A simple approach to highly functionalized benzo[b]furans from phenols and aryl iodides via aryl propargyl ethers

Article abstract of DOI:10.1016/j.tetlet.2008.04.150

A variety of mono- and disubstituted phenols are alkylated with propargyl bromide to give phenyl 2-propynyl ethers, which were further coupled with aryl iodides under Sonogashira reaction conditions to give 3-phenoxy-1-aryl-1-propyne derivatives. The latt

Full text of DOI:10.1016/j.tetlet.2008.04.150

Tetrahedron Letters 49 (2008) 4260–4264
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A simple approach to highly functionalized benzo[b]furans from phenols
and aryl iodides via aryl propargyl ethers
V. S. Prasada Rao Lingam a,b, Ramanatham Vinodkumar a, Khagga Mukkanti b,
,
*
Abraham Thomas a, Balasubramanian Gopalan a
a Glenmark Research Centre, Medicinal Chemistry Division, MIDC Mahape, Navi Mumbai 400 709, India
b Institute of Science and Technology, Jawaharlal Nehru Technological University, Kukatpally, Hyderabad 500 072, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A variety of mono- and disubstituted phenols are alkylated with propargyl bromide to give phenyl 2-pro-
pynyl ethers, which were further coupled with aryl iodides under Sonogashira reaction conditions to give
3-phenoxy-1-aryl-1-propyne derivatives. The latter compounds underwent an initial Claisen rearrange-
ment followed by ring closure to give functionalized benzo[b]furans in moderate to good yields.
Ó 2008 Elsevier Ltd. All rights reserved.
Received 27 February 2008
Revised 22 April 2008
Accepted 26 April 2008
Available online 1 May 2008
Keywords:
Aryl propargyl ethers
Benzo[b]furans
Sonogashira coupling
Claisen rearrangement
Benzo[b]furan structural motifs are present in several pharma-
ceuticals1 and natural products.2 Functionalized benzo[b]furans
also serve as versatile synthetic intermediates. Several of these
intermediates are used for the synthesis of molecules having useful
biological properties such as the Tachykinin NK1 receptor antago-
nist,3 Angiotensin-II receptor antagonists,4 calcium channel block-
ers5 and 5-lipoxygenase inhibitors.6 Traditional methods7 for the
synthesis of benzo[b]furans involve reaction of 2-halophenols with
a terminal alkyne under palladium catalysis, wherein the interme-
diate is a 2-alkynylphenol derivative as shown in Scheme 1. Even
today, this is one of the most widely used approaches for the
synthesis of benzo[b]furans.
zation of 2-acyloxy-1-bromomethylarenes9 with Cr(II)Cl2/BF3ÁOEt2,
cyclization of arylketoximes,10 cyclization of aryloxycarbonyl11
compounds, intramolecular [2+2] cycloaddition of 2-acyloxyacetic
acids,12 reaction of p-benzoquinones with 1-(N-methylanilino)-1-
methyl-thioester,13 microwave irradiation of [{2-(aryloxy)propa-
noyl}-(cyano/ethoxy-carbonyl)-methylene]triphenylphosphoranes14
and photochemical reaction of phenyliodoniumphenolate with
alkynes.15 However, all the above methods suffer the disadvantage
of either lack of commercial availability of the intermediate pre-
cursors or require several steps for precursor synthesis.
In this Letter, we report a convenient and very general proce-
dure for the synthesis of highly functionalized benzo[b]furans from
A major limitation of this approach is the lack of flexibility in
terms of substituents on the carbocyclic part of benzofuran nucleus
and only 2-substituted benzofurans are generally accessible by this
approach. Moreover, limited commercial availability of substituted
2-halophenols further limit the scope of this approach. Other less
popular approaches for the synthesis of benzo[b]furans include
cyclization of vinylic phenols8 under palladium catalysis, cycli-
R3
R3
R2
R2
HC CHCH2Br
K2CO3/THF
CH
OCH2C
OH
R1
2
R1
1
ArI (3)
Pd(0) / CuI, Et3N
R2
R2
Pd(0)
R3
X
OH
R3
R2
Ar
O
R2
R1
O
R2
R1
R1
CsF, N,N-DEA
OH
CH3
OCH2C
C Ar
Scheme 1. Literature method for the synthesis of benzo[b]furans.7
R1
R1
5
4
* Corresponding author. Tel.: +91 9963909007; fax: +91 40 23155413.
E-mail address: kmukkanti@gmail.com (K. Mukkanti).
