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Reaction of 2a,8b-Dihydrobenzo[b]cyclobute[d]pyran-3-ones with Dimethylsulfoxonium Methylide
Toru TanakaMasaki NagahamaNavnath Dnyanoba YadavHiroki IwasakiMinoru OzekiNaoto KojimaMasayuki Yamashita
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2016 Volume 64 Issue 7 Pages 1056-1061

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Abstract

Using dimethylsulfoxonium methylide as the methylene transfer reagent, 2a,8b-dihydrobenzo[b]cyclobute[d]pyran-3-ones were converted into 2,2′-biphenol derivatives as major products and dihydrodibenzofurans as minor products. The reaction mechanism was extrapolated from a deuteration experiment with CD2=S(O)(CD3)2.

Small cycloalkanes, such as cyclopropanes and cyclobutanes, play an important role in organic synthesis owing to their molecular instability and high reactivity.16) We have been interested in small cycloalkanes and have reported several reactions, including cyclopropane and cyclobutane ring opening reactions.715) In a previous study, we found that benzo[b]cyclobuta[d]pyran-3-ones 2, prepared by the [2+2]photocycloaddition reaction of 3-substituted coumarins 1 with monosubstituted alkenes, were stereoconvergently transformed into tetrahydrodibenzofuran derivatives 3 by using more than 2 equiv. of dimethylsulfoxonium methylide [CH2=S(O)Me2], which is known as Corey’s sulfur ylide and is used as the methylene transfer reagent in the Corey–Chaykovsky cyclopropanation1620) (Chart 1). The transformation of 2 into 3 was applied to the syntheses of dibenzofuran-type natural products.17,18,2127) In our continuing studies of the reaction of small cycloalkanes with CH2=S(O)Me2, we have examined with much interest the reaction of 2a-substituted 2a,8b-dihydrobenzo[b]cyclobute[d]pyran-3-one derivatives 4, which are cyclobutene derivatives that have more strain than 2, with CH2=S(O)Me2. However, contrary to our expectation, the main products were not dihydrobenzofuran 5 but 2,2′-biphenols 6. In this paper, we describe a novel skeletal transformation of 4 into 6 using CH2=S(O)Me2.

Chart 1. Skeletal Transformation of Cyclobutanes 2 and Cyclobutenes 4

Benzo[b]cyclobute[d]pyran-3-ones 4 were prepared by the [2+2]photocycloaddition reaction of 3-substituted coumarins 1 with substituted alkynes25) (Chart 1). When 4a was initially treated with 1.0 equiv. of CH2=S(O)Me2 in N,N-dimethylformamide (DMF) at room temperature (r.t.), dihydrodibenzofuran 5a was obtained in only 8% yield (Table 1, entry 1). When 2.0 equiv. of CH2=S(O)Me2 was used, the yield of 5a was improved to 38%. Unexpectedly, 2,2′-biphenol 6a was obtained in 45% yield (entry 2). When 3.0 equiv. of CH2=S(O)Me2 was used, the yield of 6a was decreased (entry 3). The use of dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), or CH2Cl2 instead of DMF as solvent gave a low or no yield of 5a and 6a (entries 46). When the reaction was carried out at 0°C, a similar result to that in entry 2 was obtained (entry 7). Both products were not obtained at 80°C (entry 8). The intermediate (vide infra) of 5a and 6a could be unstable at high temperature. From these results, the conditions shown in entry 2 were selected as the optimum conditions for the skeletal transformation of 4a to give 5a and 6a. The structures and stereochemistries of 5a and 6a were confirmed on the basis of diverse spectral data, including heteronuclear multiple bond connectivity (HMBC), 1H-detected heteronuclear multiple quantum coherence (HMQC), and nuclear Overhauser effect spectroscopy (NOESY) data, and X-ray crystallographic analysis.

Table 1. Optimization of Reaction Conditionsa)
EntryCH2=S(O)Me2 (eq.)SolventTemp. (°C)Yield of 5a (%)b)Yield of 6a (%)b)
11.0DMFr.t.8N.D.c)
22.0DMFr.t.3845
33.0DMFr.t.831
42.0DMSOr.t.6N.D.
52.0THFr.t.N.D.N.D.
62.0CH2Cl2r.t.N.D.N.D.
72.0DMF04044
82.0DMF80N.D.N.D.

a) The reactions were carried out by adding 4a (0.5 mmol) to a solution of CH2=S(O)Me2 in solvent (1 mL). b) Isolated yield. c) Not detected.

