The Journal of Organic Chemistry
ARTICLE
catalyzed, dark green for RuCl2(PPh3)3-catalyzed, or yellow for Cu salt-
catalyzed reaction after 4 h. The catalyst precipitate was completely
dissolved within 1 min after T-HYDRO addition. The flask was
equipped with a septum containing a needle to release any built-up
pressure and was stirred at 40 °C. After the specified time, a small aliquot
(about 0.10 mL) of the organic layer was taken out, and the solvent was
rapidly evaporated under high vacuum for 5 min (0.09 Torr, room
temperature). The residue was dissolved in CDCl3 and analyzed by 1H
NMR spectroscopy. Percent conversion was measured as ratio of
integral values of alkene protons of product 2 (s, 6.56 ppm) to aromatic
protons of 1 (s, 6.98 ppm).
an internal standard in toluene (20.0 mL). After completion of the
addition, the reaction mixture was stirred for 20 min at 40 °C, and then a
small aliquot (about 0.10 mL) of the organic layer was removed and the
solvent was evaporated under high vacuum over 5 min (0.09 Torr, room
temperature). The residue was dissolved in CDCl3 and analyzed by
1H NMR spectroscopy. The percent yield was determined from the
integral values of internal standard 2 (s, 6.56 ppm) and alkene proton of
18 (d, 6.44 ppm): 1H NMR (600 MHz, CDCl3) δ 8.11 (d, J = 7.6 Hz,
1 H), 7.66 (t, J = 7.5 Hz, 1 H), 7.52 (t, J = 7.6 Hz, 1 H), 7.46 (d, J = 10.1
Hz, 1 H), 7.38 (d, J = 7.5 Hz, 1 H), 6.44 (d, J = 10.1 Hz, 1 H); 13C NMR
(150 MHz, CDCl3) δ 180.9, 178.9, 145.3, 135.8, 134.8, 131.6, 130.8,
130.2, 129.8, 127.9; Rf = 0.16 (hexane/AcOEt/DCM (8:1:1)).
Oxidation of 4-Phenylphenol (15) in Toluene. 4-Phenylphe-
nol 15 (3.0 mmol, 510 mg), Rh2(cap)4(MeCN)2 (1.5 μmol, 1.1 mg) or
RuCl2(PPh3)3 (3.0 μmol, 2.9 mg), and toluene (6.0 mL) were placed in
6-dram screw-cap vial containing a magnetic stirring bar. The mixture
was sonicated to ensure maximal dissolution of the phenol in a resulting
suspension. The resulting mixture with partially undissoved phenol was
placed in an ice bath and stirred for about 3 min to allow the temperature
to equilibrate to 0 °C. T-HYDRO (12.0 mmol, 1.66 mL, 4.0 equiv) was
added via syringe dropwise over the period of 1 min with intensive
stirring. After 1 h of stirring at 250 rpm at 0 °C, another 4.0 equiv of
T-HYDRO was added via syringe all at once. The vial was removed from
the ice bath, and the reaction mixture was allowed to warm to room
temperature. The mixture was stirred at 250 rpm for 3 h at room
temperature. The mixture was transferred to 100-mL round-bottom
flask and concentrated on a rotary evaporator (20 Torr, room
temperature). The residue was dissolved in DCM, and the residue was
purified by column chromatography (neutral alumina, 18 mm diameter,
18 cm height, EtOAc/DCM/hexane (1:1:16, 250 mL)). Fractions
containing the product 16 were combined, and the solvent was
evaporated on a rotary evaporator (60 Torr, room temperature); in
the case of product with a large molecular mass the residue was further
dried under high vacuum for 20 min (0.09 Torr, room temperature) to
yield 441 mg (57%) and 278 mg (36%) of mixed peroxide 16 as a pale
yellow oil for Rh2(cap)4- and RuCl2(PPh3)3-catalyzed reactions, respec-
tively: 1H NMR (500 MHz, CDCl3) δ 7.42 ꢀ 7.33 (m, 5 H), 7.01 (m, J =
10.2 Hz, 2H), 6.33 (d, J = 10.2 Hz, 2H), 1.29 (s, 9 H); 13C NMR (125
MHz, CDCl3) δ 185.9, 150.0, 136.9, 128.9, 128.8, 125.8, 80.6, 79.6, 26.5;
Rf = 0.31 (hexane/AcOEt (10:1)); HR-MS (ESI) calcd for C16H19O3
259.13342, found 259.13258 (M þ H).
