An expedient microwave-assisted, solvent-free, solid-supported synthesis of pyrrolo[2,3-d]pyrimidine-pyrano[5,6-c]coumarin/[6,5-c]chromone derivatives by intramolecular hetero Diels-Alder reaction

Article abstract of DOI:10.1016/j.tetlet.2008.01.059

A rapid synthesis of pyrrolo[2,3-d]pyrimidine annulated pyrano[5,6-c]coumarin/[6,5-c]chromone derivatives has been accomplished in good yields via an intramolecular domino hetero Diels-Alder reaction using microwave irradiation under solvent-free, solid-s

Full text of DOI:10.1016/j.tetlet.2008.01.059

Available online at www.sciencedirect.com
Tetrahedron Letters 49 (2008) 1812–1817
An expedient microwave-assisted, solvent-free, solid-supported
synthesis of pyrrolo[2,3-d]pyrimidine-pyrano[5,6-c]coumarin/[6,5-c]-
chromone derivatives by intramolecular hetero Diels–Alder reaction
Ekambaram Ramesh, Raghavachary Raghunathan *
Department of Organic Chemistry, University of Madras, Guindy Campus, Chennai 600 025, India
Received 30 October 2007; revised 26 December 2007; accepted 10 January 2008
Available online 15 January 2008
Abstract
A rapid synthesis of pyrrolo[2,3-d]pyrimidine annulated pyrano[5,6-c]coumarin/[6,5-c]chromone derivatives has been accomplished in
good yields via an intramolecular domino hetero Diels–Alder reaction using microwave irradiation under solvent-free, solid-supported
conditions.
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords: Hetero Diels–Alder; Pyrrolopyrimidine; Pyranocoumarin; Microwave
The intramolecular Diels–Alder reaction is a powerful
method for the synthesis of many polycyclic compounds,
including natural products.1,2 However, it is a prerequisite
that activating groups have to be incorporated into the
dienophiles to achieve the desired reactivity.3,4
an important component of pharmacophores for number
of biologically active molecules of synthetic as well as
natural origin and many of them have useful medicinal
applications.13–16
Pyrrolo[2,3-a]pyrimidine nucleoside derivatives are
reported to have various biological activities such as anti-
HCV, anti-HIV type 1 and anti-HSV as well as being
adenosine kinase, aurora-A kinase and cAMP phospho-
diesterase inhibitors.17–20 Naturally occurring mycalisine
A, cadeguomycin and 2-deoxycadeguomycin21,22 (Fig. 1)
also possess a pyrrolo[2,3-a]pyrimidine moiety.
A number of coumarin derivatives have been isolated
from natural sources and their pharmacological and bio-
chemical properties depend upon the pattern of substitu-
tion. They have attracted considerable interest in recent
years because of their diverse pharmacological properties.
Coumarins serve as anti-oxidant, anti-inflammatory,
antiallergic, hepatoprotective, antiviral, anticarcinogenic,
anticoagulant and antifungal agents in addition to HIV
protease inhibitors.5–9 Many naturally occurring com-
pounds such as isoethuliacoumarin A, isoethuliacoumarin
B, isoethuliacoumarin C, ethuliacoumarin A, ethuliacoum-
arin B, pterophyllin, calonone, isocalonone, (+)-calanoide
A, soulattroide and (+)-isoferprenin10–12 possess a pyrano
coumarin skeleton. Similarly, the chromone moiety forms
We disclose here our preliminary investigation on the
rapid and expedient synthesis of novel uracil annulated pyr-
ano[5,6-c]coumarin and pyrano[6,5-c]chromone derivatives
O
COOH
HN
H2N
HO
N
N
O
*
Corresponding author. Tel.: +91 44 22351269x213, 214; fax: +91 44
HO
OH
Fig. 1.
22352494.
E-mail address: ragharaghunathan@yahoo.com (R. Raghunathan).
0040-4039/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2008.01.059

E. Ramesh, R. Raghunathan / Tetrahedron Letters 49 (2008) 1812–1817
1813
through solvent-free, microwave-assisted, Knoevenagel-
intramolecular hetero Diels–Alder reactions. 1,3-Di-
methyl-1-pyrrolo[2,3-a]pyrimidine-2,4-dione 1 was chosen
as the starting material which on treatment with the Vilsme-
ier reagent (DMF + POCl3) gave 1,3-dimethyl-2,4-dioxo-
1H-pyrrolo[2,3-d]pyrimidine-6-carbaldehyde 2 in excellent
yield.23 Treatment of 2 with 1-bromo-3-methylbut-2-ene
3a/cinnamyl bromide 3b in dry DMF in the presence of a
K2CO3 gave 4a/4b in good yields (70–80%).24 The same
reaction when carried out in 10% aqueous sodium hydrox-
ide in the presence of a catalytic amount of a PTC (TBAS)
resulted in a lower yield of the products (40–58%) (Scheme 1).