Under the optimum conditions, the scope of this reaction was explored. Benzo[b]cyclobute[d]pyran-3-ones 4bo were subjected to the optimum reaction conditions and the following results were obtained (Table 2). Cyclobutenes having a phenyl group at the 1-position and an alkyl ketone group at the 2a-position 4bd were transformed into only 2,2′-biphenols 6bd in moderate yields (entries 1–3). Compounds 4e and f having a benzoyl group at the 2a-position were transformed into 6e and f in 55 and 59% yields together with 5e and f in 19 and 23% yields, respectively (entries 4, 5). The nature of the substituent at the 2a-position would affect the selectivity of the products. In the case of cyclobutenes having an alkyl ketone group, which was a strong electron-withdrawing group, 2,2′-biphenols 6 were obtained. In the case of cyclobutenes with a n-Bu group at the 1-position 4g and phenyl and methyl groups on the cyclobutene ring 4h, corresponding products 6g and h were obtained in 22 and 49% yields, respectively (entries 6, 7). Not only the substituent at the 2a-position but also those at 1-, and 1,2-positions could be influenced the selectivity of 5 and 6 (entries 6, 7 vs. entry 2 in Table 1). Substrates 4ik having a methyl group on the phenyl group of the coumarin ring were transformed into 6ik in moderate yields without dihydrobenzofurans 5ik (entries 810). Similar to the methyl group, substrates 4lo having a trimethylsilyl (TMS) group were also transformed into 6lo in moderate yields (entries 1114).

Table 2. Substituent Effect at 1-, 2-, 2a- and 8-Positionsa)
EntryR1R2R3R4Yield of 6 (%)b)Yield of 5 (%)b)
14bHPhHi-Pr6b: 665b: N.D.c)
24cHPhHt-Bu6c: 635c: N.D.
34dHPhHAdamantyl6d: 535d: N.D.
44eHPhHPh6e: 555e: 19
54fHp-MethoxyphenylHPh6f: 595f: 23
64gHn-BuHOMe6g: 225g: N.D.
74hHPhMeOMe6h: 495h: N.D.
84iMePhHi-Pr6i: 605i: N.D.
94jMePhHt-Bu6j: 665j: N.D.
104kMePhHPh6k: 645k: N.D.
114lTMSPhHMe6l: 615l: N.D.
124mTMSPhHi-Pr6m: 495m: N.D.
134nTMSPhHt-Bu6n: 665n: N.D.
144oTMSPhHPh6o: 645o: N.D.

a) All the reactions were carried out by adding cyclobutene 4 to a solution of CH2=S(O)Me2 (2.0 eq) in DMF at r.t. b) Isolated yield. c) Not detected.

Chart 2. Labeling Reaction with CD2=S(O)(CD3)2

In order to gain further insights into the course of the skeletal transformation reaction, 4a was treated with CD2=S(O)(CD3)2, which was deprotonated predeuterated trimethylsulfoxonium salt.28) Non-deuterated 6a and monodeuterated 5a′ were obtained in 38 and 19% yields, respectively. The deuteration ratio of 5a′ was 86% (Chart 2).

A plausible reaction mechanism is shown in Chart 3. Similar to the previously reported skeletal transformation reaction of benzo[b]cyclobuta[d]pyran-3-ones 2,3) one equivalent of CH2=S(O)Me2 would attack the lactone carbonyl group to initiate ring opening to form 8. The use of one more equivalent of CH2=S(O)Me2 as the base would promote the cyclobutene ring opening and re-closure to give intermediate 12. In route A, a C–C bond would be formed between the carbon of the enolate moiety and the carbon of the dimethylsulfoxonium group, and this would be followed by aromatization accompanying cleavage of the cyclopropane ring to give 6. On the other hand, in route B, a C–O bond would be formed between the oxygen of the enolate moiety and the carbon of the dimethylsulfoxonium group to give 5.

