Experimental and theoretical study of the spectroscopic properties and the preparation of 3-benzyl-2H-pyrano[3,2-c]chromene-2,5(6H)-dione

Article abstract of DOI:10.1016/j.molstruc.2013.09.041

Compound 3-benzyl-2H-pyrano[3,2-c]chromene-2,5(6H)-dione(3), was prepared and fully characterized. The vibrational modes (FT-IR) and NMR data ( ¹H and ¹³C chemical shifts) were compared with the results of Density Functional Theory (

Full text of DOI:10.1016/j.molstruc.2013.09.041

Accepted Manuscript
Experimental and theoretical study of the spectroscopic properties and the prep-
aration of 3-benzyl-2H-pyrano[3,2-c]chromene-2,5(6H)-dione
Firouz Matloubi Moghaddam, Behzad Koushki Foroushani
PII:
S0022-2860(13)00816-8
DOI:
http://dx.doi.org/10.1016/j.molstruc.2013.09.041
MOLSTR 20038
Reference:
To appear in:
Journal of Molecular Structure
Please cite this article as: F.M. Moghaddam, B.K. Foroushani, Experimental and theoretical study of the
spectroscopic properties and the preparation of 3-benzyl-2H-pyrano[3,2-c]chromene-2,5(6H)-dione, Journal of
Molecular Structure (2013), doi: http://dx.doi.org/10.1016/j.molstruc.2013.09.041
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Experimental and theoretical study of the spectroscopic properties and the preparation
of 3-benzyl-2H-pyrano[3,2-c]chromene-2,5(6H)-dione
a*
FirouzMatloubiMoghaddam , BehzadKoushkiForoushani
a
Laboratory of Organic Synthesis and Natural Products, Department of Chemistry, Sharif
University of Technology, Azadi Street, PO Box 11155-9516, Tehran, Iran, Tel.: +98-21-
66165309; Fax: +98-21-66012983
.
ABSTRACT
Compound 3-benzyl-2H-pyrano[3,2-c]chromene-2,5(6H)-dione(3),wasprepared and fully
1
13
characterized. The vibrational modes (FT-IR) and NMR data ( H and C chemical
shifts)were compared with the results of Density Functional Theory (DFT) method at
theB3LYP/cc-PVTZ level. The calculated vibrational frequenciesand NMR chemical shifts
are in good agreement with the experimental results. The electronic (UV-Vis) spectrum was
2 2
calculated usingthe TD-DFT method in CH Cl with the Polarizable Continuum Model using
the integral equation formalism variant (IEFPCM) and was correlated to the experimental
spectra. The assignment and analysis of the frontierHOMO and LUMO orbitals indicate that
absorption band isoriginated mainly from the π→π* transitions.
Keywords: Coumarine, DFT calculations,FT-IR,NMR, Spectroscopy,UV-Vis
1

1. Introduction
Generally, coumarin derivatives are an important class of organic compounds forming
building blocks of many natural and biologically active molecules [1-3]. They have
outstanding pharmacological properties,such asantibacterial [4], antifungal [5], antiviral [6],
and anticoagulant [7].They have also been usedaschemotherapeutics [8] and biological
inhibitors [9].Moreover, theywereapplied as food additives [10], luminescence dyes [11],
laser dyes [12] and molecular switches [13].
Alongside, coumarin derivatives containing pyran-2-one frameworks(pyranobenzopyrans)
exhibit distinguished biological properties. For instance, Norneolambertellin, which isisolated
from a mycroparasite,Lambertella sp.1346, acts as an antifungal [14]. Fordianin A and
fordianin B have cytotoxicity against the A549 (human lung cancer) and human cervical
carcinoma, [15-17].
Moreover, pyranobenzopyrans are highly conjugated and this feature makes themsuitable
candidates forbeing used as fluorescent chemosensors [18], iondetectors [19], molecular
switches [20], photochromic switches [21], photosensitizers and photoinitiators [22].
The computational approaches have been applied in organic chemistry yields important
information for the molecular properties such as the energy, geometry and thermodynamic
properties [23].
In addition, these approaches have been utilized in simulation of spectroscopy data such as
NMR, IR,Raman and Uv-Vis. in polycyclic heteroatomic molecules. Due to extensive
overlapping of different signals, the elucidation and interpretation of the spectra is
difficult.DFT calculationscan simulate the spectra with acceptable precision and accuracyin
comparison with experimental counterparts, in order to explicate the molecular structure [24].
2

