was investigated (Entries 22~23). When the reaction temperature was 60 or 100 ℃, the product 3aa was obtained in moderate yield (53% and 48%, respectively). At last, the impact of the amount of Cu(OAc)₂ on the reaction was investigated (Entries 24~26). The results indicated that 1.5 equiv. of Cu(OAc)₂ gave the best yield (82%). It should be noted that in the absence of Cu(OAc)₂, none of the targeted product was observed (Entry 27). Meanwhile, product 3aa could be obtained in 20% yield in the absence of PPh₃ (Entry 28). Therefore, the optimal reaction conditions were: 10 mol% PtCl₂, 20 mol% PPh₃, 1.5 equiv. of Cu(OAc)₂ in DCE at 80 ℃ for 4 h.

  Table 1

  

  Table 1.  Optimization for the reaction conditions^a

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  Entry	Pt catalyst (mol%)	Ligand (mol%)	Additive (equiv.)	Solvent	Yieldb/%	eec/%
  1	PtCl2 (10)	PPh3 (20)	Cu(OAc)2 (3)	DCE	62
  2	Pt(COD)Cl2 (10)	PPh3 (20)	Cu(OAc)2 (3)	DCE	58
  3	Pt(acac)2 (10)	PPh3 (20)	Cu(OAc)2 (3)	DCE	36
  4	—	PPh3 (20)	Cu(OAc)2 (3)	DCE	0
  5	PtCl2 (5)	PPh3 (10)	Cu(OAc)2 (3)	DCE	39
  6	PtCl2 (20)	PPh3 (40)	Cu(OAc)2 (3)	DCE	60
  7	PtCl2 (10)	DPPP	Cu(OAc)2 (3)	DCE	Trace
  8	PtCl2 (10)	DPPE	Cu(OAc)2 (3)	DCE	Trace
  9	PtCl2 (10)	DPPF	Cu(OAc)2 (3)	DCE	41
  10	PtCl2 (10)	(S)-SEGPHOS	Cu(OAc)2 (3)	DCE	53	36
  11	PtCl2 (10)	(R, S)-PPF-tBu2	Cu(OAc)2 (3)	DCE	336	320
  12	PtCl2 (10)	(R)-BINAP	Cu(OAc)2 (3)	DCE	348	310
  13	PtCl2 (10)	(S)-DM-SEGPHOS	Cu(OAc)2 (3)	DCE	350	343
  14	PtCl2 (10)	(4S, 5S)-DIOP	Cu(OAc)2 (3)	DCE	310	35
  15	PtCl2 (10)	(2S, 4S)-BDPP	Cu(OAc)2 (3)	DCE	38	35
  16	PtCl2 (10)	PPh3	CuO (3)	DCE	3Trace
  17	PtCl2 (10)	PPh3	CuCl2 (3)	DCE	323
  18	PtCl2 (10)	PPh3	Cu(acac)2 (3)	DCE	352
  19	PtCl2 (10)	PPh3	Cu(OAc)2 (3)	1, 4-Dioxane	346
  20	PtCl2 (10)	PPh3	Cu(OAc)2 (3)	THF	351
  21	PtCl2 (10)	PPh3	Cu(OAc)2 (3)	DMF	337
  22d	PtCl2 (10)	PPh3	Cu(OAc)2 (3)	DCE	353
  23e	PtCl2 (10)	PPh3	Cu(OAc)2 (3)	DCE	348
  24	PtCl2 (10)	PPh3	Cu(OAc)2 (2)	DCE	373
  25	PtCl2 (10)	PPh3	Cu(OAc)2 (1.5)	DCE	382
  26	PtCl2 (10)	PPh3	Cu(OAc)2 (1)	DCE	365
  27	PtCl2 (10)	PPh3	—	DCE	3n.r.
  28	PtCl2 (10)	—	Cu(OAc)2 (1.5)	DCE	320
  a The reaction was carried out with Pt catalyst, ligand, additive, 1a (0.1 mmol, 1.0 equiv.) and 2a (0.2 mmol, 2.0 equiv.) in the corresponding solvent at 80 ℃ under an air atmosphere for 4 h. bIsolated yield. c Determined by HPLC with a Chiralcel OD-H column. d60 ℃. e 100 ℃.

  Next, attention was paid to the ring-opening reaction of 1a with a variety of arylsulfonyl hydrazides under the optimized reaction conditions (Table 2). In general, all of arylsulfonyl hydrazides 2a~2h as nucleophiles could react smoothly with 1a and provided the corresponding targeted products 3aa~3ah in moderate to good yields (52%~85%). The substituents attached on arylsulfonyl hydrazides had obvious electronic effect on the ring-opening reaction. Compared with arylsulfonyl hydrazides with strong electron donating groups, the ring opening reaction of arylsulfonylhydrazides with electron withdrawing groups on benzene ring was better. Arylsulfonyl hydrazides 2e~2g bearing electron-withdrawing groups could react smoothly with 1a and afforded the corresponding products 3ae~3ag in good yields (78%, 85% and 77%, respectively). Arylsulfonyl hydrazides 2b~2c bearing electron-donating groups could react with 1a and afforded the corresponding products 3ab~3ac in moderate yields (68% and 66%, respectively). 2-Chlorobenzenesulfonyl hydrazide (2d) could react with 1a and afforded ring-opening product 3ad in 60% yield. In addition to these, when 2, 4, 6-trimethyl-benzenesulfonyl hydrazide (2h) as nucleophile was employed in the reaction, the desired product 3ah was obtained in 52% yield, which probably due to steric hindrance.

  Table 2

  

  Table 2.  Platinum-catalyzed ring-opening of oxabenzonorbornadiene 1a with various arylsulfonyl hydrazides 2a~2h^a

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  Entry	Ar	Product	Yieldb/%
  1	C6H5	3aa	82
  2	4-CH3C6H4	3ab	68
  3	4-CH3OC6H4	3ac	66
  4	2-ClC6H4	3ad	60
  5	4-ClC6H4	3ae	78
  6	4-FC6H4	3af	85
  7	4-O2NC6H4	3ag	77
  8	2, 4, 6-(CH3)3C6H2	3ah	52
  a Conditions: 1a (0.1 mmol, 14.4 mg), 2 (0.2 mmol), Cu(OAc)2 (1.5 equiv.), PtCl2 (10 mol%), PPh3 (20 mol%), DCE (2 mL), 80 ℃. bIsolated yield.