Treatment of 4-hydroxycoumarin 5 with 4a in refluxing
toluene resulted in the formation of the cis-fused coumarin
7a and chromone 7b with an overall yield of 47% in the
ratio 58:42 (Scheme 2). The reaction proceeded via a
domino Knoevenagel-intramolecular hetero Diels–Alder
pathway in a one-step process.
The structures of the products were ascertained from spec-
tral data. The IR carbonyl absorption of 7a was observed
at 1640 cmꢀ1, whereas in the case of 7b it was observed
at 1732 cmꢀ1. The formation of coumarin and chromone
derivatives was confirmed by the distinguishable carbonyl
carbon in the 13C NMR, which appeared at d 165.5 ppm
for the coumarin and at d 177.1 ppm for the chromone
derivative. The 1H NMR spectrum of 7a exhibited a
doublet at d 4.23 for the Ha proton and a multiplet in
the region d 3.36–3.44 for the Hb proton. The syn-stereo-
chemistry of the products was confirmed by the coupling
constants JHa,Hb = 6.8 Hz. Further, the syn-stereochemis-
try was confirmed from the strong NOE coupling between
the Ha and Hb protons.
The 1H NMR spectrum of 7b showed a doublet at d 4.21
for the Ha proton and a multiplet in the region d 3.28–3.35
for the Hb proton. The syn-stereochemistry of the product
was confirmed by the coupling constants (JHa,Hb = 6.0 Hz)
and a strong NOE coupling between the Ha and Hb
protons.
The relative amounts of 7a and 7b formed were esti-
1
mated from the H NMR spectrum of the crude product.
R1
Br
O
N
O
O
N
R2
3a,b
DMF/POCl3
20-30 o
N
N
N
O
N
H
CHO
O
N
N
CHO
R2
O
N
H
K2CO3, DMF, rt, 12 h
C
1
2
R1
4a,b
a) R1, R2 = CH3
b) R1 = H; R2 = Ph
Scheme 1.
O
O
N
O
N
N
X
O
X
various
O
N
N
O
N
CHO
R2
conditions
O
OH
R2
R1
R1
5 X = O
6 X = S
R1, R2 = CH3
R1 = H, R2 = Ph
4a
4b
O
O
N
O
O
N
N
X
Ha
Ha
O
N
N
O
N
X
Hb
O
R1 R2
O
R1 R2
Hb
R1, R2 = CH3, X = O
R1 = H, R2 = Ph, X = O
R1, R2 = CH3, X = S
7b R1, R2 = CH3, X = O
8b R1 = H, R2 = Ph, X = O
7a
8a
9a
R1, R2 = CH3, X = S
9b
10a R1 = H, R2 = Ph, X = S
R1 = H, R2 = Ph, X = S
10b
Scheme 2.

1814
E. Ramesh, R. Raghunathan / Tetrahedron Letters 49 (2008) 1812–1817
To improve the reaction yield and the chemoselectivity,
thocoumarin 11 and b-naphthocoumarin 14, in refluxing
toluene with 4a and 4b (Schemes 2–4) and the results are
summarized in Tables 1 and 2.
we turned our attention to solid-supported microwave con-
ditions as part of our ongoing efforts to apply microwave
chemistry to synthesis.25,26
Treatment of 4-hydroxycoumarin 5 with 4b in refluxing
toluene resulted in the formation of cis-fused 8a and 8b
with an overall yield of 62% and ratio of 54:46.
The relative amounts of 8a and 8b formed were esti-
When the same reaction was carried out under micro-
wave irradiation for 5 min in toluene, the coumarin and
chromone derivatives were obtained in the ratio 65:35 with
an overall yield of 52%. We also examined the reaction,
under solvent-free conditions, simply by grinding the two
components with K-10 montmorillonite clay and irradiat-
ing the mixture under microwave conditions which affor-
ded the anticipated cycloadducts in excellent yields with
high chemoselectivity. The ratio of the coumarin and chro-
mone derivatives was found to be 74:26 with an improved
overall yield of 74% (Table 1).