Coumarine derivatives also has not been abondened in DFT studies. There are some
contributionsinDFT studies of the coumarin derivatives [25–27],however, to the best of
current researchers knowledge, no theoretical study was reported on the pyranobenzopyrans,
specifically on the pyrano[3,2-c]chromene-2,5-dione systems. The goal of this study is to
investigate the molecular structureand spectroscopic characterization of a new 3-benzyl-2H-
pyrano[3,2-c]chromene-2,5(6H)-dione (3).In addition, molecular structure parameters,
vibrational frequencies and NMR chemical shifts of the titled compound have been calculated
and compared with the experimental data. HOMO, LUMO and UV spectral analysis havealso
been used to elucidate the electronic transitions within the molecule.
2. Experimental
2.1. Materials and method
All materials used are commercially available, purchased from Merck and used
2
without any additional purification. SiO TLC plates 60F254were alsopurchased from Merck.
Melting points were determined (in sealed capillaries) on a BÜCHI Melting Point B-540
1
13
app.aratus. H-NMR and C-NMR spectra were recorded on a Bruker (Avance DRX-500)
spectrometer using CDCl as solvent at ambient temperature. Chemical shifts δ are reported
3
in ppm relative to tetramethylsilane as the internal standard. Elemental analysis were
performed by a Perkin Elmer 2004 (II) CHN analyzer.The FT-IR spectra were recorded from
-1
KBr pallets in the range of 4000-400 cm on Perkin Elmer Spectrum 2000 infrared
2 2
spectrometer.Uv-Vis spectrum was recorded by SINCO S-3150 spectrometer in CH Cl . The
preparation of 3 withatomic numbering scheme is shown in Scheme 1.
2.2. The procedure for the preparation of 3:
A mixture of 4-hydroxycoumarin (0.19 g, 1.2 mmol) and triethylamine (0.2 ml, 1.5
mmol) was stirred at room temperature for 2 min. Then, Baylis-Hillman adduct acetate 2
(0.30 g, 1 mmol)was added and the reaction mixture was heated at 90 °C and the progress of
3

reaction was monitored by TLC. After completion, the reaction mixture was cooled to room
temperature. The pure product was obtained from recrystallization of reaction mixture
frommethanol to afford 3 ( 0.26 g, 0.85 mmol).
3-benzylpyrano[3,2-c]chromene-2,5-dione(3):
˚
White powder; M.p. 183-185 C, IR (KBr): νmax.3064, 2918, 2860,1744,1717, 1076,
-
1 1
1
012 cm , H NMR (500 MHz, CDCl
.40-7.43 (m, 2H),7.68 (dd, J= 8.9, 1.5 Hz, 2H), 8.08 (d, J= 7.89 Hz, 1H); C NMR (125
): δ 36.8, 103.7, 113.1, 117.3, 123.3, 125.2, 127.2, 129.0, 129.3, 129.4, 134.0,
36.4, 136.7, 153.2, 159.1, 159.5, 160.0 .Anal. calcd for C19 : C, 74.99; H, 3.97%.
found: C, 74.85; H, 3.92%.
3
): 3.90 (s, 2H),7.27-7.30 (m, 3H), 7.31-7.38 (m, 2H),
1
3
7
MHz, CDCl
3
1
12 4
H O
3. Theoretical methods
The Molecular modeling was performed using GAMESS forcalculations[28]. In the
present work,the calculations have been carried out at DFT [29]using the hybrid B3LYP
approach [30, 31] and the cc-PVTZ basis set. The vibrational frequencies of the molecule
werecalculated for the complete equilibrium geometry obtained by the same
quantumchemical model in the gas phase. The frequency values computed at these
levelscontain known systematic errors and therefore, scaling factors 0.99 [32] and 0.98[33]
-1
-1
1
13
were used for 1700-4000 cm and 400-1700 cm ranges respectively. H and C NMR
chemical shifts of the compound were calculated using GIAO method[34-37] in CDCl and
TMS as a reference.The absorption spectra of compounds in CH Cl were calculated based
3
2
2
onthe optimized singlet-states using unrestricted TD-DFTwith thePolarizable Continuum
Model using the integral equation formalism variant(IEFPCM).GaussSumwas used to
calculate group contributions to the molecularorbitals and to simulate the UV-Vis absorption
[
38].
4