Scheme 2. General method for the synthesis of benzo[b]furan.
0040-4039/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2008.04.150

V. S. Prasada Rao Lingam et al. / Tetrahedron Letters 49 (2008) 4260–4264
4261
Table 1
Syntheses of benzo[b]furans 5 from phenyl propargyl ethers 2 and aryl iodides 3 via 3-phenoxy-1-aryl-1-propyne intermediates 4
Entry
Ether (2)
Iodide (3)
Propyne ether (4)
Yield (%)
Benzo[b]furan (5)
Time (h)
10
Yield (%)
65
Ι
O
O
1
90
CH3
O
2a
5a
4a
3a
CF
3
CF3
Ι
O
2
3
2a
91
96
10
16
64
71
CF
3
CH
3
3b
O
O
4b
5b
CH3
CH3
Ι
O
O
H C
3
CH3
H3C
CH3
3c
4c
2b
CH3
5c
H CO
3
OCH3
O
H CO
3
Ι
Ι
4
5
95
94
9
8
68
70
O
O
F
CH
3
O
F
F
3d
2c
5d
F
4d
4e
H3CO
OCH3
2c
OCH
3
CH3
3e
O
5e
F
OCH3
OCH
3
Ι
O
O
6
2c
95
8
70
OCH
F
3
CH3
3f
O
4f
5f
F
F3C
O
CF3
F C
3
Ι
Ι
F
F
7
8
96
90
4
2
73
75
CH
3
O
F
F
3g
5g
NO
F
2d
4g
F
2
O
NO2
O
Cl
NO
Cl
2
Cl
CH
3
Cl
3h
O
Cl
4h
2e
Cl
5h
COCH3
O
CH3
O
Ι
Ι
O
Cl
Cl
Cl
O
CH
9
91
85
3
70
58
Cl
Cl
CH3
3
3i
3j
O
O
2f
4i
4j
5i
Cl
F
F
O
O
10
0.5
O2N
O N
F
2
CH
3
2g
5j
NO
2
(continued on next page)

4262
V. S. Prasada Rao Lingam et al. / Tetrahedron Letters 49 (2008) 4260–4264
Table 1 (continued)
Entry
11
Ether (2)
Iodide (3)
Propyne ether (4)
Yield (%)
80
Benzo[b]furan (5)
Time (h)
0.5
Yield (%)
55
O
Ι
2g
2g
CH
O N
3
2
O
3k
NO
5k
4k
2
S
S
S
O
Ι
12
13
83
88
0.5
50
65
CH
3
O2N
O
O
3l
NO
5l
4l
2
CH
3
CH
3
O
O
3c
1
NC
NC
NC
NC
CH
3
2h
4m
5m
CN
O
14
2h
2h
3k
90
1
60
CH
3
O
O
CN
CN
4n
4o
4p
5n
S
S
O
15
16
17
18
3l
83
87
89
95
1
2
2
2
67
62
75
77
CH
3
5o
O
O
3a
3a
3a
OHC
OHC
CH
3
O
2i
5p
CHO
O
O
EtO C
2
CH
EtO2C
3
O
CO Et
2j
5q
2
4q
O
O
OHC
H3CO
CH3
H CO
3
CHO
O
OCH3
CHO
2k
5r
4r
inexpensive and readily available substituted phenols and aryl
iodides. As outlined in Scheme 2, the phenols 1 underwent smooth
alkylation16 with propargyl bromide in the presence of potassium
carbonate in tetrahydrofuran to give phenyl propargyl ethers
2a–k in quantitative yields. The alkynes 2a–k were arylated with
various aryl iodides 3a–l under Sonogashira-reaction conditions17
to give aryl propargyl ethers 4a–r in 80–96% isolated yields as
shown in Table 1. The coupling reactions for entries 1–9 were car-
ried out using catalytic amounts of Pd (PPh3)2Cl2 (0.01 equiv) and
copper (I) iodide (0.03 equiv) using triethylamine18 serving as a
base and solvent. In the case of entries 10–18, dimethyl sulfoxide
(DMSO) was used as the solvent with 1.5 equiv of triethylamine
as a base, a catalytic amount of Pd(PPh3)4 (0.01 equiv) and copper
(I) iodide (0.03 equiv) to improve the homogeneity of the reaction
mixture and thereby the yield of the reaction. Where electron-
withdrawing groups such as nitro, cyano, ester, aldehyde or keto
were present on the substrates, the use of excess triethylamine
reduced the yield in the Sonogashira19-coupling reaction. The best
yields were obtained when 1.5 equiv of triethylamine in DMSO
were employed (entries 10–18).
