Silver-catalyzed one-pot synthesis of arylnaphthalene lactones

Article abstract of DOI:10.1021/jo801213m

(Chemical Equation Presented) Arylnaphthalene lignan lactones are valuable natural products with promising anticancer and antiviral properties. In an effort to simplify their synthesis, we investigated a one-pot multicomponent coupling reaction between phenylacetylene, carbon dioxide, and 3-bromo-1-phenyl-1-propyne. After the corresponding 1,6-diyne was generated in situ, cyclization afforded the desired product. The level of regioselectivity was enhanced through the tuning of electronic properties. The use of cinnamyl bromide which led to the formation of a 1,6-enyne intermediate was also studied.

Full text of DOI:10.1021/jo801213m

Silver-Catalyzed One-Pot Synthesis of
Arylnaphthalene Lactones
Nicolas Eghbali, Jennifer Eddy, and Paul T. Anastas*
Center for Green Chemistry and Green Engineering at Yale,
Yale Chemistry Department, 225 Prospect Street,
New HaVen, Connecticut 06520
FIGURE 1. Structure of retrochinensin and daurinol.
paul.anastas@yale.edu
ReceiVed June 05, 2008
those syntheses still, however, rely on a traditional multistep
chemistry and are lacking in terms of atom economy and/or
efficiency.2,4 As an alternative approach, carbon dioxide has
been recognized as a potential valuable C1 carbon source for
the preparation of esters.5 In an effort to utilize CO2 and simplify
the preparation of arylnaphthalene lignan lactones, we investi-
gated a one-pot multicomponent coupling approach. Building
on Inoue’s work,6 it was envisioned that the coupling between
phenylacetylene, carbon dioxide, and 3-bromo-1-phenyl-1-
propyne would generate the corresponding 1,6-diyne which
could further cyclize to the naphthalene core through a [2 + 2
+ 2] cycloaddition.7
Initially, CuI was chosen as the catalyst for the desired
transformation, namely the coupling between phenylacetylene,
carbon dioxide, and 3-bromo-1-phenyl-1-propyne. The major
compound isolated from this reaction was, however, the coupling
product between phenylacetylene and 3-bromo-1-phenyl-1-
propyne. Carbon dioxide was not incorporated into the final
product, even when the pressure was increased.8
Arylnaphthalene lactones were successfully prepared when
the catalyst was switched to silver iodide. 4-phenylnaphtho[2,3-
c]furan-1(3H)-one 2a and 9-phenylnaphtho[2,3-c]furan-1(3H)-
one 3a were obtained in 41% and 25% yield, respectively
(entries 3, Table 1). The ratio of regioisomers was slightly in
favor of compound 2a. The major byproduct of the reaction
was identified as the corresponding symmetrical carbonate.6
Silver complexes AgSbF6 and AgOAc were also effective to
catalyze this reaction (entries 7 and 8, Table 1). Unexpectedly
gold(I) iodide and gold(I) chloride, which have demonstrated
promising catalytic activities for the coupling of phenylacety-
lene, carbon dioxide, and alkyl halides,9 failed to deliver the
desired product.
Arylnaphthalene lignan lactones are valuable natural products
with promising anticancer and antiviral properties. In an
effort to simplify their synthesis, we investigated a one-pot
multicomponent coupling reaction between phenylacetylene,
carbon dioxide, and 3-bromo-1-phenyl-1-propyne. After the
corresponding 1,6-diyne was generated in situ, cyclization
afforded the desired product. The level of regioselectivity
was enhanced through the tuning of electronic properties.
The use of cinnamyl bromide which led to the formation of
a 1,6-enyne intermediate was also studied.
Arylnaphthalene lignan lactones are part of a large family of
phytoestrogen natural products which has received widespread
interest in the last decades due to their biological activities.1
Specific examples include the known antiviral and antitumor
agents daurinol and retrochinensin (Figure 1).2,3 Several syn-
thetic methodologies have been developed to access the
naphthalene core; this includes cross-coupling reactions and
cycloadditions of 1,6-diynes to generate the C-ring.4 Most of
Monitoring the silver-catalyzed reaction by 1H NMR revealed
that the coupling step was completed in less than 2 h while
compound 1a slowly cyclized over 6 h. To verify whether AgI
had any effect on the cyclization, pure samples of the 1,6-diyne
1a were heated in DMAc for 3 h. The results were the same in
(1) Westcott, N. D.; Muir, A. D. Phytochem. ReV. 2003, 2, 401. Suzuki, S.;
Umezawa, T. J. Wood Sci. 2007, 53, 273. Clavel, T.; Dore, J.; Blaut, M. Nutr.
