Synthesis of 1,4-phenanthrenequinones via stannic chloride-induced cyclizations

Full text of DOI:10.1021/jo981352f

1720
J . Org. Chem. 1999, 64, 1720-1722
nes featuring an intramolecular Lewis acid-mediated
cyclization-dehydration sequence.
Syn th esis of 1,4-P h en a n th r en equ in on es via
Sta n n ic Ch lor id e-In d u ced Cycliza tion s
George A. Kraus* and Alex Melekhov
Department of Chemistry, Iowa State University,
Ames, Iowa 50011
Received J uly 13, 1998
Substituted 1,4-phenanthrenequinones such as 1 are
useful building blocks for the preparation of novel
materials. Katz and others have shown that compounds
such as 1 can be transformed into helicenes by Diels-
Alder reactions.1 Certain 1,4-phenanthrenequinones also
have potential as synthetic intermediates for natural
products synthesis. Additionally, some naturally occur-
ring 1,4-phenanthrenequinones such as cypripedium (2)
are biologically active.2 Kraus and Carpenter have de-
termined that some 1,4-phenanthrenequinones exhibit
inhibitory activity in vitro against the equine infectious
anemia virus.3
The route begins with known arylacetaldehydes 3a -d
that are readily available from substituted arylacetic
acids through borane reduction followed by Dess-Martin
oxidation.10 In our experience, the Dess-Martin oxidation
proved to be superior to the Swern oxidation (DMSO,
(COCl)2) and the PCC oxidation. The resulting aryl-
acetaldehydes are reacted with aryllithium 411 from -78
°C to ambient temperature followed by deprotection with
a catalytic amount of 1 M sulfuric acid in 3:1 THF/water
to afford hydroquinones 5a -d in 70-76% yields. The use
of the ethoxyethyl protecting group on the hydroquinone
was crucial, since attempted removal of the methoxy-
methyl protecting group led to partial deprotection plus
significant dehydration of the benzylic alcohol. DDQ
oxidation of 5 provides the corresponding hydroxy ben-
zoquinones 6a -d in 90-95% yields.
Most 1,4-phenanthrenequinones are prepared by pho-
tochemical cyclizations of stilbenes or Diels-Alder reac-
tions involving styrenes and benzoquinones. Mallory and
co-workers have demonstrated that certain stilbenes
undergo photocyclization in the presence of oxidizing
agents to afford hydroquinone dimethyl ethers that yield
1,4-phenanthrenequinone upon oxidation.4 Rosen and
Weber first demonstrated that benzoquinone reacted with
styrenes to generate 1,4-phenanthrenequinones in 20-
30% yield.5 Subsequently, Manning and co-workers im-
proved the reaction conditions.6 Kelly and co-workers
used this reaction to prepare a key intermediate for the
synthesis of the aglycon of chartreusin.7 Recently, Car-
reno and co-workers further improved the Diels-Alder
cycloaddition route using arylsulfinyl benzoquinones as
effective dienophiles.8 Kita enhanced the diene compo-
nent using an innovative silicon tether.9 We describe
herein a quinone-based route to 1,4-phenanthrenequino-
Initially, we evaluated the cyclization using 6a and
boron trifluoride etherate under a range of reaction
conditions. Although the reaction provided a 35% isolated
yield of quinone 7a in methylene chloride, the reaction
did not proceed in ether or THF. With stannic chloride
in methylene chloride the yield of adduct 7a was 41%.
Presumably, dehydration of the benzylic alcohol occurred
after cyclization but before oxidation to the phenan-
threnequinone. Since the modest yield might be related
to a redox process between the starting quinone and the
initially formed phenanthrene hydroquinone, the reaction
was conducted in the presence of oxidizing agents. DDQ
proved to be more efficient than oxygen, affording 7d in
an isolated yield of 74% Using these conditions, quinones
6a -c were then transformed into 7a -c in 71%, 68%, and
(1) Nuckolls, C.; Katz, T. J .; Castellanos, L. J . Am. Chem. Soc. 1996,
118, 3767-3768.
(2) Schmalle, H. W.; J archow, O. H.; Hausen, B. M.; Werdin, R.;
Schulz, K. H.; Krohn, K.; Loock, U. Acta Crystallogr. Sect. A 1984, 40,
C63-C64.
(3) Kraus, G. A.; Melekhov, A.; Carpenter, S.; Wannemuhler, Y.
