Synthesis of fluorenone derivatives through Pd-catalyzed dehydrogenative cyclization

Article abstract of DOI:10.1021/ol302181z

Palladium-catalyzed dual C-H functionalization of benzophenones to form fluorenones by oxidative dehydrogenative cyclization is reported. This method provides a concise and effective route toward the synthesis of fluorenone derivatives, which shows outstanding functional group compatibility.

Full text of DOI:10.1021/ol302181z

SUPPORTING INFORMATION
For
Synthesis of Fluorenone Derivatives through Palladium-Catalyzed Dehydrogenative Cyclization
Hu Li,† Ru-Yi Zhu,† Wen-Juan Shi,† Ke-Han He,† and Zhang-Jie Shi*†‡
† Beijing National Laboratory of Molecular Sciences (BNLMS) and Key Laboratory of Bioorganic
Chemistry and Molecular Engineering of Ministry of Education, College of Chemistry and Green
Chemistry Center, Peking University, Beijing 100871, China
‡ State Key Laboratory of Organometallic Chemistry, Chinese Academy of Sciences, Shanghai
200032, China
S1

General Experimental Section
Analytic Methods. 1H NMR and 13C NMR data were obtained on Bruker 400M nuclear resonance
spectrometers unless otherwise specified. CDCl3 and CD3OD as solvent and tetramethylsilane
(TMS) as the internal standard were employed. Chemical shifts were reported in units (ppm) by
1
1
assigning TMS resonance in the H NMR spectrum as 0.00 ppm. The data of H NMR was
reported as follows: chemical shift, multiplicity (s = singlet, d = doublet, t = triplet, m = multiplet
and br = broad), coupling constant (J values) in Hz and integration. Chemical shifts for 13C NMR
spectra were recorded in ppm from TMS using the central peak of CDCl3 (77.0 ppm) as the
internal standard. Flash chromatography was performed using 200‐300 mesh silica gel with the
indicated solvent system according to standard techniques. Analytical thin‐layer chromatography
(TLC) was performed on pre‐coated, glass‐backed silica gel plates. HRMS (ESI and EI) analyses
were performed by Analytical Instrumentation Center, Peking University, and Institute of
Chemistry, Chinese Academy of Sciences, respectively.
General preparation for chemicals. Palladium(II) acetate were purchased from Sinocompand
Technology Co., Ltd. Silver(I) oxide, 99+ % (metals basis) was purchased from Alfa Aesar,
benzophenones were from Sinopharm Chemical Reagent Co., Ltd. Potassium carbonate was
domestic reagent, and was grinded into power before used. Trifluoroacetic acid (TFA), 4,4’-
difluorobenzophenone were from J&K Chemical Ltd. Other reagents were from Alfa Aesar. All
reagents were directly used from purchased without any further purification unless otherwise
specified.
S2

General Experimental Procedures
General procedures for preparation of substrates 1 (eq S1). The subtrates 1f, 1l, 1m were
synthesized by oxidation of corresponding alcohols A. The corresponding phenyl magnesium
bromide (1.3 eq) prepared in situ was added dropwisely to the corresponding benzaldehyde in
anhydrous THF in N2 atmosphere at 0 ℃, and stirred at room temperature overnight. Then the
reaction was quenched by saturated NH4Cl (aq), extracted by EtOAc, dried over Na2SO4, and
evaporated in vacuum, further purified by flash chromatography on silica gel with petroleum
ether/EtOAc (10:1) to afford the corresponding alcohols. And these alcohols were dissolved in
CH2Cl2, then PCC (1.5 eq) was added. The reaction was monitored by TLC for full conversion, then
was quenched by saturated NH4Cl (aq), extracted by EtOAc, dried over Na2SO4, and evaporated in
vacuum, further purified by flash chromatography on silica gel with petroleum ether/EtOAc (15:1)
to afford the products 1.
The deuterium-labeled substrates 1x and 1y were prepared as shown in eq S2. The preparation
of the corresponding brominated alcohols B was similar to alcohols A in eq S1. Then to a dried
and degassed bottle, B was added and dissolved in anhydrous THF at –78 ℃, nBuLi (4 eq) was
added dropwisely in 0.5 h, then stirred for another 1.0 h. The reaction was quenched by D2O (40
eq) at –78 ℃, and stirred for another 0.5 h, and then warmed to room temperature, extracted
by EtOAc for three times, dried over Na2SO4, and evaporated in vacuum, further purified by flash
chromatography on silica gel with petroleum ether/EtOAc (30:1) to afford the deuterium-labeled
alcohols, which were oxidized into the ketones 1 by PCC and further purified by flash
chromatography on silica gel with petroleum ether/EtOAc (20:1). The white solid 1x was obtained
in 76 % yield, and the white solid 1y was in 65 % yield.
S3

