A facile access to polycyclic homo- and heteroaromatic hydrocarbons based on the ceric ammonium nitrate-promoted oxidative addition of 3-aryl-1- [(trimethylsilyl)oxy]cyclohexenes to ethyl vinyl ether

Full text of DOI:10.1021/jo982195n

3364
J . Org. Chem. 1999, 64, 3364-3368
Sch em e 1
A F a cile Access to P olycyclic Hom o- a n d
Heter oa r om a tic Hyd r oca r bon s Ba sed on
th e Cer ic Am m on iu m Nitr a te-P r om oted
Oxid a tive Ad d ition of
3-Ar yl-1-[(tr im eth ylsilyl)oxy]cycloh exen es
to Eth yl Vin yl Eth er
Anna Belli Paolobelli and Renzo Ruzziconi*
Dipartimento di Chimica Universita` di Perugia,
Via Elce di Sotto 8, 06100 Perugia, Italy
Paolo Lupattelli, Patrizia Scafato, and
Caterina Spezzacatena
Dipartimento di Chimica Universita` della Basilicata,
Via N. Sauro 85, 85100 Potenza, Italy
Received November 2, 1998
The synthesis of fused polycyclic aromatic hydrocar-
bons is always a fascinating undertaking because this
class of compounds is spread over different topics of
organic chemistry, from biochemistry (in connection with
their cancerogenic properties)1 to stereochemistry (chiral
helicenes).2 Several methods have been developed to
synthesize polycyclic aromatic hydrocarbons, most of
which are based on the acid-catalyzed cyclization of a
methylenecarbonyl-substituted aromatic ring bearing an
aryl group on the adjacent carbon.3 In some cases, the
synthesis of these compounds involves a poly(phosphoric
acid)-catalyzed ring closure of a biaryl-2-yl acetaldehyde.4
All of the above-mentioned procedures exhibit a scarce
regioselectivity when substituted aromatic rings are
involved in the cyclization step.
eomeric acyclic (2) and cyclic (3) acetals (Scheme 1). This
mixture was previously employed in the synthesis of
substituted 3,4-dihydro(2H)phenanthren-1-ones.7 How-
ever, attempts to transform the latter into the corre-
sponding 1-phenanthrenols (5) by oxidation with dichlo-
rodicyanobenzoquinone (DDQ) were unsuccessful even
under very drastic conditions.8
Nevertheless, we show here that the above acetal
mixture proves to be particularly versatile, allowing
access to either regioselectively substituted 1-phenan-
threnols (5) or 4-arylbenzo[b]furans (6) depending on the
reaction conditions.
Thus, after reflux of 2 + 3 in benzene, in the presence
of 2 equiv of DDQ, followed by the acid-catalyzed cycliza-
tion of the resulting 4-aryl-2-alkoxy-2,3-dihydrobenzofu-
ran (4) in aqueous 80% H2SO4, 1-phenanthrenols are
obtained in fairly good yields (Scheme 1). Results are
reported in Table 1.
Alternatively, 4-arylbenzo[b]furans (6) are obtained in
satisfactory yields (Table 2) by simple addition of a
catalytic amount of p-toluenesulfonic acid to the DDQ-
benzene refluxing mixture.10
Our continuous interest in carbon-carbon-bond-form-
ing reactions by ceric ammonium nitrate (CAN)-promoted
oxidative addition of an R-carbonylalkyl radical to electron-
rich alkenes5 spurred us to test the possibility of extend-
ing this method to the synthesis of fused polycyclic
aromatic hydrocarbons.
Resu lts a n d Discu ssion
The approach reported in this paper is based on the
CAN-promoted oxidative addition of 3-aryl-1-[(trimeth-
ylsilyl)oxy]cyclohexenes (1), easily accessible in very good
yield by the method of Reetz,6 to the ethyl vinyl ether in
methanol, which leads to a complex mixture of diaster-
* To whom correspondence should be addressed. Email: Ruzzchor@
unipg.it.
(1) (a) Harvey, R. G. Polycyclic Aromatic Hydrocarbons: Chemistry
and Carcinogenicity; Cambridge University Press: Cambridge, U.K.,
1991; Chapter 4. (b) Bradsher, C. K. Chem. Rev. 1987, 87, 1277-1297.
(2) Eliel, E. L.; Wilen, S. H. Stereochemistry of Organic Compounds;
J ohn Wiley & Sons: New York, 1994; Chapter 14.
According to the suggested mechanism (Scheme 2),
both 5 and 6 form from the common precursor 4. In
(7) Belli Paolobelli, A.; Lupattelli, P.; Ruzziconi, R.; Scafato, P J .
Org. Chem. 1998, 63, in press.
(3) Reference 1a; Chapter 7.
(8) It is known that DDQ is unable to oxidize cyclic ketones to
phenols unless they are previously transformed into the corresponding
enol acetates.9 Cyclic ketones can be transformed into the correspond-
ing phenols by palladium-catalyzed dehydrogenation, but it requires
very high temperatures and long reaction times.9
(9) Fu, P. P.; Harvey, R. G. Chem. Rev. 1978, 78, 317-361 and
references therein.
(10) In the few examples reported in the literature, 4-arylbenzo[b]-
furans have been obtained as minor components of regioisomeric
mixtures by poly(phosphoric acid)-catalyzed cyclization of aryloxyacet-
aldehyde acetals11a or by radical phenylation of benzo[b]furan.11b The
(4) Blum, J .; Bergmann, E. D. J . Org. Chem. 1967, 32, 344.
