Reinvestigation of prototropic photochromism: 3-Benzoyl-2-benzylchromones

Article abstract of DOI:10.1016/S0040-4020(03)01211-0

The synthesis of a series of new nine 3-benzoyl-2-benzylchromones is developed through a classical and an optimized Kostanecki-Robinson method involving an o-hydroxyphenyl-β-diketone and an acid anhydride. The different spectrokinetic studies carried out in solution and in polymer matrixes have highlighted the main structure/photochromic parameters relationships and the influence of the medium on the photochromic properties.

Full text of DOI:10.1016/S0040-4020(03)01211-0

Tetrahedron 59 (2003) 7725–7731
Reinvestigation of prototropic photochromism:
3-benzoyl-2-benzylchromones
*
V. Rossollin, V. Lokshin, A. Samat and R. Guglielmetti
´ ´ ´ ´
Faculte des Sciences de Luminy, Universite de la Mediterranee, UMR CNRS 6114, Case 901 13288 Marseille Cedex 9, France
Received 5 June 2003; revised 31 July 2003; accepted 31 July 2003
Abstract—The synthesis of a series of new nine 3-benzoyl-2-benzylchromones is developed through a classical and an optimized
Kostanecki–Robinson method involving an o-hydroxyphenyl-b-diketone and an acid anhydride. The different spectrokinetic studies carried
out in solution and in polymer matrixes have highlighted the main structure/photochromic parameters relationships and the influence of the
medium on the photochromic properties.
q 2003 Elsevier Ltd. All rights reserved.
1. Introduction
specific way about 30 years ago,5 but not developed
thereafter, seem to be promising by a broad range of
possible structural variations and potential photochromic
properties (Scheme 1).6
The recent marketing of variable optical transmission
glasses based on thermoreversible organic photochromes
involving electrocyclisation reactions such as spirooxazines
and chromenes has known growing success.1,2 The two
main limitations of these compounds, regarding their
applications, arise from the high dependency of the
photochromic properties of these molecules to the tempera-
ture and also their relatively low fatigue resistance.2,3
This work presents a synthetic approach to a series of such
chromones and a preliminary study of their photochromic
properties under continuous irradiation conditions.
2. Results and discussion
2.1. Synthesis
In order to by-pass these disadvantages, the conception of
new systems involving hydrogen transfer has been under-
taken. In such systems the reversible hydrogen shift between
two centers of the molecule induces a modification of the
electronic structure and then a change in absorption spectra.
The principal advantages of these prototropic systems are:
(i) they are thermally and/or photochemicaly reversible and
they could probably present a good resistance to the
fatigue;4 (ii) they do not involve important structural
modification: then lower activation energy for the thermal
decoloration could be expected compared to systems
involving electrocyclisation which induce important mol-
ecular motion. On the other hand, this limited molecular
reorganization makes the prototropic system able to work as
well in constrained medium (rigid polymeric matrix, solid
state) or not constrained medium (solution, flexible
polymeric matrix).
To prepare 3-benzoyl-2-benzylchromones, the Kostanecki–
Robinson method7–13 has been chosen (Way 1, Scheme 2).
This old and efficient method involving the Baker–
Venkataraman rearrangement allows introduction of a
large range of substituents. The two main precursors for
this approach are the o-hydroxyphenyl-b-diketones and an
acid anhydride. Nevertheless, this reaction leads to
undesirable by-products. For instance the cyclisation of
the o-acyl intermediate gives a coumarine (Way 2, Scheme
2), while the tricarbonylated intermediate leads to various
flavones substituted or not in 3-position14 (Ways 3 and 4,
Scheme 2).
Most of the o-hydroxyphenyl-b-diketones are obtained
using a traditional method involving a reaction between o-
hydroxy acetophenone and acid chloride,15 followed by a
Baker–Venkataraman rearrangement16,17 (Scheme 3). A
diethylamino group has been introduced using a thermal
condensation between a b-ketonic ester and a conveniently
substituted phenol18,19 (Scheme 4). Finally the Claisen
condensation20 between the o-hydroxy acetophenone and
Among the prototropic photochromic systems, compounds
such as 3-benzoyl-2-benzylchromones, described in a
Keywords: photochromism; prototropism; photoenolisation; chromones.