The deuterium-labeled substrate 1z was prepared as shown in eq S3. To a solution of conc.
H2SO4 (143 mL) and H2O (40 mL) at 0℃, d6 - benzene (1.0 eq, 19.5 mL) was added, then NaBrO3
(1.1 eq, 36.8 g) was added in four portions in 1 h. The mixture was stirred for 10 h at 0℃ and
diluted by water and extracted by n-hexane, washed by water and the organic layers were
evaporated at 10 ℃ in water bath. The residue was distilled under reduced pressure (40 ℃, 20
mbar) to afford light yellow oil with the yield of 50%, which was confirmed by GC-MS. The
corresponding alcohol C and product 1z were synthesized similarly to eq S1. And the white solid
1z was obtained in 46 % yield.
S4

General procedures for Pd(II)-catalyzed dehydrogenative cyclization. Under air atmosphere,
Pd(OAc)2 (0.01 mmol, 2.2 mg), Ag2CO3 (0.30 mmol, 69.5 mg), K2CO3 (0.50 mmol, 69.1 mg) and the
benzophenone (1a)(0.20 mmol, 36.4 mg) were added into a Schlenk tube dried by hot-gun. The
tube was stopped and degassed with N2 for three times. Then trifluoroacetic acid (TFA) (0.50 mL)
was added by syringe. The mixture was stirred under N2 atmosphere at 140 ℃ for 24 h. Then
the mixture was cooled down to room temperature and evaporated in vacuum and further
purified by flash chromatography on silica gel with petroleum ether/ethyl acetate (15:1) to give
the product 2a (30.6 mg, 85%) as a yellow solid.
Table S1. Base Screening for Pd(II)-Catalyzed Dehydrogenative Cyclizationa
a Reactions were conducted with 0.20 mmol of 1a, 0.01 mmol of Pd(OAc)2, 0.30 mmol of Ag2O, and 0.5 mL of TFA,
140 ℃, 24 h, N2 atmosphere. b GC yields were given using dodecane as the internal standard. And isolated yields
were shown in the parentheses.
Procedure for the deuterium labeling experiments. According to eqs S4 and S5, under air
atmosphere, Pd(OAc)2 (0.01 mmol, 2.2 mg), Ag2CO3 (0.30 mmol, 69.5 mg), K2CO3 (0.50 mmol,
69.1 mg) and the 84% deuteriumed benzophenone (1x) (0.20 mmol, 43.0 mg) [or 87%
deuteriumed benzophenone (1y)(0.20 mmol, 43.0 mg)] were added into a Schlenk tube dried by
hot-gun. The tube was stopped and degassed with N2 for three times. Then trifluoroacetic acid
(TFA) (0.50 mL) was added by syringe. The mixture was stirred under N2 atmosphere at 140 ℃
for 4 h. Then the mixture was cooled down to room temperature and evaporated in vacuum and
further puried by flash chromatography on silica gel with petroleum ether/ethyl acetate (30:1) to
1
give the product 2x or 2y as a yellow solid. For 2x, H NMR (400 MHz, CDCl3): δ = 2.44 (s, 3H),
6.91 - 6.96 (m, 1H), 7.12 - 7.18 (m, 2H), 7.30 (s, 1H), 7.55 (d, J = 8 Hz, 1H), 7.64 (q, J = 4 Hz, 0.39H).
For 2y, 1H NMR (400 MHz, CDCl3): δ = 2.43 (s, 3H), 6.91-6.95 (m, 1H), 7.12-7.17 (m, 2H), 7.29 (s,
1H), 7.54 (d, J = 8 Hz, 0.44H), 7.62 (q, J = 4 Hz, 1H).
According to eq S6, under air atmosphere, Pd(OAc)2 (0.01 mmol, 2.2 mg), Ag2CO3 (0.30
mmol, 69.5 mg), K2CO3 (0.50 mmol, 69.1 mg) , 4-methylbenzophenone (1b) (0.10 mmol, 19.6 mg)
and full deuteriumed benzophenone (1z) (0.10 mmol, 20.1 mg) were added into a Schlenk tube
dried by hot-gun. The tube was stopped and degassed with N2 for three times. Then
trifluoroacetic acid (TFA) (0.50 mL) was added by syringe. The mixture was stirred under N2
atmosphere at 140 ℃ for 4 h. Then the mixture was cooled down to room temperature and
S5