  The scope of this ring-opening reaction was further expanded to various oxabenzonorbornadienes 1b~1f. The results showed that the reaction of various oxabenzonorbornadienes with arylsulfonyl hydrazides proceeded smoothly to afford corresponding target product in moderate to excellent yields (Table 3). The ring-opening reactions of oxabenzonorbornadienes 1d~1f with various arylsulfonyl hydrazides proceeded smoothly to afford the expected products with good to excellent yields (up to 89%). Oxabenzonorbornadienes 1d and 1f bearing bromine and fluorine groups showed better reaction efficiency than 1e bearing methyl group. Besides, bulkier substrate 1g afforded product 3ga in 52% yield, indicating that steric hindrance on substrate 1g had a negative impact on this ring-opening transformation. Interestingly, the corresponding products 2-arylnaphthalenes 4ba~4cb could be obtained in good yields (up to 78%) rather than ring-opening products 3 when methoxy substituted oxabenzonorbornadienes 1b~1c were used to react with various arylsulfonyl hydrazides.

  Table 3

  

  Table 3.  Platinum-catalyzed ring-opening of oxabenzonorbornadienes 1b~1g with various arylsulfonyl hydrazides^a

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  Entry	1	Ar	3	Yieldb/% of 3	4	Yieldb/% of 4
  1	1b	C6H5			4ba	68
  2	1b	4-CH3C6H4			4bb	66
  3	1b	4-FC6H4			4bf	78
  4	1c	C6H5			4ca	70
  5	1c	4-CH3C6H4			4cb	72
  6	1d	C6H5	3da	83
  7	1d	4-CH3C6H4	3db	80
  8	1d	4-FC6H4	3df	88
  9	1e	C6H5	3ea	71
  10	1e	4-ClC6H4	3ee	72
  11	1e	4-O2NC6H4	3eg	70
  12	1f	C6H5	3fa	87
  13	1f	4-CH3C6H4	3fb	80
  14	1f	4-FC6H4	3ff	89
  15	1g	C6H5	3ga	52
  aConditions: 1 (0.1 mmol, 14.4 mg), 2 (0.2 mmol), Cu(OAc)2 (1.5 equiv.), PtCl2 (10 mol%), PPh3 (20 mol%), DCE (2 mL), 80 ℃. bIsolated yield.

  The cis-1, 2-configuration of compound 3db was undoubtedly confirmed by X-ray single crystal diffraction analysis (Figure 1). The single crystal was obtained by diffusion method from a mixed solvent of petroleum ether and ethyl acetate.

  Figure 1

  

  Figure 1.  X-ray single crystal diffraction analysis of compound 3db

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  To further evaluate the reaction effect on the scale of preparation, scaled-up reaction was then conducted under the current standard conditions. The desired product 3aa was obtained in 68% yield (0.302 g), indicating the application of this method in synthetic chemistry (Scheme 1).

  Scheme 1

  

  Scheme 1.  Scaled-up experiment of 3aa

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  According to our experimental results and the general mechanism of desulfurization coupling reactions, ^[20] a plausible mechanism for this ring-opening reaction is proposed (Scheme 2). Initially, ligand PPh₃ reacts with PtCl₂ to give the active catalyst Pt(PPh₃)₂Cl₂. Then Pt(PPh₃)₂Cl₂ is treated with arylsulfonyl hydrazide 2 to result in complex A, which undergoes β-hydride elimination to give sulfonyl diazene B and release Pt(PPh₃)₂. Pt(0)(PPh₃)₂ is then oxidized by Cu(OAc)₂ or O₂ from air to regenerate the active catalyst Pt(PPh₃)₂Cl₂[Pt(PPh₃)₂X₂]. Meanwhile, one of chlorine atom of Pt(PPh₃)₂Cl₂ is replaced by sulfonyl diazene B to give intermediate C. Intermediate C releases nitrogen and sulfur dioxide, affording arylplatinum D, which then undergoes exo-1, 2-addition with substrate 1a to yield intermediate E. β-Oxygen atom elimination of intermediate E occurs and provides new Pt intermediate F. Protonation of the intermediate F affords product 3 and a Pt(PPh₃)₂. Further dehydration of 3 gives 2-arylnaphthalene 4.

  Scheme 2

  

  Scheme 2.  Plausible mechanism

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  3.   Conclusions

  In summary, an efficient platinum-catalyzed syn-stereocontrolled ring-opening of oxabicyclic alkenes with arylsulfonyl hydrazides via the release of N₂ and SO₂ in situ under mild conditions has been developed. This synthetic protocol provides a useful tool for the construction of cis-2-aryl-1, 2-dihydronaphthalen-1-ols 3 and 2-aryl-naphthalenes 4 in good to excellent yields. The different substituents of oxabicyclic alkenes play a crucial role in the control of targeted product. The electron-withdrawing groups in the substrate are advantageous for the ring-opening reaction, and the dehydrated compounds are more readily available when oxabenzonorbornadienes bearing a strong donor group were used. Further studies toward the evaluating of the biological and pharmaceutical activities of these target compounds are going on in our laboratory.

  4.   Experimental section

  4.1   General information

  All ¹H NMR and ¹³C NMR spectra were recorded at 600 and 150 MHz respectively, using CDCl₃/CD₃OD as the solvent. ¹⁹F NMR spectra were recorded at 564 MHz at 25 ℃ in CDCl₃/ CD₃OD. The chemical shifts of all ¹H NMR and ¹³C NMR spectra were referenced to the residual signal of CDCl₃ (δ 7.26 for the ¹H NMR spectra and δ 77.00 for the ¹³C NMR spectra) or CD₃OD (δ 3.31 for the ¹H NMR spectra and δ 49.00 for the ¹³C NMR spectra). Enantiomeric excesses were determined with a Chiralcel OD-H column eluting with a mixture of hexane and propan-2-ol (V:V=95:5, 1.0 mL/min, λ=254 nm). Infrared spectra (IR) were obtained with thin film samples on a PerkinElmer Spectrum Two spectrometer. HRMS were obtained from mass spectrometer (ESI-TOF). Melting points were recorded on an electrothermal digital melting point apparatus and were uncorrected. The crystal structure determination was carried out by an X-ray diffraction apparatus. Unless otherwise stated, all starting materials, catalysts, and solvents were commercially available and were used as purchased. Anhydrous solvent 1, 4-dioxane, tetrahydrofuran (THF) and N, N-dimethylformamide (DMF) were used without any pretreatment. Substrates of oxabenzonorbornadienes (1a~1g) were synthesized according to the known procedures.^[3c] Flash column chromatography was performed using the indicated solvent system on Qingdao-Haiyang silica gel (200~300 mesh).