Unpublished results.
(4) Mallory, F. B.; Mallory, C., W. In Organic Reactions; Daulen,
W. G., Ed.; Wiley: New York, 1984; Vol. 30.
(5) Rosen, B. I.; Weber, W. P. J . Org. Chem. 1977, 42, 3463-3465.
(6) Manning, W. B.; Tomaszewski, J . E.; Muschik, G. M.; Sato, R. I.
J . Org. Chem. 1977, 42, 3465-3467. Manning, W. B.; Kelly, T. P.;
Muschik, G. M. J . Org. Chem. 1980, 45, 2535-2536.
(7) Kelly, T. R.; Magee, J . A.; Weibel, F. R. J . Am. Chem. Soc. 1980,
102, 798-799.
(8) Carren˜o, M. C.; Mahugo, J .; Urbano, A. Tetrahedron Lett. 1997,
38, 3047-3050.
(9) Kita, Y.; Yasuda, H.; Tanmura, O.; Tamura, Y. Tetrahedron Lett.
1984, 25, 1813-1816.
(10) Dess, D. B.; Martin, J . C. J . Am. Chem. Soc, 1991, 113, 7277.
Dess, D. B.; Martin, J . C. J . Org. Chem. 1983, 48, 4155. Ireland, R. E.;
Liu, L. J . Org. Chem. 1993, 58, 2899.
(11) Kraus, G. A.; Pezzanite, J . J . Org. Chem. 1979, 44, 2480.
10.1021/jo981352f CCC: $18.00 © 1999 American Chemical Society
Published on Web 02/17/1999

Notes
J . Org. Chem., Vol. 64, No. 5, 1999 1721
benzene (1.10 g, 4.31 mmol) in ether (20 mL) at 0 °C under Ar
was added t-BuLi (1.65M in pentane, 2.50 mL, 4.12 mmol), and
the resulting solution was stirred for 0.5 h. Then it was cooled
to -78 °C, a solution of 3a (824 mg, 3.92 mmol) in dry THF (5
mL) was added dropwise via a syringe pump, and the resulting
mixture was allowed to slowly warm to room temperature.
Saturated NH4Cl was added, the aqueous layer was extracted
with ether, and the combined organic fractions were washed with
water. After concentration, the residue was dissolved in 4:1
THF-H2O (50 mL) and treated with five drops of 1 M H2SO4.
After complete deprotection (TLC control, ca. 4-6 h), ether was
added, the aqueous layer was extracted with ether, and the
combined organic fractions were washed with water and brine
and dried. Removal of the solvent followed by SGC (30% EtOAc
in hexanes) afforded 5a (929 mg, 74%) as a slowly solidifying
clear oil: 1H NMR ((CD3)2CO) δ 2.88 (dd, J ) 8.1, 13.5 Hz, 1 H),
3.01 (dd, J ) 5.4, 13.5 Hz, 1 H), 3.68 (s, 3 H), 3.75 (s, 6 H), 4.71
(br d, J ) 3.6 Hz, 1 H), 5.06-5.09 (m, 1 H), 6.50 (s, 2 H), 6.57
(dd, J ) 3.0, 8.4 Hz, 1 H), 6.64-6.67 (m, 2 H), 7.62 (br s, 1 H),
8.02 (br s, 1 H); 13C NMR ((CD3)2CO) δ 44.5, 55.4, 59.6, 72.8,
107.1, 113.8, 114.2, 116.3, 130.7, 134.8, 136.8, 147.7, 150.2, 153.1;
IR (neat) cm-1 3366, 1594, 1495; HRMS m/z M+ calcd 320.1260,
obsd 320.1265.
2-(3,4-Dim eth oxyp h en yl)-1-(2,5-d ih yd r oxyp h en yl)eth a -
n ol (5b). Following the general procedure described above and
using 3b (520 mg, 2.89 mmol) as a starting material, 5b (636
mg, 76%) was obtained as a white foam: 1H NMR ((CD3)2CO) δ
2.87 (dd, J ) 8.1, 13.5 Hz, 1 H), 3.00 (dd, J ) 4.8, 13.5 Hz, 1 H),
3.72 (s, 3 H), 3.75 (s, 3 H), 4.69 (d, J ) 4.2 Hz, 1 H), 5.01-5.07
(m, 1 H), 6.56 (dd, J ) 2.7, 8.4 Hz, 1 H), 6.63-6.66 (m, 2 H),
6.72-6.76 (m, 2 H), 6.81 (d, J ) 7.8 Hz, 1 H), 7.65 (s, 1 H), 8.04
(s, 1 H); 13C NMR ((CD3)2CO) δ 43.8, 55.1, 55.3, 73.0, 111.8,
113.7, 113.8, 114.1, 116.2, 121.7, 130.8, 131.8, 147.7, 148.0, 149.1,
150.2; IR (neat) cm-1 3400, 1592, 1514.