Res. ReV. 2006, 19, 187.
(2) Anastas, P. T.; Stevenson, R. J. Nat Prod. 1991, 54, 1687. Flanagan,
S. R.; Harrowven, D. C.; Bradley, M. Tetrahedron 2002, 58, 5989.
(3) Cow, C.; Leung, C.; Charlton, J. L Chem. Can. J. 2000, 78, 553.
Gordaliza, M.; Garcia, P. A.; Miguel del Corral, J. M.; Castro, M. A.; Gomez-
Zurita, M. A. Toxicon 2004, 44, 441.
(4) Klemm, L. H.; Gopinath, K. W.; HsuLee, D.; Kelly, F. W.; Trod, E.;
McGuire, T. M. Tetrahderon 1966, 22, 1797. For recent reviews, see: Sellars,
J. D.; Steel, P. G. Eur. J. Org. Chem. 2007, 3815. Ward, R. S. Tetrahedron
1990, 46, 5029.
(5) Aresta, M.; Dibenedetto, A Dalton Trans. 2007, 2975. Sakakura, T.; Choi,
J.-C.; Yasuda, H. Chem. ReV. 2007, 107, 2365. Omae, I. Catal. Today 2006,
115, 33.
(6) Fukue, Y.; Oi, S.; Inoue, Y. J. Chem. Soc., Chem. Commun. 1994, 2091.
(7) For reviews on [2 + 2 + 2] cycloaddition, see: Chopade, P. R.; Louie,
J. AdV. Synth. Catal. 2006, 348, 2307. Kotha, S.; Brahmachary, E.; Lahiri, K.
Eur. J. Org. Chem. 2005, 4741. Clayden, J.; Moran, W. J. Org. Biomol. Chem.
2007, 5, 1028. For a recent review on dehydro-Diels-Alder reaction: Wessig,
P.; Mu¨ller, G. Chem. ReV. 2008, 108, 2051.
(8) The coupling reaction (entry 1, Table 1) was also run in a pressure vessel
under a higher carbon dioxide pressure (ca 10 atm); however, the results remain
the same.
6932 J. Org. Chem. 2008, 73, 6932–6935
10.1021/jo801213m CCC: $40.75 2008 American Chemical Society
Published on Web 08/06/2008

TABLE 1. Preparation of Arylnaphthalene Lactones 2a and 3a
TABLE 2. Synthesis of Various Arylnaphthalene Lactones Using
the Silver-Catalyzed One-Pot Multi-component Coupling Reaction
productb
entrya
catalyst
time (h)
T (°C)
1a
2a
3a
1
2
3
4
5
6
7
8
9
CuI
CuBr
AgI
AgI
AgI
AgBr
AgOAc
AgSbF6
AuI
8
8
8
4
48
8
8
8
8
8
100
100
100
100
rt
100
100
100
100
100
<1
<1
41.2
27.9
<1
25.8
14.4
28.2
10.2
23.8
33.2
21.4
20.5
19.8
18.2
10
AuCl
a Reaction conditions: The catalyst (5-10 mol %) was placed under 1
atm of CO2 gas. DMAc (0.6 mL), K2CO3 (1.16 mmol), phenylacetylene
(0.5 mmol), and 3-bromo-1-phenyl-1-propyne (0.5 mmol) were
successively added. b The percentage given refers to the isolated yield.
the absence or presence of a catalyst (e.g., AgI, AuI). As
expected, the cyclization is mainly a thermal process. Running
the reaction at rt over 2 days resulted in the formation of a small
amount of 1a.
Although the regioisomers 2a and 3a could be separated by
chromatography, further investigations were conducted to
determine whether one of the products could be generated
preferentially, if not exclusively.
In an effort to expand the scope of the reaction and address
the problem of regioselectivity, several substituted phenylacety-
lenes were tested under the previous conditions. Results are
presented in Table 2.
As expected, electron-donating groups placed on the aromatic
ring of the phenylacetylene tend to favor the formation of
compounds 2 while electron-withdrawing groups favored the
formation of isomers 3. For instance, 3f was isolated as major
product (entry 5); only a trace of its isomer 2f was observed by
1HNMR (characteristic peaks include 5.16 ppm and 8.48 ppm).