(5) (a) Baciocchi, E.; Ruzziconi, R. Synthetic Application of Substitu-
tion and Addition Reactions Promoted by Cerium(IV) Ammonium
Nitrate. In Free Radicals in Synthesis and Biology; Minisci, F., Ed.;
NATO ASI Series C. Kluwer Academic Publishers: Dordrecht, The
Netherlands, 1989; Vol. 260, pp 155-185. (b) Baciocchi, E.; Casu, A.;
Ruzziconi, R. Teterahedron Lett. 1989, 30, 3707-3710. (c) Belli
Paolobelli, A.; Pizzo, F.; Ceccherelli, P.; Ruzziconi, R. J . Org. Chem.
1995, 60, 4954-4958. (d) Belli Paolobelli, A.; Ruzziconi, R. J . Org.
Chem. 1996, 61, 6434-6437.
(6) Reetz, M. T.; Kindler, A. J . Organomet. Chem. 1995, 502, C5-
C7.
present procedure could represent
a valuable alternative in the
regioselective synthesis of 4-arylbenzo[b]furans.
10.1021/jo982195n CCC: $18.00 © 1999 American Chemical Society
Published on Web 04/10/1999

Notes
J . Org. Chem., Vol. 64, No. 9, 1999 3365
Ta ble 1. Su bstitu ted 1-P h en a n th r en ols fr om
3-Ar yl[(tr im eth ylsilyl)oxy]cycloh exen es 1
Ch a r t 1
cyclization
Y in 1 time of 4, h
yield ratio
Y in 5
in 5,a
%
6-Y/8-Yb
H
24
6
18
3
24
20
48
H
27
45
30
61
38
3-CH3
4-CH3
3-OCH3
4-OCH3
3-F
6-CH3 + 8-CH3
7-CH3
6-OCH3 + 8-OCH3
7-OCH3
6-F + 8-F
7-F
77/23
67/33
88/12
40
c
4-F
a
Yield of isolated product calculated with respect to the starting
b
3-aryl-1-[(trimethylsilyl)oxy]cyclohexenes. Determined by GLC,
MS and 1H NMR analyses of the regioisomeric mixtures. c 4-(4-
Fluorophenyl)benzofuran was recovered in 53% yield.
reaction medium. Cyclization of 8 on the adjacent aryl
group, followed by H2O elimination, gives 5. Now, the
reaction time strongly depends on the nature of the
substituent Y, as expected for an electrophilic aromatic
substitution. With little activated or nonactivated aryl
groups, the cyclization process in aqueous sulfuric acid
can be so slow that, besides 5, a considerable amount of
the corresponding 4-arylbenzofuran can be obtained.13 In
the case of 4 (Y ) 4-F), the cyclization to 7-fluoro-1-
phenanthrenol was completely inhibited and only 4-(p-
fluorophenyl)benzo[b]furan was isolated in 53% yield.
Table 1 also reports the regioselectivity ratios (6-Y/8-
Y) for the cyclization of 2 + 3 bearing 3-Y-substituted
aryl groups. As expected, the trend of the 6-Y/8-Y ratios
is like that of the para/ortho reactivity ratios observed,
for the same substituents, in several electrophilic sub-
stitution reactions of monosubstituted benzenes.14 Ac-
cordingly, the 3-fluoro derivative shows the highest
regioselectivity ratio.
Ta ble 2. 4-Ar ylben zo[b]fu r a n s fr om
3-Ar yl[(tr im eth ylsilyl)oxy]cycloh exen es 1
Y in 1
reaction time, h
yield of 6,a
%
H
3.0
2.5
2.5
2.0
2.5
3.0
3.0
49
52
55
b
58
45
53
3-CH3
4-CH3
3-OCH3
4-OCH3
3-F
4-F
a
Yield of isolated product calculated with respect to the starting
b
3-aryl-1-[(trimethylsilyl)oxy]cyclohexenes. A regioisomeric mix-
ture of 5 (Y ) 6-OCH3, and 8-OCH3, 6Y/8Y ) 2:1) was obtained in
39% yield.
Sch em e 2
An example of the wide applicability of the method is
the synthesis of the unknown hydroxynaphthothiophenes
10 and 12 (Chart 1), starting from 3-(2-thienyl)- (9) and
its regioisomer 3-(3-thienyl)-1-[(trimethylsilyl)oxy]cyclo-
hexene (11). The latter were, in turn, prepared in up to
90% yields from the corresponding thienylmagnesium
bromides15 and 3-oxocyclohexene according to the Reetz
method. The CAN-promoted oxidative addition of 9 and
11 to ethyl vinyl ether, followed by DDQ-promoted
oxidation in refluxing benzene with subsequent cycliza-
tion in 80% sulfuric acid for 3 h, gave 10 (65%) and 12
(72%), respectively.