2-(4-Met h oxyp h en yl)-1-(2,5-d ih yd r oxyp h en yl)et h a n ol
(5c). Following the general procedure described above and using
3c (168 mg, 1.12 mmol) as a starting material, 5c (204 mg, 70%)
was obtained as a clear foam: 1H NMR ((CD3)2CO) δ 2.85 (dd,
J ) 8.4, 13.5 Hz, 1 H), 2.99 (dd, J ) 4.5, 13.5 Hz, 1 H), 3.75 (s,
3 H), 4.68 (d, J ) 4.5 Hz, 1 H), 5.00-5.05 (m, 1 H), 6.55 (dd, J
) 3.0, 9.3 Hz, 1 H), 6.64 (d, J ) 9.3 Hz, 1 H), 6.68 (d, J ) 3.0
Hz, 1 H), 6.80 (d, J ) 8.7 Hz, 2 H), 7.14 (d, J ) 8.7 Hz, 2 H),
7.73 (s, 1 H), 8.09 (s, 1 H); 13C NMR ((CD3)2CO) δ 43.4, 54.6,
72.8, 113.4, 113.7, 114.1, 116.2, 130.6, 131.0, 131.3, 147.6, 150.2,
158.3; IR (neat) cm-1 3370, 1601, 1490; HRMS m/z M+ calcd
260.1049, obsd 260.1044.
2-P h en yl-1-(2,5-d ih yd r oxyp h en yl)eth a n ol (5d ). Following
the general procedure described above and using commercially
available phenylacetaldehyde (335 mg, 2.79 mmol) as a starting
material, 5d (455 mg, 71%) was obtained as a white foam: 1H
NMR (CDCl3) δ 3.01 (d, J ) 6.3 Hz, 2 H), 3.78 (br s, 1 H), 4.87
(t, J ) 6.3 Hz, 1 H), 6.39 (d, J ) 3.6 Hz, 1 H), 6.58 (dd, J ) 7.8,
3.6 Hz, 1 H), 6.63 (d, J ) 7.8 Hz, 1 H), 6.73 (br s, 1 H), 7.11-
7.24 (m, 5 H), 7.77 (br s, 1 H); 13C NMR (CDCl3) δ 44.0, 75.9,
114.0, 115.5, 117.6, 126.8, 128.1, 128.6, 129.6, 137.8, 148.6, 149.2;
IR (neat) cm-1 3390, 1634, 1497.
70% yields, respectively. It is interesting to note that the
cyclization to quinone 7b was regioselective.
Hydroxy quinone 8 was next prepared. The substituent
pattern was designed to permit the synthesis of 5,6-
disubstituted phenanthrenequinones that could not be
prepared by cyclization of 6b. Compound 8 was readily
prepared from 6-bromo-4-methoxy-3-benzyloxyphenyl ac-
etaldehyde (9), readily available by a reaction sequence
recently employed by Overman in his synthesis of mor-
phinans.12 Unexpectedly, this quinone did not react using
the stannic chloride conditions. Compound 10, derived
from 2-methoxyphenylacetaldehyde, also failed to cyclize.
In view of the results with 6a -d , the rationale for the
failed cyclizations is unclear.
Phenanthrenequinones 7a -d were prepared in five
steps from commercially available phenylacetic acids. The
mild reaction conditions employed in this sequence will
undoubtedly permit access to a wide variety of function-
alized quinones. The use of substituted benzoquinone
precursors, combined with the regioselectivity of this
procedure, further increases the scope of this chemistry.
The biological activity of the phenanthrenequinones will
be reported in due course.