In the opposite situation, product 2e was predominant over 3e
with a ratio close to 4:1.
a Reaction conditions: The catalyst (5-10 mol %) was placed under 1
atm of CO2. DMAc (0.6 mL), K2CO3 (1.16 mmol), phenylacetylene (0.5
mmol), and 3-bromo-1-phenylpropyne (0.5 mmol) were successively
added. The reaction mixture was heated at 100 °C for 8 h. b The
percentage given below each compound refers to the isolated yield;
carbonate byproduct, phenylacetylene dimer, and sometimes a significant
amount of starting reagents were also isolated.
SCHEME 1. Preparation of Compound 5a
Finally, the reactivity of the corresponding 1,6-enyne inter-
mediate 4a was studied. When 3-bromo-1-phenyl-1-propyne was
replaced by the commercially available trans-cinnamyl bromide,
a small quantity of 3a,4-dihydro-9-phenylnaphtho[2,3-c]furan-
1(3H)-one 5a was generated (Scheme 1). Although the reaction
was successful, the major product remained the symmetrical
carbonate resulting from the coupling of cinnamyl bromide and
potassium carbonate. The product was obtained using AgOAc
as catalyst. Again, copper salts were ineffective and no product
could be isolated. Compound 5a very slowly aromatized to 3a
upon exposure to air.
(9) When 1-bromo-2-pentyne was reacted with carbon dioxide and pheny-
lacetylene in the presence of a catalytic amount of gold iodide, the corresponding
coupling product 6a was obtained in 43% yield. No other products were detected;
in particular, no carbonate byproduct was generated. The remainder of the starting
material was recovered at the end of the reaction. This constitutes a significant
improvement in terms of reaction purity.
J. Org. Chem. Vol. 73, No. 17, 2008 6933

TABLE 3. Green Chemistry Metrics for the One-Pot Synthesis of
Arylnaphthalene Lactone 2a
130.0, 132.8, 134.4, 136.2, 140.1, 142.2; HRMS calcd for C18H12O2
(M + H)+ 261.0910, found 261.0907.
8-Methoxy-4-phenylnaphtho[2,3-c]furan-1(3H)-one (2b): 1H
NMR (500 MHz, CDCl3) δ 4.00 (s, 3H), 5.17 (s, 2H), 6.84 (d, 1H,
J ) 7.15 Hz), 7.28 (m, 3H), 7.44 (m, 4H), 8.90 (s, 1H); 13C NMR
(125 MHz, CDCl3) δ 55.8, 69.5, 104.5, 118.0, 121.4, 122.0, 126.4,
128.3, 128.9, 129.2, 129.3, 133.5, 135.9, 136.2, 139.3, 157.2, 171.5;
HRMS calcd for C19H14O3 (M + H)+ 291.1016, found 291.1015.
9-(2-Methoxyphenyl)naphtho[2,3-c]furan-1(3H)-one (3b): 1H
NMR (500 MHz, CDCl3) δ 3.63 (s, 3H), 5.38 (s, 2H), 7.04 (m,
2H), 7.13 (d, 1H, J ) 8.35 Hz), 7.42 (m, 4H), 7.55 (t, 1H, J ) 7.3
Hz), 7.71 (d, 1H, J ) 9.4 Hz), 7.82 (s, 1H), 7.88 (d, 1H, J ) 8.35
Hz); 13C NMR (125 MHz, CDCl3) δ 56.2, 68.7, 111.5, 120.6, 120.8,
123.9, 127.0, 128.3, 128.5, 128.9, 130.5, 131.7, 132.1, 133.4, 136.8,
139.2, 140.6, 157.9, 169.9; HRMS calcd for C19H14O3 (M + H)+
291.1016, found 291.1011.
general and green chemistry metrics11
% yield
41
no. of steps
1
no. of catalysts
no. of solvents
type of solvent
E-factor
% atom economy
% effective mass yield
% carbon efficiency
% reaction mass efficiency
1
1
organic
19.41
76.20
7.85
23.06
11.18
From a green chemistry perspective, the use of an alkyl halide
constitutes the major shortcoming of the approach.10 Switching
to the corresponding alcohol (e.g., 3-phenyl-2-propyn-1-ol) is
a more desirable alternative and is currently under investigation.
The current strategy nevertheless remained an improvement as
the E-factor is significantly reduced compared to the traditional
multistep synthesis (Table 3).