Chart 3. Plausible Reaction Mechanism

In conclusion, we have found that CH2=S(O)Me2 promoted the skeletal transformation of cyclobutene derivatives 4 into 2,2′-biphenols 6. In contrast to the transformation of 2, structurally similar substrate 4 was transformed into 6 as the major product with or without 5. The reaction proceeded with the cyclopropanation to 13, a cyclopropane ring cleavage, and finally aromatization. These steps were clarified in the deuteration experiment with CD2=S(O)(CD3)2.

Experimental

General

Melting points (mp) were measured with a Yanaco MP micro-melting point apparatus and uncorrected. NMR spectra were measured on JEOL EX-270 (1H: 270 MHz), JEOL AL-300 (1H: 300 MHz; 13C: 75.5 MHz), and Varian INOVA 400NB (1H: 400 MHz; 13C: 100 MHz) spectrometers with tetramethylsilane as the internal standard. Chemical shifts are reported in ppm. IR spectra were measured with Shimadzu IR-435 and Shimadzu FTIR-8400 spectrophotometer. A JEOL JMS-GC mate spectrometer was used for low-resolution and high-resolution electron ionizations MS (LR-EI-MS and HR-EI-MS). Silica gel 60 (grade 7734, 60–230 mesh, Merck) and Silica gel 60N (Kanto Chemical Co., Inc.) for column chromatography and Silica gel 60 F254 plate (0.5 mm and 1 mm in thickness, Merck) for preparative TLC were used.

Typical Procedure for the Synthesis of 2,2′-Biphenol

To a suspension of (CH3)3S(O)I (91 mg, 0.41 mmol) in DMF (2 mL), NaH (60% in mineral oil, 16 mg, 0.41 mmol) was added with stirring, and the whole was stirred for 30 min at r.t. under N2 atmosphere. Starting material 4a (70 mg, 0.20 mmol) was added slowly to the reaction mixture, and the stirring was continued overnight. After completion of the reaction, the mixture was acidified with 10% HCl aq. and extracted with ethyl acetate. The combined extracts were washed with water and brine, dried over Na2SO4, and evaporated. The residue was purified by silica gel column chromatography (n-hexane : AcOEt=3 : 1) to yield 5a (30 mg, 45%) and 6a (25 mg, 38%).

Methyl (4aRS,9bSR)-4a,9b-Dihydro-4-hydroxy-1-phenyldibenzofuran-3-carboxylate (5a)

Pale yellow powder. mp 169.8–171.3°C (AcOEt). 1H-NMR (400 MHz, CDCl3) δ: 3.84 (3H, s), 5.03 (1H, dd, J=11.8, 0.8 Hz), 5.73 (1H, d, J=11.9 Hz), 6.58–6.70 (3H, m), 6.92 (1H, d, J=8.1 Hz), 7.07–7.12 (1H, m), 7.31–7.35 (1H, m), 7.39–7.44 (2H, m), 7.49–7.52 (2H, m), 12.36 (1H, s). 13C-NMR (100 MHz, CDCl3) δ: 43.8, 52.2, 80.0, 100.4, 109.7, 115.9, 121.1, 124.8, 126.2, 127.5, 128.0, 128.2, 128.5, 128.7, 139.3, 157.6, 165.5, 170.7. IR (CHCl3) 1658, 1591 cm−1. LR-EI-MS m/z: 320 (M+, 46.8), 289 (23.1), 288 (100.0). HR-EI-MS Calcd for C20H16O4: 320.1048. Found: 320.1046. Anal. Calcd for C20H16O4: C; 74.99, H; 5.03. Found: C; 74.71, H; 4.92.

(5a′)

1H-NMR (400 MHz, CDCl3) δ: 3.84 (3H, s), 5.03 (1H, s), 5.73 (0.14H, d, J=11.9 Hz), 6.58–6.70 (3H, m), 6.91–6.93 (1H, m), 7.07–7.12 (1H, m), 7.26–7.35 (1H, m), 7.39–7.44 (2H, m), 7.49–7.52 (2H, m), 12.36 (1H, s). HR-EI-MS Calcd for C20H15DO4: 321.1111. Found: 321.1105.