Exp er im en ta l Section
3,4,5-Tr im eth oxyp h en yla ceta ld eh yd e (3a ). To a stirred
solution of 3,4,5-trimethoxyphenylacetic acid (1.13 g, 5 mmol)
in dry THF (20 mL) at 0 °C under Ar was added a 1 M THF
solution of BH3‚THF complex (10 mL, 10 mmol). After 4 h, water
was carefully added with cooling, and the reaction mixture was
diluted with ether, washed with NaHCO3 solution, water, and
brine, and dried. Solvents were removed, and the residue was
dissolved in methylene chloride (20 mL) and added to a stirred
solution of Dess-Martin reagent (2.54 g, 6 mmol) in CH2Cl2 (20
mL). After 1 h, the solution was diluted with ether and stirred
for an additional 10 min with a mixture of saturated aqueous
NaHCO3 (20 mL) and 25% aqueous Na2S2O3 (20 mL). The
aqueous layer was separated and extracted with ether, and the
combined organic fractions were washed with saturated NaH-
CO3, water, and brine and dried. Evaporation of the solvents
followed by SGC (20% EtOAc in hexanes) afforded pure aldehyde
(0.90 g, 86%) as a clear oil that gave spectral data identical to
that previously reported.13
3,4-Dim eth oxyp h en yla ceta ld eh yd e (3b). Following the
general procedure described above and starting with (3,4-
dimethoxyphenyl)acetic acid (0.98 g, 5 mmol), 3b (0.76 g, 85%)
was obtained as a clear oil that gave spectral data identical to
that previously reported.14
4-Meth oxyp h en yla ceta ld eh yd e (3c). Following the general
procedure described above and starting with 4-methoxyphen-
ylacetic acid (0.83 g, 5 mmol), 3c (0.66 g, 88%) was obtained as
a clear oil that gave spectral data identical to that previously
reported.14
2-(3,4,5-Tr im et h oxyp h en yl)-1-(3,6-d ioxo-1,4-cycloh exa -
d ien yl)eth a n ol (6a ). To a chilled to ca. 10 °C solution of 5a
(880 mg, 2.75 mmol) in dioxane (15 mL) under Ar was added
DDQ (655 mg, 2.89 mmol), and the resulting mixture was stirred
for 0.5 h. Then it was filtered, the filtrate was concentrated, and
the residue was purified by SGC (20% EtOAc in hexanes) to
afford quinone 6a (831 mg, 95%) as a brown semisolid: 1H NMR
(CDCl3) δ 2.36 (br s, 1 H), 2.57 (dd, J ) 9.3, 13.5 Hz, 1 H), 3.09
(dd, J ) 3.3, 13.5 Hz, 1 H), 3.81 (s, 3 H), 3.84 (s, 6 H), 4.86-4.90
(m, 1 H), 6.46 (s, 2 H), 6.74-6.76 (m, 2 H), 6.83-6.85 (m, 1 H);
13C NMR (CDCl3) δ 44.0, 56.2, 60.9, 69.1, 106.3, 131.4, 133.0,
2-(3,4,5-Tr im et h oxyp h en yl)-1-(2,5-d ih yd r oxyp h en yl)-
eth a n ol (5a ). To a stirred solution of 1,4-bis(1-ethoxyethoxy)-
(12) Hong, C. Y.; Kado, N.; Overman, L. E. J . Am. Chem. Soc. 1993,
115, 11028-11029. Mosset, P., Gre´e, R. Synth. Commun. 1985, 15,
749-757.
(13) Haridas, K.; Dev, S. Indian J . Chem. Sect. B 1987, 26, 1018-
1020.
(14) Chikashita, H.; Morita, Y.; Itoh, K. Synth. Commun. 1987, 17,
677-684.

1722 J . Org. Chem., Vol. 64, No. 5, 1999
Notes
136.5, 136.8, 137.0, 149.4, 153.4, 187.4, 187.7; IR (neat) cm-1
3441, 1658, 1586; HRMS m/z M+ calcd 318.1103, obsd 318.1109.
2-(3,4-Dim et h oxyp h en yl)-1-(3,6-d ioxo-1,4-cycloh exa d i-
en yl)eth a n ol (6b). Oxidation of 5b (330 mg, 1.14 mmol) under
the same conditions provided 6b (315 mg, 96%) as a light-brown
foam: 1H NMR (CDCl3) δ 2.19 (d, J ) 6.3 Hz, 1 H), 2.63 (dd, J
) 8.7, 13.5 Hz, 1 H), 3.11 (dd, J ) 3.6, 13.5 Hz, 1 H), 3.86 (s, 3
H), 3.88 (s, 3 H), 4.84-4.88 (m, 1 H), 6.75-6.81 (m, 6 H); 13C
NMR (CDCl3) δ 43.2, 55.9, 56.0, 69.3, 11.4, 112.5, 121.6, 129.5,
131.5, 136.5, 136.8, 148.2, 149.2, 149.4, 187.4, 187.7; IR (neat)
cm-1 3505, 2937, 1659, 1516; HRMS m/z M+ calcd 288.0998, obsd
288.1006.