Attempted Claisen rearrangement20 (Table 1, entry 1) by pyro-
lysis of 3-phenoxy-1-phenyl-1-propyne 4a at 180 °C in the absence

V. S. Prasada Rao Lingam et al. / Tetrahedron Letters 49 (2008) 4260–4264
4263
R3
R1
R3 Ar
References and notes
R2
R2
[3,3]-shift
C
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Heterocycles 1989, 29, 1255–1261; (e) Yue, D.; Larock, R. C. J. Org. Chem. 2002,
67, 1905–1909; (f) Larock, R. C.; Yum, E. K.; Doty, M. J.; Sham, K. K. C. J. Org.
Chem. 1995, 60, 3270–3271; (g) Bernini, R.; Caccha, S.; Salve, I. D.; Fabriza, G.
Synthesis 2007, 6, 873–882.
8. (a) Hosokawa, T.; Maeda, K.; Koga, K.; Moritani, I. Tetrahedron Lett. 1973, 14,
739–740; (b) Casiraghi, G.; Casnati, G.; Pugli, G.; Sartori, G.; Terenghi, C.
Synthesis 1977, 122–123; (c) Hosokawa, T.; Miyagi, S.; Murahashi, S.-I.; Sonodo,
A. J. Chem. Soc., Chem. Commun. 1978, 687–688.
9. (a) Ledoussal, B.; Gorgues, A.; Le Coq, A. J. Chem. Soc., Chem. Commun. 1986,
171–172; (b) Ledoussal, B.; Gorgues, A.; Le Coq, A. Tetrahedron 1987, 43, 5841–
5852.
10. (a) Sheradsky, T. J. Heterocycl. Chem. 1967, 4, 413–414; (b) Kaminsky, D.;
Shavel, J. J.; Meltzer, R. I. Tetrahedron Lett. 1967, 8, 859–861; (c) Mooradian, A.;
Dupoint, P. E. Tetrahedron Lett. 1967, 8, 2867–2870; (d) Bender, D. R.; Hearst, J.
E.; Rapoport, H. J. Org. Chem. 1979, 44, 2176–2180; (e) Alemagna, A.; Baldoli, C.;
Buttero, P. D.; Licandro, E.; Maiorana, S. J. Chem. Soc., Chem. Commun. 1985,
417–418.
11. (a) Tarbell, D. S.; Carman, R. M.; Chapman, D. D.; Cremer, S. E.; Cross, A. D.;
Huffman, K. R.; Kunstmann, M.; McCorkindale, N. J.; McNally, J. G.; Rosowsky,
A.; Varino, F. H. L.; West, R. L. J. Am. Chem. Soc. 1961, 83, 3096–3113; (b)
Macleod, J. K.; Worth, B. R. Tetrahedron Lett. 1972, 13, 237–240.
12. (a) Horaguchi, T.; Matsuda, S.; Tanemura, K.; Suzuki, T. J. Heterocycl. Chem.
1987, 24, 965–969; (b) Brady, W. T.; Gu, Y.-Q. J. Heterocycl. Chem. 1988, 25,
969–971.
13. Takahata, T.; Anazawa, A.; Moriyama, K.; Yamazaki, Y. J. Chem. Soc., Perkin
Trans. 1 1987, 1501–1504.
14. Rama Rao, V. V. V. N. S.; Reddy, G. V.; Yadla, R.; Narsaiah, B.; Rao, P. S. Arkivoc
2005, iii, 211–220.
15. Spyroudis, S. P. J. Org. Chem. 1986, 51, 3453–3456.
16. Ishii, H.; Ishikawa, T.; Takeda, S.; Ueki, S.; Suzuki, M. Chem. Pharm. Bull. 1992,
40, 1148–1153.
CH2
C Ar
OCH2C
Ar
O
R1
4
A
R3
R1
R3 Ar
R2
R2
ring closure
C
CH3
O
CH2
OH
R1
5
B
Scheme 3. Proposed mechanism for the formation of benzo[b]furans.
of solvent resulted in a tarry material and no identifiable product
was formed in the mixture. Reaction of 4a in polyethylene glycol21
(PEG) up to 220 °C resulted in recovery of the starting material.