  4.2   General procedure for the synthesis of products 3 and 4

  All experiments were carried out under air. PtCl₂ (2.7 mg, 10 mol%), PPh₃ (5.2 mg, 20 mol%), oxabicyclic alkenes 1 (0.1 mmol), arylsulfonyl hydrazides 2 (2 equiv., 0.2 mmol), Cu(OAc)₂ (27.2 mg, 0.15 mmol) and DCE (2.0 mL) were simultaneously added to a 10 mL round-bottomed flask. The mixture was stirred at 80 ℃ in oil bath for 4 h. After cooling to room temperature, 10 mL of water was added to the reaction mixture, which then was extracted by ethyl acetate (10 mL×3). The organic layers were combined and dried with anhydrous MgSO₄, and then filtered. The filtrate was concentrated under vacuum, and the resulting residue was purified by column chromatography on silica gel (200~300 mesh) using ethyl acetate/petroleum ether or ethyl acetate/hexane to obtain the desired products 3 and 4.

  (1S*, 2R*)-2-Phenyl-1, 2-dihydronaphthalen-1-ol  (3aa): Colorless oil (18.3 mg, 82%). ¹H NMR (600 MHz, CDCl₃) δ: 7.36~7.27 (m, 6H), 7.28~7.26 (m, 2H), 7.19~7.16 (m, 1H), 6.71 (dd, J=9.6, 2.0 Hz, 1H), 6.13 (dd, J=9.6, 4.0 Hz, 1H), 4.93 (d, J=5.9 Hz, 1H), 3.88 (ddd, J=6.0, 4.0, 2.1 Hz, 1H), 1.56 (s, 1H); ¹³C NMR (150 MHz, CDCl₃) δ: 137.8, 136.1, 132.7, 129.7, 129.3, 128.7, 128.4, 128.3, 128.0, 127.5, 126.7, 126.4, 71.3, 47.4; IR (film) v: 3445, 2925, 1495, 1449, 1128, 765, 691 cm^-1; HRMS (ESI-TOF) calcd for C₁₆H₁₁O [M-3H]^- 219.0810, found 219.0810.

  (1S*, 2R*)-2-(p-Tolyl)-1, 2-dihydronaphthalen-1-ol  (3ab): Colorless oil (16.1 mg, 68%). ¹H NMR (600 MHz, CDCl₃) δ: 7.34 (d, J=7.2 Hz, 1H), 7.30~7.22 (m, 2H), 7.17~7.10 (m, 5H), 6.68 (dd, J=9.6, 1.9 Hz, 1H), 6.11 (dd, J=9.6, 4.1 Hz, 1H), 4.91 (t, J=6.6 Hz, 1H), 3.83 (ddd, J=6.1, 4.2, 2.0 Hz, 1H), 2.31 (s, 3H), 1.49 (d, J=7.8 Hz, 1H); ¹³C NMR (150 MHz, CDCl₃) δ: 137.1, 136.2, 134.3, 132.7, 129.9, 129.4, 129.1, 128.2, 128.1, 127.9, 126.6, 126.3, 71.3, 46.9, 21.0; IR (film) v: 3437, 2920, 1512, 1451, 1374, 1184, 1071, 786 cm^-1; HRMS (ESI-TOF) calcd for C₁₇H₁₃O [M-3H]^- 233.0966, found 233.0970.

  (1S*, 2R*)-2-(4-Methoxyphenyl)-1, 2-dihydronaphthalen-1-ol (3ac): Colorless oil (16.7 mg, 66%). ¹H NMR (600 MHz, CDCl₃) δ: 7.35 (dd, J=7.3, 0.5 Hz, 1H), 7.29~7.23 (m, 2H), 7.18~7.14 (m, 3H), 6.84 (d, J=8.7 Hz, 2H), 6.68 (dd, J=9.6, 1.9 Hz, 1H), 6.10 (dd, J=9.6, 4.3 Hz, 1H), 4.93 (t, J=5.9 Hz, 1H), 3.81 (ddd, J=6.2, 4.3, 2.0 Hz, 1H), 3.77 (s, 3H), 1.49 (d, J=6.9 Hz, 1H); ¹³C NMR (150 MHz, CDCl₃) δ: 159.0, 136.2, 132.7, 130.3, 130.0, 129.1, 128.2, 128.0, 128.0, 126.5, 126.3, 114.1, 71.3, 55.2, 46.4; IR (film) v: 3448, 2925, 1601, 1512, 1242, 1174, 1025, 796 cm^-1; HRMS (ESI-TOF) calcd for C₁₇H₁₃O₂ [M-3H]^- 249.0916, found 249.0916.

  (1S*, 2R*)-2-(2-Chlorophenyl)-1, 2-dihydronaphthalen-1-ol (3ad): Colorless oil (15.4 mg, 60%). ¹H NMR (600 MHz, CDCl₃) δ: 7.45 (dd, J=7.5, 1.8 Hz, 1H), 7.42~7.34 (m, 3H), 7.31~7.22 (m, 4H), 6.76 (dd, J=9.6, 2.7 Hz, 1H), 6.10~6.04 (m, 1H), 4.91 (d, J=5.0 Hz, 1H), 4.51 (dt, J=5.3, 2.9 Hz, 1H), 1.64 (s, 1H); ¹³C NMR (150 MHz, CDCl₃) δ: 136.9, 135.2, 134.1, 132.1, 131.0, 129.5, 129.0, 128.8, 128.4, 128.3, 128.0, 127.9, 126.9, 126.7, 69.1, 44.0; IR (film) v: 3414, 2923, 1469, 1456, 1257, 1071, 1031, 808 cm^-1; HRMS (ESI-TOF) calcd for C₁₆H₁₀ClO [M-3H]^- 253.0418, found 253.0421.