evaporated in vacuum and further purified by flash chromatography on silica gel with petroleum
ether/ethyl acetate (30:1) to give the product 2z as a yellow solid. 1H NMR (400 MHz, CDCl3): δ =
2.42 (s, 3H), 7.08 (d, J = 8Hz, 0.96H), 7.25-7.29 (m, 0.89H), 7.32 (s, 0.99H), 7.45-7.49 (m, 1.11H),
7.54 (d, J = 8Hz, 0.87H), 7.63 (d, J = 8Hz, 0.67H).
S6

Characterization of Substrates in Details
1
4-Fluoro-4'-methylbenzophenone-2-d (1x). White solid. H NMR (400 MHz, CDCl3): δ = 2.44 (s,
3H), 7.13-7.18 (m, 2H), 7.29 (d, J = 8 Hz, 2H), 7.69 (d, J = 8 Hz, 2H), 7.82 (q, J = 4 Hz, 1.16 H).
1
4-Methyl-4'-fluorobenzophenone-2-d (1y). White solid. H NMR (400 MHz, CDCl3): δ = 2.43 (s,
3H), 7.14 (t, J = 8 Hz, 2H), 7.27-7.29 (m, 2H), 7.68 (d, J = 8 Hz, 1.13H), 7.80-7.83 (m, 2 H).
4’-Methylbenzophenone-2,3,4,5,6-d (1z). White solid. 1H NMR (400 MHz, CDCl3): δ = 2.43 (s, 3H),
7.27 (d, J = 12 Hz, 2H), 7.72 (d, J = 8 Hz, 2H).
S7

Characterization of Products in Details
9H-Fluoren-9-one (2a). Yellow solid (30.6 mg, 85%). NMR spectral data of the compound are in
accordance with previous report.1
2-Methyl-9H-fluoren-9-one (2b). Yellow solid (34.9 mg, 90%). NMR spectral data of the
compound are in accordance with previous report.1
2-Methyl-9H-fluoren-9-one (2c). Yellow solid (33.0 mg, 85%). NMR spectral data of the
compound are in accordance with previous report.2
2,3-Dimethyl-9H-fluoren-9-one (2d). Yellow solid (37.9 mg, 91%). NMR spectral data of the
compound are in accordance with previous report.3
3,6-Dimethyl-9H-fluoren-9-one (2e). Yellow solid (39.1 mg, 94%).1H NMR (400 MHz, CDCl3):
δ=7.0 (d, J = 8 Hz, 1H), 7.20 (s, 1H), 7.45 (d, J = 8 Hz, 1H), 2.30 (s, 3H); 13C NMR (100 MHz, CDCl3):
δ = 22.12, 121.03, 124.09, 129.43, 132.39, 144.67, 145.45, 193.36. HRMS (ESI): found: 209.09614,
calcd. for C15H13O ([M+H]+): 209.09609.
S8