In conclusion, we investigated the three-component coupling
reaction between phenylacetylene, carbon dioxide, and 3-bromo-
1-phenyl-1-propyne. Under the reaction conditions, the 1,6-diyne
generated in situ undergoes a subsequent [2 + 2 + 2] cyclization
affording the corresponding arylnaphthalene lactones. The
regioselectivity was enhanced by tuning the electronic properties
of the substrates.
6-Methoxy-8-methyl-4-phenylnaphtho[2,3-c]furan-1(3H)-
1
one (2c): H NMR (500 MHz, CDCl3) δ 2.81 (s, 3H), 3.76 (s,
3H), 5.24 (s, 2H), 6.93 (s, 1H), 7.14 (s, 1H), 7.41 (d, 2H, J ) 7.8
Hz), 7.50 (m, 3H), 8.64 (s, 1H); 13C NMR (125 MHz, CDCl3) δ
20.3, 55.5, 69.8, 102.7, 120.7, 120.8, 123.0, 128.7, 129.5, 129.7,
133.3, 137.0, 137.7, 139.0, 139.9, 160.1, 172.2; HRMS calcd for
C20H16O3 (M + H)+ 305.1172, found 305.1171.
9-(4-Methoxy-2-methylphenyl)naphtho[2,3-c]furan-1(3H)-
1
one (3c): H NMR (500 MHz, CDCl3) δ 1.87 (s, 3H), 3.82 (s,
3H), 5.40 (s, 2H), 6.81 (d, 1H, J ) 9.5 Hz), 6.86 (s, 1H), 7.00 (d,
2H, J ) 8.45 Hz), 7.40 (t, 1H, J ) 6.35, 8.45 Hz), 7.57 (t, 2H, J
) 10.55, 9.5 Hz), 7.83 (s, 1H), 7.90 (d, 1H, J ) 7.4 Hz); 13C NMR
(125 MHz, CDCl3) δ 20.5, 55.6, 68.7, 111.5, 115.8, 120.4, 121.0,
127, 127.2, 128.3, 128.5, 129.0, 131.1, 133.5, 136.7, 138.4, 140.5,
142.1, 160.0, 170.0; HRMS calcd for C20H16O3 (M + H)+ 305.1172,
found 305.1170.
Experimental Section
5,7,8-Trimethyl-4-phenylnaphtho[2,3-c]furan-1(3H)-one (2d):
1H NMR (500 MHz, CDCl3) δ 1.84 (s, 3H), 2.31 (s, 3H), 2.7 (s,
3H), 5.02 (s, 2H), 7.2 (m, 2H), 7.4 (m, 3H), 8.6 (s, 1H); 13C NMR
(125 MHz, CDCl3) δ 20.3, 20.5, 22.0, 70.5, 121.3, 123.6, 128.1,
129.1, 131.4, 131.7, 133.7, 134.4, 135.3, 139.3, 141.1, 141.4, 172.2;
HRMS calcd for C21H18O2 (M + H)+ 303.1379, found 303.1378.
9-(2,3,5-Trimethylphenyl)naphtho[2,3-c]furan-1(3H)-one (3d):
1H NMR (500 MHz, CDCl3) δ 1.82 (s, 3H), 2.19 (s, 3H), 2.27 (s,
3H), 5.38 (s, 1H), 6.84 (s, 1H), 7.08 (s, 1H), 7.39 (t, 1H, J ) 6.7,
8.35 Hz), 7.57 (m, 2H), 7.82 (s, 1H), 7.89 (d, 1H, J ) 8.35 Hz);
13C NMR (125 MHz, CDCl3) δ 19.6, 19.7, 20.0, 68.7, 120.3, 120.7,
127.0, 128.4, 128.5, 129.0, 131.2, 131.7, 132.0, 133.4, 133.9, 136.7,
137.0, 140.5, 142.6, 170.0; HRMS calcd for C21H18O2 (M + H)+
303.1379, found 303.1379.
5,7-Dimethoxy-4-phenylnaphtho[2,3-c]furan-1(3H)-one (2e):
1H NMR (500 MHz, CDCl3) δ 3.37 (s, 3H), 3.89 (s, 3H), 4.98 (s,
2H), 6.49 (d, 1H, J ) 3.95 Hz), 6.87 (d, 1H, J ) 2.5 Hz), 7.15 (d,
2H, J ) 7.7 Hz), 7.30 (m, 3H), 8.24 (s, 1H); 13C NMR (125 MHz,
CDCl3) δ 55.7, 55.9, 70.3, 100.5, 102.3, 123.2, 124.0, 125.0, 127.2,
128.0, 133.8, 137.2, 138.5, 140.7, 158.4, 159.0, 171.8; HRMS calcd
for C20H16O4 (M + H)+ 321.1121, found 321.1119.