Methyl 2,2′-Dihydroxy-5-phenylbiphenyl-3-carboxylate (6a)

Colorless needles. mp 160.5–161.5°C (AcOEt). 1H-NMR (300 MHz, CDCl3) δ: 4.03 (3H, s), 6.48 (1H, s), 7.02–7.11 (2H, m), 7.32–7.37 (3H, m), 7.42–7.46 (2H, m), 7.57–7.59 (2H, m), 7.81 (1H, d, J=2.4 Hz), 8.16 (1H, d, J=2.4 Hz), 11.99 (1H, s). 13C-NMR (75 MHz, CDCl3) δ: 52.8, 113.0, 118.3, 121.3, 125.3, 126.8, 127.4, 127.9, 128.0, 128.9, 129.8, 131.2, 133.7, 137.1, 139.4, 153.9, 156.5, 171.1. IR (CHCl3): 3331, 3000, 1668, 1599 cm−1. LR-EI-MS m/z: 320 (M+, 49.1), 288 (100.0), 271 (43.5). HR-EI-MS Calcd for C20H16O4: 320.1048. Found: 320.1041. Anal. Calcd for C20H16O4: C; 74.99, H; 5.03, Found: C; 74.97, H; 5.31. All measurements were made on a Rigaku RAXIS RAPID imaging plate area detector with graphite monochromated CuKα radiation at 23 °C. The structure was solved by SHELX-97 and expanded using Fourier techniques (DIRDIF-99). C20.50H18O4.50 (C20H16O4–1/2 CH3OH); orthorhombic (0.30×0.10×0.10 mm); space Group Pccn (#56); unit cell dimension a=33.263(2) Å, b=14.5957(8) Å, c=7.2287(4) Å, V=3509.5(3) Å3; Z=8; Dcalc=1.281 g/cm3; μ(CuKα)=7.367 cm−1; 31345 reflections measured (2θ max 136.3°), unique 3202 (Rint=0.030); the final refinement gave R1=0.0543 (I>2.00σ(I)) and wR2=0.1750 (CCDC No. 144037).

1-(2,2′-Dihydroxy-5-phenylbiphenyl-3-yl)-2-methylpropan-1-one (6b)

Pale yellow amorphism. 1H-NMR (400 MHz, CDCl3) δ: 1.33 (6H, d, J=7.0 Hz), 3.78 (1H, hept, J=7.0 Hz), 6.70 (1H, s), 7.03–7.11 (2H, m), 7.31–7.53 (5H, m), 7.54–7.58 (2H, m), 7.82 (1H, d, J=2.2 Hz), 8.06 (1H, d, J=2.2 Hz), 13.9 (1H, s). 13C-NMR (100 MHz, CDCl3) δ: 19.4, 35.3, 118.2, 118.5, 121.4, 125.4, 126.9, 127.5, 128.1, 129.0, 129.1, 129.8, 131.2, 133.5, 137.8, 139.7, 154.0, 158.0, 211.9. IR (CHCl3): 3333, 2955, 1630, 1593 cm−1. LR-EI-MS m/z: 332 (M+, 35.4), 289 (100.0). HR-EI-MS Calcd for C22H20O3: 332.1412. Found: 332.1408.

1-(2,2′-Dihydroxy-5-phenylbiphenyl-3-yl)-2,2-dimethylpropan-1-one (6c)

Yellow amorphism. 1H-NMR (400 MHz, CDCl3) δ: 1.56 (9H, s), 6.68 (1H, s), 7.04–7.11 (2H, m), 7.31–7.40 (3H, m), 7.46–7.50 (2H, m), 7.54–7.57 (2H, m), 7.79 (1H, d, J=2.3 Hz), 8.34 (1H, d, J=2.3 Hz). 13C-NMR (100 MHz, CDCl3) δ: 29.0, 45.0, 117.6, 118.5, 121.4, 125.8, 126.8, 127.5, 129.1, 129.3, 129.5, 129.8, 131.2, 132.4, 137.0, 139.9, 154.1, 158.6, 213.3. IR (CHCl3): 3336, 1621 cm−1. LR-EI-MS m/z: 346 (M+, 11.0), 289 (100.0), 271 (28.8). HR-EI-MS Calcd for C23H22O3: 346.1569. Found: 346.1566.

