A rapid access to indolo[2,1-a]pyrrolo[4′,3′:4,5]pyrano[5,6-c]coumarin/[6,5-c]chromone derivatives by domino Knoevenagal intramolecular hetero Diels-Alder reactions

Article abstract of DOI:10.1016/j.tetlet.2006.12.106

Knoevenagal condensation of indole-2-carbaldehyde containing an internal dienophile with coumarins, followed by domino intramolecular hetero Diels-Alder reaction, provides polycyclic heterocycles. Different approaches for stereo- and chemoselective synthe

Full text of DOI:10.1016/j.tetlet.2006.12.106

Tetrahedron Letters 48 (2007) 1385–1389
A rapid access to indolo[2,1-a]pyrrolo[40,30:4,5]-
pyrano[5,6-c]coumarin/[6,5-c]chromone derivatives by domino
Knoevenagal intramolecular hetero Diels–Alder reactions
Rathna Durga R. S. Manian, Jayadevan Jayashankaran and Raghavachary Raghunathan*
Department of Organic Chemistry, University of Madras, Guindy Campus, Chennai 600 025, India
Received 29 September 2006; revised 14 December 2006; accepted 19 December 2006
Available online 22 December 2006
Abstract—Knoevenagal condensation of indole-2-carbaldehyde containing an internal dienophile with coumarins, followed by dom-
ino intramolecular hetero Diels–Alder reaction, provides polycyclic heterocycles. Different approaches for stereo- and chemoselec-
tive synthesis of indolo[2,1-a]pyrrolo[40,30:4,5]pyrano[5,6-c]coumarin and indolo[2,1-a]pyrrolo[40,30:4,5]pyrano[6,5-c]chromone
derivatives are described.
ꢀ 2006 Elsevier Ltd. All rights reserved.
The intramolecular Diels–Alder reaction1 is a powerful
method for the synthesis of many polycyclic com-
pounds, including natural products. However, it is a pre-
requisite that activating groups have to be built into
dienophiles to achieve the desired reactivity.2
We report here the initial results showing that the sol-
vent-free, microwave assisted domino Knoevenagal
intramolecular hetero Diels–Alder reaction is a rapid
and expedient way for the preparation of highly pure
indolo-pyrrolo-pyrano-coumarin derivatives.
Coumarin derivatives are widespread in Nature and are
reported to have various biological activities such as
anticoagulant, insecticidal, antihelminthic, hypnotic,
antifungal, phytoalexin and HIV protease inhibition.3
Many naturally occurring compounds were found to
possess a pyranocoumarin skeleton such as isoethulia-
coumarin A, isoethuliacoumarin B, isoethuliacoumarin
C, ethuliacoumarin A, ethuliacoumarin B, and ptero-
phyllin 3.4,5 Similarly, the indole ring system is present
in drug candidates having an interesting biological activ-
ity and in numerous natural alkaloids that cover a wide
range of structural types.6 Consequently, much effort
has been devoted to developing new methods for the
construction of indole compounds.7
Optimization of the reaction conditions was carried out
using the Knoevenagal hetero Diels–Alder reaction of 4-
hydroxy coumarin 6 with 1-(3-methylbut-2-enyl)-indole-
2-carbaldehyde 5a as a model reaction. Treatment of
ethyl-1H-indole-2-carboxylate 1 and 1-bromo-3-methyl-
but-2-ene 2a in benzene with 50% aqueous sodium
hydroxide in the presence of a catalytic amount of
TEBA at room temperature for 2 h furnished ethyl-1-
(3-methylbut-2-enyl)-1H-indole-2-carboxylate 3a in a
moderate yield, whereas treatment of 1 and 2a with
sodium hydride in DMF resulted in a lower yield of
3a (40%). Ester 3a was then reduced to alcohol 4a with
LiAlH4 in dry THF at 0 ꢁC in an 82% yield. Alcohol 4a
was then oxidized with activated MnO2 in dichloro-
methane under N2 at room temperature. However, we
found the yield was only 56%, hence we performed the
oxidation under Swern conditions to give 5a in an 85%
yield8 (Scheme 1).