6,8-Dimethoxy-9-phenylnaphtho[2,3-c]furan-1(3H)-one (3e):
1H NMR (500 MHz, CDCl3) δ 3.75 (s, 6H), 5.38 (s, 2H), 6.45 (d,
2H, J ) 2.05 Hz), 6.54 (t, 1H, J ) 2.4 Hz), 7.43 (t, 1H, J ) 7.75,
6.6 Hz), 7.57 (t, 1H, J ) 7.75 Hz), 7.81 (d, 1H, J ) 8.8 Hz), 7.84
(s, 1H), 7.89 (d, 1H, J ) 8.85 Hz); 13C NMR (125 MHz, CDCl3)
δ 55.8, 68.5, 100.8, 108.7, 120.3, 120.7, 127.2, 128.4, 128.6, 129.1,
133.1, 136.6, 136.8, 140.5, 142.4, 160.8, 169.7; HRMS calcd for
C20H16O4 (M + H)+ 321.1121, found 321.1122.
Representative Procedure for the Silver-Catalyzed
One-Pot Synthesis of Arylnaphthalene Lactones 2a and 3a. In
a round-bottom flask fitted with a condenser and a stir bar was
introduced the catalyst AgI (23.4 mg, 0.1 mmol) under CO2
atmosphere (1 atm). After addition of 1 mL of DMAc, potassium
bicarbonate (160.1 mg, 1.16 mmol), phenylacetylene (0.11 mL, 1
mmol), and 3-bromo-2-phenyl-1-propyne (195 mg, 1 mmol), the
mixture was placed in an oil bath at 100 °C. After 8 h, the reaction
mixture was cooled and extracted with ethyl acetate to afford a
2:1 mixture of products 2a and 3a. The products were purified by
column chromatography using 1:5 ethyl acetate/hexane.
3-Phenyl-2-propyn-1-ol phenylpropiolate (1a): 1H NMR (500
MHz, CDCl3) δ 4.99 (s, 2H), 7.29 (m, 6H), 7.41 (m, 3H), 7.53 (d,
2H, J ) 7.05 Hz); 13C NMR (125 MHz, CDCl3) δ 54.2, 80.0, 82.0,
87.3, 87.4, 119.3, 122.0, 127.5, 128.3, 128.6, 128.7, 128.9, 130.8,
132.0, 133.1, 153.3; HRMS calcd for C18H12O2 (M + H)+ 261.0910,
found 261.09093.
1
4-Phenylnaphtho[2,3-c]furan-1(3H)-one (2a): H NMR (500
MHz, CDCl3) δ 5.20 (s, 2H), 7.32 (d, 2H, J ) 7.55 Hz), 7.49 (m,
5H), 7.74 (d, 1H, J ) 7.55 Hz), 8.03 (d, 1H, J ) 6.45 Hz), 8.46 (s,
1H); 13C NMR (125 MHz, CDCl3) δ 69.5, 123.0, 125.9, 126.4,
126.7, 128.4, 129.0, 129.3, 130.1, 133.7, 134.1, 134.9, 135.8, 138.4,
171.2; HRMS calcd for C18H12O2 (M + H)+ 261.0910, found
261.09063.
1
9-Phenylnaphtho[2,3-c]furan-1(3H)-one (3a): H NMR (500
MHz, CDCl3) δ 5.39 (s, 2H), 7.32 (m, 2H), 7.42 (t, 1H, J ) 7.85,
8.35 Hz), 7.47 (m, 3H), 7.58 (t, 1H, J ) 7.45 Hz), 7.74 (d, 1H, J
) 8.80 Hz), 7.84 (s, 1H), 7.90 (d, 1H, J ) 8.35 Hz); 13C NMR
(125 MHz, CDCl3) δ 68.1, 120.2, 126.7, 128.0, 128.1, 128.3, 128.6,
4-(3,5-Bis(trifluoromethyl)phenyl)naphtho[2,3-c]furan-1(3H)-
one (3f): 1H NMR (500 MHz, CDCl3) δ 0.43 (s, 2H), 7.51 (t, 1H,
J ) 8.2 Hz), 7.58 (d, 1H, J ) 8.15 Hz), 7.64 (t, 1H, J ) 8.1, 7.45
Hz) 7.80 (s, 2H), 7.95 (s, 2H), 7.97 (s, 1H); 13C NMR (125 MHz,
CDCl3) δ 68.9, 121.0, 122.2, 127.2, 128.2, 129.0, 129.5, 131.0,
131.7, 132.0, 132.5, 136.8, 136.9, 138.4, 140.5, 169.6; HRMS calcd
for C20H10F6O2 (M + H)+ 397.0657, found 397.0642.