Adamantan-1-yl (2,2′-Dihydroxy-5-phenylbiphenyl-3-yl)ketone (6d)

Pale yellow amorphism. 1H-NMR (400 MHz, CDCl3) δ: 1.74–1.94 (6H, br), 2.06–2.22 (3H, br), 2.27 (6H, d, J=2.7 Hz), 6.78 (1H, s), 7.03–7.11 (2H, m), 7.24–7.41 (3H, m), 7.47–7.51 (2H, m), 7.56–7.58 (2H, m), 7.78 (1H, d, J=2.2 Hz), 8.55 (1H, d, J=2.2 Hz). 13C-NMR (100 MHz, CDCl3) δ: 27.8, 28.3, 36.6, 36.6, 40.0, 48.4, 115.3, 118.1, 118.5, 121.3, 121.4, 122.8, 125.9, 126.2, 126.7, 126.9, 127.4, 127.6, 128.0, 128.2, 128.9, 129.1, 129.6, 129.7, 131.1, 132.1, 136.8, 138.4, 140.0, 154.1, 158.5, 212.7. IR (CHCl3): 2891, 1686 cm−1. LR-EI-MS m/z: 424 (M+, 6.5), 289 (22.6), 55.1 (100.0). HR-EI-MS Calcd for C29H28O3: 424.2038. Found: 424.2041.

(2,2′-Dihydroxy-5-phenylbiphenyl-3-yl)phenylketone (6e)

Yellow amorphism. 1H-NMR (300 MHz, CDCl3) δ: 7.05–7.14 (2H, m), 7.33–7.80 (10H, m), 7.77–7.80 (2H, m), 7.87–7.91 (2H, m) 13.3 (1H, s). 13C-NMR (75 MHz, CDCl3) δ: 118.5, 119.4, 121.4, 125.3, 126.8, 127.5, 128.6, 128.7, 129.0, 129.4, 129.9, 131.2, 131.7, 132.5, 133.2, 137.4, 137.7, 139.4, 154.1, 158.1, 202.3. IR (CHCl3): 1617 m−1. LR-EI-MS m/z: 366 (M+, 89.0), 348 (79.6), 271 (70.0), 105 (100.0). HR-EI-MS Calcd for C25H18O3: 366.1256. Found: 366.1253.

[(4aRS,9bSR)-(4a,9b-Dihydro-4-hydroxy-1-phenyldibenzofuran-3-yl)]phenylketone (5e)

Light yellow powder (AcOEt). mp 177.4–179.1°C. 1H-NMR (400 MHz, CDCl3) δ: 5.09 (1H, d, J=10.6 Hz), 5.48 (1H, d, J=10.4 Hz), 6.70–6.98 (3H, m), 7.12 (1H, dd, J=0.9, 1.1 Hz), 7.13–7.16 (1H, m), 7.29–7.60 (8H, m), 7.60–7.62 (2H, m). 13C-NMR (100 MHz, CDCl3) δ: 43.9, 81.3, 106.9, 110.1, 119.2, 121.4, 124.5, 125.8, 127.1, 127.5, 128.1, 128.3, 128.5, 128.7, 128.8, 128.9, 131.4, 132.1, 133.9, 139.6, 158.5, 181.0, 193.3. IR (CHCl3): 1597 cm−1. LR-EI-MS m/z: 366 (M+, 100.0), 365 (61.9), 348 (41.6), 289 (28.1), 271 (35.7). HR-EI-MS Calcd for C25H18O3: 366.1256. Found: 366.1254. Anal. Calcd for C25H18O3⋅H2O: C; 78.11, H; 5.24. Found: C; 78.29, H; 5.16.

[2,2′-Dihydroxy-5-(4-methoxyphenyl)-3-yl]phenylketone (6f)

Yellow amorphism. 1H-NMR (400 MHz, CDCl3) δ: 3.83 (3H, s), 6.64 (1H, s), 6.93–6.96 (2H, m), 7.08–7.14 (2H, m), 7.35–7.43 (4H, m), 7.54–7.58 (2H, m), 7.63–7.79 (1H, m), 7.82–7.83 (2H, m), 7.84–7.85 (2H, m), 13.30 (1H, s). 13C-NMR (100 MHz, CDCl3) δ: 55.4, 114.4, 118.5, 119.3, 121.4, 125.4, 127.8, 128.6, 128.6, 129.4, 129.9, 131.2, 131.3, 131.9, 132.5, 132.9, 137.4, 137.5, 154.1, 157.6, 159.3, 202.4. IR (CHCl3): 1614 cm−1. LR-EI-MS m/z: 396 (M+, 100.0), 378 (90.0), 363 (25.0), 301 (33.7). HR-EI-MS Calcd for C26H20O4: 396.1361. Found: 396.1358.