1
mated from the H NMR spectra of the crude products.
The carbonyl absorption of 8a was observed at
1644 cmꢀ1, whereas in the case of 8b it was observed at
1728 cmꢀ1 in the IR spectra.
The formation of coumarin and chromone derivatives
was confirmed by the distinguishable carbonyl carbon in
the 13C NMR, which appeared at d 162.0 for the coumarin
1
and at d 178.2 for the chromone derivative. The H NMR
To investigate the synthetic scope of this cycloaddition
reaction, we reacted 5, 4-hydroxy-thiocoumarin 6, a-naph-
spectrum of 8a showed a doublet at d 4.63 for the Ha pro-
ton and a multiplet in the region d 3.36–3.40 for the Hb
Table 1
Results obtained from the domino Knoevenagel–hetero Diels–Alder reaction of 1,3-diones with 4a under various conditions
Entry
1,3-Dione
Conditions
Time
Ratio of products
Coumarin Chromone
Overall yield (%)
S
O
O
A
B
C
4.5 h
5 min
10 min
55
62
75
45
38
25
45
52
75
1
OH
O
A
B
C
5.0 h
5 min
10 min
58
65
74
42
35
26
47
52
74
2
3
OH
A
B
C
5.5 h
10 min
12 min
54
62
70
46
38
30
48
57
77
O
O
O
OH
O
A
B
C
5.7 h
12 min
16 min
50
61
78
50
39
22
51
60
77
4
OH
Method A: toluene reflux; method B: toluene/MW; method C: K-10 montmorillonite clay/MW.
O
O
O
N
N
O
O
O
Ha
N
O
N
various
O
O
N
N
CHO
R2
Ha
O
N
N
O
N
conditions
O
OH
O
R1 R2
Hb
O
R1 R2
R1
Hb
11
R1, R2 = CH3
4b R1 = H, R2 = Ph
4a
R1, R2 = CH3
R1 = H, R2 = Ph
R1, R2 = CH3
R1 = H, R2 = Ph
12a
12b
13b
13a
Scheme 3.

E. Ramesh, R. Raghunathan / Tetrahedron Letters 49 (2008) 1812–1817
1815
O
N
O
O
N
N
O
Ha
N
O
Ha
N
O
O
O
various
O
N
CHO
R2
O
N
N
O
N
O
conditions
O
R1 R2
OH
Hb
O
R1 R2
Hb
R1
14
R1, R2 = CH3
15b R1, R2 = CH3
16b R1 = H, R2 = Ph
15a R1, R2 = CH3
16a R1 = H, R2 = Ph
4a
4b
1
2
R = H, R = Ph
Scheme 4.
Table 2
Results obtained from the domino Knoevenagel–hetero Diels–Alder reaction of 1,3-diones with 4b under various conditions
Entry
1,3-Dione
Conditions
Time
Ratio of products
Coumarin Chromone
Overall yield (%)
A
B
C
3 h
2 min
30 s
51
64
72
49
36
28
65
74
81
S
O
O
1
OH
O
2
3
4
A
B
C
3.5 h
2.5 min
40 s
54
65
75
46
35
25
62
77
84
OH
O
O
O
A
B
C
4.5 h
3.0 min
45 s
53
67
77
47
33
23
64
75
89
OH
O
A
B
C
4.25 h
3.0 min
47 s
64
75
80
36
25
20
61
79
85
OH
Method A: toluene reflux; method B: toluene/MW; method C: K-10 montmorillonite clay/MW.
proton. The syn-stereochemistry of the products was con-
firmed by the coupling constant JHa,Hb = 6.1 Hz.
The intramolecular, domino, Knoevenagel–hetero Diels–
Alder reaction proved to be a useful protocol to prepare
these interesting compounds. Of the various conditions
employed, the solvent-free approach on a solid support
accelerated by microwaves proved to be synthetically
useful in achieving high degrees of chemo- and stereoselec-
tivity with a substantial reduction in reaction time.
1
In the H NMR spectrum of 8b, a doublet at d 4.55
appeared for the Ha proton whilst the Hb proton resonated
as a multiplet in the region d 3.48–3.52. The syn-stereo-
chemistry of the product was confirmed by the coupling
constant JHa,Hb = 6.8 Hz. Further, the syn-stereochemistry
of the derivative was confirmed by a strong NOE coupling
between protons Ha and Hb.