4. Results and discussion
4.1. Structural properties
The theoretical bond length and bond angle values were calculated by DFT-B3LYP/6-cc-
PVTZ method.Since thecrystal structure of3was not obtainable, the optimized geometrical
structure was compared with another analogous8-N,N-Dimethylamino-2,2-dimethyl-2H-
pyrano[3,2-c]chromen-5-one[39].From the structural data given in Table 1, it is observed that
the average relative error for different bond lengths and bond angles is 1.02 % and 0.59 %
respectively.This verifies that the experimental results are in good agreement with the level of
calculations. As seen from Table 1, optimized bond lengths and bond angles are slightly
different from the experimental ones.It occurs, becausethe conditions of theoretical
calculations and experimental onesare different and the corresponding values obtained by X-
ray diffraction did not belong to the same structure as 3.
<
Scheme1>
<
Table 1>
4
.2. Vibrational spectra
The main goal of this part is to properly assign the experimental IRfrequencies to the
computed vibrational modes of 3. Therefore, we performed a frequency calculation analysis.
It is obvious that the calculated frequencies by the basis of quantum mechanical force
fields method differ from corresponding experimental quantities due to some
reasons:Calculated vibrational frequencies often use the harmonicoscillator approximation. In
most cases, this model is not well suited to describe the molecular vibrations and it causes
systematic errors in the calculated harmonic vibrational[40]. In addition, the intrinsic
deficiencyofthe approximate nature of calculation methods and the use of finite basis sets
increases the deviation of calculated frequencies from the experimental ones [41-43].To
5

overcome these problems, the scaling factor is commonly used in order to correct the
calculated value to match the experimental observable such as the vibrational frequencies.The
−1
scaling factors 0.98 and 0.99 were usedfor the region below 1800 cm and above 1800
−1
cm respectively. To assign the observed peaks, vibrational frequencies were analyzedand
were compared with calculated FT-IRof the corresponding compound by performing one to
one correlation and the results are shown in Table 2.
<
Table 2>
4
.2.1. Carbon–hydrogen vibrations:
-
The aromatic C–H stretching vibrations are usually presented in the region 3000–3100 cm
1
[
44]. In this region, the vibrations are not affected by the substitution. The intensities of the
corresponding peaksare a multiplicity of weak to moderate intensities. In this study,
-1
following C–H stretching vibrationsare observed:the band at3064 cm is related toasymmetric
C-H stretching for aromaticC-H bonds.The intensities of the vibrations are weak and hard to
-1
assign due to the low dipole moment changes in C-H bonds. The signal at2918 and 2860 cm
is attributed toasymmetric and symmetricC-H vibrations for CH . Aliphatic CH stretching
2
2
-1
vibrations mainly consist of two parts falling in the region below 3000 cm . Asymmetric
stretching vibrations exhibit a peak in higher frequencies than the symmetric ones.
The C–H in-plane bending modes have medium intensities andare represented in the region
−1
-1
8
50–1350 cm . For aromatic rings 1 and 2, the bands observed at 1491 and 1463 cm are
assigned to the C–H in-plane rocking and scissoring vibrations of aromatic rings 1 and 2
−1
respectively. Their calculated equivalent frequenciesare 1493 and 1463 cm .
Other C-H stretching bands are complex and overlapped with other in-plane bendings,
specifically with CH
2
wagging movements. Some of their experimental bands are: 1112,
-1
1
173, 1266, 1382 and 1397 cm which are assigned to the corresponding calculated ones
-1
as1123, 1178, 1249, 1382 and 1392 cm respectively. The C–H out-of-plane bending
6