*
Corresponding author. Tel.: þ33-4-91-82-94-05; fax: þ33-4-91-82-93-
01; e-mail: samat@luminy.univ-mrs.fr
0040–4020/$ - see front matter q 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/S0040-4020(03)01211-0

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V. Rossollin et al. / Tetrahedron 59 (2003) 7725–7731
Scheme 1.
the ethylpicolinate allowed the introduction of a pyridine
ring (Scheme 5).
products (especially flavones15 which are often the major
products of the reaction, Scheme 2).
Among the synthesized b-diketones 1–9, compounds 2, 7
and 8 are new.
Nine new chromones have been prepared. Table 1 shows
that, in the cases where methods (a) and (b) have been
compared, the last one is the most efficient.
The homoveratric anhydride prepared from the reaction of
dicyclohexylcarbodiimide (DCC) with the corresponding
acid has been used to perform the Kostanecki–Robinson
reaction (Scheme 6), methoxy groups on the B-cycle
improving the photochromic response of the 3-benzoyl-2-
benzylchromones.
2.2. Photochromic behaviour
When they are submitted to UV irradiation, the chromones
undergo a thermally reversible colour change due to a
benzylic proton transfer towards the carbonyl group of the
benzoyl substituent (Scheme 8).
In this last reaction the sodium salt of the acid is generally
added (method (a), Scheme 7). Sodium hydride6 has been
used also as base (method (b), Scheme 7) in order to favour
the formation of the expected chromone instead of by-
The photochromic behaviour of the new 3-benzoyl-2-
benzylchromones has been evaluated under continuous
irradiation (xenon lamp) at room temperature using toluene
Scheme 2.

V. Rossollin et al. / Tetrahedron 59 (2003) 7725–7731
7727
Scheme 3.
Scheme 4.
Scheme 5.
Scheme 6.
and acetonitrile as solvents. The photostationary state is
reached, when possible, after several tens of minutes of
irradiation. In order to avoid degradation reaction occurring
generally after a long period of illumination, the irradiation
has been performed only for 3 min. An example of kinetic
behaviour is given on Figure 1 for compound 10.
Figure 1. Kinetics of 10 in toluene and 0.4% of DABCO (5£1023 M, 258C,
150 W Xenon lamp). Absorbance is measured at 474 nm (lmax of the
coloured form).
compared with those obtained with the unsubstitued 3-
benzoyl-2-benzylchromone (19) (Scheme 9) taken as
reference.
The detail of the experimental conditions is given in Section
4.
Three parameters are considered in order to characterize the
coloured form: (i) the maximum wavelength of absorption
(lmax); (j) the thermal decolouration rate (kD); (k) the
Spectrokinetic data are summarized in Table 2 and
Table 1. Structure and preparation of 3-benzoyl-2-benzylchromones
Compounds
R1
R2
R3
R4
X
Yield (%) method (a)
Yield (%) method (b)
Precursors
10
11
12
13
14
15
16
17
18
H
F
CH3
H
H
H
H
F
H
H
H
CH3
H
H
H
H
H
H
H
H
H
OCH3
CH3
H
N(Et)2
N(Et)2
H
H
H
H
H
Cl
CH3
H
H
H
CR1
CR1
CR1
CR1
CR1
CR1
CR1
CR1
N
31
26
44
–
–
–
13
–
–
43
67
62
25
28
31
40
53
19
1
2
3
4
5
6
7
8
9

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V. Rossollin et al. / Tetrahedron 59 (2003) 7725–7731
Scheme 7.
Concerning the wavelength of absorption of the coloured
form (lmax), from a general point of view the introduction of
two methoxy groups on the B cycle induces a bathochromic
shift when compared to the compound 19. In contrast, the
introduction of electrondonor groups on the C cycle gives a
high hypsochromic shift.
Table 2. Photochromic parameters obtained under continuous irradiation in
toluene and acetonitrile solutions (150 W Xenon lamp, 258C)
Compounds
Toluene
Acetonitrile
max (nm)
kD (s21
,1025
)
l
0
lmax (nm)
A3
10
11
12
13
14
15
16
17
18
19
474
461
458
454
474
478
450
440
471
460
0.61
0.35
0.15
0.9
0.75
0.62
1.4a
1.8a
0.21
0.32
443
440
446
432
450
450
1.3£1022
All the new compounds described show a very slow thermal
decolouration due to the high stability of the photoenolic
coloured forms in non polar solvent. However, in the case of
compounds 11 and 18, the introduction of substituents in the
ortho position of the A-cycle or the presence of a
heteroatom in place of a carbon atom in the ortho position
in the same cycle induces a clear acceleration of the rate
constants.