Reactions using Hg (OCOCF3)2 in chloroform did not proceed at
all and the starting material remained intact even after 12 h of
reflux.22 Reactions under Lewis acid (AgBF4)23 catalysis resulted
in a complex mixture. The caesium chloride (CsCl)24 catalyzed
reaction in N,N-diethylaniline (N,N-DEA) resulted in an unidentifi-
able less polar product along with the unreacted alkyne ether 4a.
The reaction catalyzed by caesium fluoride (CsF) in N,N-DEA25
resulted in the formation of the desired benzo[b]furan 5a in a
65% isolated yield.
The generality of this approach was studied using selectively
substituted phenols 1 and aryl iodides 3 as shown in Table 1. To
our delight, we found that the present method tolerated a wide
range of substituents on both of the aryl rings. In addition to this,
it was also observed that electron deficient phenols showed excel-
lent reactivity and formed products in shorter reaction times (en-
tries 10–18), whilst prolonged reaction times were required for
electron rich phenols (entries 1–9). Even sterically demanding,
ortho-substituted aryl iodides (entries 4 and 7) delivered good
yields of benzo[b]furans 5 under these conditions.
The general transition states involved in the thermolytic Claisen
rearrangement and cyclization of aryl prop-2-ynyl ether 4 are
shown in Scheme 3.23,24 Intermediate 4 on [3,3]-sigmatropic rear-
rangement gives the allenyl dienone A, which on enolization gives
thermodynamically more stable phenol B. The phenoxide anion
formed in the presence of caesium fluoride would cyclize to
benzo[b]furan 5. No trace of dihydro-2H-1-benzopyran was de-
tected in all the cases studied.21
In conclusion, we have developed a novel three-step procedure
for the synthesis of highly functionalized 2-methyl-3-aryl-
benzo[b]furans from commercially available, suitably functional-
ized phenols and substituted aryl iodides. The present method
can be utilized to synthesize various functionalized analogues of
Isoparvifuran,2b,c a known anti-fungal agent. The present method
has several advantages: simple reaction conditions and experimen-
tal simplicity combined high functional group tolerance. We
believe that this methodology will be a valuable addition to the
existing methods in the field of benzo[b]furan synthesis which
allows the preparation of annelated benzofuran analogues for bio-
logical screening. Further work is in progress towards generating
synthetic routes for the recently isolated and naturally occurring
benzo[b]furan compounds from Dalbergia Cochinchinensis Pierre
(Leguminosae)2c,26 and the details will be published elsewhere.
17. (a) Sonagashira, K.; Tohda, Y.; Hagihara, N. Tetrahedron Lett. 1975, 16, 4467–
4470; (b) Chinchilla, R.; Nájera, C. Chem. Rev. 2007, 107, 874–922. and
references cited therein.
18. Typical procedure for the Sonogashira coupling: Method A for compounds 4a–i: To
a
solution of 2f (1.0 g, 4.974 mmol) and 4-iodoacetophenone 3i (1.23 g,
4.999 mmol) and Pd(PPh3)2Cl2 (35 mg, 0.049 mmol) in triethylamine (5.0 mL)
was added CuI (28.5 mg, 0.149 mmol) under nitrogen atmosphere. The
a
reaction mixture was stirred at room temperature for 3 h. The mixture was
diluted with EtOAc (50 mL), washed with water (3 Â 50 mL) and dried over
anhydrous Na2SO4. The residue obtained after evaporation of the solvent was
purified by silica gel column chromatography using 20% EtOAc in petroleum
ether to give 1.45 g (91%) of 4i as an off-white solid; mp 80–83 °C; IR (KBr)
3069, 2288, 1678, 1585, 1482, 1381, 1265, 832 cmÀ1 1H NMR (300 MHz,
;
CDCl3) d 2.58 (s, 3H), 4.99 (s, 2H), 6.92 (dd, J = 1.8, 6.3 Hz, 1H), 7.13 (d,
J = 1.8 Hz, 1H), 7.28 (d, J = 8.1 Hz, 1H), 7.48 (d, J = 8.1 Hz, 2H), 7.87 (d, J = 8.1 Hz,
2H); 13C NMR (75 MHz, CDCl3) d 26.6, 57.7, 85.6, 87.3, 114.7, 121.6, 122.2,
126.4 (2C), 128.0, 130.8, 131.8 (2C), 132.7, 136.5, 153.3, 196.9; MS m/z (+
cAPCI): 319.16 (M)+; Anal. Calcd for C17H12Cl2O2: C, 63.97; H, 3.79. Found: C,
63.94; H 3.83.