General Procedure for Rh2(cap)4-Catalyzed Oxidation of
Anilines with 5 M TBHP in Decane or with T-HYDRO. The
substituted aniline (2.0 mmol), Rh2(cap)4(MeCN)2 (14.8 mg, 0.020
mmol), and DCE (4.0 mL) were placed in a 4-dram screw-cap vial
containing a magnetic stirring bar. The suspension was heated to 40 °C
in an oil bath, and 5 M TBHP solution in decane (1.6 mL, 8.0 mmol, 4.0
equiv) or T-HYDRO (1.1 mL, 8.0 mmol, 4.0 equiv) was added all at
once via syringe. The reaction solution/mixture was loosely capped to
release any built-up pressure and stirred for 20 min at 40 °C. Then the
reaction mixture was transferred to a 100-mL round-bottom flask and
concentrated under reduced pressure, and the residue was purified by
column chromatography (silica gel, DCM/AcOEt/hexane). Fractions
containing the product were combined, and the solvent was evaporated
under reduced pressure followed by additional drying under high
vacuum for 20 min (0.09 Torr, room temperature).
’ ASSOCIATED CONTENT
S
Supporting Information. Kinetic data and product char-
b
acterization (1H and 13C spectra) of new compounds. This
material is available free of charge via the Internet at http://
pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: mdoyle3@umd.edu.
Oxidation of 4-Phenylphenol (15) in tert-Butyl Alcohol. 4-
Phenylphenol 15 (1.0 mmol, 170 mg), Rh2(cap)4(MeCN)2 (10.0 μmol,
7.4 mg) or RuCl2(PPh3)3 (20.0 μmol, 19.2 mg), and tert-butyl alcohol
(5.0 mL) were placed in 6-dram screw-cap vial containing a magnetic
stirring bar. The mixture was sonicated to facilitate a complete dissolu-
tion of the phenol. The resulting mixture was placed in an oil bath and
warmed to 40 °C. T-HYDRO (10.0 mmol, 1.38 mL, 10 equiv) was
added via syringe all at once, and the reaction was stirred at 40 °C. The
reaction mixture was transferred to 100-mL round-bottom flask and
concentrated on a rotary evaporator (20 Torr, room temperature). The
residue was dissolved in DCM, and the residue was purified by column
chromatography (neutral alumina, 18 mm diameter, 18 cm height,
EtOAc/DCM/hexane (1:1:16, 250 mL)). Fractions containing 16 were
combined, and the solvent was evaporated on a rotary evaporator (60
Torr, room temperature). The residue was further dried under high
vacuum for 20 min (0.09 Torr, room temperature) to yield 433 mg
(56%) and 124 mg (16%) mixed peroxide 16 as a pale yellow oil for
Rh2(cap)4 and RuCl2(PPh3)3 catalyzed reactions, respectively.
’ ACKNOWLEDGMENT
The support of the National Science Foundation (CHE-
0748121) for this research is gratefully acknowledged. We also
thank Matthew Evans for control experiments.
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Oxidation of 2-Naphthol (17). Rh2(cap)4(MeCN)2 (0.50 μmol,
1.1 mg) and toluene (10.0 mL) were placed in a 50-mL Erlenmeyer flask,
and the suspension was warmed to 40 °C. T-HYDRO (12.0 mmol,
1.66 mL, 4.0 equiv) was added via syringe dropwise followed immedi-
ately by dropwise addition over 5 min of a solution of 2-naphthol 17
(3.0 mmol, 432 mg) and peroxide 2 (1.0 mmol, 308 mg) that was used as
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dx.doi.org/10.1021/jo1024865 |J. Org. Chem. 2011, 76, 2585–2593