0
,1025
,1025
,1025
,1025
,1025
2.3£1023
,1025
No photochromism
No photochromism
447
430
a
At a concentration of 1023 mol/l and irradiation flux¼800 W/m2.
The studied chromones being very sensitive to the nature
of the medium, supplementary experiments were carried
out in solution in the presence of additives but also in
polymer matrix. Then, the addition of amino base
(DABCO) in the toluenic solution (0.4% compared to
the photochrome concentration) increases the thermal
decolouration rate significantly (10 to 103 times depend-
ing on the considered compound). On the contrary, the
addition of nickel salt in acetonitrile (20%) allows a
better observation of the photochromism by decreasing
the thermal decolouration rate. The study realized in
polyurethane (PU) and polymethylmethacrylate (PMMA)
polymer matrixes with compounds 10 and 18 shows that
the nature of the polymer plays a significant role on the
spectrokinetic parameters. Then changing PU
(Tg¼2208C) by PMMA (Tg¼þ1258C) leads to an
hypsochromic shift of the absorption of the coloured
form (Dlmax¼210 and 220 nm, respectively, for 10 and
18) and to a decrease in the thermal fading rates (£0.16
and £0.08, respectively, for 10 and 18).
Scheme 8.
Scheme 9.
3. Conclusion
0
colorability A3 which is the absorbance measured after
3 min of irradiation.
The synthesis of a series of nine new 3-benzoyl-2-
benzylchromones has been performed through an optimized
Kostanecki–Robinson method. A structure/photochromic
parameters relationship has been established for these
compounds for which the photochromism involves a
photoenolisation reaction.
In acetonitrile as solvent an average hypsochromic shift of
25 nm is observed compared to that in toluene. Moreover, if
the thermal decolouration rates are very slow in toluene,
they become extremely fast in acetonitrile and are not
evaluable, the absorbances obtained after 3 min of
irradiation being very weak (0.02–0.10). Then the follow-
ing discussion is related to results obtained in toluene.
Complementary studies carried out in solution and in
polymer matrixes showed also the influence of the medium on

V. Rossollin et al. / Tetrahedron 59 (2003) 7725–7731
7729
the photochromic properties. Structure variation and modifi-
cation of the medium allow to improve the photochromic
behaviour and especially the thermal stability of the photoenol
form, regarding applications for variable optical transmission
materials. The main limitations in this aim is nevertheless the
weaker photosensibility (10 to 102 times) towards conven-
tional photochromic pigments involving electrocyclisation
reaction (spirooxazines, naphthopyranes).
4.2.2. 1-(4-Diethylamino-2-hydroxyphenyl)-3-phenyl-
propane-1,3-dione (7). A mixture of 7.71 g (43.4 mmol)
of 2-(diethylamino)phenol and 6.95 g (36.23 mmol) of
ethylbenzoylacetate was heated at 2008C in an erlenmeyer.
After cooling, the residue was purified by column
chromatography, eluent pentane/Et2O (80/20). Crystallisa-
tion gave a yellow solid, yield 28%, mp 129 (from ethanol).
1H NMR (CDCl3): 100% enolic form; 1.21 (6H, t,
J¼7.1 Hz); 3.40 (4H, q, J¼7.1 Hz); 6.10 (1H, s); 6.23
(1H, d, J¼9.1 Hz); 6.64 (1H, s); 7.45–7.50 (3H, m); 7.59
(1H, d, J¼9.1 Hz); 7.90 (2H, d, J¼7.5 Hz); 12.70 (1H, s);
15.40 (1H, s).
4. Experimental
4.1. Materials and methods
4.2.3. (2,6-Difluorobenzoyl) ethylacetate (8a). Under
argon atmosphere, 36.8 g (0.36 mol) of Et3N and 42.5 g
(0.45 mol) of MgCl2 were added to a solution cooled at 10–
158C of 62.8 g (0.37 mol) of potassium monoethylmalonate
in 550 ml of CH3CN. The mixture was stirred 2.5 h at
ambient temperature, then cooled to 08C. 31.2 g (0.18 mol)
of 2,6-difluorobenzoyl chloride were added slowly and 3.6 g
(0.04 mol) of Et3N were again added. After stirring at
ambient temperature, the solvent was evaporated and
300 ml of toluene was added to the residue. The mixture
was cooled to 10–158C and hydrolized with 250 ml of a
solution of hydrochloric acid (12%). The organic layer was
separated, washed two times with 65 ml of solution of HCl
(12%) and water. The solvent was evaporated and the
residue was purified by column chromatography, eluent
CH2Cl2 to give colorless liquid. Yield 31%. 1H NMR
(CDCl3): 1.23 (3H, t, J¼6.9 Hz); 3.91 (2H, s, J¼6.9 Hz);
4.19 (2H, q); 7.28–7.32 (3H, m).