Acknowledgement
19. Method B: For entries 10–18, to a solution of compounds 2g–k (5 mmol) in dry
DMSO (20 mL) was added iodide (3) (5 mmol), (PPh3)4Pd (0.05 mmol) and CuI
(0.15 mmol) followed by triethylamine (7.5 mmol). The reaction mixture was
The authors thank Glenmark Pharmaceuticals Limited for grant-
ing permission to carry out the present research work.

4264
V. S. Prasada Rao Lingam et al. / Tetrahedron Letters 49 (2008) 4260–4264
stirred at room temperature for 6–8 h under a nitrogen atmosphere. The
J = 7.8 Hz, 1H), 7.44 (d, J = 8.4 Hz, 2H); MS m/z (+ cAPCI): 257.43 (M+H)+; Anal.
Calcd for C16H13FO2: C, 74.99; H, 5.11. Found C, 75.05; H 5.07.
reaction mixture was diluted with EtOAc (50 mL) and washed with water
(3 Â 50 mL) followed by brine (20 mL) and then dried over anhydrous Na2SO4.
The residue obtained after evaporation of the solvent was purified by silica gel
column chromatography using 20% EtOAc in petroleum ether to give pure
products 4j–r.
Spectral data for 5g: viscous oil; IR (neat) 2927, 1605, 1484, 1316, 1172, 1129,
1035 cmÀ1 1H NMR (300 MHz, CDCl3) d 2.28 (s, 3H), 6.55 (d, J = 8.1 Hz, 1H),
;
6.75 (t, J = 8.2 Hz, 1H), 7.31 (d, J = 7.2 Hz, 1H), 7.51–7.63 (m, 2H), 7.80 (d,
J = 7.8 Hz, 1H); MS m/z (À cAPCI): 311.09 (MÀH)À; Anal. Calcd for C16H9F5O: C,
61.55; H, 2.91. Found C, 61.61; H, 2.94.
20. (a) Sarcevic, N.; Zsindely, J.; Schmid, H. Helv. Chim. Acta 1973, 56, 1457–1476;
(b) Bruhn, J.; Zsindely, J.; Schmid, H. Helv. Chim. Acta 1978, 61, 2542–2559.
21. Gopalsamy, A.; Balasubramanian, K. K. J. Chem. Soc., Chem. Commun. 1988, 28–
29.
22. Balasubramanian, T.; Balasubramanian, K. K. Tetrahedron Lett. 1991, 32, 6641–
6644; Bates, D. K.; Jones, M. C. J. Org. Chem. 1978, 40, 3775–3777.
23. Koch-Pomeranz, U.; Hansen, H. -J.; Schmid, H. Helv. Chim. Acta 1973, 56, 2981–
3004.
Spectral data for 5h: yellow solid; mp 190–193 °C; IR (KBr) 2922, 1597, 1515,
1352, 1166, 957, 857 cmÀ1 1H NMR (300 MHz, CDCl3) d 2.60 (s, 3H), 7.29 (s,
;
1H), 7.38 (s, 1H), 7.60 (d, J = 8.1 Hz, 2H), 8.34 (d, J = 7.8 Hz, 2H); MS m/z (À
cAPCI): 321.14 (MÀH)À; Anal. Calcd for C15H9Cl2NO3: C, 55.93; H, 2.82; N, 4.35.
Found C, 56.00; H, 2.85; N, 4.30.
Spectral data for 5l: Yellow solid; mp 135–137 °C; IR (KBr) 3083, 1523, 1433,
1356, 1220, 1180, 1122, 1069, 920 cmÀ1 1H NMR (300 MHz, CDCl3) d 2.72 (s,
;
24. Ghosh, S. C.; De, A. J. Chem. Soc., Perkin Trans. 1 1999, 3705–3708.
25. Typical procedure for the Claisen rearrangement and ring closure: A mixture of 4i
(600 mg, 1.879 mmol) and CsF (514 mg, 3.383 mmol) in N,N-diethylaniline
(10 mL) was refluxed for 3 h under a nitrogen atmosphere. The mixture was
cooled to room temperature, diluted with EtOAc (50 mL) and washed with 5 N
HCl (3 Â 50 mL) and water (2 Â 50 mL) and then dried over anhydrous Na2SO4.
The residue obtained after evaporation of the solvent was purified by silica gel
column chromatography using 5% EtOAc in petroleum ether as eluent to give
421 mg (70%) of 5i as a white solid; mp 99–101 °C; IR (KBr) 2917, 1680, 1604,
3H), 7.17–7.20 (m, 2H), 7.35 (t, J = 7.8 Hz, 1H), 7.43 (d, J = 5.1 Hz, 1H), 8.00 (d,
J = 7.8 Hz, 1H), 8.11 (d, J = 8.4 Hz, 1H); MS m/z (+ cAPCI): 260.24 (M+H)+; Anal.