(10) Anastas, P. T.; Warner, J. C. Green Chemistry: Theory and Practice;
Oxford University Press: New York, 1998. Anastas, P.; Horvath, I. T. Chem.
ReV. 2007, 107, 2169.
(11) For a review on the green chemistry metrics, see: Constable, D. J. C.;
Curzons, A. D.; Cunningham, V. L. Green Chem. 2002, 4, 521. Andraos, J.
Org. Process Res. DeV. 2005, 9, 149.
6934 J. Org. Chem. Vol. 73, No. 17, 2008

4-(Naphthalen-1-yl)-naphtho[2,3-c]furan-1(3H)-one (2g): 1H
NMR (500 MHz, CDCl3) δ ABq system 4.90 (d, 1H, J ) 14.85
Hz), 5.09 (d, 1H, J ) 14.85 Hz), 7.14 (d, 1H, J ) 8.95 Hz), 7.27
(t, 1H, J ) 8, 6.95 Hz), 7.45 (m, 6H), 7.92 (d, 1H, J ) 9.95 Hz),
7.96 (d, 1H, J ) 8 Hz), 8.08 (d, 1H, J ) 7.95 Hz), 8.55 (s, 1H);
13C NMR (125 MHz, CDCl3) δ 69.9, 123.5, 125.6, 126.0, 126.7,
126.8, 127.3, 128.0, 129.1, 129.5, 130.6, 132.0, 132.8, 133.6, 134.0,
134.3, 136.2, 140.1, 171.6; HRMS calcd for C22H14O2 (M + H)+
311.1066, found 311.1067.
3.00 (m, 1H), 3.40 (m, 1H), 3.98 (t, 1H, J ) 9.8 Hz), 4.67 (t, 1H,
J ) 12.25, 9.85 Hz), 6.89 (d, 1H, J ) 8.8 Hz), 7.11 (t, 1H, J )
7.95, 7.2 Hz), 7.23 (m, 4H), 7.37 (m, 3H); 13C NMR (125 MHz,
CDCl3) δ 33.4, 36.0, 71.6, 122.5, 127.7, 128.2, 128.4, 128.9, 129.5,
130.2, 134.7, 135.8, 136.3, 147.7, 168.6; HRMS calcd for C18H14O2
(M + H)+ 263.1066, found 263.1066.
Acknowledgment. This research was supported by Yale
University. The authors are grateful to Dr. Tukiet T. Lam for
mass spectroscopy analysis.
1
7-Phenylphenanthro[2,3-c]furan-8(10H)-one (3g): H NMR
(500 MHz, CDCl3) δ 5.47 (s, 2H), 7.34 (m, 2H), 7.49 (m, 3H),
7.65 (m, 4H), 7.85 (d, 1H, J ) 8.1 Hz), 8.71 (d, 1H, J ) 8.05 Hz),
8.73 (s, 1H); 13C NMR (125 MHz, CDCl3) δ 67.4, 114.2, 119.7,
122.5, 123.9, 126.2, 126.8, 127.1, 127.3, 127.3, 127.8, 128.6, 129.1,
130.4, 131.7, 133.6, 133.8, 140.7, 141.1, 168.7; HRMS calcd for
C22H14O2 (M + H)+ 311.1066, found 311.1067.
Supporting Information Available: Additional experimental
procedures, compound characterizations, and details for the
green chemistry metrics. This material is available free of charge
via the Internet at http://pubs. acs. org.
9-Phenyl-3a,4-dihydronaphtho[2,3-c]furan-1(3H)-one (5a).
1HNMR (500 MHz, CDCl3) δ 2.82 (t, 1H, J ) 19.60, 14.75 Hz),
JO801213M
J. Org. Chem. Vol. 73, No. 17, 2008 6935