2-(4-Meth oxyp h en yl)-1-(3,6-d ioxo-1,4-cycloh exa d ien yl)-
eth a n ol (6c). Oxidation of 5c (242 mg, 0.93 mmol) under the
same conditions provided 6c (232 mg, 97%) as a yellow oil: 1H
NMR (CDCl3) δ 2.14 (br s, 1 H), 2.65 (dd, J ) 8.7, 13.5 Hz, 1 H),
3.10 (dd, J ) 3.6, 13.5 Hz, 1 H), 3.80 (s, 3 H), 4.82-4.86 (m, 1
H), 6.71-6.79 (m, 3 H), 6.86 (d, J ) 8.7 Hz, 2 H), 7.15 (d, J )
8.7 Hz, 2 H); 13C NMR (CDCl3) δ 42.6, 55.4, 69.5, 114.3, 128.8,
130.6, 131.6, 136.5, 136.8, 149.3, 158.8, 187.4, 187.7; IR (neat)
cm-1 3480, 1657, 1612.
7.92 (m, 1 H), 8.16 (d, J ) 9.0 Hz, 1 H), 8.20 (d, J ) 9.0 Hz, 1 H)
9.54 (d, J ) 3.3 Hz, 1 H); 13C NMR (CDCl3) δ 122.0, 127.2, 128.0,
128.8, 130.0, 130.3, 132.3, 135.3, 135.9, 136.6, 140.6, 142.3, 186.1,
188.4; IR (neat) cm-1 1670, 1660, 1620.
(5-Ben zyloxy-2-b r om o-4-m et h oxyp h en yl)a cet a ld eh yd e
(9). To a solution of 5-benzyloxy-2-bromo-4-methoxybenzalde-
hyde15 (321 mg, 1 mmol) in CH2Cl2 (4 mL) were added trimeth-
ylsulfonium methylsulfate (245 mg, 1.3 mmol) and 50% aqueous
NaOH (0.5 mL), and the resulting mixture was vigorously stirred
for 3 h at room temperature. Water (5 mL) and ether (10 mL)
were added, and the organic phase was separated. The aqueous
phase was extracted with ether (10 mL), and the combined
organic fractions were washed with water and brine and dried.
After removal of the solvents, the residue was dissolved in dry
THF (10 mL) and treated with BF3‚Et2O (13 µL, 0.1 mmol). After
0.5 h, the solution was diluted with ether, washed with water
and brine, and dried. Concentration followed by SGC purification
of the residue (15% EtOAc in hexanes) afforded 9 (275 mg, 82%)
as a clear oil: 1H NMR (CDCl3) δ 3.72 (d, J ) 1.8 Hz, 2 H), 3.87
(s, 3 H), 5.10 (s, 2 H), 6.74 (s, 1 H) 7.10 (s 1 H), 7.30-7.42 (m, 5
H), 9.67 (t, J ) 1.8 Hz, 1 H); 13C NMR (CDCl3) δ 50.1, 56.3,
71.4, 115.7, 116.2, 116.9, 124.2, 127.5, 128.2, 128.7, 136.5, 147.9,
149.9, 198.7; IR (neat) cm-1 2950, 1735, 1533.
2-(5-Ben zyloxy-2-br om o-4-m eth oxyp h en yl)-1-(3,6-d ioxo-
1,4-cycloh exa d ien yl)eth a n ol (8). Following the protocol de-
scribed for 6 and starting with 9 (101 mg, 0.30 mmol), 8 (99 mg,
74% over two steps) was prepared as a brown foam: 1H NMR
(CDCl3) δ 2.45 (d J ) 6 Hz, 1 H), 2.87 (dd, J ) 7.8, 13.8 Hz, 1
H), 3.11 (dd, J ) 4.8, 13.8 Hz, 1 H), 3.83 (s, 3 H), 4.80-4.84 (m,
1 H), 5.10 (s, 2 H), 6.55 (s, 1 H), 6.68 (d, J ) 9.9 Hz, 1 H), 6.72
(d, J ) 9.9 Hz, 1 H), 6.80 (s, 1 H), 6.98 (s, 1 H), 7.28-7.42 (m,
5 H); 13C NMR (CDCl3) δ 42.5, 56.3, 69.0, 71.3, 115.7, 116.1,
117.4, 127.6, 128.1, 128.2, 128.7, 131.6, 136.3, 136.6, 136.9, 147.3,
148.7, 149.4, 187.5, 187.6; IR (neat) cm-1 3425, 1656, 1590;
HRMS m/z M+ calcd 442.0417, obsrd 442.0409.