As another example, 1-chrysenol (14; Chart 2) has been
prepared in 65% yield from 3-(â-naphthyl)-1-[(trimeth-
ylsilyl)oxy]cyclohexene (13), again obtained in up to 90%
yield from â-naphthylmagnesium bromide and 3-oxocy-
clohexene. In this respect, the unsuccessful attempt to
synthesize 1-benzo[c]phenanthrenol from the regioiso-
meric 3-(R-naphthyl)-1-[(trimethylsilyl)oxy]cyclohexene
(15) can be considered an exception. Despite the higher
reactivity of naphthyl with respect to the phenyl group
in aromatic substitution reactions, oxidation of 2 + 3 (Ar
) R-naphthyl) with DDQ in refluxing benzene, followed
by the reaction of the resulting 4-(R-naphthyl)-2,3-dihy-
dro-2-alkoxybenzofuran in 80% sulfuric acid, gave 4-(R-
naphthyl)benzofuran (16) in 65% of yield.
refluxing benzene, the acid-catalyzed elimination of
EtOH to give the 4-arylbenzofuran 6 (path a) is the most
important process.12 As a matter of fact, the formation
of 6 is quite fast and irrespective of the nature of Y.
However, with powerful electron-releasing Y groups in
a conjugative position with respect to the attacked site,
the electrophilic aromatic substitution of the R-alkoxy-
carbocation 7, in equilibrium with 4, efficaciously com-
petes to give 5 after EtOH elimination (path b). This was
observed in the case of 2 + 3 (Y ) 3-OCH3), where a
regioisomeric mixture of 5 (Y ) 6-OCH3 and 8-OCH3, 6-Y/
8-Y ) 2:1) was exclusively formed. In aqueous 80%
sulfuric acid, at lower temperature, the hydrolysis of 4,
giving the protonated aldehyde 8 (path c) prevails,
because of stabilization by the high polarity of the
(13) The acid-promoted opening of the previously formed benzofuran
could also be envisaged, but blank experiments have shown that less
than 5% phenanthrenol is obtained, after 24 h, by reacting 6 with 80%
aqueous H2SO4.
(14) Stock, L. M.; Brown, H. C. Adv. Phys. Org. Chem. 1963, 1, 35-
154.
(11) (a) Barker, P.; Finke, P.; Thompson, K. Synth. Commun. 1989,
19, 257-265. (b) Vernin, G.; Coen, S.; Metzger, J .; Pa´rka´nyi, C. J .
Heterocycl. Chem. 1979, 16, 97-103. Spagnolo, P.; Tiecco, M.; Tundo,
A. Martelli, G. J . Chem. Soc., Perkin Trans. 1 1972, 556-559.
(12) The elimination of EtOH most probably occurs by a DDQ-
promoted E2 mechanism favored by the low polarity of the solvent and
by the relatively high temperature.
(15) Brandsma, L.; Verkruijsse, H. Preparative Polar Organometallic
Chemistry 1; Springer-Verlag: Berlin, Germany, 1987; pp 118 and 157.

3366 J . Org. Chem., Vol. 64, No. 9, 1999
Notes
was separated from the slurry, washed with water (250 mL),
and dried over sodium sulfate. After solvent evaporation, the
residual oil was dissolved in benzene (250 mL) together with
DDQ (8.6 g, 38 mmol) and the solution was refluxed for 2 h.
After cooling, the resulting brown mixture was filtered and
washed with ether, and the solvent was evaporated. The crude
product was rapidly passed through a 20 cm column of silica
gel to completely remove DDQ. The resulting 2-alkoxy-4-aryl-
2,3-dihydrobenzofurans were identified by the following spec-
troscopic characteristics and were used for the synthesis of
Y-substituted phenanthrenols without further purification. Ex-
cept for the absorption of the aromatic protons, which depends
on the nature as well as the position of the Y substituent, all of
the 2-alkoxy-4-aryl-2,3-dihydrobenzofurans exhibited nearly
Ch a r t 2
1
identical H NMR spectra characterized by four peaks at δ 5.72
for the 2-methoxy derivative and δ 5.6 for the 2-ethoxy derivative
(X portion of an ABX system, 1 H) and eight peaks at δ 3.5-3.0
(AB portion of an ABX system, 2 H) assigned to three protons
of the dihydrofuran ring, a singlet (3 H) at δ 3.5 (-OCH3 group),
two complex multiplets at δ 4.0 and 3.7 assigned to the two
diastereotopic protons of the 2-OCH2CH3 group, and a triplet
at δ 1.2 (OCH2CH3). All of the products exhibited a strong IR
absorption at 1250-1200 cm-1, typical of an acetalic C-O
stretching. The mass spectrum showed M+ for both 2-methoxy
and 2-ethoxy derivatives, with the latter having 100% relative
intensity. The spectral characteristics of the mixture of 2-alkoxy-
4-(p-tolyl)-2,3-d ih yd r oben zofu r a n are reported as represen-
tative. R ) CH3: 1H NMR (CDCl3) δ 7.36-7.17 (m, 4 H), 7.19
(t, J ) 7.8 Hz, 1 H), 6.99 (d, J ) 7.8, Hz, 1H) 6.88 (d, J ) 7.8
Hz, 1 H), 5.77 (dd, J ) 6.7 and 2.2 Hz, 1 H),3.54 (s, 3 H), 3.43
(dd, J ) 16.5 and 6.5 Hz, 1 H), 3.15 (ddd, J ) 16.5, 5.7, and 2.0
Hz, 1 H), 2.42 (s, 3 H); MS m/z (%) 240 (M+, 100), 225 (67), 209
(74), 208 (70), 195 (38), 181 (45), 165 (67), 152 (33), 89 (15). R )
C2H5: 1H NMR δ 7.36-7.17 (m, 4 H), 7.19 (t, J ) 7.8 Hz, 1 H),
6.99 (d, J ) 7.8 Hz, 1 H) 6.88 (d, J ) 7.8 Hz, 1 H),5.66 (dd, J )
6.5 and 1.8 Hz, 1 H), 4.10-3.89 (m, 1 H), 3.73-3.60 (m, 1 H),
3.43 (dd, J ) 16.5 and 6.5 Hz, 1 H), 3.15 (ddd, J ) 16.5, 5.7, and
2.0 Hz, 1 H), 2.42 (s, 3 H), 1.25 (t, J ) 7.0 Hz, 3 H); MS m/z (%)
254 (M+, 100), 239 (27), 225 (20), 209 (51), 208 (60), 197 (40),
179 (32), 165 (28), 152 (12); IR (mixture of acetal with R ) CH3
and C2H5) 3070, 3031, 2927, 2820, 1605, 1581, 1447, 1237, 1209,
Ch a r t 3
A plausible explanation is that the steric hindrance
between the ortho-hydrogen of the phenyl ring and the
pery-hydrogen of the naphthyl group forces the two
aromatic moieties in the carbocation 17 to lie on two
perpendicular planes, thus moving the reactive sites
away (Chart 3).