(4aRS,9bSR)-[4a,9b-Dihydro-4-hydroxy-1-(4-methoxyphenyl)dibenzofuran-3-yl]phenylketone (5f)

Yellow amorphism. 1H-NMR (400 MHz, CDCl3) δ: 3.84 (3H, s), 5.05 (1H, d, J=10.4 Hz), 5.47 (1H, d, J=10.4 Hz), 6.67 (1H, s), 6.72–6.77 (2H, m), 6.90–6.94 (2H, m), 6.97 (1H, d, J=8.1 Hz), 7.12–7.16 (1H, m), 7.36–7.41 (2H, m), 7.45–7.52 (3H, m), 7.58–7.62 (2H, m). 13C-NMR (100 MHz, CDCl3) δ: 44.0, 55.3, 81.3, 107.0, 110.0, 114.2, 117.5, 121.4, 124.4, 126.6, 127.0, 128.2, 128.4, 128.6, 128.9, 131.3, 132.1, 134.0, 158.5, 159.1, 180.4, 193.3. IR (CHCl3): 1603 cm−1. LR-EI-MS m/z: 396 (M+, 17.0), 378 (9.9), 57 (100.0), 129 (18.3), 125 (10.8), 123 (10.6). HR-EI-MS Calcd for C26H20O4: 396.1361. Found: 396.1366.

Methyl 5-Butyl-2,2′-dihydroxybiphenyl-3-carboxylate (6g)

Brown oil. 1H-NMR (400 MHz, CDCl3) δ: 0.93 (3H, t, J=7.3 Hz), 1.35–1.41 (2H, m), 1.56–1.64 (2H, m), 2.59 (2H, t, J=7.7 Hz), 3.99 (3H, s), 7.01–7.08 (2H, m), 7.26–7.34 (2H, m), 7.40 (1H, d, J=2.4 Hz), 7.74 (1H, d, J=2.4 Hz), 11.0–13.0 (1H, br). 13C-NMR (100 MHz, CDCl3) δ: 13.9, 22.2, 33.6, 34.7, 52.7, 112.3, 118.3, 121.2, 125.6, 127.1, 129.1, 129.6, 131.1, 134.8, 138.7, 153.9, 155.1, 171.2. IR (CHCl3): 3346, 1667 cm−1. LR-EI-MS m/z: 300 (M+, 30.1), 268 (100.0), 251 (29.7), 187 (54.3). HR-EI-MS Calcd for C18H20O4: 300.1361. Found: 300.1361.

Methyl 2,2′-Dihydroxy-4-methyl-5-phenylbiphenyl-3-carboxylate (6h)

Yellowish amorphism. 1H-NMR (400 MHz, CDCl3) δ: 2.45 (3H, s), 4.02 (3H, s), 6.76 (1H, s), 6.97–7.01 (1H, m), 7.05 (1H, dd, J=1.3, 6.4 Hz), 7.25–7.43 (8H, m), 12.4 (1H, s). 13C-NMR (100 MHz, CDCl3) δ: 20.8, 52.8, 113.5, 118.2, 121.2, 124.7, 125.5, 127.0, 128.2, 129.5, 129.7, 131.1, 136.5, 138.2, 138.5, 141.2, 153.9, 156.7, 172.9. IR (CHCl3): 1655 cm−1. LR-EI-MS m/z: 334 (M+, 23.6), 302 (100.0), 285 (47.0). HR-EI-MS Calcd for C21H18O4: 334.1205. Found: 334.1212.