2,3,6-Trimethyl-9H-fluoren-9-one (2f). Yellow solid (41.8 mg, 94%). 1H NMR (400 MHz, CDCl3): δ
= 2.26, 2.31, 2.40 (s, each 3H), 7.02 (d, J = 4 Hz, 1H), 7.24 (s, 2H), 7.39 (s, 1H), 7.49 (d, J= 8 Hz); 13
C
NMR (100 MHz, CDCl3): δ = 19.90, 20.70, 22.14, 120.78, 121.61, 124.06, 125.43, 128.98, 132.27,
132.85, 137.45, 142.37, 143.81, 145.00, 145.41, 193.87. HRMS (ESI): found: 223.11185, calcd. for
C16H15O ([M+H]+): 223.11174.
1
3,6-Diphenyl-9H-fluoren-9-one (2g). Yellow solid (30.6 mg, 46%). H NMR (400 MHz, CDCl3): δ =
7.42-7.43 (m, 2H), 7.46-7.52 (m, 6H), 7.64-7.66 (m, 4H), 7.70-7.72 (m, 2H), 7.76 (s, 2H); 13C NMR
(100 MHz, CDCl3): δ = 119.17, 124.70, 127.24, 128.06, 128.47, 128.99, 133.55, 140.20, 144.87,
147.81, 193.12. HRMS (ESI): found: 333.12750, calcd. for C25H17O ([M+H]+): 333.12739.
3-tert-Butyl-9H-fluoren-9-one (2h). Yellow solid (39.7 mg, 84%). NMR spectral data of the
compound are in accordance with previous report.4
1-Methyl-9H-fluoren-9-one (2i). Yellow solid (14.0 mg, 36%). NMR spectral data of the
compound are in accordance with previous report.7
3-Methoxy-9H-fluoren-9-one (2j). Yellow solid (30.3 mg, 72%). NMR spectral data of the
compound are in accordance with previous report.8
S9

3,6-Dimethoxy-9H-fluoren-9-one(2k). Yellow solid (35.1 mg, 73%). NMR spectral data of the
compound are in accordance with previous report.5
3-Fluoro-2-methyl-9H-fluoren-9-one (2l). Yellow solid (36.5 mg, 86%). 1H NMR (400 MHz, CDCl3):
δ = 2.23 (s, 3H), 7.06 (d, J = 8 Hz, 1H), 7.24-7.28 (m, 1H), 7.37-7.38 (m, 1H), 7.42-7.46 (m, 2H),
7.58 (d, J = 8 Hz); 13C NMR (100 MHz, CDCl3): δ = 14.62 (d, J = 3 Hz), 108.01 (d, J = 26 Hz), 124.11,
125.47 (d, J = 18 Hz), 127.69 (d, J = 7 Hz), 129.23, 129.91 (d, J = 3 Hz), 134.47, 134.58, 143.08 (d, J
= 3 Hz), 144.80 (d, J = 10 Hz), 164.23, 166.75, 192.46. HRMS (ESI): found: 213.07114, calcd. for
C14H10FO ([M+H]+): 213.07102.
1
3-Fluoro-6-methyl-9H-fluoren-9-one (2m). Yellow solid (38.6 mg, 91%). H NMR (400 MHz,
CDCl3): δ = 2.32 (s, 3H), 6.80-6.85 (m, 1H), 7.00-7.04 (m, 2H), 7.16 (s, 1H), 7.42 (d, J = 8 Hz, 1H),
7.49-7.53 (m, 1H); 13C NMR (100 MHz, CDCl3): δ = 22.10, 108.20 (d, J = 24 Hz), 115.32 (d, J = 23
Hz), 121.43, 124.23, 126.16 (d, J = 10 Hz), 130.25, 132.33, 143.13 (d, J = 2 Hz), 145.87, 147.33 (d, J
= 10 Hz), 167.15 (d, J = 253 Hz), 191.76. HRMS (ESI): found: 213.07112, calcd. for C14H10FO
([M+H]+): 213.07102.
3-Hydroxy-9H-fluoren-9-one (2n). Yellow solid (32.9 mg, 84%). NMR spectral data of the
compound are in accordance with previous report.8
S10

1-Fluoro-6-methoxy-9H-fluoren-9-one (2o). Yellow solid (9.1 mg, 20%). NMR spectral data of the
compound are in accordance with previous report.8
1
1-Hydroxy-3-methoxy-9H-fluoren-9-one (2p). Yellow solid (12.7 mg, 28% Yield). H NMR (400
MHz, CDCl3): δ = 3.87 (s, 3H), 6.19 (d, J = 4 Hz, 1H), 6.62 (d, J = 4 Hz, 1H), 7.30-7.31 (m, 1H),
7.46-7.47 (m, 2H), 7.60-7.62 (m, 1H), 8.52 (brs, 1H); 13C NMR (100 MHz, CDCl3): δ = 56.01, 99.96,
102.72, 120.93, 123.60, 128.85, 129.36, 134.04, 136.68, 143.08, 145.45, 159.44, 168.09, 194.58.
HRMS (ESI): found: 227.07041, calcd. for C14H11O3 ([M+H]+): 227.07027.
3-Fluoro-9H-fluoren-9-one (2q). Yellow solid (25.7 mg, 65%). NMR spectral data of the
compound are in accordance with previous report.2
3-Chloro-9H-fluoren-9-one (2r). Yellow solid (29.1 mg, 68%). NMR spectral data of the
compound are in accordance with previous report.2
1
3,6-Difluoro-9H-fluoren-9-one (2s). Yellow solid (26.4 mg, 61%). H NMR (400 MHz, CDCl3): δ =
6.98-7.02 (m, 2H), 7.18-7.19 (m, 2H), 7.67-7.68 (m, 2H). 13C NMR (100 MHz, CDCl3): δ =108.78 (d,
J = 24 Hz), 116.26 (d, J = 23 Hz), 126.46 (d, J = 10 Hz), 145.85, 130.74, 167.24 (d, J = 254 Hz),
190.31. HRMS (ESI): found: 217.04603, calcd. for C13H7F2O ([M+H]+): 217.04595.
S11