Exp er im en ta l Section
1H and 13C NMR spectra were recorded at 300 and 75 MHz,
respectively, using TMS as internal standard. IR spectra were
registered in CHCl3 in the 4000-625 cm-1 range. GLC analyses
were performed on a 30 m SPB-20 capillary column. Mass
spectra were registered at 70 eV. Melting points are uncorrected.
Rea gen ts a n d Solven ts. With the exception of ethyl vinyl
ether, which was distilled before use, all of the organic reagents
(Aldrich), of the highest grade of purity, were used as received.
Ceric ammonium nitrate (Baker 99%) was dried by heating at
80 °C for 1 h before use. Absolute methanol (Carlo Erba, ACS
grade) was used without further purification. Tetrahydrofuran
and diethyl ether were distilled from KOH in the presence of
CuCl and redistilled from sodium wires in the presence of
benzophenone. 3-Aryl-1-[(trimethylsilyl)oxy]cyclohxenes (1) were
prepared in 85-95% of yield by CuI‚LiCl-catalyzed conjugate
addition of the corresponding arylmagnesium bromides to 3-oxo-
cyclohexene in the presence of chlorotrimethylsilane according
to the procedure of Reetz.6 GLC analysis showed a purity grade
of up to 95% in all cases, with the only impurity being
represented by the corresponding regioisomer 3-aryl-3-[(tri-
methylsilyl)oxy]cyclohexene.6 Apart from the specific absorptions
of the substituents on the aromatic ring, all of the 3-aryl-
substituted 1-[(trimethylsilyl)oxy]cyclohexenes exhibited very
similar 1H NMR spectra; that of 3-(m -tolyl)-1-[(tr im eth ylsi-
lyl)oxy]cycloh exen e (CDCl3) is reported as representative: δ
7.2-7.0 (m, 4 H), 4.93 (m, 1 H), 3.44 (m, 1 H), 2.35 (s, 3 H),
2.4-1.3 (m, 6 H), 0.23 (s, 9 H).
Syn th esis of 4-Ar yl-2-a lk oxy-2,3-d ih yd r oben zofu r a n s.
Ceric ammonium nitrate (25 g, 46 mmol) was dissolved in
methanol (250 mL), and to the brown solution were added
powdery calcium carbonate (9.2 g, 92 mmol) and ethyl vinyl ether
(7 mL, 5.3 g, 73 mmol) successively. To the resulting suspension
was added, dropwise and under vigorous stirring, a solution of
3-aryl-1-[(trimethylsilyl)oxy]cyclohexene (19 mmol) dissolved in
ethyl vinyl ether (7 mL, 5.3 g, 73 mmol). The mixture was made
to react at 20 °C until complete decolorization (ca. 30 min) and
then filtered on Celite. Most of the solvent was evaporated at
reduced pressure, the remainder was added in portions to diethyl
ether (250 mL) under vigorous stirring, and the ethereal phase
1110, 1097, 937, 775 cm-1
.
Syn th esis of 4-Ar ylben zo[b]fu r a n s. The same procedure
was employed in the synthesis of 4-arylbenzo[b]furan except that
p-toluenesulfonic acid (1.0 mmol), in addition to DDQ, was added
to the solution of the acetals in benzene, and the mixture was
refluxed for the times reported in Table 2. After the usual
workup, the following products were isolated and identified by
their spectroscopic and analytical characteristics.
4-P h en ylben zofu r a n (oil): 1H NMR (CDCl3) δ 7.62-7.59 (m,
3 H), 7.49-7.42 (m, 3 H), 7.37-7.28 (m, 3 H), 6.90 (dd, J ) 2.1
and 0.8 Hz, 1 H); 13C NMR (CDCl3) δ 155.3, 145.1, 140.1, 135.3,
128.6, 128.4, 127.3, 125.8, 124.4, 122.3, 110.3, 106.0; IR (film)
3119, 3058, 3030, 1601, 1569, 1413, 1248, 1141, 754, 700 cm-1
;
MS m/z (%) 194 (M+, 100), 165 (65), 139 (14), 115 (4), 82 (9).
Anal. Calcd for C14H10O (194.23): C, 85.57; H, 5.19. Found: C,
85.28; H, 5.22.