1-(2,2′-Dihydroxy-6′-methyl-5-phenylbiphenyl-3-yl)-2-methylpropan-1-one (6i)

Yellowish oil. 1H-NMR (300 MHz, CDCl3) δ: 1.32 (6H, d, J=6.8 Hz), 2.36 (3H, s), 3.79 (1H, hept, J=6.8 Hz), 6.54 (1H, s), 6.94 (1H, t, J=7.5 Hz), 7.14 (1H, dd, J=1.3, 7.7 Hz), 7.20–7.24 (1H, m), 7.39–7.57 (5H, m), 7.80 (1H, d, J=2.4 Hz), 8.06 (1H, d, J=2.2 Hz), 13.9 (1H, s). 13C-NMR (75 MHz, CDCl3) δ: 16.6, 19.4, 35.3, 118.3, 120.9, 125.0, 126.9, 127.3, 127.5, 128.0, 129.0, 129.0, 129.4, 131.1, 133.4, 137.9, 139.7, 152.2, 158.1, 211.9. IR (CHCl3): 3650–3300, 1629, 1594 cm−1. LR-EI-MS m/z: 346 (M+, 27.4), 303 (100.0). HR-EI-MS Calcd for C23H22O3: 346.1569. Found: 346.1570.

1-(2,2′-Dihydroxy-6′-methyl-5-phenylbiphenyl-3-yl)-2,2-dimethylpropan-1-one (6j)

Yellowish powder (AcOEt/n-hexane). mp 67.5–70.1°C. 1H-NMR (300 MHz, CDCl3) δ: 1.55 (9H, s), 2.36 (3H, s), 6.53 (1H, s), 6.94 (1H, t, J=7.5 Hz), 7.14 (1H, dd, J=1.5, 7.7 Hz), 7.22 (1H, dd, J=1.5, 7.3 Hz), 7.20–7.55 (5H, m), 7.70 (1H, d, J=2.2 Hz), 8.30 (1H, d, J=2.4 Hz), 14.0 (1H, s). 13C-NMR (75 MHz, CDCl3) δ: 16.5, 29.0, 45.0, 117.6, 120.8, 125.3, 126.8, 127.1, 127.4, 128.8, 129.0, 129.1, 129.7, 131.0, 132.3, 137.0, 139.9, 152.2, 158.7, 213.2. IR (CHCl3): 3650–3300, 1723, 1620, 1592 cm−1. LR-EI-MS m/z: 360 (M+, 13.6), 303 (100.0). HR-EI-MS Calcd for C24H24O3: 360.1725. Found: 360.1731.

(2,2′-Dihydroxy-6′-methyl-5-phenylbiphenyl-3-yl)phenylketone (6k)

Yellowish crystals (AcOEt/n-hexane). mp 76.1–78.3°C. 1H-NMR (300 MHz, CDCl3) δ: 2.38 (3H, s), 6.48 (1H, s), 6.97 (1H, t, J=7.5 Hz), 7.18–7.66 (10H, m), 7.77 (2H, d, J=7.3 Hz), 7.86 (1H, d, J=2.2 Hz), 7.89 (1H, d, J=2.2 Hz), 13.2 (1H, s). 13C-NMR (75 MHz, CDCl3) δ: 16.5, 119.4, 121.0, 124.9, 126.8, 127.2, 127.5, 128.6, 128.9, 129.0, 129.0, 129.4, 131.2, 131.6, 132.5, 133.1, 137.5, 137.9, 139.4, 152.2, 158.2, 202.3. IR (CHCl3): 3650–3300, 1616 cm−1. LR-EI-MS m/z: 380 (M+, 77.5), 362 (100.0), 285 (73.2), 105 (85.5), 77 (57.7). HR-EI-MS Calcd for C26H20O3: 380.1412. Found: 380.1413.

1-(2,2′-Dihydroxy-5-phenyl-6′-trimethylsilylbiphenyl-3-yl)ethanone (6l)

White powder (AcOEt/n-hexane). mp 166.5–168.1°C. 1H-NMR (300 MHz, CDCl3) δ: 0.34 (9H, s), 2.74 (3H, s), 6.74 (1H, s), 7.03 (1H, t, J=7.3 Hz), 7.31–7.55 (7H, m), 7.80 (1H, d, J=2.2 Hz), 7.97 (1H, d, J=2.2 Hz), 13.5 (1H, s). 13C-NMR (75 MHz, CDCl3) δ: -0.80, 26.9, 119.8, 121.1, 124.5, 126.8, 127.5, 128.73, 128.76, 129.0, 129.2, 132.5, 133.6, 135.5, 138.2, 139.5, 157.3, 158.6, 205.5. IR (CHCl3): 3650–3300, 1594, 1534 cm−1. LR-EI-MS m/z: 376 (M+, 63.4), 361 (42.7), 343 (100.0), 164 (40.7). HR-EI-MS Calcd for C23H24O3Si: 376.1495. Found: 376.1490.