Solvents (Carlo Erba) were used without further purifi-
cation other than drying over molecular sieves. 1H and
13C NMR spectra were recorded on a Bruker BM 250
1
spectrometer (250 and 62.5 MHz, respectively, for H and
13C) using tetramethylsilane as internal standard. Chemi-
cal shifts are given in ppm and coupling constants in Hz.
Melting points (8C), measured in capillary tubes on a
Buchi 510 apparatus, are uncorrected. Column chroma-
tography was performed on silica gel Merck 60 (70–230
mesh). Elemental analysis was performed by the
Microanalytical Center of the CNRS. The reported
1
compounds identification was made by H NMR.
Photochromic measurements were performed in toluene
solutions of spectrometric grade (Aldrich) at 208C (^0.28),
at a concentration of 5£1023 mol/l and a irradiation
flux¼1000 W/m2. The analysis cell (optical pathlength
10 mm) was placed in a thermostated copper block inside
the sample chamber of a Cary 50 spectrometer. An Oriel
150 W high pressure Xe lamp was used for irradiation.
4.2.4. 1-(4-Diethylamino-2-hydroxyphenyl)-3-(2,6-
difluorophenyl)propane-1,3-dione
(8).
0.86 g
(5.21 mmol) of 2-(diethylamino)phenol and 1 g
(4.34 mmol) of 8a were heated in an erlenmeyer at 1608C.
After cooling, the residue was purified by column
chromatography, eluent pentane/Et2O (80/20). Crystallisa-
tion gave a yellow solid, yield 37%, mp 78 (from ethanol).
1H NMR (CDCl3): 100% enolic form; 1.20 (6H, t,
J¼7.1 Hz); 3.39 (4H, q, J¼7.1 Hz); 6.10 (1H, s); 6.20
(1H, d, J¼9.2 Hz); 6.34 (1H, s); 6.97 (2H, dd, J¼8.3 Hz);
7.38 (1H, dd, J¼8.3 Hz); 7.45 (1H, d, J¼9.2 Hz); 12.55
(1H, s); 15.08 (1H, s).
4.2. Starting materials
Homoveratric acid (Aldrich), sodium hydride (Aldrich),
DBU (Lancaster), 5 (Aldrich), 6 (Aldrich) were commer-
cially available. Compounds 1,5 3,21 4,22 923 and the
homoveratric anhydride24 were prepared according to
previously described methods.
4.2.1. 3-(2,6-Difluorophenyl)-1-(2-hydroxyphenyl)pro-
pane-1,3-dione (2). 6.8 g (50 mmol) of 20-hydroxyaceto-
phenone and 11.2 g (70 mmol) of 2,6-difluorobenzoyl
chloride were solubilized in 10 ml of pyridine. The mixture
was stirred at ambient temperature during 30 min. The
solution was carefully acidified with a cold solution (1N) of
hydrochloric acid, and the precipitate was collected by
filtration, washed repeatedly with water and dried. The
ortho-acylated derivative formed was solubilized in 20 ml
of dried DMSO, and the solution was added slowly to a
stirred suspension of 1.5 g (60 mmol) of sodium hydride
powder in 50 ml of dried DMSO. After 1 h, at ambient
temperature, the mixture was slowly carried out in a icy
satured solution of oxalic acid. The precipitate was collected
by filtration, washed repeatedly with water and dried to give
2 as a yellow powder. Crystallisation gave a yellow solid,
4.3. General methods for the synthesis of chromones
Method A. 2.08 mmol of the diketone, 4.16 mmol of the
homoveratric acid anhydride and 4.16 mmol of sodium salt
of homoveratric acid were heated at 1608C during 4 h. After
cooling, the mixture was solubilized in CH2Cl2. The organic
layer was washed three times with a saturated solution of
NaHCO3, dried with MgSO4 and evaporated. The residue
was purified by column chromatography, eluent CH2Cl2/-
Et2O (90/10).