4-(m -Tolyl)ben zofu r a n (oil): 1H NMR (CDCl3) δ 7.64 (dd,
J ) 2.0 and 0.7 Hz, 1 H), 7.50-7.29 (m, 6 H), 7.20 (bd, J ) 7.3
Hz, 1 H), 6.94 (dd, J ) 2.0 and 0.9 Hz, 1 H), 2.43 (s, 3 H); 13C
NMR δ 155.3, 145.0, 140.0, 138.3, 135.4, 129.2, 128.6, 128.1,
125.8, 125.5, 124.4, 122.3, 110.3, 106.1, 21.5; IR (film) 3120, 3027,
2920, 2854, 1604, 1532, 1472, 1248, 1140, 1037, 756 cm-1; MS
m/z (%) 208 (M+, 100), 178 (15), 165 (8), 152 (2). Anal. Calcd for
C15H12O (208.26): C, 86.51; H, 5.81. Found: C, 86.32; H, 5.71.
4-(p-Tolyl)ben zofu r a n : 1H NMR (CDCl3) δ 7.62 (d, J ) 2.2
Hz, 1 H), 7.52-7.25 (AA′XX′ system, 4 H), 7.45 (dt, J ) 7.5 and
1.1 Hz, 1 H), 7.33 (t, J ) 7.5 Hz, 1 H), 7.28 (d, J ) 7.5 Hz, 1 H),
6.91 (dd, J ) 2.2 and 0.8 Hz, 1 H), 2.40 (s, 3 H); 13C NMR δ
155.3, 145.0, 137.2, 137.1, 135.3, 129.4, 128.3, 125.7, 124.4, 122.2,
110.1, 106.1, 21.2; IR (film) 3122, 3025, 2921, 2854, 1608, 1531,
1475, 1248, 1141, 1036, 756 cm-1; MS m/z (%) 208 (M+, 100),
179 (22), 178 (23), 165 (12), 152 (7), 89 (3). Anal. Calcd for
C15H12O (208.26): C, 86.51; H, 5.81. Found: C, 86.27; H, 5.70.
4-(p-An isyl)ben zofu r a n : mp 90-91 °C; 1H NMR (CDCl3) δ
7.64 (d, J ) 2.0 Hz, 1 H), 7.57-7.00 (AA′XX′ system, 4 H), 7.46
(d, J ) 7.8 Hz, 1 H), 7.34 (t, J ) 7.8 Hz, 1 H), 7.28 (d, J ) 7.8

Notes
J . Org. Chem., Vol. 64, No. 9, 1999 3367
Hz, 1 H), 6.93 (dd, J ) 2.0 and 0.8 Hz, 1 H), 3.86 (s, 3 H); 13C
NMR δ 159.1, 155.3, 145.0, 135.0, 132.6, 129.5, 125.6, 124.4,
122.0, 114.2, 109.9, 106.1, 55.3; IR (CHCl3) 3000, 2597, 2837,
1609, 1534, 1514, 1478, 1247, 1177, 1031, 836 cm-1; MS (70 eV)
m/z (%) 224 (M+, 100), 209 (70), 181 (11), 152 (35), 112 (5). Anal.
Calcd for C15H12O2 (224.26): C, 80.34; H, 5.39. Found: C, 80.09;
H, 5.47.
4-(p-F lu or op h en yl)ben zofu r a n : 1H NMR (CDCl3) δ 7.56 (m,
1 H), 7.50-7.39 (m, 3 H), 7.28-7.04 (m, 4 H), 6.79 (dd, J ) 1.1
and 0.7 Hz, 1 H); 13C NMR δ 162.3 (d, J ) 245 Hz), 155.3, 145.3,
136.1 (d, J ) 5 Hz), 134.2, 129.9 (d, J ) 8.2 Hz), 125.7, 124.5,
122.3, 115.6 (d, J ) 21.3 Hz), 110.5, 105.8; IR (CCl4) 3164-2970,
1610, 1518, 1482, 1220, 1152, 912, 841 cm-1; MS m/z (%) 212
(M+, 100), 183 (67), 165 (2), 157 (8), 133 (4), 106 (5), 91 (8). Elem
anal. Calcd for C14H9FO (212.22): C, 79.23; H, 4.27. Found: C,
78.98; H, 4.29.
4-(m -F lu or op h en yl)ben zofu r a n : 1H NMR (CDCl3) δ 7.71
(d, J ) 2.0 Hz, 1 H), 7.58 (d, J ) 7.9 Hz, 1 H), 7.52-7.30 (m, 5
H), 7.19-7.10 (m, 1 H), 6.98 (dd, 2.0 and 1.1 Hz, 1 H); 13C NMR
δ 163.1 (d, J ) 247 Hz), 155.3, 145.5, 142.3, 134.0, 130.1, (d, J
) 8.5 Hz), 125.7, 115.3 (d, J ) 22.4 Hz), 114.2, (d, J ) 20.9 Hz),
110.9, 105.8; IR (CCl4) 3072-2960, 1613, 1583, 1479, 1419, 1261,
1148, 805, 701 cm-1; MS m/z (%) 212 (M+, 100), 183 (61), 157
(8), 133 (6), 92 (8). Elem anal. Calcd for C14H9FO (212.22): C,
79.23; H, 4.27. Found: C, 79.01; H, 4.12.