-1
vibrations contribute mainly to 696 and762 cm . Theseare also assigned to the calculated
-1
ones as 706 and764 cm . It is obvious that, in most cases, there is agood agreement between
the experimental and theoretical results.
4
.2.2. Carbon-Carbon vibrations:
Aromatic ring C-C stretching bands usually appear in range of 1200-1650 cm and
thestretchingis not substitution sensitive. For titled compound3, the vibrations fall in region
-1
-
1
-1
1
567-1605 cm . The band observed in 1636 cm exhibits the asymmetric stretching of
=C vibration. They consist of a mixture of two modes which is related to the calculated
one as 1636 cm . Other observed frequencies are 1567 and 1605 cm whichare assigned to
C
1
2
-
1
-1
-1
their calculatedcounterparts as 1549 and 1612 cm .
.2.3. Carbon-Oxygen vibrations
The experimental spectrum of 3exhibits two strongabsorbances at 1744 and 1717 cm . The
4
-1
-1
analysis of the calculated counterparts at 1712and 1736cm indicates two asymmetric and
symmetricstretchingsfor two carbonyl groups. The absorptions at 1076, 1012, 908 and 935
-1
-1
cm in observed spectrum are assigned to 1060 cm as asymmetric stretching of C4-O bond,
-1
-1
1
006 cm as twisting vibrations of C13-O and C4-O, 906 cm as rocking vibration of C6-O
-1
-1
9
08 cm and942 cm as in-plane bending of C13-O and C4-O.As seen from Figure 1, there is
a good correlation between the experimental and calculated frequencies (unscaled).
Figure1>
<
4
.3. NMR calculation:
After the geometry optimization of compound 3, Gauge-Including Atomic Orbital (GIAO)
1
3
1
method was used for predicting C NMR and H NMR chemical shifts using DFT-B3LYP
functional with cc-PVTZ method.
7

1
3
1
The relationship between the experimental C and H chemical shifts (δexp) and (GIAO)
magnetic isotropic shielding constants (δcalc) is usually linear and described by the following
equation: δexp= a+bδcalc[45]. The slope and intercept of the least-square correlation are
utilized to predict chemical shifts andthe linear correlation coefficient (r) is used to verify the
precision and the agreement between the experimental and theoretical data. In the present
study, the correlation coefficient for proton chemical shift is determined as 0.9641. This
1
3
proves fair agreement between the experimental and their calculated data while for C NMR,
1
13
there is a good agreement (r= 0.9977) (Figure 2). The accurate prediction of H NMR and C
NMR spectra of a molecule is directly proportional to intermolecular forces (solute-solvent).
Since protons are placed on the periphery of the molecule, they are more susceptible to take
intermolecular effects, rather than carbon atoms and therefore, some inconsistencies are
observed in 1H NMR spectra [46].According to the comparison between calculated data and
experimental counterparts, the calculated chemical shifts are in acceptable agreement with the
1
experimental results. In HNMR spectrum, one singlet peakis observed at 3.90 δppm for CH
2
.
The multiplet peaks between 7.27-7.31 and 7.31-7.38 δppm show the protons of phenyl group
C19-C23). The peaks at 7.40-7.43 and 7.66-7.69 δppmrepresent the protons of (C7- C10 and
(
C16) which are more shielded. Compound 3 has 17 different carbon atoms, as expected from
the structure.Theproposed assignment for experimental signals and their calculated
counterparts are presented in Table 3.
<
Table 3>
<
Figure 2>
4
.4. UV-Viscalculations:
Electronic absorption spectrum of 3has been investigated in CH
B3LYP/cc-PVTZ method and has been compared with experimental counterpart (Figure 3).
2 2
Cl using TD-DFT at
8

<Figure3>
Singlet excited states were calculated to predict the transition energies. Experimental and
calculated electronic transitions, oscillator strengths and their assignments for compound 3 is
presented in Table 4.
<
Table 4>
The spectrum shows two bands, a long wavelength band covering the 330–390 nm
regionwith a maxima at 351 nmand a medium wavelength coveringthe 250–320 nm
regionwith a maxima at 277 nm. The absorptionobserved at 277 nm is related to thesinglet
state HOMO-1→L transitions.The calculated counterpart for this maxima is 314 nm.The
maximum wavelength (351 nm) corresponds to the electronic transition from the highest
occupied molecular orbital (HOMO) to lowest unoccupied molecular orbital (LUMO) with
9
7% contribution.The calculated equivalent for this wavelength is 342 nm, which show
acceptable agreement with theoretical value. However, the calculated spectrum shows an
absorption bands at 303 nm. The latter was not observed experimentally.
Energy levels and band gap for the frontier orbitals were shown to understand scheme of
present compound (Figure 4).
<
Figure 4>
Conclusion
In this study, compound 3-benzyl-2H-pyrano[3,2-c]chromene-2,5(6H)-dione has been
investigated as a potent candidate to be used as a pharmaceutical compound and
1
chemosensor. This compound was fully characterized by elemental analysis, UV-Vis, IR, H
1
3
1
13
NMR, C NMR. For the first time, FT-IR, H NMR, C NMR andUv-Vis spectra of the
title compound was recorded and simulated by DFT approaches. The TD-DFT approach in
the solution (CH
2
Cl
2
) were applied to assign the electronic transitions observed in the Uv-Vis
9