Method B. 2 mmol of the diketone, 3 mmol of the
homoveratric acid anhydride and 3.4 mmol of sodium
hydride were refluxed 4 h in 6 ml of toluene. After cooling,
CH2Cl2 was added to the mixture. The organic layer was
washed three times with a solution of NaHCO3 (10%), dried
with MgSO4 and evaporated. The residue was purified by
column chromatography, eluent CH2Cl2/Et2O (90/10).
1
yield 65%, mp 126 (from methanol). H NMR (CDCl3):
100% enolic form; 6.58 (1H, s); 6.90 (1H, dd, J¼8.0 Hz);
6.98–7.04 (3H, m); 7.37–7.51 (2H, m); 7.68 (1H, d,
J¼8.1 Hz); 11.92 (1H, s); 15.09 (1H, s).

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V. Rossollin et al. / Tetrahedron 59 (2003) 7725–7731
3.95 (3H, s, OCH3); 4.06 (2H, s, CH2); 6.40–6.77 (4H, m,
H-8, H-20, H-50 and H-60); 6.8500(1H, d, J¼8.9 Hz, H-6); 7.33
(2H, dd, J¼7.7, 7.3 Hz, H-3 and H-500); 7.040 7 (1H, dd,
J¼7.3 Hz, H-400); 7.80 (2H, d, J¼7.3 Hz, H-2 and H-600);
7.95 (1H, d, J¼7.4 Hz, H-5). 13C NMR (CDCl3): 38.1 (t);
55.7 (2*q); 55.9 (q); 100.3 (d); 111.2 (d); 112.3 (d); 114.7
(d); 117.1 (s); 121.5 (d); 122.8 (s); 127.3 (d); 127.3 (s);
128.6 (2*d); 129.5 (2*d); 133.7 (d); 137.3 (s); 148.2 (s);
148.9 (s); 157.7 (s); 164.4 (s); 165.8 (s); 175.6 (s); 194.1 (s).
Anal. calcd for C26H22O6: C, 72.55; H, 5.15; found: C,
72.53, H, 5.17.
4.3.1. 3-Benzoyl-2-(3,4-dimethoxybenzyl)[4H-1]benzo-
pyran-4-one (10). Method A: 31%, Method B: 43% yield.
Crystallisation gave a white solid, mp 135 (from methanol).
1H NMR (CDCl3): 3.70 (3H, s, OCH3); 3.81 (3H, s, OCH3);
3.88 (2H, s, CH2); 6.72 (1H, d, J¼8.2 Hz, H-50); 6.75 (1H, s,
H-2000); 6.86 (1H, d, J¼008.2 Hz, H-60); 7.36–7.47 (4H, m, H-8,
H-3 , H-400 and H-5 ); 7.57 (1H, dd,J¼7.5, 7.9 Hz, H-6);
7.68 (1H, dd, J¼7.5, 7.6 Hz, H-7); 7.87 (2H, d, J¼7.2 Hz,
H-200 and H-600); 8.15 (1H, d, J¼7.9 Hz, H-5); 13C NMR
(CDCl3): 38.2 (t); 55.6 (q); 55.8 (q); 111.2 (d); 112.3 (d);
117.9 (d); 121.5 (d); 122.9 (s); 123.3 (s); 125.4 (d); 125.9
(d); 127.1 (s); 128.6 (2*d); 129.4 (2*d); 133.7 (d); 134.1 (d);
137.1 (s); 148.2 (s); 148.9 (s); 155.9 (s); 166.3 (s); 176.2 (s);
193.9 (s). Anal. calcd for C25H20O5: C, 74.99; H, 5.03;
found: C, 74.89, H, 5.07.
4.3.5. 3-Benzoyl-6-chloro-2-(3,4-dimethoxybenzyl)-7-
methyl[4H-1]benzopyran-4-one(14). Method B: 28%
yield. Crystallisation gave a yellow solid, mp 159 (from
methanol). 1H NMR (CDCl3): 2.47 (3H, s, CH3); 3.70 (3H,
s, OCH3); 3.80 (3H, s, OCH3); 3.85 (2H, s, CH2); 6.72–6.84
(3H, m, H-20, H-50 and H-60); 7.34 (1H, s, H-8); 7.42 (2H,
dd, J¼7.2, 7.3 Hz, H-300 and H-500); 7.57 (1H, dd, J¼7.3 Hz,
H-400); 7.85 (2H, d, J¼7.2 Hz, H-200 and H-600); 8.08 (1H, s,
H-5). 13C NMR (CDCl3): 21.1 (q); 38.5 (t); 55.9 (q); 56.1
(q); 111.5 (d); 112.6 (d); 120.1 (d); 121.8 (d); 122.6 (s);
123.1 (s); 125.7 (d); 127.3 (s); 128.9 (2*d); 129.7 (2*d);
132.4 (d); 134.5 (d); 137.3 (s); 143.8 (d); 148.6 (s); 149.2
(s); 154.9 (s); 166.7 (s); 174.3 (s); 193.9 (s). Anal. calcd for
C26H21O5Cl: C, 69.57; H, 4.72; Cl, 7.90; found: C, 69.52, H,
4.79; Cl, 7.85.