2-(2-Meth oxyp h en yl)-1-(3,6-d ioxo-1,4-cycloh exa d ien yl)-
eth a n ol (10). Following the general procedure described for 3a
and starting with 2-methoxyphenylacetic acid (0.83 g, 5 mmol),
2-methoxyphenylacetaldehyde (0.64 g, 85%) was obtained as a
clear oil that gave spectral data identical to that previously
reported.14
The addition of aryllithium 4 to 2-methoxyphenylacetaldehyde
(110 mg, 0.73 mmol) was conducted following the general
procedure described for 5a , affording 2-(2-methoxyphenyl)-1-(2,5-
dihydroxyphenyl)ethanol (116 mg, 61%) as a clear semisolid: 1H
NMR ((CD3)2CO) δ 2.96-3.11 (m, 2 H), 3.82 (s, 3 H), 4.81 (br s,
1 H), 5.06-5.10 (m, 1 H), 6.54-6.57 (m, 2 H), 6.63 (d, J ) 7.2
Hz, 1 H), 6.82 (t, J ) 7.5 Hz, 1 H), 6.93 (d, J ) 7.5 Hz, 1 H),
7.10-7.20 (m, 2 H), 7.64 (br s, 1 H), 8.10 (br s, 1 H); 13C NMR
((CD3)2CO) δ 38.8, 54.9, 72.4, 110.4, 113.7, 114.2, 116.4, 120.2,
127.2, 127.5, 130.5, 131.3, 148.2, 150.0, 157.9; IR (neat) cm-1
3395, 1605, 1520.
2-P h en yl-1-(3,6-d ioxo-1,4-cycloh exa d ien yl)eth a n ol (6d ).
Oxidation of 5d (141 mg, 1.08 mmol) under the same conditions
provided 6d (127 mg, 92%) as a brown foam: 1H NMR (CDCl3)
δ 2.24 (br s, 1 H), 2.71 (dd, J ) 7.8, 13.5 Hz, 1 H), 3.15 (dd, J )
3.3, 13.5 Hz, 1 H), 4.88-4.91 (m, 1 H), 6.74-6.78 (m, 3 H), 7.23-
7.35 (m, 5 H); 13C NMR (CDCl3) δ 43.5, 69.4, 127.2, 127.3, 128.9,
129.5, 131.6, 136.5, 136.8, 137.0, 187.4, 187.7; IR (neat) cm-1
3210, 1666, 1635.
5,6,7-Tr im eth oxy-1,4-p h en a n th r en equ in on e (7a ). To a
solution of hydroxyquinone 6a (76 mg, 0.24 mmol) in dry
methylene chloride (5 mL) at -78 °C under Ar was added a 1 M
solution of SnCl4 in CH2Cl2 (0.24 mL, 0.24 mmol) followed by
DDQ (54 mg, 0.24 mmol), and the resulting mixture was allowed
to slowly warm to room temperature. Then it was diluted with
ether washed with aqueous NH4Cl and brine and dried. Con-
centration followed by SGC (15% EtOAc in hexanes) afforded
1
7a (51 mg, 71%) as a bright orange solid: mp 141 °C; H NMR
(CDCl3) δ 3.91 (s, 3 H), 3.97 (s, 3 H), 3.99 (s, 3 H), 6.77 (d, J )
9 Hz, 1 H), 6.93 (s, 1 H), 7.02 (d, J ) 9 Hz, 1 H), 7.82 (d, J ) 7
Hz, 1 H), 7.92 (d, J ) 7 Hz, 1 H); 13C NMR (CDCl3) δ 56.1, 60.9,
61.2, 102.8, 120.2, 121.5, 130.8, 131.8, 133.4, 134.8, 135.2, 140.4,
143.9, 150.4, 155.8, 184.9, 186.8; IR (neat) cm-1 1680, 1655, 1620;
MS m/z (CI) 298 (100); HRMS m/z (M+) calcd 298.08412, obsd
298.08411. Anal. Calcd for C17H14O5: C, 68.45; H, 4.73. Found:
C, 68.39, H, 5.13.