O
O
O
The intended product from the Knoevenagal hetero
Diels–Alder reaction, 8a,15b-cis-8,8-dimethyl-8,8a,
9,15b-tetrahydroindolo[2,1-a]pyrrolo[40,30:4,5]pyrano[5,
6-c]coumarin 7a was always accompanied by 8a,15b-cis-
8,8-dimethyl-8,8a,9,15b-tetrahydroindolo[2,1-a]pyrrolo-
[40,30:4,5]pyrano[6,5-c]chromone derivative 8a, as shown
pterophyllin 3
*
Corresponding author. Tel.: +91 44 09444333883; e-mail:
ragharaghunathan@yahoo.com
0040-4039/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2006.12.106

1386
R. D. R. S. Manian et al. / Tetrahedron Letters 48 (2007) 1385–1389
derivative. The 1H NMR spectrum of 7a showed a dou-
R1
blet at d 4.52 for the Ha proton and a multiplet in the
region d 3.38–3.43 for the Hb proton. The cis-stereo-
chemistry of products 7a and 8a was confirmed by the
coupling constant JHa,Hb = 8.0 Hz. Further, the cis-ste-
reochemistry of derivative 7a was confirmed by a strong
NOE coupling.
R
Br
2a,b
COOEt
R1
COOEt
N
N
50% aq. NaOH, PTC
rt, 1-2 h
H
or
1
NaH, DMF, rt, 1 h
R
3a,b
LiAlH4, THF
The different reactions for the preparation of a-naphtho-
coumarin, a-naphtho-chromone, b-naphtho-coumarin
and b-naphtho-chromone derivatives are summarized
in Schemes 3 and 4. Table 1 shows the isolated yields
for the different reaction conditions employed.
rt, 2-3 h, N2 atm
MnO2, CH2Cl2,
rt, 12-15 h, N2 atm
CHO
R1
CH2OH
R1
N
or
N
Swern oxidation
The results reported in Table 1 show that the careful
optimization of the conditions leads to short reactions,
high yields and mixtures that are easy to separate.
4a,b
R
5a,b
R
a) R, R1 = CH3
b) R = H; R1 = Ph
The 1H NMR spectra of compounds 10a,b, 11a,b, 13a,b
and 14a,b confirmed the all-cis configuration of the new
compounds with vicinal coupling constants of around
7.6 Hz. Moreover, the coumarin and chromone deriva-
tives were distinguished by their carbonyl resonances.
Scheme 1. Preparation of N-alkenylindole-2-carbaldehydes.
in Scheme 2.9 The relative amounts of 7a and 8a formed
were estimated from the 1H NMR spectrum of the crude
mixture.
The above results prompted us to extend the methodol-
ogy to domino Knoevenagal hetero Diels–Alder reac-
tion of compounds 6, 9 and 12 with aldehyde 5b.
Accordingly, 5b was readily prepared from ethyl-1H-in-
dole-2-carboxylate and cinnamyl bromide as described
along the lines for the preparation of 5a and the results
are summarized in Table 2.
Table 1 shows how crucial the choice of reaction condi-
tions is in determining the trend of the reaction. A mod-
erate yield of 7a was obtained by reflux in ethanol,
whereas 7a was formed in a 72% yield under microwave
irradiation (entry 1). On the other hand, solvent-free,
solid-supported reaction under microwave irradiation
afforded a very good yield of 7a (86%).
The reactions were successfully carried out with high
chemoselectivities under microwave irradiation in etha-
nol. To improve the chemoselectivity, we further exam-
ined the reaction of 6 and 5b by grinding with K-10
Montmorillonite clay followed by microwave irradia-
tion and obtained a significant reduction in the reaction
time with an improved chemoselectivity and yield (Table
2, entry 1).
The structure of the products was ascertained from spec-
tral data. The IR carbonyl absorption of 7a was ob-
served at 1634 cmꢀ1, whereas in the case of 8a it was
observed at 1724 cmꢀ1
.
The formation of coumarin and chromone derivatives
was confirmed by the distinguishable carbonyl carbon
in the 13C NMR, which appeared at d 161.54 ppm for
the coumarin and at d 178.12 ppm for the chromone
The polycyclic derivatives obtained were readily sepa-
rated by chromatography on silica gel, and their struc-
O
O
O
O
various
CHO
R
N
conditions
N
O
OH
R1
R1
6
R
5a R = R1 = CH3
5b R = H, R1 = Ph
O
Ha
O
O
Ha
O
N
N
O
O
R1
H
R1
H
bR
bR
8a R = R1 = CH3
8b R = H, R1 = Ph
7a R = R1 = CH3
7b R = H, R1 = Ph
Scheme 2. Reaction of N-alkenyl indole-2-carbaldehydes with coumarin.