  (1S*, 2R*)-2-(4-Chlorophenyl)-1, 2-dihydronaphthalen-1-ol (3ae): White solid (20.0 mg, 78%). m.p. 113.0~114.0 ℃; ¹H NMR (600 MHz, CDCl₃) δ: 7.33~7.24 (m, 5H), 7.20~7.14 (m, 3H), 6.70 (dd, J=9.6, 2.0 Hz, 1H), 6.06 (dd, J=9.6, 4.1 Hz, 1H), 4.89 (d, J=6.0 Hz, 1H), 3.81 (ddd, J=6.0, 4.1, 2.0 Hz, 1H), 1.55 (s, 1H); ¹³C NMR (150 MHz, CDCl₃) δ: 136.3, 135.9, 133.1, 132.4, 130.6, 129.2, 128.6, 128.4, 128.4, 128.2, 126.5, 126.4, 71.2, 46.7; IR (film) v: 3424, 2909, 1484, 1413, 1189, 1089, 1012, 801 cm^-1; HRMS (ESI-TOF) calcd for C₁₆H₁₀ClO [M-3H]^- 253.0418, found 253.0422.

  (1S*, 2R*)-2-(4-Fluorophenyl)-1, 2-dihydronaphthalen-1-ol (3af): White solid (20.4 mg, 85%). m.p. 100.0~101.0 ℃; ¹H NMR (600 MHz, CDCl₃) δ: 7.34~7.16 (m, 6H), 7.01~6.93 (m, 2H), 6.70 (dd, J=9.6, 2.0 Hz, 1H), 6.08 (dd, J=9.6, 4.1 Hz, 1H), 4.91 (t, J=6.8 Hz, 1H), 3.84 (ddd, J=6.1, 4.2, 2.0 Hz, 1H), 1.46 (d, J=8.1 Hz, 1H); ¹³C NMR (150 MHz, CDCl₃) δ: 162.2 (d, J=240.0 Hz), 136.0, 133.3 (d, J=3.2 Hz), 132.5, 130.8 (d, J=8.0 Hz), 129.6, 128.4, 128.3, 128.1, 126.5, 126.4, 115.4 (d, J=21.3 Hz), 71.2, 46.5; ¹⁹F NMR (564 MHz, CDCl₃) δ: -115.4 (s); IR (film) v: 3420, 2922, 1484, 1456, 1410, 1086, 1012, 832 cm^-1; HRMS (ESI-TOF) calcd for C₁₆H₁₀FO [M-3H]^- 237.0713, found 237.0715.

  (1S*, 2R*)-2-(4-Nitrophenyl)-1, 2-dihydronaphthalen-1-ol (3ag): Pale-yellow solid (20.6 mg, 77%). m.p. 122.3~123.6 ℃; ¹H NMR (600 MHz, CDCl₃) δ: 8.15 (d, J=8.7 Hz, 2H), 7.44 (d, J=8.6 Hz, 2H), 7.33 (dd, J=11.5, 4.1 Hz, 2H), 7.29~7.27 (m, 1H), 7.21 (d, J=7.3 Hz, 1H), 6.77 (dd, J=9.6, 2.0 Hz, 1H), 6.08 (dd, J=9.6, 3.8 Hz, 1H), 4.93 (s, 1H), 3.95 (t, J=5.7 Hz, 1H), 1.60 (s, 1H); ¹³C NMR (150 MHz, CDCl₃) δ: 147.2, 146.5, 135.6, 132.1, 130.2, 129.0, 128.8, 128.5, 128.1, 126.8, 126.7, 123.6, 71.2, 47.3; IR (film) v: 3417, 2922, 1591, 1513, 1339, 1107, 1071, 857 cm^-1; HRMS (ESI-TOF) calcd for C₁₆H₁₀NO₃ [M-3H]^- 264.0658, found 264.0658.

  (1S*, 2R*)-2-Mesityl-1, 2-dihydronaphthalen-1-ol (3ah): Colorless oil (13.8 mg, 52%). ¹H NMR (600 MHz, CD₃OD) δ: 7.36~7.31 (m, 2H), 7.26~7.19 (m, 2H), 6.87 (s, 2H), 6.61 (dd, J=9.6, 3.3 Hz, 1H), 6.16 (d, J=9.6 Hz, 1H), 4.69 (d, J=4.9 Hz, 1H), 4.14~4.10 (m, 1H), 2.47 (s, 3H), 2.33 (s, 3H), 2.25 (s, 3H); ¹³C NMR (150 MHz, CD₃OD) δ: 140.4, 137.7, 137.3, 136.7, 135.1, 134.3, 133.5, 131.8, 130.1, 129.8, 129.6, 128.1, 127.5, 125.2, 71.1, 44.8, 22.0, 21.1, 20.9; IR (film) v: 3420, 2919, 1520, 1485, 1453, 1079, 812, 761 cm^-1; HRMS (ESI-TOF) calcd for C₁₉H₁₇O [M-3H]^- 261.1279, found 261.1277.

  1, 4-Dimethoxy-6-phenylnaphthalene  (4ba): Colorless oil (17.9 mg, 68%). ¹H NMR (600 MHz, CDCl₃) δ: 8.44 (d, J=1.7 Hz, 1H), 8.27 (d, J=8.7 Hz, 1H), 7.78~7.74 (m, 3H), 7.46 (dd, J=10.6, 4.8 Hz, 2H), 7.35 (dt, J=8.4, 1.1 Hz, 1H), 6.70~6.66 (m, 2H), 3.95 (d, J=1.9 Hz, 6H); ¹³C NMR (150 MHz, CDCl₃) δ: 149.7, 149.4, 141.3, 138.4, 128.7, 127.4, 127.2, 126.6, 125.4, 125.3, 122.4, 119.8, 103.6, 103.3, 55.7; IR (film) v: 2940, 1599, 1462, 1364, 1272, 1229, 1097, 755 cm^-1; HRMS (ESI-TOF) calcd for C₁₈H₁₇O₂ [M+H]⁺ 265.1229, found 265.1225.