spectra. The calculated vibrational frequencies and chemical shift values were compared with
the experimental counterparts. The calculated vibrational spectrum and NMR chemical shifts
are in good agreement with the experimental results. The electronic absorption calculated
using the TD-DFT method was assigned to the experimental data. Good agreement between
the experimental and theoretical results were observed. Moreover, The HOMO–LUMO
energy gap of title compound is determined as 3.53 e.v.
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1
3

Schemes and Figures captions:
Scheme1.Synthesis pathway and atom numbering for 3-benzyl-2H-pyrano[3,2-c]chromene-
2,5(6H)-dione (3)
Figure 1. Correlation between the experimental FT-IR and calculated wavenumbers by the
B3LYP/cc-PVTZ level for 3;νexp = 1.0581νcal- 47.904, r = 0.9992
1
Figure 2.Correlation between the experimental H-NMR (δexp = 0.924δcal+ 47.904, r =
1
3
0
.9641) and C-NMR (δ = 1.0424δ - 5.5899, r = 0.9977) and calculated the B3LYP/cc-
exp cal
PVTZ for 3.
Figure3. Calculated (a) and experimental (b) UV-Vis spectrum of 3
Figure4. The frontier molecular orbitals of 3
1
4

a
Table 1.Structural parameters for 3 calculated by B3LYP/cc-PVTZ level
Structural
parameters
Bond length (Å)
C1-O12
C1-C2
C2-C4
O3-C4
O5-C4
O5-C6
C2-C13
C13-C14
C6-C11
C10-C11
C9-C10
C8-C9
B3LYP/ cc-
PVTZ
a
Experimental
Relative error (%)
1.339
1.369
1.454
1.208
1.377
1.368
1.427
1.354
1.400
1.403
1.380
1.399
1.385
1.389
1.350
1.363
1.446
1.205
1.389
1.376
1.449
1.326
1.406
1.403
1.351
1.420
1.405
1.366
0.82
0.44
0.55
0.25
0.86
0.58
1.52
2.11
0.43
0
2.15
1.48
1.42
1.68
C7-C8
C6-C7
Bond angle ( )
◦
C1-C2-C4
120.1
118.9
121.0
125.7
117.6
120.8
117.2
123.2
122.0
121.7
117.2
121.1
124.6
116.4
119.0
120.3
118.9
119.2
125.6
117.5
121.5
116.6
122.9
121.8
120.5
116.9
122.6
126.3
117.6
116.1
0.17
0
C1-C2-C13
C4-C2-C13
O3-C4-C2
O3-C4-O5
O12-C1-C2
O12-C1-C11
C4-O5-C6
C2-C1-C11
O5-C6-C11
O5-C6-C7
C7-C6-C11
C1-C11-C10
C1-C11-C6
C6-C11-C10
1.51
0.080
0.085
0.58
0.52
0.24
0.16
1.0
0.26
1.22
1.35
1.02
2.50
a
ref [39]
1
5