Acknowledgements
Under microwave irradiation, the reaction proceeded to
form 8a as the major product (65%) and 8b as the minor
product (35%). Better results were obtained when the reac-
tion was performed under microwave irradiation and
solvent-free conditions using K-10 montmorillonite clay
as a solid support. The ratio of the products formed under
these conditions was 75:25 with an overall yield of 84%.
To conclude, we have accomplished the synthesis of
novel polycyclic heterocyclic ring systems containing cou-
marin and chromone moieties under mild conditions.27
E.R. thanks CSIR-SRF, New Delhi, for financial
support, R.R. thanks DST-FIST for NMR facilities and
financial assistance.
Supplementary data
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.tetlet.
2008.01.059.

1816
E. Ramesh, R. Raghunathan / Tetrahedron Letters 49 (2008) 1812–1817
column chromatography (100–200 mesh) using hexane–ethyl acetate
References and notes
(8:2) as eluent.
Compound 4a: Pale yellow solid, mp: 152 °C; 1H NMR (400 MHz,
CDCl3): 1.75 (s, 3H), 2.01 (s, 3H), 3.41 (s, 3H), 3.78 (s, 3H ), 5.18 (d,
J = 4.5 Hz, 2H), 5.33 (t, J = 4.5 Hz, 1H), 7.38 (s, 1H), 9.49 (s, 1H);13C
NMR (100 MHz, CDCl3): d 20.2, 24.3, 30.4, 30.1, 32.4, 104.8, 117.7,
117.9, 130.9, 132.2, 150.4, 158.8, 147.5, 178.6; MS (EI) m/z: 275 (M+);
Anal. Calcd for C14H17N3O3: C, 61.09; H, 6.18; N, 15.27. Found: C,
60.77; H, 6.14; N,15.23.
Compound 4b: Pale yellow solid, mp: 170 °C; 1H NMR (400 MHz,
CDCl3): d 3.42 (s, 3H), 3.82 (s, 3H), 5.54 (d, J = 4.8 Hz, 2H), 6.22 (d,
J = 16.1 Hz 1H ), 6.35 (dt, J = 16.1 Hz, 1H), 7.02–7.73 (m, 5H), 7.45
(s, 1H), 9.58 (s, 1H); 13C NMR (100 MHz, CDCl3): d 29.5, 33.6, 31.5,
104.5, 117.7, 126.4 128.0, 128.7, 128.9, 130.5, 131.0, 133.2, 133.4,
135.2, 146.6, 150.1, 157.3, 178.3 ppm; MS (EI) m/z: 323 (M+); Anal.
Calcd for C18H17N3O3: C,66.87; H, 5.26; N, 13.00. Found: C, 66.77;
H, 5.23; N, 13.14.
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Organic Synthesis; Wasserman, H. H., Ed.; Academic Press: San
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Chromenes, Chromanones and Chromones; Ellis, G. P., Ed.; John
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B., Eds.; North-Holland Publishing Co.: New York, 1974.
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25. Rathna Durga, R.; Jayashankaran, J.; Raghunathan, R. Tetrahedron
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2007, 48, 1835–1839.
27. General procedure for the intramolecular domino Knoevenagel–hetero
Diels–Alder reaction: Method A: To a refluxing solution of unsym-
metrical 1,3-dione (1 mmol) in 10 mL of dry toluene, aldehyde 4a or
4b (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 chroma-
tography using hexane/ethyl acetate (7:3).
12. Mitaku, S.; Skaltsounis, A. L.; Tillequin, F.; Koch, M.; Pusset, J.;
Chauviere, G. J. Nat. Prod. 1985, 48, 772–773.
13. Buslig, B. S., Ed.Flavonoids in Living Systems: Advances in Exper-
imental Medicine and Biology; Manthy, J. A., Ed.; Plenum: New
York, 1998; Vol. 439.
14. Korkina, G. L.; Afanas’ev, I. B. In Sies, H., Ed.; Adv. Pharmacol.
1997, 38, 151.
15. Groundwater, P. W.; Solomon, K. R. H.; Drewe, J. A.; Munawar, M.
A. In Progress in Medicinal Chemistry; Ellis, G. P., Luscombe, D. K.,
Eds.; Elsevier: Amsterdam, 1996; Vol. 33, p 233.
16. Negwer, M. Organic Chemical Drugs and their Synonyms, 7th ed.;
Akademie: Stuttgart, 1994.
17. Varaprasad, C. V. N. S.; Ramasamy, S. K.; Girardet, J. L.; Gunic, E.;
Lai, V.; Zhong, Z.; An, H.; Hong, Z. Bioorg. Chem. 2007, 35, 25–
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899–902.