  1, 4-Dimethoxy-6-(p-tolyl)naphthalene  (4bb): White solid (18.4 mg, 66%). m.p. 113.2~114.4 ℃; ¹H NMR (600 MHz, CDCl₃) δ: 8.42 (d, J=1.6 Hz, 1H), 8.25 (d, J=8.7 Hz, 1H), 7.75 (dd, J=8.7, 1.9 Hz, 1H), 7.65 (d, J=8.1 Hz, 2H), 7.26 (d, J=7.8 Hz, 2H), 6.67 (q, J=8.3 Hz, 2H), 3.95 (d, J=3.0 Hz, 6H), 2.40 (s, 3H); ¹³C NMR (150 MHz, CDCl₃) δ: 149.7, 149.5, 138.4, 138.3, 137.0, 129.5, 127.2, 126.6, 125.2, 125.2, 122.4, 119.4, 103.6, 103.1, 55.7, 21.1; IR (film) v: 2937, 1594, 1520, 1459, 1359, 1267, 1232, 1104, 804 cm^-1; HRMS (ESI-TOF) calcd for C₁₉H₁₉O₂ [M+H]⁺ 279.1385, found 279.1380.

  6-(4-Fluorophenyl)-1, 4-dimethoxynaphthalene    (4bf): White solid (22.0 mg, 78%). m.p. 110.5~111.6 ℃; ¹H NMR (600 MHz, CDCl₃) δ: 8.37 (d, J=1.8 Hz, 1H), 8.25 (d, J=8.7 Hz, 1H), 7.71~7.68 (m, 3H), 7.14 (t, J=8.7 Hz, 2H), 6.70 (dd, J=14.6, 7.1 Hz, 2H), 3.96 (d, J=1.5 Hz, 6H); ¹³C NMR (150 MHz, CDCl₃) δ: 162.5 (d, J=244.9 Hz), 149.2 (d, J=27.6 Hz), 137.4, 129.0 (d, J=8.06 Hz), 126.4 (d, J=33.1 Hz), 125.8, 125.3, 125.1, 122.6, 121.7, 119.7, 115.6 (d, J=21.6 Hz), 103.7, 103.2 (d, J=28.56 Hz), 55.7; ¹⁹F NMR (564 MHz, CDCl₃) δ: -115.9 (s); IR (film) v: 2955, 1599, 1510, 1456, 1364, 1268, 1225, 1104, 827 cm^-1; HRMS (ESI-TOF) calcd for C₁₈H₁₆FO₂ [M+H]⁺ 283.1134, found 283.1130.

  2, 3-Dimethoxy-6-phenylnaphthalene (4ca): White solid (18.5 mg, 70%). m.p. 121.0~122.0 ℃; ¹H NMR (600 MHz, CDCl₃) δ: 7.92 (d, J=1.3 Hz, 1H), 7.76 (d, J=8.4 Hz, 1H), 7.73~7.71 (m, 2H), 7.62 (dd, J=8.4, 1.8 Hz, 1H), 7.48 (t, J=7.7 Hz, 2H), 7.37 (t, J=7.5 Hz, 1H), 7.19 (s, 1H), 7.15 (s, 1H), 4.03 (d, J=1.8 Hz, 6H); ¹³C NMR (150 MHz, CDCl₃) δ: 149.8, 149.5, 141.3, 136.9, 129.4, 128.7, 128.3, 127.2, 127.0, 126.8, 124.3, 123.8, 106.5, 106.0, 55.8; IR (film) v: 2928, 1601, 1495, 1252, 1235, 1166, 1128, 1003, 854 cm^-1; HRMS (ESI-TOF) calcd for C₁₈H₁₇O₂ [M+H]⁺ 265.1229, found 265.1225.

  2, 3-Dimethoxy-6-(p-tolyl)naphthalene  (4cb): White solid (20.0 mg, 72%). m.p. 136.2~137.3 ℃; ¹H NMR (600 MHz, CDCl₃) δ: 7.88 (d, J=1.4 Hz, 1H), 7.73 (d, J=8.4 Hz, 1H), 7.60~7.58 (m, 3H), 7.27 (d, J=7.8 Hz, 2H), 7.15 (d, J=22.1 Hz, 2H), 4.01 (d, J=2.2 Hz, 6H), 2.41 (s, 3H); ¹³C NMR (150 MHz, CDCl₃) δ: 149.7, 149.4, 138.4, 136.9, 136.7, 129.5, 129.4, 128.2, 127.0, 126.7, 124.0, 123.8, 106.5, 106.1, 55.8, 21.1; IR (film) v: 2948, 1602, 1456, 1360, 1268, 1232, 1097, 812 cm^-1; HRMS (ESI-TOF) calcd for C₁₉H₁₉O₂ [M+H]⁺ 279.1385, found 279.1383.

  (1S*, 2R*)-6, 7-Dibromo-2-phenyl-1, 2-dihydronaphthalen-1-ol (3da): Colorless oil (31.5 mg, 83%). ¹H NMR (600 MHz, CD₃OD) δ: 7.59 (s, 1H), 7.50 (s, 1H), 7.26~7.17 (m, 5H), 6.66 (dd, J=9.6, 1.7 Hz, 1H), 6.23 (dd, J=9.6, 4.6 Hz, 1H), 4.93 (d, J=6.4 Hz, 1H), 3.78 (ddd, J=6.4, 4.6, 1.8 Hz, 1H); ¹³C NMR (150 MHz, CD₃OD) δ: 139.5, 138.9, 135.6, 134.0, 132.5, 131.8, 130.5, 129.1, 128.0, 127.0, 124.3, 123.9, 71.1, 48.2; IR (film) v: 3396, 2912, 1655, 1495, 1444, 1257, 1076, 890, 801 cm^-1; HRMS (ESI-TOF) calcd for C₁₆H₉Br₂O [M-3H]^- 374.9021, found 374.9024.

  (1S*, 2R*)-6, 7-Dibromo-2-(p-tolyl)-1, 2-dihydronaphthalen-1-ol (3db)(CCDC 1966855): Colorless oil (31.4 mg, 80%). ¹H NMR (600 MHz, CDCl₃) δ: 7.58 (s, 1H), 7.39 (s, 1H), 7.10 (d, J=7.9 Hz, 2H), 7.04 (d, J=8.0 Hz, 2H), 6.58 (dd, J=9.7, 1.0 Hz, 1H), 6.19 (dd, J=9.6, 4.9 Hz, 1H), 4.95 (s, 1H), 3.81~3.77 (m, 1H), 2.31 (s, 3H), 1.52 (s, 1H); ¹³C NMR (150 MHz, CDCl₃) δ: 137.7, 137.3, 133.6, 132.2, 132.0, 131.4, 130.7, 129.6, 129.1, 126.2, 123.9, 123.5, 70.2, 46.2, 21.0; IR (film) v: 3417, 2915, 1510, 1464, 1260, 1107, 1072, 887 cm^-1; HRMS (ESI-TOF) calcd for C₁₇H₁₁Br₂O [M-3H]^- 388.9177, found 388.9183.