R. D. R. S. Manian et al. / Tetrahedron Letters 48 (2007) 1385–1389
Table 1. The reaction times and yields of the domino reactions under various conditions
1387
Entry Aldehyde
1,3-Dione
Conditions
Time
Ratio of products
Overall yield (%)
Coumarin Chromone
O
O
A Ethanol/reflux
B Ethanol/MW
C K-10 montmorillonite clay/MW 35 min
5.5 h
10 min
65
75
86
35
25
14
58
72
86
CHO
CHO
CHO
1
2
N
N
N
OH
A Ethanol/reflux
B Ethanol/MW
C K-10 montmorillonite clay/MW 4.0 min 88
6.0 h
15 min
51
70
49
30
12
58
73
88
O
O
O
OH
O
3
A Ethanol/reflux
B Ethanol/MW
C K-10 montmorillonite clay/MW 3.5 min 89
6.0 h
13 min
58
78
42
22
11
65
72
85
OH
O
O
O
O
various
CHO
R
N
conditions
N
O
OH
R1
R1
R
5a R = R1 = CH3
5b R = H, R1 = Ph
9
O
Ha
O
O
Ha
O
N
N
O
O
R1
H
R1
H
bR
bR
11a R = R1 = CH3
10a R = R1 = CH3
10b R = H, R1 = Ph
11b R = H, R1 = Ph
Scheme 3. Reaction of N-alkenyl indole-2-carbaldehydes with a-naphtho-coumarin.
O
O
O
O
various
CHO
R
N
conditions
N
O
OH
R1
R1
R
5a R = R1 = CH3
5b R = H, R1 = Ph
12
O
Ha
O
O
Ha
O
N
O
N
O
R1
H
R1
bR
H
bR
13a R = R1 = CH3
13b R = H, R1 = Ph
14a R = R1 = CH3
14b R = H, R1 = Ph
Scheme 4. Reaction of N-alkenyl indole-2-carbaldehydes with b-naphtho-coumarin.

1388
R. D. R. S. Manian et al. / Tetrahedron Letters 48 (2007) 1385–1389
Table 2. Results obtained from the domino Knoevenagal hetero Diels–Alder reaction of coumarins and 5b under various conditions
Entry Aldehyde
1,3-Dione
Conditions
Time
Ratio of
products
Overall yield (%)
Coumarin Chromone
O
O
A Ethanol/reflux
B Ethanol/MW
C K-10 montmorillonite clay/MW 2.5 min 87
5.5 h
12 min
68
78
32
22
13
61
78
93
CHO
H
N
1
2
OH
Ph
O
O
O
A Ethanol/reflux
B Ethanol/MW
C K-10 montmorillonite clay/MW 3.0 min 95
5.5 h
10 min
54
75
46
25
5
62
76
94
CHO
H
N
N
Ph
OH
O
CHO
H
3
A Ethanol/reflux
B Ethanol/MW
C K-10 montmorillonite clay/MW 3.0 min 84
6.5 h
8 min
60
76
40
24
16
66
75
90
OH
Ph
tures were assigned by 1H NMR analysis. The cis config-
uration of the pyrrolo-pyrano ring of the products was
4. Mahmoud, A. A.; Ahmed, A. A.; Linuma, M.; Tanaka, T.
Phytochemistry 1998, 47, 543.
5. Mulholland, D. A.; Lourine, S. E.; Taylor, D. A. H.; Dean,
F. M. Phytochemistry 1998, 47, 1641.
1
assigned by H NMR analysis, being significantly sup-
ported by the small coupling constant. Similarly, the
large coupling constant supports the trans configuration
of the benzylic proton (R = H) in 7b, 8b, 10b, 11b, 13b
and 14b. Further, the regioisomers were distinguished
by their characteristic carbonyl resonances.
6. (a) Li, J. J., Gribble, G. W. In Palladium in Heterocyclic
Chemistry; Baldwin, J. E., Williams, F. R. S. M. R., Eds.;
Pergamon Press: New York, 2000; Vol. 20, pp 73–181; (b)
Glennon, R. A. J. Med. Chem. 1987, 33, 1–12.
7. (a) Balme, G.; Bouyssi, D.; Lomberget, T.; Monteiro, N.
Synthesis 2003, 2115–2134; (b) Li, J. J.; Gribble, G. W.