4.3.2. 3-(2,6-Difluorobenzoyl)-2-(3,4-dimethoxyben-
zyl)[4H-1]benzopyran-4-one (11). Method A: 26%,
Method B: 67% yield. Crystallisation gave a pink solid,
4.3.6. 3-Benzoyl-2-(3,4-dimethoxybenzyl)-6-methyl[4H-
1]benzopyran-4-one (15). Method B: 31% yield. Crystal-
1
mp 150 (from methanol). H NMR (CDCl3): 3.85 (3H, s,
1
lisation gave a white solid, mp 111 (from methanol). H
OCH3); 3.88 (3H, s, OCH3); 4.16 (2H, s, CH2); 6.82 (1H, d,
J¼7.9 Hz, H-50); 6.93 (2H,0 dd, J¼8.2 Hz, H-300 and H-500);
7.00 (1H, d, J¼8.0 Hz, H-060 ); 7.04 (1H, s, H-20); 7.32–7.42
(3H, m, H-6, H-8 and H-4 ); 7.62 (1H, dd, J¼7.1 Hz, H-7);
8.07 (1H, d, J¼7.9 Hz, H-5); 13C NMR (CDCl3): 37.8 (t);
55.8 (q); 55.9 (q); 111.2 (d); 111.7 (2*d, JCF¼24.4 Hz);
112.5 (d); 117.9 (d); 121.7 (d); 123.4 (s); 123.7 (s); 125.7
(d); 125.8 (d); 127.4 (s); 132.7 (d, JCF¼10.3 Hz); 134.3 (d);
148.3 (s); 149.0 (s); 155.6 (s); 158.4 (2*s, JCF¼242.9 Hz);
170.4 (s); 175.9 (s); 187.8 (s). Anal. calcd for C25H18O5F2:
C, 68.80; H, 4.16; F, 8.71; found: C, 68.82, H, 4.21; F, 8.67.
NMR (CDCl3): 2.39 (3H, s, CH3); 3.69 (3H, s, OCH3); 3.78
(3H, s, OCH3); 3.85 (2H, s, CH2); 6.71–6.85 (3H, m, H-20,
H-50 and H-60); 7.35 (2H, dd, J¼7.4, 8.5 Hz, H-300 and H-
500); 7.40–7.45 (2H, m, H-7 and H-8); 7.54 (1H, dd,
J¼7.4 Hz, H-400); 7.86–7.96 (3H, m, H-5, H-200 and H-600).
13C NMR (CDCl3): 20.9 (q); 39.1 (t); 55.6 (q); 55.8 (q);
110.9 (d); 112.3 (d); 119.4 (d); 122.1 (d); 122.9 (s); 123.4
(s); 126.1 (d); 126.2 (d); 127.5 (s); 129.1 (2*d); 130.1 (2*d);
133.3 (d); 133.9 (d); 137.6 (s); 148.5 (s); 148.9 (s); 155.5 (s);
168.9 (s); 175.2 (s); 193.4 (s). Anal. calcd for C26H22O5: C,
75.35; H, 5.35; found: C, 75.29, H, 5.36.
4.3.3. 2-(3,4-Dimethoxybenzyl)-3-(2,4,6-trimethylben-
zoyl)[4H-1]benzopyran-4-one (12). Method A: 44%,
Method B: 62% yield. Crystallisation gave a beige solid,
4.3.7. 3-Benzoyl-7-diethylamino-2-(3,4-dimethoxyben-
zyl)[4H-1]benzopyran-4-one (16). Method A: 13% yield.