  (1S*, 2R*)-6, 7-Dibromo-2-(4-fluorophenyl)-1, 2-dihydronaphthalen-1-ol (3df): Colorless oil (35.0 mg, 88%). ¹H NMR (600 MHz, CD₃OD) δ: 7.59 (s, 1H), 7.50 (s, 1H), 7.20~7.14 (m, 2H), 6.98~6.94 (m, 2H), 6.66 (dd, J=9.6, 1.5 Hz, 1H), 6.21 (dd, J=9.6, 4.7 Hz, 1H), 4.92 (d, J=6.4 Hz, 1H), 3.81~3.77 (m, 1H); ¹³C NMR (150 MHz, CD₃OD) δ: 163.5 (d, J=241.7 Hz), 139.4, 135.5, 134.6 (d, J=2.7 Hz), 133.8, 132.4, 132.2 (d, J=8.0 Hz), 131.8, 127.2, 124.3, 124.0, 115.7 (d, J=21.6 Hz), 71.0, 47.3; ¹⁹F NMR (564 MHz, CD₃OD) δ: -118.4 (s); IR (film) v: 3414, 2915, 1596, 1510, 1464, 1219, 1155, 887 cm^-1; HRMS (ESI-TOF) calcd for C₁₆H₈Br₂FO [M-3H]^- 392.8927, found 392.8932.

  (1S*, 2R*)-6, 7-Dimethyl-2-phenyl-1, 2-dihydronaphthalen-1-ol (3ea): Pale-yellow oil (17.8 mg, 71%). ¹H NMR (600 MHz, CD₃OD) δ: 7.25 (dd, J=5.9, 1.2 Hz, 4H), 7.21~7.16 (m, 1H), 7.08 (s, 1H), 6.94 (s, 1H), 6.63 (dd, J=9.6, 2.2 Hz, 1H), 6.02 (dd, J=9.6, 3.8 Hz, 1H), 4.78 (d, J=5.7 Hz, 1H), 3.74 (ddd, J=5.9, 3.8, 2.3 Hz, 1H), 2.25 (d, J=5.9 Hz, 6H); ¹³C NMR (150 MHz, CD₃OD) δ: 140.9, 137.1, 137.0, 135.4, 132.0, 130.6, 130.2, 129.2, 129.1, 128.9, 128.6, 127.7, 72.3, 49.1, 19.7, 19.5; IR (film) v: 3399, 2919, 1648, 1487, 1089, 1061, 1018, 887 cm^-1; HRMS (ESI-TOF) calcd for C₁₈H₁₅O [M-3H]^- 247.1124, found 247.1132.

  (1S*, 2R*)-2-(4-Chlorophenyl)-6, 7-dimethyl-1, 2-dihydronaphthalen-1-ol (3ee): Colorless oil (20.5 mg, 72%). ¹H NMR (600 MHz, CD₃OD) δ: 7.25~7.21 (m, 4H), 7.09 (s, 1H), 6.94 (s, 1H), 6.64 (dd, J=9.6, 1.9 Hz, 1H), 5.99 (dd, J=9.6, 4.0 Hz, 1H), 4.80 (d, J=5.9 Hz, 1H), 3.74 (ddd, J=6.0, 4.0, 2.1 Hz, 1H), 2.26 (d, J=5.0 Hz, 6H); ¹³C NMR (150 MHz, CD₃OD) δ: 139.6, 137.2, 137.1, 135.2, 133.4, 132.1, 131.8, 129.6, 129.2, 129.1, 129.0, 128.6, 72.0, 48.3, 19.7, 19.5; IR (film) v: 3414, 2920, 1510, 1489, 1311, 1253, 1094, 887 cm^-1; HRMS (ESI-TOF) calcd for C₁₈H₁₄ClO [M-3H]^- 281.0734, found 281.0738.

  (1S*, 2R*)-6, 7-Dimethyl-2-(4-nitrophenyl)-1, 2-dihydronaphthalen-1-ol (3eg): Colorless oil (20.7 mg, 70%). ¹H NMR (600 MHz, CDCl₃) δ: 8.17 (d, J=8.5 Hz, 2H), 7.46 (d, J=8.5 Hz, 2H), 7.10 (s, 1H), 6.99 (s, 1H), 6.71 (d, J=8.3 Hz, 1H), 6.00 (dd, J=9.5, 3.5 Hz, 1H), 4.86 (d, J=5.4 Hz, 1H), 3.93 (s, 1H), 2.27 (d, J=9.6 Hz, 6H), 1.59 (s, 1H); ¹³C NMR (150 MHz, CDCl₃) δ: 147.1, 147.0, 137.0, 136.9, 133.0, 130.2, 129.7, 128.9, 128.2, 128.1, 127.0, 123.5, 71.1, 47.6, 19.7, 19.5; IR (film) v: 3427, 2925, 1591, 1512, 1342, 1306, 1257, 1104, 850 cm^-1; HRMS (ESI-TOF) calcd for C₁₈H₁₄NO₃ [M-3H]^- 292.0974, found 292.0982.