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D. L.; Galemmo, R. A. Bioorg. Med. Chem. Lett. 2006, 16, 5778–
5783.
Method B: A mixture of unsymmetrical dione (1 mmol) and the
corresponding aldehyde (1 mmol) in dry ethanol was irradiated using
a microwave oven (Kenstar, 600 W power) until the disappearance of
the starting material. After removal of the solvent, the crude reaction
mixture was subjected to flash column chromatography as reported in
method A.
Method C: A mixture of 1,3-dione (1 mmol), the corresponding
aldehyde (1 mmol) and K-10 montmorillonite clay (1.0 g) was
thoroughly ground in a mortar. The reaction mixture was irradiated
with a microwave (600 W) until the disappearance of the starting
material as evidenced by thin layer chromatography. After comple-
tion of the reaction, the clay was separated by filtration and the
product extracted with dichloromethane (2 ꢁ 15 mL). Removal of the
solvent and the purification of the crude reaction mixture by flash
column chromatography gave the pure product.
20. Klump, S.; Frey, M.; Kleefeld, G.; Sauer, A.; Eger, K. Biochem.
Pharmacol. 1989, 38, 949–953.
21. Wade, A. E.; Krawczyk, S. H.; Townsend, B. L. Tetrahedron Lett.
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7a,15b-cis-6,7-Dihydro-2,4-dioxo-3,5,8,8-tetramethyl-7,7a,8,15b-tetra-
hydropyrimido[2,3-b]pyrrolizino[40,30:4,5] pyrano[5,6-c]coumarin 7a:
;
Yellow solid, mp: 230–232 °C; IR (KBr): 1640 cmꢀ1 1H NMR
22. Edstrom, E. D.; Wei, Y. Tetrahedron Lett. 1994, 35, 8989–8990.
23. Experimental procedure for compound 2: 2,4-Dioxo-tetrahydropyr-
role[2,3-d]pyrimidine 1 (0.01 mol) in DMF (10 mL) was added slowly
with stirring and exclusion of moisture to a mixture of DMF (0.4 mol)
and POCl3 (0.01 mol), keeping the temperature between 20 and 30 °C.
After cooling to 0 °C, the resulting yellow solid was filtered and the
solid was heated with water (10 mL) at 60–80 °C for 45 min. After
cooling, the resulting precipitate was filtered, washed with H2O and
then recrystallized from ethyl acetate. Purple solid, mp: 282 °C 1H
NMR (400 MHz, DMSO): 3.30 (s, 3H), 3.57 (s, 3H), 6.81 (s, 1H), 9.32
(s, 1H), 12.2 (s, 1H, br s).; MS (EI) m/z: 207 (M+); Anal. Calcd for
C9H9 N3O3: C, 52.17; H, 4.38; N, 20.28. Found: C, 51.90; H, 4.41; N,
20.24.
(300 MHz, CDCl3): d 1.51 (s, 3H), 1.58 (s, 3H), 3.32 (s, 3H), 3.36–3.44
(m, 1Hb), 3.62 (s, 3H), 4.16 (dd, J = 7.3, 9.9 Hz, 1H), 4.23 (d,
J = 6.8 Hz, 1Ha), 4.49 (dd, J = 8.4, 9.9 Hz, 1H), 6.65 (s, 1H), 7.21–
7.27 (m, 2H), 7.45–7.51 (m, 2H); 13C NMR (75 MHz, CDCl3): d
25.36, 26.15, 26.40, 28.05, 30.06, 32.60, 45.09, 49.86, 70.40, 76.60,
104.56, 105.80, 121.28, 123.46, 125.4, 128.80, 132.46, 133.30, 138.5,
149.5, 151.40, 158.80, 165.5 ppm; MS (EI) m/z: 419.43 (M+); Anal.
Calcd for C23H21N3O5: C, 65.86; H, 5.05; N, 10.02. Found: C, 66.00;
H, 5.15; N, 9.89.