3-(Trifluoromethyl)-9H-fluoren-9-one (2t). Yellow solid (23.8 mg, 48%). NMR spectral data of the
compound are in accordance with previous report.5
7H-Benzo[c]fluoren-7-one (2u). Yellow solid (22.1 mg, 48%). NMR spectral data of the compound
are in accordance with previous report.2, 4
S12

References
[1] Zhao, J.; Yue, D.-W.; Campo, M. A.; Larock, R. C. J. Am. Chem. Soc. 2007, 129, 5288.
[2] Thirunavukkarasu, V. S.; Parthasarathy, K.; Cheng, C.-H. Angew. Chem., Int. Ed. 2008, 47,
9462.
[3] Zhang, X.-X.; Larock, R. C. Org. Lett. 2005, 7, 3973.
*4+ Crawford, J. J.; Fleming, B. J.; Kennedy, A. R.; Klett, J.; O’Hara, C. T.; Orr, S. A. Chem. Commun.
2011, 47, 3772.
[5] Moorthy, J. N.; Samanta, S. J. Org. Chem. 2007, 72, 9786.
[6] Rodríguez, D.; Martínez-Esperoón, M. F.; Navarro-Vázquez, A.; Castedo, L.; Domínguez, D.; Saá,
C. J. Org. Chem. 2004, 69, 3842.
[7] Liu, T.-P.; Liao, Y.-X.; Xing, C.-H.; Hu, Q.-S. Org. Lett. 2011, 13, 2452.
[8] Coelho, P. J.; Carvalho, L. M.; Rodrigues, S.; Oliveira-Campos, A. M. F.; Dubest, R.; Aubard, J.;
Samat, A.; Guglielmetti, R. Tetrahedron. 2002, 58, 925.
S13

NMR Spectra of Mechanistic Study Experiments
3-Fluoro-6-methyl-9H-fluoren-9-one-2-d (2x)
3-Fluoro-6-methyl-9H-fluoren-9-one-8-d (2y)
S14

3-Methyl-9H-fluoren-9-one-5,6,7,8-d (2z)
S15

NMR Spectral of Substrates
4-Fluoro-4'-methylbenzophenone-2-d (1x)
4-Methyl -4'-fluorobenzophenone-2-d (1y)
S16

4’-Methylbenzophenone-2,3,4,5,6-d (1z)
S17

NMR Spectral of Products
9H-Fluoren-9-one (2a)
S18

3-Methyl-9H-fluoren-9-one (2b)
S19

2-Methyl-9H-fluoren-9-one (2c)
S20

2,3-Dimethyl-9H-fluoren-9-one (2d)
S21

3,6-Dimethyl-9H-fluoren-9-one (2e)
S22

2,3,6-Trimethyl-9H-fluoren-9-one (2f)
S23

3,6-Diphenyl-9H-fluoren-9-one（2g）
S24

3-tert-Butyl-9H-fluoren-9-one (2h)
S25

1-Methyl-9H-fluoren-9-one (2i)
S26

3-Methoxy-9H-fluoren-9-one (2j)
S27

3,6-Dimethoxy-9H-fluoren-9-one (2k)
S28

3-Fluoro-2-methyl-9H-fluoren-9-one (2l)
S29

3-Fluoro-6-methyl-9H-fluoren-9-one (2m)
S30