  (1S*, 2R*)-6, 7-Difluoro-2-phenyl-1, 2-dihydronaphthalen-1-ol (3fa): Yellow oil (22.4, 87%). ¹H NMR (600 MHz, CDCl₃) δ: 7.33~7.28 (m, 3H), 7.21~7.17 (m, 3H), 6.98 (dd, J=10.5, 7.6 Hz, 1H), 6.60 (dd, J=9.7, 1.7 Hz, 1H), 6.16 (dd, J=9.6, 4.5 Hz, 1H), 4.95 (d, J=6.4 Hz, 1H), 3.84 (t, J=4.8 Hz, 1H), 1.56 (s, 1H); ¹³C NMR (150 MHz, CDCl₃) δ: 150.7 (dd, J=26.5, 12.8 Hz), 149.1 (dd, J=28.5, 12.9 Hz), 136.1, 133.2 (t, J=4.1 Hz), 130.4 (d, J=2.4 Hz), 129.5 (dd, J=6.2, 4.1 Hz), 129.3, 128.8, 127.8, 126.5, 116.0 (d, J=18.5 Hz), 115.0 (d, J=17.6 Hz), 70.4, 46.6; ¹⁹F NMR (564 MHz, CDCl₃) δ: -138.3 (d, J=21.5 Hz), -139.8 (d, J=20.3 Hz); IR (film) v: 3424, 2919, 1591, 1502, 1374, 1306, 1071, 875 cm^-1; HRMS (ESI-TOF) calcd for C₁₆H₉F₂O [M-3H]^- 255.0622, found 255.0626.

  (1S*, 2R*)-6, 7-Difluoro-2-(p-tolyl)-1, 2-dihydronaphthalen-1-ol (3fb): Colorless oil (21.8 mg, 80%). ¹H NMR (600 MHz, CDCl₃) δ: 7.18 (dd, J=10.5, 8.0 Hz, 1H), 7.10 (dd, J=23.9, 8.0 Hz, 4H), 6.97 (dd, J=10.5, 7.7 Hz, 1H), 6.58 (dd, J=9.7, 1.3 Hz, 1H), 6.14 (dd, J=9.7, 4.6 Hz, 1H), 4.94 (s, 1H), 3.80 (t, J=5.3 Hz, 1H), 2.32 (s, 3H), 1.50 (s, 1H); ¹³C NMR (150 MHz, CDCl₃) δ: 150.6 (dd, J=20.2, 13.2 Hz), 149.0 (dd, J=22.1, 12.9 Hz), 137.6, 133.3 (t, J=4.5 Hz), 132.7, 130.7, 130.7, 129.6, 129.1, 126.4, 115.9 (d, J=18.5 Hz), 114.9 (d, J=18.0 Hz), 70.3, 46.1, 21.0; ¹⁹F NMR (564 MHz, CDCl₃) δ: -138.4 (d, J=20.3 Hz), -140.0 (d, J=20.3 Hz); IR (film) v: 3410, 2923, 1507, 1449, 1378, 1308, 1072, 883 cm^-1; HRMS (ESI-TOF) calcd for C₁₇H₁₁F₂O [M-3H]^- 269.0779, found 269.0785.

  (1S*, 2R*)-6, 7-Difluoro-2-(4-fluorophenyl)-1, 2-dihydronaphthalen-1-ol (3ff): Colorless oil (24.6 mg, 89%). ¹H NMR (600 MHz, CDCl₃) δ: 7.21~7.12 (m, 3H), 7.04~6.94 (m, 3H), 6.59 (dd, J=9.6, 1.3 Hz, 1H), 6.12 (dd, J=9.6, 4.6 Hz, 1H), 4.92 (s, 1H), 3.80 (t, J=5.0 Hz, 1H), 1.51 (s, 1H); ¹³C NMR (150 MHz, CDCl₃) δ: 162.4 (d, J=244.7 Hz), 150.7 (dd, J=19.2, 12.8 Hz), 149.0 (dd, J=20.6, 13.1 Hz), 133.0 (t, J=4.1 Hz), 131.8 (d, J=3.2 Hz), 130.8 (d, J=7.8 Hz), 130.3 (d, J=2.3 Hz), 129.4 (dd, J=6.2, 4.0 Hz), 126.6, 115.9 (d, J=18.5 Hz), 115.6 (d, J=20.9 Hz), 115.1 (d, J=17.9 Hz), 70.3, 45.8; ¹⁹F NMR (564 MHz, CDCl₃) δ: -114.7 (s), -138.0 (d, J=20.3 Hz), -139.5 (d, J=20.3 Hz); IR (film) v: 3424, 2922, 1597, 1505, 1313, 1221, 1104, 878 cm^-1; HRMS (ESI-TOF) calcd for C₁₆H₈F₃O [M-3H]^- 273.0528, found 273.0534.

  (1S*, 2R*)-2-Phenyl-1, 2-dihydrotriphenylen-1-ol  (3ga): White solid (16.8 mg, 52%). m.p. 156~158 ℃; ¹H NMR (600 MHz, CDCl₃) δ: 8.80~8.69 (m, 2H), 8.35~8.30 (m, 1H), 8.29~8.24 (m, 1H), 7.73~7.59 (m, 5H), 7.55 (dd, J=8.0, 0.9 Hz, 2H), 7.50~7.46 (m, 2H), 7.42~7.37 (m, 1H), 6.49 (ddd, J=9.8, 2.3, 1.5 Hz, 1H), 5.44 (s, 1H), 4.07~4.00 (m, 1H), 1.56 (s, 1H); ¹³C NMR (150 MHz, CDCl₃) δ: 140.1, 130.8, 130.6, 130.6, 129.8, 129.2, 128.8, 128.7, 128.6, 127.3, 127.2, 126.9, 126.8, 126.5, 126.4, 124.1, 123.9, 123.8, 123.1, 123.1, 67.6, 48.1; IR (film) v: 3486, 2996, 1525, 1510, 1108, 775, 710 cm^-1; HRMS (ESI-TOF) calcd for C₂₄H₁₅O [M-3H]^- 319.1124, found 319.1125.

  4.3   Procedure for the scaled-up synthesis of product 3aa

  The experiment was carried out under air. PtCl₂ (0.054 g, 10 mol%), PPh₃ (0.105 g, 20 mol%), oxabicyclic alkenes 1a (0.288 g, 2.0 mmol), arylsulfonyl hydrazides 2a (0.689 g, 4.0 mmol), Cu(OAc)₂ (0.544 g, 3.0 mmol) and DCE (20.0 mL) were simultaneously added to a 50 mL round-bottomed flask. The mixture was stirred at 80 ℃ in oil bath for 4 h. After cooling to room temperature, 30 mL of water was added to the reaction mixture, which then was extracted by ethyl acetate (20 mL×3), The organic layers were combined and dried with anhydrous MgSO₄, and then filtered. The filtrate was concentrated under vacuum, and there sulting residue was purified on silica gel [eluent: V(ethyl acetate):V(petroleum ether)=1:20] to obtain product 3aa as a colorless oil (0.302 g, 68%).