6,7-Dim eth oxy-1,4-p h en a n th r en equ in on e (7b). Cycliza-
tion of 6b (69 mg, 0.24 mmol) afforded 7b (44 mg, 68%) as an
orange solid: mp 234 °C (lit.5 mp 236 °C); 1H NMR (CDCl3) δ
4.04 (s, 3 H), 4.10 (s, 3 H), 6.90 (s, 2 H), 7.11 (s, 1 H), 7.97 (d, J
) 7.5 Hz, 1 H), 8.02 (d, J ) 7.5 Hz, 1 H), 9.06 (s, 1 H); 13C NMR
(CDCl3) δ 56.0, 56.2, 106.1, 106.7, 121.0, 125.3, 126.5, 130.8,
133.1, 134.0, 136.1, 140.5, 151.4, 153.2, 186.0, 188.7; IR (neat)
cm-1 1670, 1650, 1620.
6-Meth oxy-1,4-p h en a n th r en equ in on e (7c): Cyclization of
6c (28 mg, 0.11 mmol) afforded 7c (18 mg, 70%) as an orange
solid: mp 192 °C (lit.5 mp 195 °C); 1H NMR (CDCl3) δ 4.01 (s, 3
H), 6.90 (d, J ) 10.2 Hz, 1 H), 6.94 (d, J ) 10.2 Hz, 1 H), 7.28
(dd, J ) 2.8, 9.0 Hz, 1 H), 7.76 (d, J ) 9.0 Hz, 1 H), 8.00 (d, J )
8.4 Hz, 1 H), 8.08 (d, J ) 8.4 Hz, 1 H), 9.02 (d, J ) 2.8 Hz, 1 H);
13C NMR (CDCl3) δ 55.6, 105.5, 120.0, 121.9, 125.4, 130.2, 132.0,
132.6, 132.8, 135.0, 135.9, 140.8, 161.6, 186.2, 188.5; IR (neat)
cm-1 1660, 1620. Anal. Calcd for C15H10O3: C, 75.62; H, 4.23.
Found: C, 75.80, H, 4.34.
1,4-P h en a n th r en equ in on e (7d ). Cyclization of 6d (77 mg,
0.34 mol) afforded 7d (52 mg, 74%) as a light-yellow solid: mp
146 °C (lit.5 mp 145 °C); 1H NMR (CDCl3) δ 6.94 (d, J ) 11.4
Hz, 1 H), 6.99 (d, J ) 11.4 Hz, 1 H), 7.64-7.78 (m, 2 H), 7.89-
Oxidation of 2-(2-methoxyphenyl)-1-(2,5-dihydroxyphenyl)-
ethanol (184 mg, 0.71 mmol) under the same conditions as
described for 6a provided 10 (173 mg, 95%) as a light-brown oil:
1H NMR (CDCl3) δ 3.00 (dd, J ) 6.8, 13.5 Hz, 1 H), 3.17 (dd, J
) 4.5, 13.5 Hz, 1 H), 3.80 (s, 3 H), 4.92-4.96 (m, 1 H), 6.56 (s,
1 H), 6.68 (dd, J ) 2.4, 9.9 Hz, 1 H), 6.75 (d, J ) 9.9 Hz, 1 H),
6.84-6.93 (m, 2 H), 7.06 (dd, J ) 7.5, 1.6 Hz, 1 H), 7.22 (td, J )
7.5, 1.6 Hz, 1 H); 13C NMR (CDCl3) δ 37.8, 55.6, 69.4, 110.7,
121.2, 125.0, 128.7, 131.2, 131.7, 136.3, 136.9, 149.7, 157.3, 187.6,
187.8; IR (neat) cm-1 2936, 1658, 1520.
Ack n ow led gm en t. We thank the Environmental
Protection Agency for support of this research.
Su p p or tin g In for m a tion Ava ila ble: NMR spectra for
obtained compounds. This material is available free of charge
via the Internet at http://pubs.acs.org.
(15) Bolton, R. E.; Moody, C. J .; Rees, C. W.; Togo, G. J . Chem. Soc.,
Perkin. Trans. 1 1987, 931-932.
J O981352F