137.0, 133.7, 132.7, 130.2, 129.0, 128.8, 127.8, 125.9, 123.9, 122.8,
121.5, 114.5, 110.8, 21.3; IR (CHCl3) 3594 (free OH), 3323
(associated OH), 3081, 3058, 2998-2855), 1623, 1577, 1460,
1261, 1142, 831 cm-1; MS m/z (%) 208 (M+, 100), 179 (22), 165
(33), 152 (9), 104 (8), 95 (7), 76 (8). Anal. Calcd for C15H12
(208.26): C, 86.51; H, 5.81. Found: C, 86.40; H, 5.87.
O
7-Meth oxy-1-p h en a n th r en ol: mp 208-210 °C; 1H NMR
(acetone-d6) δ 9.07 (s, 1 H), 8.63 (d, J ) 9.1 Hz, 1 H), 8.22 (d, J
) 9.1 Hz, 1 H), 8.17 (d, J ) 8.4 Hz, 1 H), 7.72 (d, J ) 9.1 Hz, 1
H), 7.45 (t, J ) 7.8 Hz, 1 H), 7.40 (d, J ) 2.7 Hz, 1 H), 7.26 (dd,
J ) 9.1 and 2.7 Hz, 1 H), 7.04 (d, J ) 7.8 Hz, 1 H), 3.94 (s, 3 H);
13C NMR δ 159.4, 154.6, 134.7, 132.8, 127.9, 125.8, 125.6, 125.4,
122.1, 122.0, 117.8, 114.8, 110.1, 109.3, 55.6; IR (CDCl3) 3620
(free OH), 3400 (associated OH), 3014, 2947, 2881, 1542-1503,
1202, 1046, 928, 715 cm-1; MS m/z (%) 224 (M+, 100), 209 (5),
195 (7), 181 (42), 165 (5), 152 (34), 112 (5). Elem anal. Calcd for
C15H12O2 (224.26): C, 80.34; H, 5.39. Found: C, 80.21; H, 5.45.
6-Meth oxy-1-p h en a n th r en ol: 1H NMR (acetone-d6) δ 9.08,
(bs, 1 H), 8.24 (d, J ) 6.7 Hz, 1 H), 8.20 (s, 1 H), 8.11 (d, J ) 9.1
Hz, 1 H), 7.87 (d, J ) 8.7 Hz, 1 H), 7.72 (d, J ) 9.1 Hz, 1 H),
7.46 (t, J ) 8 Hz, 1 H), 7.01 (d, J ) 8.0 Hz, 2 H), 4.03 (s, 3 H);
MS m/z (%) 224 (M+, 100), 209 (33), 181 (44), 152 (45). Elem
anal. (mixture of 6-OCH3 and 8-OCH3 regioisomers). Calcd for
C15H12O2 (224.26): C, 80.34; H, 5.39. Found: C, 80.20; H, 5.45.
1
8-Meth oxy-1-p h en a n th r en ol: H NMR (acetone-d6) δ 9.13
(bs, 1 H), 8.18 (d, J ) 8.0 Hz, 1 H), 8.30 (d, J ) 8.0 Hz, 1 H),
8.16 (bs, 2 H), 7.56 (t, J ) 8.0 Hz, 1 H), 7.48 (t, J ) 8.0 Hz, 1 H),
7.26 (d, J ) 8.8 Hz, 1 H), 7.26 (d, J ) 8.8 Hz, 1 H), 4.02 (s, 3 H).
IR (mixture of 6-OCH3 and 8-OCH3 regioisomers, CDCl3) 3594
(free OH), 3311 (associated OH), 3071, 3000, 2937, 2837, 1618,
1603, 1577, 1461, 1263, 1135, 841 cm-1; MS m/z (%) 224 (M+,
100), 209 (45), 181 (41), 152 (42). Elem anal. (mixture of 6-OCH3
and 8-OCH3 regioisomers). Calcd for C15H12O2 (224.26): C, 80.34;
H, 5.39. Found: C, 80.19; H, 5.43.
H2SO4-P r om oted Cycliza tion of 2-Alk oxy-4-a r yl-2,3-d i-
h yd r oben zofu r a n s. The above mixtures of 2-alkoxy-4-aryl-2,3-
dihydrobenzofurans were dissolved in 5 mL of methanol and
added, dropwise under vigorous stirring, to 80% aqueous H2-
SO4. After a suitable time (see Table 1) the mixture was
cautiously poured into cold water and extracted with dichlo-
romethane (3 × 50 mL). The organic phase was dried with
sodium sulfate, and the solvent was evaporated. Chromatogra-
phy on silica gel using a 1:1 mixture of petroleum ether-diethyl
ether as the eluent gave pure 5 identified by the following
spectral and analytical characteristics. The (6-Y-/8-Y-) ratios in
5 (Y ) -OCH3, -CH3, and -F) were determined by GLC, MS,
6-F lu or o-1-p h en a n th r en ol: 1H NMR (acetone-d6) δ 10.2 (bs,
1 H), 8.48 (dd, J ) 11.5 and 2.2 Hz, 1 H), 8.17 (d, J ) 8.3 Hz, 1
H), 8.10 (d, J ) 9.1 Hz, 1 H), 7.75 (dd, J ) 9.1 and 5.3 Hz, 1 H),
7.74 (d, J ) 9.1 Hz, 1 H), 7.49-7.42 (m, 2 H), 7.10 (d, J ) 7.6
Hz, 1 H); 13C NMR δ 160.9 (d, J ) 240 Hz), 153.8, 131.3 (d, J )
9.5 Hz), 130.8 (d, J ) 9.5 Hz), 128.6, 127.8, 127.2, 124.5, 122.0,
120.0, 115.5 (d, J ) 22 Hz), 114.0, 110.9, 108.2 (d, J ) 22 Hz);
MS m/z (%) 212 (M+, 80), 183 (100), 157 (7), 133 (3), 91 (2).