Crystallisation gave a yellow solid, mp 132 (from
methanol). 1H NMR (CDCl3): 1.19 (6H, t, J¼6.9 Hz,
CH3); 3.39 (4H, q, J¼6.9 Hz, NCH2); 3.69 (3H, s, OCH3);
3.80 (5H, s, CH2 and OCH3); 6.41 (1H, s, H-8); 6.65–6.86
(4H, m, H-6, H-20, H-50 and H-60); 7.39 (2H, dd, J¼7.5,
7.7 Hz, H-300 and H-500); 7.53 (1H, dd, J¼7.5 Hz, H-400);
7.88–7.93 (3H, m, H-5, H-200 and H-600). 13C NMR (CDCl3):
12.6 (q); 38.3 (t); 44.9 (t); 55.8 (q); 96.4 (d); 110.8 (d); 111.3
(d); 112.4 (s); 112.5 (d); 121.6 (d); 122.7 (s); 127.3 (d);
128.0 (s); 128.7 (2*d); 129.6 (2*d); 133.7 (d); 137.8 (s);
148.3 (s); 149.1 (s); 152.3 (d); 158.7 (s); 165.0 (s); 175.5 (s);
195.0 (s). Anal. calcd for C29H29O5N: C, 73.87; H, 6.20; N,
2.97; found: C, 73.59, H, 6.22; N, 3.01.
1
mp 135 (from methanol). H NMR (CDCl3): 2.23 (6H, s,
CH3); 2.28 (3H, s, CH3); 3.86 (3H, s, OCH3); 3.89 (3H, s,
OCH3); 4.20 (2H, s, CH2); 6.82 (2H, s, H-300 and H-500); 6.83
(1H, d, J¼8.2 Hz, H-50); 7.03 (1H, d, J¼8.3 Hz, H-60); 7.06
(1H, s, H-20); 7.33 (1H, dd, J¼7.7, 7.8 Hz, H-6); 7.39 (1H, d,
J¼7.5 Hz, H-8); 7.63 (1H, dd, J¼7.5, 7.7 Hz, H-7); 8.07
(1H, d, J¼7.8 Hz, H-5). 13C NMR (CDCl3): 20.3 (2*q); 21.3
(q); 38.1 (t); 56.0 (2*q); 111.4 (s); 112.9 (d); 117.8 (d);
121.9 (d); 123.9 (s); 124.2 (s); 125.7 (d); 126.3 (d); 127.6
(s); 129.2 (2*d); 134.2 (d); 134.7 (2*s); 138.9 (s); 139.2 (s);
148.5 (s); 149.1 (s); 155.6 (s); 170.4 (s); 175.6 (s); 197.3 (s).
Anal. calcd for C28H26O5: C, 76.00; H, 5.92; found: C,
75.87, H, 6.00.
4.3.8. 7-Diethylamino-3-(2,6-difluorobenzoyl)-2-(3,4-
dimethoxybenzyl)[4H-1]benzopyran-4-one (17). Method
B: 53% yield. Crystallisation gave a yellow solid, mp 168
(from methanol). 1H NMR (CDCl3): 1.18 (6H, t, J¼7.0 Hz,
4.3.4. 3-Benzoyl-2-(3,4-dimethoxybenzyl)-7-meth-
oxy[4H-1]benzopyran-4-one (13). Method B: 25% yield.
Crystallisation gave a beige solid, mp 178 (from methanol).
1H NMR (CDCl3): 3.84 (3H, s, OCH3); 3.89 (3H, s,OCH3);

V. Rossollin et al. / Tetrahedron 59 (2003) 7725–7731
7731
Durr, H., Bouas-Laurent, H., Eds.; Elsevier: Amsterdam,
1990; Chapter 17.
CH3); 3.43 (4H, q, J¼7.0 Hz, NCH2); 3.85 (3H, s, OCH3);
3.87 (3H, s, OCH3); 4.12 (2H, s, CH2); 6.35 (1H, s, H-8);
6.65 (1H, d, J¼9.1 Hz, H-6); 6.83 (1H, d, 0J0 ¼8.2 Hz, H-50);
6.91 (2H, dd,0 J¼8.1 Hz, H-300 0and H-5 ); 7.01 (1H, d,
J¼8.3 Hz, H-6 ); 7.04 (1H, s, H-2 ); 7.36 (1H, dd, J¼8.1 Hz,
H-400); 7.85 (1H, d, J¼9.1 Hz, H-5). 13C NMR (CDCl3):
12.2 (q); 37.5 (t); 44.5 (t); 55.7 (q); 96.0 (d); 110.6 (d); 111.1
(d); 111.5 (d); 111.9 (JCF¼24.8 Hz, 2*d); 112,4 (s); 119.5
(JCF¼16.3 Hz, s); 121.5 (d); 123.0 (s); 126.7 (s); 128.0 (s);
132.1 (JCF¼10.1 Hz, s); 148.0 (s); 148.8 (s); 152.1 (s); 157.9
(s); 158.2 (JCF¼240 Hz, 2*s); 166.2 (s); 174.6 (s); 188.4 (s).
