Synthesis and reactivity of photochromic 2H-chromenes based on 3-carboxylated coumarins

Article abstract of DOI:10.1002/hlca.200390264

New photochromic 2H-chromenes (=2H-1-benzopyrans) including a 3-carboxylated coumarin nucleus were synthesized from hydroxycoumarins, and, in one case, the corresponding trimethoxysilylcarboxamide was prepared. The photochromic behavior was studied under flash-photolysis conditions. The introduction of electron-withdrawing substituents in this position of the coumarin nucleus led to a global and significant bathochromic shift in the spectra of the open forms and to an interesting intensification in the colorability.

Full text of DOI:10.1002/hlca.200390264

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Helvetica Chimica Acta Vol. 86 (2003)
Synthesis and Reactivity of Photochromic 2H-Chromenes Based on
3-Carboxylated Coumarins
by Nuno M. F. S. A. Cerqueiraa), LÌgia M. Rodriguesa), Ana M. F. Oliveira-Campos*a), LuÌs H. Melo de
Carvalhob), Paulo J. Coelhob), Roger Dubestc), Jean Aubardc), Andre¬ Samatd), and Robert Guglielmettid)
a) Centro de QuÌmica, IBQF, Universidade do Minho, Largo do PaÁo, P-4700-320 Braga
(e-mail: amcampos@quimica.uminho.pt)
b) Centro de QuÌmica Vila Real, Universidade de Tras-os-Montes e Alto Douro, Quinta de Prados,
¬
P-5001-911 Vila Real
c
¬
) ITODYS, UMR CNRS 7086, Universite de Paris VII, 1 rue Guy de la Brosse, F-75005 Paris
d
¬
¬
¬
) Faculte des Sciences de Luminy, Universite de la Mediterranee, UMR CNRS,
F-6114, 13288 Marseille Cedex 9
New photochromic 2H-chromenes (ˆ2H-1-benzopyrans) including a 3-carboxylated coumarin nucleus
were synthesized from hydroxycoumarins, and, in one case, the corresponding trimethoxysilylcarboxamide was
prepared. The photochromic behavior was studied under flash-photolysis conditions. The introduction of
electron-withdrawing substituents in this position of the coumarin nucleus led to a global and significant
bathochromic shift in the spectra of the open forms and to an interesting intensification in the colorability.
1. Introduction.
Photochromic systems based on 2H-1-benzopyrans (ˆ2H-
chromenes) constitute an important research field to which, in the last decade, intense
research efforts have been devoted due to their applications in variable optical
transmission materials and to some potential applications in optical switches and
memories [1][2].
Their photochromic behavior is based on a reversible pyran ring opening induced
upon near UV irradiation that converts a colorless form to a set of quasi-planar forms
(Scheme 1), constituting a system with a distinct absorption spectrum. The back
reaction may occur through a thermal process or by irradiation with visible light.
Scheme 1
For applications in the field of variable transmission materials, the molecules
involved should be incorporated in convenient host matrices in a stable manner. This
can be achieved either by dispersing the photochrome in or covalently coupling the

Helvetica Chimica Acta Vol. 86 (2003)
3245
photochrome to the matrix, provided that the photochromic entity is not destroyed and
the photochromic characteristics are not lost.
In the course of the search for new photochromic molecules [3 5], it was decided
to study new 2H-chromenes, which contain a coumarin nucleus. In our previous work
on photochromic compounds based on the coumarin system [6], it was found that some
2H-chromenes, namely compounds Ref 1, and especially Ref 2 and Ref 3, exhibited
interesting coloration efficiencies, and their open forms showed an extended
absorption range in the visible region that could be useful for applications in the
field of variable optical transmission materials.
The coumarin moiety can be built with different substitution patterns, namely with
ester substituents in the 3-position, offering a way to form further covalent bonds to
various polymeric matrices (for example, through an ester or an amide linkage)
allowing the build-up of supramolecular systems containing a photoreactive entity.
Here, we describe the synthesis and the photochromic properties of ethoxycarbonyl-
substituted 2H-chromenes of this type, in order to verify the validity of this approach.
The ethoxycarbonyl substituent has been chosen not only for its electronic effects,
but also because of its synthetic potential. The latter aspect was tested through the
preparation of an amide containing a silylated side chain according to the method
described by Karkkainen et al. for organic light-emitting devices, including coumarin
dyes, covalently bound to a siloxane matrix [7].
The spectrokinetics parameters, in solution, of the novel compounds were
determined to evaluate the effects of the substitution on the photochromic behavior.
2. Results and Discussion. 2.1. Synthesis. 2H-Chromenes can be easily prepared
from phenolic precursors. The most versatile method is based on a one-pot reaction of a
phenol with an alkynol under acidic catalysis. The reaction is considered to proceed via
a Claisen rearrangement of aryl propargyl ethers formed by phenol O-alkylation,
followed by enolization, [1,5] H-migration, and finally electrocyclic ring closure
(Scheme 2). Alternatively, Ti(OEt)4 catalyzed condensation with a,b-unsaturated
carbonyl compounds can be used [3].
Scheme 2