8-F lu or o-1-p h en a n th r en ol: 1H NMR (acetone-d6) δ 10.35
(bs, 1 H); 8.52 (d, J ) 8.1 Hz, 1 H), 8.25 (d, J ) 9.7 Hz, 1 H),
8.18 (d, J ) 9.0 Hz), 8.12 (d, J ) 9.1 Hz, 1 H), 7.85 (d, J ) 9.7
Hz, 1 H), 7.76 (d, J ) 9.0 Hz, 1 H), 7.12 (d, J ) 7.6 Hz, 1 H),
7.49-7.42 (m, 2 H); MS m/z (%) 212 (M+, 100), 183 (98), 157 (8),
106 (10), 91 (7); IR (CCl4) (mixture of 6-F and 8-F regioisomers,
6-F/8-F ) 6.4) 3620 (free OH), 3405 (associated OH), 2930, 1605,
1581, 1465, 1274-1207, 1123, 839, 748 cm-1. Elem anal.
1
and H NMR analyses of the regioisomeric mixtures.16 For little
activated or nonactivated aryl groups, 4-arylbenzofuran was also
isolated in 5-20% yield.
1-P h en a n th r en ol: mp 100-102 °C; H NMR (acetone-d6) δ
1
9.10 (bs, 1 H), 8.71 (d, J ) 8.1 Hz, 1 H), 8.25 (d, J ) 8.4 Hz, 1
H), 8.21 (d, J ) 9.3 Hz, 1 H), 7.92 (d, J ) 7.2 Hz, 1 H), 7.74 (d,
J ) 9.1 Hz, 1 H), 7.64-7.56 (m, 1 H), 7.46 (t, J ) 8.0 Hz, 1 H),
7.08 (d, J ) 7.6 Hz, 1 H); 13C NMR δ 154.6, 133.1, 132.6, 131.1,
129.3, 127.9, 127.4, 127.3, 126.2, 124.0, 123.1, 121.5, 114.9, 111.2;
IR (CHCl3) 3591 (free OH), 3307 (associated OH), 3090, 1601,
1577, 1456, 1259, 1110 cm-1; MS m/z (%) 194 (M+, 77), 165 (100),
139 (8), 115 (3), 82 (3). Anal. Calcd for C14H10O (194.23): C,
85.57; H, 5.19. Found: C, 85.31; H, 5.26.
6-Meth yl-1-p h en a n th r en ol: 1H NMR (acetone-d6) δ 8.56 (s,
1 H), 8.27 (d, J ) 8.4 Hz, 1 H), 8.16 (d, J ) 9.1 Hz, 1 H), 8.00
(bs, 1 H), 7.83 (d, J ) 8.1 Hz, 1 H), 7.72 (d, J ) 9.1 Hz, 1 H),
7.45 (d, J ) 8.1 Hz, 1 H), 7.09 (d, J ) 8.4 Hz, 1 H), 2.59 (s, 3 H);
MS m/z (%) 208 (M+, 100), 179 (23), 165 (50), 152 (13), 139 (3).
8-Meth yl-1-p h en a n th r en ol: 1H NMR (acetone-d6) δ 8.62 (d,
J ) 8.2 Hz, 1 H), 8.28 (d, J ) 9.0 Hz, 1 H), 7.96 (d, J ) 9.4 Hz,
1 H), 7.48-7.45 (m, 2 H), 7.53 (t, J ) 7.4 Hz, 1 H), 7.10 (d, J )
7.4 Hz, 1 H), 2.74 (s, 3 H); IR (mixture of 6-CH3 and 8-CH3
regioisomers, 6-CH3/8-CH3 ) 3.4, CDCl3) 3593 (free OH), 3298
(associated OH), 3055, 2999-2854, 1605, 1582, 1281, 1261, 946,
840 cm-1; MS m/z (%) 208 (M+, 100), 179 (24), 165 (49), 152 (12),
139 (3). Anal. Calcd for C15H12O (208.26): C, 86.51; H, 5.81.
Found: C, 86.38; H, 5.96.
(mixture of 6-F and 8-F regioisomers). Calcd for
C
14H9FO
(212.22): C, 79.23; H, 4.27. Found: C, 79.21; H, 4.34.
1
6-Hyd r oxy[1,2-b]n a p h th oth iop h en e: mp 130-132 °C; H
NMR (acetone-d6) δ 9.22 (bs, 1 H), 8.21 (d, J ) 9.0 Hz, 1 H),
7.87 (d, J ) 9.0 Hz, 1 H), 7.71 (d, J ) 5.3 Hz, 1 H), 7.63 (dd, J
) 7.8 and 0.7 Hz, 1 H), 7.56 (d, J ) 5.3 Hz, 1 H), 7.43 (t, J ) 7.8
Hz, 1 H), 7.01 (dd, J ) 7.8 and 0.7 Hz, 1 H); 13C NMR δ 155.1,
139.8, 137.6, 128.3, 127.4, 126.4, 126.1, 122.5, 121.5, 120.2, 115.4,
109.6; IR (CDCl3) 3691 (free OH), 3294 (broad, associated OH),
1623-1585, 1358, 1266, 1108, 863, 839 cm-1; MS m/z (%) 200
(M+, 100), 171 (82), 127 (12), 100 (10). Elem anal. Calcd for
C12H8OS (200.26): C, 71.97; H, 4.02. Found: C, 72.18; H, 4.07.