7a,15b-cis-6,7-dihydro-2,4-dioxo-3,5,8,8-tetramethyl-7,7a,8,15b-tetra-
hydropyrimido[2,3-b]pyrrolizino[40,30:4,5]pyrano[6,5-c]chromone 7b:
;
Yellow solid, mp: 247–249 °C; IR (KBr): 1732 cmꢀ1 1H NMR
(300 MHz, CDCl3): d 1.54 (s, 3H), 1.57 (s, 3H), 3.30 (s, 3H), 3.28–3.35
(m, 1Hb), 3.68 (s, 3H), 4.03 (dd, J = 7.1 Hz, 1H), 4.21(d, J = 6.0 Hz,
1Ha), 4.32 (dd, J = 8.4 Hz, 1H), 6.62 (s, 1H), 7.22–7.37 (m, 2H), 7.35–
7.42 (m, 2H); 13C NMR (75 MHz, CDCl3): d 24.30, 25.05, 24.40,
27.05, 32.16, 31.50, 45.15, 48.80, 69.40, 75.60, 105.50, 111.80, 122.24,
123.36, 125.4, 127.96, 130.46, 134.30, 136.5, 145.5, 153.40, 153.80,
177.1 ppm; MS (EI) m/z: 419.43 (M+); Anal. Calcd for C23H21N3O5:
C, 65.86; H, 5.05; N, 10.02. Found: C, 65.98; H, 5.20; N, 9.87.
24. Experimental procedure for compounds 4a/4b: 1,3-Dimethyl-2,4-dioxo-
1H-pyrrolo[2,3-d]pyrimidine-6-carbaldehyde 2 (10 mmol) in DMF
(20 mL) was treated with solid K2CO3 (16 mmol) and 1-bromo-3-
methylbut-2-ene (12 mmol) or cinnamyl bromide (12 mmol) and the
mixture was stirred overnight at 20 °C. Water (50 mL) was added to
the mixture and the aqueous layer was extracted with ethyl acetate
(4 ꢁ 20 mL).The combined organic layer was dried (MgSO4) and the
solvent was removed in vacuo and the crude product subjected to

E. Ramesh, R. Raghunathan / Tetrahedron Letters 49 (2008) 1812–1817
1817
7a,15b-cis-6,7-dihydro-3,5-dimethyl-2,4-dioxo-8-phenyl-7,7a,8,15b-tetra-
hydropyrimido[2,3-b]pyrrolizino[40,30:4,5]pyrano[5,6-c]coumarin 8a:
7a,15b-cis-6,7-dihydro-3,5-dimethyl-2,4-dioxo-8-phenyl-7,7a,8,15b-tetra-
hydropyrimido[2,3-b]pyrrolizino[40,30:4,5]pyrano[6,5-c]chromone 8b:
;
Yellow solid, mp: 248–249 °C; IR (KBr): 1728 cmꢀ1 1H NMR
Yellow solid, mp: 241–242 °C; IR (KBr): 1644 cmꢀ1
,
1H NMR
(300 MHz, CDCl3): d 3.28 (s, 3H), 3.32 (s, 3H), 3.90 (dd, J = 7.0,
10.1 Hz, 1H), 3.36–3.40 (m, 1Hb), 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 (d, 1H), 7.03–7.29
(m, 9H); 13C NMR (75 MHz, CDCl3): d 29.5, 31.5, 33.6, 37.4, 42.8,
77.9, 91.2, 100.5, 105.7, 117.2, 119.3, 121.5, 125.5, 125.6, 126.8, 127.8,
127.9, 128.4, 128.6, 138.5, 140.9, 150.2, 151.4, 158.3, 162.0 ppm; MS
(EI) m/z: 467.47 (M+); Anal. Calcd for C27H21N3O5: C, 69.37; H,
4.53; N, 8.99. Found: C, 69.51; H, 4.64; N, 8.76.
(300 MHz, CDCl3): d 3.37 (s, 3H), 3.38 (s, 3H), 3.48–3.52 (m, 1Hb),
3.89 (dd, J = 7.2, 10.0 Hz, 1H), 4.35 (dd, J = 7.2, 10.0 Hz, 1H), 4.55
(d, J = 6.8 Hz, 1Ha), 5.35 (d, J = 9.6 Hz, 1H), 6.12 (s, 1H), 7.07–7.31
(m, 9H); 13C NMR (75 MHz, CDCl3): d 29.1, 31.2, 32.4, 37.6, 42.0,
77.3, 90.9, 100.3, 104.6, 116.2, 118.4, 121.3, 125.2, 125.8, 126.9, 127.1,
130.6, 128.4, 128.5, 138.3, 140.4, 150.8, 151.2, 158.1, 178.2 ppm; MS
(EI) m/z: 467.47 (M+); Anal. Calcd for C27H21N3O5: C, 69.37; H,
4.53; N, 8.99. Found: C, 69.55; H, 4.70; N, 8.80.