Anal. calcd for C29H27O5NF2: C, 68.63; H, 5.36; N, 2.76; F,
7.49; found: C, 68.71, H, 5.43; N, 2.82; F, 7.56.
5. Huffman, K. R.; Loy, M.; Ullman, E. F. J. Am. Chem. Soc.
1965, 87, 5417.
6. JP Patent (Sumitomo Chemicals), Fev, N8 49-110583, 1973.
7. Kostanecki, S. V.; Rozycki, A. Chemische Berichte 1901, 34,
102.
8. (a) Allan, J.; Robinson, R. J. Chem. Soc. 1924, 125, 219. (b)
Robinson, R.; Baker, W. J. Chem. Soc. 1925, 127, 1424.
9. Miya, M. B.; Ramadas, S.; Krupadanam, G. L. D. Indian.
J. Chem. Sect. B—Org. Chem. Incl. Med. Chem. 1998, 37, 579.
10. Kotali, A.; Harris, P. A. Org. Prep. Proc. Int. 1994, 26, 159.
11. Zammattio, F.; Brion, J. D.; Belachmi, L.; Lebaut, G.
J. Heteroycl. Chem. 1991, 28, 2013.
4.3.9. 2-(3,4-Dimethoxybenzyl)-3-(2-pyridoyl)[4H-1]ben-
zopyran-4-one (18). Method B: 19% yield. Crystallisation
gave a beige solid, mp 151 (from methanol). 1H NMR
(CDCl3): 3.70 (6H, s, OCH3); 3.86 (2H, s, CH2); 6.67 (1H,
d, J¼7.8 Hz, H-50); 6.84 (1H, d, J¼7.7 Hz, H-60); 6.86 (1H,
s, H-20); 7.23–7.36 (3H, m, H-6, H-8 and H-400); 7.54 (1H,
dd, J¼7.1 Hz, H-7); 7.78 (1H, dd, J¼7.7 Hz, H-500); 7.99–
8.04 (2H, m, H-300 and H-600); 8.48 (1H, d, J¼7.3 Hz, H-5).
13C NMR (CDCl3): 38.2 (t); 55.7 (q); 55.8 (q); 111.7 (d);
112.4 (d); 117.9 (d); 121.7 (d); 122.7 (d); 123.4 (s); 123.6
(s); 125.3 (d); 125.6 (d); 127.1 (d); 127.4 (s); 133.9 (d);
136.9 (d); 148.2 (s); 148.9 (s); 149.1 (d); 154.2 (s); 156.1 (s);
166.6 (s); 176.5 (s); 195.1 (s). Anal. calcd for C24H19O5N:
C, 71.81; H, 4.77; N, 3.49; found: C, 71.63, H, 4.92; N, 3.54.
12. Boers, F.; Deng, B. L.; Lemiere, G.; Lepoivre, J.; DeGroot, A.;
Dommisse, R.; Vlietinck, A. J. Arch. Pharm. 1997, 330, 313.
13. Price, W. A.; Silva, A. M. S.; Cavaleiro, J. A. S. Heterocycles
1993, 36, 2601.
14. Zweig, A.; Henderson, W. A., Jr.; Huffman, K. R. Photo-
graphic Sci. Engng 1973, 17, 451.
15. Furniss, B. S.; Hannaford, A. J.; Rogers, V.; Smith, P. W. G.;
Tatchell, A. R. Vogel’s Practical Organic Chemistry, 4th ed.;
Longmann: London, 1978.
16. (a) Baker, W. J. Chem. Soc. 1933, 55, 1381. (b) Mahal, H. S.;
Venkataraman, K. Curr. Sci. 1933, 4, 214. (c) Mahal, H. S.;
Venkataraman, K. J. Chem. Soc. 1934, 56, 1767.
17. Deng, B. L.; Lepoivre, J. A.; Lemiere, G.; Dommisse, R.;
Claeys, M.; Boers, F.; DeGroot, A. Liebig Ann.—Rec. 1997,
2169.
18. Mentzer, C.; Molho, D.; Vercier, P. C.R. Acad. Sci. 1951, 232,
1488.
References
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