Calcd for C13H9NO3S: C, 60.22; H, 3.50; N, 5.40; S, 12.37. Found C, 60.17; H,
3.56; N, 5.43; S, 12.43.
Spectral data for 5m: off-white solid; mp 136–138 °C; IR (KBr) 2921, 2230,
1607, 1514, 1429,1247, 1184, 948 cmÀ1 1H NMR (300 MHz, CDCl3) d 2.42 (s,
;
3H), 2.57 (s, 3H), 7.23–7.35 (m, 5H), 7.51 (d, J = 7.5 Hz, 1H), 7.74 (d, J = 7.8 Hz,
1H); MS m/z (+ cAPCI): 248.30 (M+H)+; Anal. Calcd for C17H13NO: C, 82.57; H,
5.30; N, 5.66. Found C, 82.60; H, 5.26; N, 5.71.
1463, 1398, 1258, 1155, 922 cmÀ1
;
1H NMR (300 MHz, CDCl3) d 2.42 (s, 3H),
Spectral data for 5q: viscous oil, IR (neat) 2981, 1714, 1608, 1425, 1291, 1174,
2.66 (s, 3H), 7.07 (d, J = 8.4 Hz, 1H), 7.18 (d, J = 8.1 Hz, 1H), 7.47 (d, J = 7.8 Hz,
2H), 8.00 (d, J = 7.8 Hz, 2H); 13C NMR (75 MHz, CDCl3) d 12.56, 26.70, 115.04,
117.03, 123.86, 124.03, 124.50, 126.74, 127.65 (2C), 131.09 (2C), 136.04,
136.29, 149.95, 154.27, 197.49; MS m/z (À cAPCI): 319.23 (M)À; Anal. Calcd for
1038, 950 cmÀ1 1H NMR (300 MHz, CDCl3) d 1.46 (t, J = 7.2 Hz, 3H), 2.60 (s,
;
3H), 4.47 (q, J = 7.5 Hz, 2H), 7.23–7.27 (m, 1H), 7.33–7.36 (m, 1H), 7.42–7.46
(m, 4H), 7.72 (d, J = 7.8 Hz, 1H), 7.88 (d, J = 7.8 Hz, 1H); MS m/z (+ cAPCI):
281.03 (M+H)+; Anal. Calcd for C18H16O3: C, 77.12; H, 5.75. Found C, 77.15; H,
5.80.
C17H12Cl2O2: C, 63.97; H, 3.79. Found C, 64.01; H, 3.83.Spectral data for 5c:
white solid; mp 77–79 °C; IR(KBr) 2914, 1513, 1421, 1254, 1180, 1113,
Spectral data for 5r: Off-white solid; mp 140–142 °C; IR (KBr) 2842, 1698,
952 cmÀ1 1H NMR (300 MHz, CDCl3) d 2.42 (s, 3H), 2.53 (s, 6H), 7.04–7.14 (m,
;
1613, 1429, 1265, 1184, 1009 cmÀ1 1H NMR (300 MHz, CDCl3) d 2.58 (s, 3H),
;
2H), 7.29 (d, J = 7.8Hz, 2H), 7.38–7.41 (m, 3H); MS m/z (+ cAPCI): 237.47
(M+H)+; Anal. Calcd for C17H16O: C, 86.40; H, 6.82. Found C, 86.43; H, 6.76.
Spectral data for 5f: white solid; mp 69–72 °C; IR (KBr) 2951, 1605, 1514, 1441,
4.08 (s, 3H), 7.35 (s, 1H), 7.37–7.40 (m, 1H), 7.46–7.49 (m, 4H), 7.68 (s, 1H),
9.94 (s, 1H); MS m/z (+ cAPCI):267.19 (M+H)+; Anal. Calcd for C17H14O3: C,
76.68; H, 5.30. Found C, 76.71; H, 5.34.
1247, 1175, 1035, 948 cmÀ1
;
1H NMR (300 MHz, CDCl3) d 2.57 (s, 3H), 3.91 (s,
26. Nigel, C. V. Nat. Prod. Rep. 2007, 24, 417–464.
3H), 6.99–7.02 (m, 1H), 7.06 (d, J = 8.4 Hz, 2H), 7.12–7.19 (m, 1H), 7.33 (d,