-1
Table 2.Experimental, calculated (unscaled and scaled) vibrational frequencies (cm ) and
a
IR intensity of 3calculated by B3LYP/cc-PVTZ level
B3LYP/cc-PVTZ
Experimental
Entry
Assignment
-1
Unsacl
ed
Scale
d
Intensi
ty
(cm )
1
2
3
4
5
6
ν(C-H)ring1,2asym.
3064w
2918w
2860w
3181
3055
3030
1771
1747
1669
3149
3025
3000
1736
1712
1636
49.6
10.3
ν(CH ) asym
2
ν(CH ) sym
11.7
2
ν(C =O, C =O) asym.
1744m
1717s
1636s
399.2
1886.1
408.7
4
13
ν(C
4
=O, C13=O) sym.
ν(C15=C16) asym.
ν(C =C10
=C ))ring2asym.
ν(C
9
,
7
1605m
1645
1612
159.8
C
7
8
8
9
1
=C
2
)
1567s
1491s
1463s
1397m
1382w
1581
1523
1489
1420
1410
1549
1493
1459
1392
1382
522.1
67.1
ρ(C-H)ring2
(C-H)ring2
1
1
1
0
1
2
ρ
r
92.1
τ(C =C ), ω(CH )
156.1
112.9
1
2
2
δ(C -H), ω(CH )
1
6
2
δ(C -H), τ(C -H, C -
1
6
10
7
1
1
1
3
4
5
1266m
1173s
1112s
1274
1202
1135
1249
1178
1123
88.6
46.2
65.8
H)ring2
ρ(C-H)ring1,2, δ(C10
-
H)ring2
ρ
r
(C
8
9 7
-H, C -H), δ(C -
H, C10-H)
1
1
1
1
2
2
6
7
8
9
0
1
ν(C -O)asym
4
1076s
1012s
908s
935
1082
1026
924
1060
1006
906
98.9
589
τ (C13-O, C -O)
4
τ (C=C)ring2, ρ(C -O)
59.7
299.2
138
6
δ(C -O, C -O)
961
942
1
3
4
γ (C-H)ring2
762s
696s
780
764
γ (C-H)ring1
720
706
69.5
a
b
w= weak, s= strong, m= medium. ν= stretching, δ= in plane bending, γ= out of plane
bending, ρ = rocking, ω= wagging, ρ= scissoring, τ= twisting , asym= anti-symmetric, sym=
symmetric, ring1= C18-C23, ring2= C6-C11
r
1
6

1
13
a
Table 3. Experimental and calculated H and C NMR chemical shifts (ppm)
Atom
H NMR
C17-H
C16-H
C7-H
C19-H
C23-H
C21-H
C9-H
C10-H
C22-H
C20-H
C8-H
Experimental
B3LYP/cc-PVTZ
1
3.90
3.52
6.81
7.17
7.17
7.17
7.28
7.3
7.66-7.69
7.66-7.69
7.27-7.30
7.27-7.30
7.27-7.30
7.40-7.43
7.40-7.43
7.31-7.38
7.31-7.38
7.40-7.43
8.09
7.3
7.33
7.33
7.58
7.96
C10-H
1
3
C
NMR
C17
C2
C11
C7
36.8
103.7
113.1
117.3
123.3
125.2
127.2
129.0
129.3
129.4
134
136.4
136.7
153.2
159.1
159.5
160.0
40.1
106
114.8
116.8
124.2
124.4
126.7
128.4
129.9
131.3
133.7
136.9
137.0
153.8
155.3
156.1
160.6
C10
C9
C21
C20,22
C19,23
C15
C8
C18
C16
C6
C4
C13
C1
a
3
In CDCl -DMSO(95:5 % V/V)
1
7

Table 4.Experimental and calculated electronic transitions, oscillator strengths and their
a
assignments for compound 3
Calculated
Experimental
ꢀE
Major contribution
Character
λ
ꢀE
nm) (eV)
ƒ
os
λ (nm),
(
(eV)
3.5
4.5
-
H→L (97%)
H-1→L(85%),
H-3→L (48%)
π→π*
π→π*
π→π*
342
3.6 0.51
4.0 0.00
4.1 0.02
351
277
-
314
303
a ƒos = Oscillator strength, H = Highest occupied molecular orbital, L = Lowest unoccupied
molecular orbital
1
8

Scheme 1
1
4
O
1
9
17
1
5
18
23
20
12
O
13
OAc O
10
1
OH
0
11
16
Et N, 90 C
9
8
3
21
2
22
Ph
OMe
Solvent-free
O
1
O
6
4
O
O
3
7
5
2
3
1
9

Figure 1
2
0

Figure 2

Figure3
2
2

Figure 4
2
3

The Main goal of this study is to investigate the synthesis and molecular structure, spectroscopic
characterization of a new 3-benzyl-2H-pyrano[3,2-c]chromene-2,5(6H)-dione (3).In addition,
molecular structure parameters, vibrational frequencies and NMR chemical shifts of the titled
compound have been calculated and compared with the experimental data. HOMO, LUMO and
UV spectral analysis have been used to elucidate the electronic transitions within the molecule.
14
O
1
9
17
1
5
18
23
20
12
O 13
1
OAc O
10
OH
0
11
16
Et N, 90 C
9
8
3
21
2
22
Ph
OMe
Solvent-free
O
1
O
6
4
O
O 3
7
5
2
3