  Supporting Information  The ¹H NMR, ¹³C NMR spectra of compounds 3 and 4, the ¹⁹F NMR spectra of compounds 3af, 3df, 3fa, 3fb, 3ff, and 4bf, HPLC chromatograms of compound 3aa, and the X-ray single crystal diffraction analysis of compound 3db. The Supporting Information is available free of charge via the Internet at http://sioc-journal.cn/.

  
  
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  Figure 1  X-ray single crystal diffraction analysis of compound 3db

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  Scheme 1  Scaled-up experiment of 3aa

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  Scheme 2  Plausible mechanism

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  Table 1.  Optimization for the reaction conditions^a

  Entry	Pt catalyst (mol%)	Ligand (mol%)	Additive (equiv.)	Solvent	Yieldb/%	eec/%
  1	PtCl2 (10)	PPh3 (20)	Cu(OAc)2 (3)	DCE	62
  2	Pt(COD)Cl2 (10)	PPh3 (20)	Cu(OAc)2 (3)	DCE	58
  3	Pt(acac)2 (10)	PPh3 (20)	Cu(OAc)2 (3)	DCE	36
  4	—	PPh3 (20)	Cu(OAc)2 (3)	DCE	0
  5	PtCl2 (5)	PPh3 (10)	Cu(OAc)2 (3)	DCE	39
  6	PtCl2 (20)	PPh3 (40)	Cu(OAc)2 (3)	DCE	60
  7	PtCl2 (10)	DPPP	Cu(OAc)2 (3)	DCE	Trace
  8	PtCl2 (10)	DPPE	Cu(OAc)2 (3)	DCE	Trace
  9	PtCl2 (10)	DPPF	Cu(OAc)2 (3)	DCE	41
  10	PtCl2 (10)	(S)-SEGPHOS	Cu(OAc)2 (3)	DCE	53	36
  11	PtCl2 (10)	(R, S)-PPF-tBu2	Cu(OAc)2 (3)	DCE	336	320
  12	PtCl2 (10)	(R)-BINAP	Cu(OAc)2 (3)	DCE	348	310
  13	PtCl2 (10)	(S)-DM-SEGPHOS	Cu(OAc)2 (3)	DCE	350	343
  14	PtCl2 (10)	(4S, 5S)-DIOP	Cu(OAc)2 (3)	DCE	310	35
  15	PtCl2 (10)	(2S, 4S)-BDPP	Cu(OAc)2 (3)	DCE	38	35
  16	PtCl2 (10)	PPh3	CuO (3)	DCE	3Trace
  17	PtCl2 (10)	PPh3	CuCl2 (3)	DCE	323
  18	PtCl2 (10)	PPh3	Cu(acac)2 (3)	DCE	352
  19	PtCl2 (10)	PPh3	Cu(OAc)2 (3)	1, 4-Dioxane	346
  20	PtCl2 (10)	PPh3	Cu(OAc)2 (3)	THF	351
  21	PtCl2 (10)	PPh3	Cu(OAc)2 (3)	DMF	337
  22d	PtCl2 (10)	PPh3	Cu(OAc)2 (3)	DCE	353
  23e	PtCl2 (10)	PPh3	Cu(OAc)2 (3)	DCE	348
  24	PtCl2 (10)	PPh3	Cu(OAc)2 (2)	DCE	373
  25	PtCl2 (10)	PPh3	Cu(OAc)2 (1.5)	DCE	382
  26	PtCl2 (10)	PPh3	Cu(OAc)2 (1)	DCE	365
  27	PtCl2 (10)	PPh3	—	DCE	3n.r.
  28	PtCl2 (10)	—	Cu(OAc)2 (1.5)	DCE	320
  a The reaction was carried out with Pt catalyst, ligand, additive, 1a (0.1 mmol, 1.0 equiv.) and 2a (0.2 mmol, 2.0 equiv.) in the corresponding solvent at 80 ℃ under an air atmosphere for 4 h. bIsolated yield. c Determined by HPLC with a Chiralcel OD-H column. d60 ℃. e 100 ℃.

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  Table 2.  Platinum-catalyzed ring-opening of oxabenzonorbornadiene 1a with various arylsulfonyl hydrazides 2a~2h^a

  Entry	Ar	Product	Yieldb/%
  1	C6H5	3aa	82
  2	4-CH3C6H4	3ab	68
  3	4-CH3OC6H4	3ac	66
  4	2-ClC6H4	3ad	60
  5	4-ClC6H4	3ae	78
  6	4-FC6H4	3af	85
  7	4-O2NC6H4	3ag	77
  8	2, 4, 6-(CH3)3C6H2	3ah	52
  a Conditions: 1a (0.1 mmol, 14.4 mg), 2 (0.2 mmol), Cu(OAc)2 (1.5 equiv.), PtCl2 (10 mol%), PPh3 (20 mol%), DCE (2 mL), 80 ℃. bIsolated yield.

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  Table 3.  Platinum-catalyzed ring-opening of oxabenzonorbornadienes 1b~1g with various arylsulfonyl hydrazides^a

  Entry	1	Ar	3	Yieldb/% of 3	4	Yieldb/% of 4
  1	1b	C6H5			4ba	68
  2	1b	4-CH3C6H4			4bb	66
  3	1b	4-FC6H4			4bf	78
  4	1c	C6H5			4ca	70
  5	1c	4-CH3C6H4			4cb	72
  6	1d	C6H5	3da	83
  7	1d	4-CH3C6H4	3db	80
  8	1d	4-FC6H4	3df	88
  9	1e	C6H5	3ea	71
  10	1e	4-ClC6H4	3ee	72
  11	1e	4-O2NC6H4	3eg	70
  12	1f	C6H5	3fa	87
  13	1f	4-CH3C6H4	3fb	80
  14	1f	4-FC6H4	3ff	89
  15	1g	C6H5	3ga	52
  aConditions: 1 (0.1 mmol, 14.4 mg), 2 (0.2 mmol), Cu(OAc)2 (1.5 equiv.), PtCl2 (10 mol%), PPh3 (20 mol%), DCE (2 mL), 80 ℃. bIsolated yield.

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