Palladium in Heterocyclic Chemistry; Pergamon: Oxford,
2000; (c) Gribble, G. W. J. Chem. Soc., Perkin Trans. 1
2000, 1045–1075; (d) Pindur, U.; Adam, R. J. Heterocycl.
Chem. 1988, 25, 1.
8. Experimental procedure for compound 5a: 1-(3-Methylbut-2-
enyl)-2-carbethoxyindole 3a: 1-Bromo-3-methylbut-2-ene
(16 mmol), TEBA (0.5 mmol) and 50% NaOH (20 mL)
were added to a solution of 2-carbethoxyindole (10 mmol)
in benzene (64 mL). The mixture was vigorously stirred at
room temperature for 2 h. The organic layer was separated,
washed with water and dried over MgSO4. The solvent was
evaporated under reduced pressure to give a 65% yield (mp
65–67 ꢁC) of 3a. IR (KBr): 1709 cmꢀ1; 1H NMR (400 MHz,
CDCl3): d 1.00 (t, J = 7.0 Hz, 3H), 1.72 (s, 3H), 1.79 (s,
3H), 4.32 (q, J = 7.0 Hz, 2H), 5.12 (d, J = 5.8 Hz, 2H), 5.20
(t, J = 5.8 Hz, 1H), 6.65 (s, 1H), 7.15–7.23 (m, 2H),
7.27 (d, J = 8.0 Hz, 1H), 7.30 (d, J = 8.0 Hz, 1H); 13C
NMR (100 MHz, CDCl3): d 18.52, 20.10, 22.52, 42.36,
58.91, 110.53, 122.37, 124.59, 124.82, 125.08, 126.99,
128.14, 130.05, 135.52, 140.55, 163.43; MS: m/z = 257
(M+).
In conclusion, the solvent-free microwave assisted syn-
thesis of indolo[2,1-a]pyrrolo[40,30:4,5]pyrano[5,6-c]cou-
marin and indolo[2,1-a]pyrrolo[40,30:4,5]pyrano[6,5-c]-
chromone derivatives through the domino Knoevenagal
hetero Diels–Alder reaction presented in this Letter is an
environmentally friendly methodology allowing the fac-
ile preparation of these important polycyclic materials.
These strategies might be a promising tool for develop-
ing new routes to natural compounds bearing function-
alized coumarin and chromone skeletons.
Acknowledgement
R.D. and J.J. thank the CSIR-SRF, New Delhi, for
financial support.
References and notes
1. For reviews on the intramolecular Diels–Alder reaction,
see: (a) Roush, W. R. In Comprehensive Organic Synthesis;
Trost, B. M., Fleming, I., Eds.; Pergamon: Oxford, UK,
1991; Vol. 5, Chapter 4.4, pp 513–550; (b) Fallis, A. G. Acc.
Chem. Res. 1999, 32, 464.
2. (a) House, H. O.; Cronin, T. H. J. Org. Chem. 1965, 30,
1061; (b) Roush, W. R. J. Am. Chem. Soc. 1978, 100, 3599;
(c) Roush, W. R.; Peseckis, S. M. J. Am. Chem. Soc. 1981,
103, 6696; (d) Shea, K. J.; Gilman, J. W. Tetrahedron Lett.
1983, 24, 657.
1-(3-Methylbut-2-enyl)-2-hydroxymethylindole 4a: A solu-
tion of 3a (0.73 mmol) in dry THF (5 mL) was added
dropwise, under N2 to a suspension of LiAlH4 (0.88 mmol)
in dry THF (40 mL) at 0 ꢁC. The mixture was stirred at
room temperature for 3 h. MeOH (1 mL) was slowly added,
and the solvent was removed under reduced pressure. After
addition of water (2 mL), the aqueous layer was adjusted to
pH 7 with 0.1 M HCl and extracted with CH2Cl2. The
organic layer was dried over MgSO4 and evaporated to give
an 82% yield (mp 89–91 ꢁC) of 4a. IR (KBr): 3392 cmꢀ1; 1H
NMR (400 MHz, CDCl3): d 1.25 (br s, 1H), 1.71 (s, 3H),
1.87 (s, 3H), 4.78 (d, J = 6.0 Hz, 1H), 4.84 (d, J = 6.2 Hz,
2H), 5.23 (t, J = 6.2 Hz, 1H), 6.46 (s, 1H), 7.07–7.26 (m,
3. Rastogi, R. P.; Mehrotra, B. N. In Compendium of Indian
Medicinal Plants; Rastogi, R. P., Ed.; CDRI and P & I
Directorate: Lucknow and New Delhi, 1993; Vol. 3, p 273.