1
6-Hyd r oxy[2,1-b]n a p h th oth iop h en e: mp 162-164 °C; H
NMR (acetone-d6) δ 9.16 (bs, 1 H), 8.22 (d, J ) 9.0 Hz, 1 H),
8.09 (d, J ) 5.4 Hz, 1 H), 8.00 (s, 1 H), 7.95 (d, J ) 9.0 Hz, 1 H),
7.76 (d, J ) 5.5 Hz, 1 H), 7.44 (t, J ) 7.9 Hz, 1 H), 7.01 (d, J )
7.6 Hz, 1 H); 13C NMR δ 154.7, 138.5, 136.6, 131.7, 127.9, 126.7,
123.3, 122.7, 120.0, 120.0, 115.8, 109.3; IR (CDCl3) 3591 (free
OH), 3310 (associated OH), 1622, 1583, 1264, 1132, 893, 845
cm-1; MS m/z (%) 200 (M+, 93), 171 (100), 145 (3), 127 (10), 85
(4). Elem anal. Calcd for C12H8OS (200.26): C, 71.97; H, 4.02.
Found: C, 72.31; H, 4.10.
7-Meth yl-1-p h en a n th r en ol: 1H NMR (acetone-d6) δ 9.18 (bs,
1 H), 8.48 (d, J ) 8.5 Hz, 1 H), 8.08 (d, J ) 8.1 Hz, 1 H), 8.05 (d,
J ) 8.9 Hz, 1 H), 7.58 (s, 1 H), 7.55 (d, J ) 8.9 Hz, 1 H), 7.34
(dd, J ) 8.4 and 1.6 Hz, 1 H), 7.32 (t, J ) 8.1 Hz, 1 H), 6.94 (d,
J ) 7.6 Hz, 1 H), 2.38 (s, 3 H); 13C NMR (acetone-d6) δ 154.7,
(16) The 1H NMR absorption at the highest δ values of the aromatic
pattern was assigned to H-5. It appears as a singlet for 6-Y-substituted
phenanthrenols (a doublet, J ) 11 Hz, was observed for Y ) F),
whereas a doublet (J ∼ 8 Hz) was observed for the 8-Y regioisomers.
For Y ) CH3, the singlet at δ 2.59 was assigned to 6-CH3 and that at
δ 2.74 to 8-CH3 on the analogy of the CH3 absorptions in â- and
R-methylnaphthalene (δ 2.46 and 2.65, respectively).
1
4-(r-Na p h th yl)ben zofu r a n : H NMR (CDCl3) δ 7.90 (bt, J
) 7.3 Hz, 2 H), 7.82 (dd, J ) 6.2 and 3.2 Hz, 1 H), 7.74 (d, J )
8.5 Hz, 1 H), 7.58-7.30 (m, 7 H), 6.41 (dd, J ) 1.1 and 0.7 Hz,
1 H); 13C NMR δ 154.8, 144.9, 137.8, 134.0, 133.8, 131.7, 128.3,
127.9, 127.8, 127.3, 126.2, 126.0, 125.8, 125.3, 124.3, 124.2, 110.5,

3368 J . Org. Chem., Vol. 64, No. 9, 1999
Notes
106.5; IR (CDCl3) 3051, 1591, 1532, 1414, 1395, 1248, 1139, 1041,
132.9, 131.4, 129.6, 129.3, 129.2, 127.6, 127.3, 124.1, 123.8, 122.6,
783, 761 cm-1; MS m/z (%) 244 (M+, 100), 215 (81), 189 (15),
122.2, 120.5, 115.2, 110.5. Elem anal. Calcd for
(244.29): C, 88.50; H, 4.95. Found: C, 88.42; H, 5.13.
C18H12O
163 (6), 107 (19), 94 (24). Elem anal. Calcd for
C18H12O
(244.29): C, 88.50; H, 4.95. Found: C, 88.17; H, 5.07.
1
Ackn owledgm en t. This work was carried out within
the framework of TMR (Training and Mobility of
Researchers) European Program (Contract No.
ERBFMRXCT970120).
1-Ch r ysen ol: mp 278-280 °C (dec); H NMR (acetone-d6) δ
9.22 (bs, 1 H), 8.93 (d, J ) 8.4 Hz, 1 H), 8.83 (d, J ) 9.2 Hz, 1
H), 8.81 (d, J ) 9.4 Hz, 1 H), 8.50 (d, J ) 9.4 Hz, 1 H), 8.39 (d,
J ) 8.4 Hz, 1 H), 8.08 (d, J ) 8.9 Hz, 2 H), 7.75 (td, J ) 7.7 and
0.8 Hz, 1 H), 7.67 (t, J ) 7.7 Hz, 1 H), 7.55 (t, J ) 7.6 Hz, 1 H),
7.13 (d, J ) 7.6 Hz, 1 H); 13C NMR (acetone-d6) δ 154.7, 133.1,
J O982195N