1-(2,2′-Dihydroxy-5-phenyl-6′-trimethylsilylbiphenyl-3-yl)-2-methylpropan-1-one (6m)

Yellowish crystals (AcOEt/n-hexane). mp 173.4–175.5°C. 1H-NMR (300 MHz, CDCl3) δ: 0.35 (9H, s), 1.32 (6H, d, J=6.8 Hz), 3.76 (1H, hept, J=6.8 Hz), 6.79 (1H, s), 7.05 (1H, t, J=7.3 Hz), 7.32–7.38 (2H, m), 7.42–7.47 (3H, m), 7.54–7.57 (2H, m), 7.80 (1H, d, J=2.2 Hz), 8,00 (1H, d, J=2.0 Hz), 13.9 (1H, s). 13C-NMR (75 MHz, CDCl3) δ: −0.80, 19.4, 35.3, 118.3, 121.2, 124.7, 126.9, 127.5, 127.9, 128.8, 129.0, 129.5, 132.5, 133.5, 135.4, 138.0, 139.7, 158.0, 158.7, 211.9. IR (CHCl3): 3650–3300, 1630, 1593 cm−1. LR-EI-MS m/z: 404 (M+, 55.3), 389 (21.3), 345 (100.0), 75 (49.2). HR-EI-MS Calcd for C25H28O3Si: 404.1808. Found: 404.1809.

1-(2,2′-Dihydroxy-5-phenyl-6′-trimethylsilylbiphenyl-3-yl)-2,2-dimethylpropan-1-one (6n)

Yellowish solid (AcOEt/n-hexane). mp 150.0–152.5°C. 1H-NMR (300 MHz, CDCl3) δ: 0.35 (9H, s), 1.54 (9H, s), 6.80 (1H, s), 7.05 (1H, t, J=7.3 Hz), 7.32–7.39 (2H, m), 7.43–7.48 (3H, m), 7.52–7.56 (2H, m), 7.77 (1H, d, J=2.2 Hz), 8.30 (1H, d, J=2.2 Hz), 14.0 (1H, s). 13C-NMR (75 MHz, CDCl3) δ: -0.80, 28.9, 45.0, 117.5, 121.1, 125.0, 126.7, 127.4, 128.6, 129.0, 129.1, 129.8, 132.3, 132.4, 135.3, 137.2, 139.9, 158.5, 158.6, 213.2. IR (CHCl3): 3650–3300, 1620, 1591 cm−1. LR-EI-MS m/z: 418 (M+, 26.5), 361 (53.6), 345 (100.0), 302 (23.0). HR-EI-MS Calcd for C26H30O3Si: 418.1964. Found: 418.1959.

(2,2′-Dihydroxy-5-phenyl-6′-trimethylsilylbiphenyl-3-yl)phenylketone (6o)

Yellow powder (AcOEt/n-hexane). mp 203.0–205.0°C. 1H-NMR (300 MHz, CDCl3) δ: 0.36 (9H, s), 6.76 (1H, s), 7.06 (1H, t, J=7.4 Hz), 7.29–7.65 (10H, m), 7.78–7.83 (2H, m), 7.86 (1H, d, J=2.4 Hz), 7.88 (1H, d, J=2.4 Hz), 13.3 (1H, s). 13C-NMR (75 MHz, CDCl3) δ: −0.78, 119.3, 121.2, 124.6, 126.8, 127.5, 128.6, 128.8, 129.0, 129.1, 129.4, 131.6, 132.5, 132.5, 133.2, 135.5, 137.5, 138.0, 139.4, 158.0, 158.6, 202.4. IR (CHCl3): 3650–3300, 1615, 1594 cm−1. LR-EI-MS m/z: 438 (M+, 40.6), 423 (22.1), 405 (46.7), 105 (100.0). HR-EI-MS Calcd for C28H26O3Si: 438.1651. Found: 438.1658.

Acknowledgments

This work was financially supported in part by Japan Society for the Promotion of Science (JSPS) KAKENHI (22590023) and the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan Supported Program for the Strategic Research Foundation at Private Universities, 2015–2019.

Conflict of Interest

The authors declare no conflict of interest.

Supplementary Materials

The online version of this article contains supplementary materials.

References
 
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