R. D. R. S. Manian et al. / Tetrahedron Letters 48 (2007) 1385–1389
1389
2H), 7.30 (d, J = 8.0 Hz, 1H), 7.58 (d, J = 8.0 Hz, 1H); 13
NMR (100 MHz, CDCl3): d 18.01, 25.46, 41.76, 57.47,
101.57, 109.60, 119.50, 120.82, 120.92, 121.85, 127.46,
134.55, 137.43, 138.45; MS: m/z = 215 (M+).
C
chromatography using hexane:ethyl acetate as eluent gave
pure products.
8a,15b-cis-8,8-Dimethyl-8,8a,9,15b-tetrahydroindolo[2,1-a]-
pyrrolo[40,30:4,5]pyrano[5,6-c]coumarin 7a: Pale yellow
1-(3-Methylbut-2-enyl)-indole-2-carbaldehyde 5a: To
a
solid, mp: 260–262 ꢁC; IR (KBr): 1634 cmꢀ1 1H NMR
;
solution of oxalyl chloride (76.7 mmol) in CH2Cl2
(200 mL) was added DMSO (0.12 mol) at ꢀ78 ꢁC. After
stirring for 30 min at ꢀ78 ꢁC, a solution of 4a (38.4 mmol)
in CH2Cl2 (25 mL) was added and stirring continued at
ꢀ78 ꢁC for 30 min. The reaction mixture was treated with
triethylamine(0.23 mol), allowed to warm to room temper-
ature and stirred for a further 30 min. The reaction mixture
was diluted with 1 M HCl (20 mL), washed with saturated
sodium bicarbonate solution and brine, then dried and
concentrated to give 5a in an 85% yield (mp 80–82 ꢁC). IR
(500 MHz, CDCl3): d 1.54 (s, 3H), 1.57 (s, 3H), 3.38–3.43
(m, 1Hb), 4.00 (dd, J = 7.2, 9.7 Hz, 1H), 4.32 (dd, J = 8.0,
9.7 Hz, 1H), 4.52 (d, J = 8.0 Hz, 1Ha), 6.64 (s, 1H), 7.01–
7.77 (m, 8H); 13C NMR (125 MHz, CDCl3): d 25.43, 26.77,
32.60, 44.72, 50.47, 97.00, 109.20, 119.47, 120.45, 120.87,
121.18, 121.76, 122.83, 123.86, 124.33, 126.78, 128.23,
128.75, 129.45, 130.23, 131.91, 161.54 ppm; mass m/z: 357
(M+). Anal. Calcd for C23H19NO3: C, 77.29; H, 5.36; N,
3.92. Found: C, 77.41; H, 5.50; N, 3.80.
8a,15b-cis-8,8-Dimethyl-8,8a,9,15b-tetrahydroindolo[2,1-a]-
pyrrolo[40,30:4,5]pyrano[6,5-c]chromone 8a: Yellow solid,
1
(KBr): 1673 cmꢀ1; H NMR (400 MHz, CDCl3): d 1.75 (s,
3H), 1.82 (s, 3H), 4.87 (d, J = 6.0 Hz, 2H), 5.33 (t,
J = 6.0 Hz, 1H), 6.39 (s, 1H), 7.17–7.24 (m, 2H), 7.29 (d,
J = 7.8 Hz, 1H), 7.35 (d, J = 7.8 Hz, 1H), 9.57 (s, 1H); 13C
NMR (100 MHz, CDCl3): d 19.34, 21.56, 37.81, 110.74,
119.53, 121.23, 125.26, 126.13, 126.85, 127.12, 129.05,
129.64, 132.85, 183.09; MS: m/z = 213 (M+).
mp: 232–234 ꢁC; IR (KBr): 1724 cmꢀ1 1H NMR (500
;
MHz, CDCl3): d 1.72 (s, 3H), 1.76 (s, 3H), 2.92–3.03 (m,
1Hb), 3.79 (dd, J = 7.2, 9.7 Hz, 1H), 4.25 (dd, J = 8.0,
9.7 Hz, 1H), 4.44 (d, J = 8.0 Hz, 1Ha), 6.75 (s, 1H), 6.89–
7.76 (m, 8H); 13C NMR (125 MHz, CDCl3): d 24.26, 26.72,
34.26, 43.18, 48.75, 52.75, 98.10, 111.11, 116.28, 117.76,
118.15, 119.03, 119.82, 120.15, 122.16, 123.03, 123.85,
125.78, 127.00, 128.62, 129.01, 131.73, 178.12 ppm; mass
m/z: 357 (M+). Anal. Calcd for C23H19NO3: C, 77.29; H,
5.36; N, 3.92. Found: C, 77.43; H, 5.52; N, 4.05.
9. General procedure for the intramolecular domino Knoevena-
gel hetero Diels–Alder reaction:
Method A: To a refluxing solution of 1,3-dione (1 mmol) in
10 mL of dry ethanol, aldehyde 5a or 5b (1 mmol) was
added and the reaction mixture was refluxed until the
disappearance of the starting material as evidenced by thin
layer chromatography. After completion of the reaction,
the solvent was evaporated and the residue was subjected
to flash column chromatography using hexane:ethyl
acetate.
Method B: A solution of 1,3-dione (1 mmol) and the
corresponding aldehyde (1 mmol) in dry ethanol was
irradiated using a microwave oven (Kenstar, 600 W power)
until thin layer chromatography showed the disappearance
of the starting material. After removal of the solvent, the
crude reaction mixture was subjected to flash column
chromatography using hexane:ethyl acetate to yield the
products.
Method C: A mixture of activated ketone or 1,3-dione
(1 mmol), aldehyde (1 mmol) and K-10 montmorillonite
clay (1.0 g) was thoroughly ground in a mortar. The
reaction mixture was irradiated using a microwave oven
(Kenstar, 600 W power) until complete disappearance of
the starting material as evidenced by thin layer chromato-
graphy. After completion of the reaction, the clay was
separated by filtration and the product extracted with
dichloromethane (2 · 15 mL). Removal of the solvent and
purification of the crude reaction mixture by flash column
8a,15b-cis-8-Phenyl-8,8a,9,15b-tetrahydroindolo[2,1-a]pyr-
rolo[40,30:4,5]pyrano[5,6-c]coumarin 7b: Yellow solid, mp:
220–222 ꢁC; IR (KBr): 1628 cmꢀ1 1H NMR (500 MHz,
;
CDCl3): d 3.36–3.40 (m, 1Hb), 3.92 (dd, J = 7.0, 10.1 Hz,
1H), 4.16 (dd, J = 8.0, 10.1 Hz, 1H), 4.63 (d, J = 6.1 Hz,
1Ha), 4.66 (d, J = 9.7 Hz, 1H), 6.56 (s, 1H), 7.06–7.73 (m,
13H); 13C NMR (125 MHz, CDCl3): d 38.53, 44.26, 52.31,
56.07, 109.13, 112.15, 115.26, 121.93, 122.64, 123.23,
124.01, 124.20, 125.33, 126.24, 128.86, 129.52, 131.53,
133.27, 134.28, 137.94, 140.26, 163.90 ppm; mass m/z: 405
(M+). Anal. Calcd for C27H19NO3: C, 79.98; H, 4.72; N,
3.45. Found: C, 80.14; H, 4.83; N, 3.30.
8a,15b-cis-8-Phenyl-8,8a,9,15b-tetrahydroindolo[2,1-a]pyr-
rolo[40,30:4,5]pyrano[6,5-c]chromone 8b: Yellow solid, mp:
215–217 ꢁC; IR (KBr): 1715 cmꢀ1 1H NMR (500 MHz,
;
CDCl3): d 3.48–3.52 (m, 1Hb), 3.89 (dd, J = 7.2, 10.0 Hz,
1H), 4.35 (dd, J = 8.0, 10.0 Hz, 1H), 4.55 (d, J = 8.2 Hz,
1Ha), 5.35 (d, J = 9.6 Hz, 1H), 6.12 (s, 1H), 6.73–7.68 (m,
13H); 13C NMR (125 MHz, CDCl3): d 36.25, 42.76, 58.91,
60.73, 107.26, 113.71, 118.18, 119.23, 121.15, 121.34,
122.45, 124.75, 124.82, 125.24, 126.58, 127.37, 129.21,
130.32, 133.65, 135.52, 136.15, 142.45, 179.89 ppm; mass
spectrum m/z: 405 (M+). Anal. Calcd for C27H19NO3: C,
79.98; H, 4.72; N, 3.45. Found: C, 80.10; H, 4.85; N, 3.34.