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Helvetica Chimica Acta Vol. 86 (2003)
6-, 7- and 8-Hydroxycoumarins 2a 2c containing an ester group at C(3) were
prepared in high yield through the Knoevenagel condensation of the corresponding
dihydroxybenzaldehydes 1a 1c with diethyl malonate [8] (Scheme 3).
Scheme 3
Hydroxybenzocoumarin 5 was prepared in four steps from 2,7-dihydroxynaphtha-
lene. Methylation of 2,7-dihydroxynaphthalene gave the corresponding 2,7-dimethoxy-
naphthalene, which was subsequently formylated with DMF/POCl3 to give the
naphthalene-1-carbaldehyde 3 in 50% yield. Demethylation of 3 with BBr3 gave 2,7-
dihydroxynaphthalene-1-carbaldehyde (4; 52%), which was then converted in good
yield (80%) to the corresponding coumarin as reported before (Scheme 4).
Scheme 4
Our previous results [6] on the synthesis of 2H-chromenes from hydroxycoumarins
indicate that, for these types of molecules, the cyclization by the propynol method gives
better yields compared to the a,b-unsaturated aldehyde/Ti(OEt)4 method.
Condensation of 3-(ethoxycarbonyl)-hydroxycoumarins 2a, 2b, and 5 with 1,1-
diphenylprop-2-yn-1-ol with TsOH as catalyst gave 2 H-chromenes 6 9 in low yields.
Different solvents were used depending on the solubility of the starting material. The
reaction of coumarin 2a and 5 with 1,1-diphenylprop-2-yn-1-ol was completely
regiospecific, providing the chromenes 6 and 9, respectively, as the only isomers. A
similar reaction applied to hydroxycoumarin 2b gave a mixture of the linear chromene
7, as the major product, together with a minor amount of the angular compound 8. No
reaction was observed with the hydroxycoumarin 2c either by the propynol method or
the Ti(OEt)4 method. This result was somehow expected in view of what was observed
before [6] with 8-hydroxycoumarin, where only traces of the final chromene were
detected.

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Basic hydrolysis of chromene 7 in EtOH gave the acid 10, which was then converted
in 89% yield to its N-(3-(trimethoxysilyl)propyl) carboxamide 11 by the mixed
anhydride method (ClCOOEt/(3-aminopropyl)trimethoxysilane) [9] (Scheme 5).
Scheme 5
2.2. Photochromic Properties. The photochromic characteristics of the compounds
were determined by the flash-irradiation technique coupled to a rapid spectrometer.
Details of the procedure are described in the Exper. Part. Results obtained for the new
compounds are summarized in Table 1, where the parent coumarins Ref 1, Ref 2, and
Ref 3 are also included for comparison. The values of kD are given for the wavelength
at which A0 is maximum (l1 in all cases). Calculations give similar values when
compounds have two wavelengths of absorption. As an example, for compound 10, the
spectrum of the closed form and a set of spectra of the open form are also shown
(Figs. 1 and 2, resp.). Calculations of kD at both wavelengths (l1 and l2) are given in
Table 2.
The photochromic parameters taken into account were: absorption wavelengths of
the open forms, rate constants of thermal bleaching (kD), and coloration ability or
−colorability× (measured as the absorbance A0 immediately after the flash irradiation).
A0 is expressed by: A0 ˆ eOF ¥ fcol ¥ k ¥ [CF]0, (at low concentration), where k depends on
experimental conditions, eOF is the molar absorptivity of the open form at lmax, fcol is the
photocoloration quantum yield, and [CF]0 is the initial concentration of the closed form
[10].
All of the compounds described exhibit photochromic behavior at room temper-
ature in toluene solution. Irradiation of compounds 7, 8, 10, and 11 led to open forms
with broad visible absorption spectra.
From a general point of view, compared to the parent reference coumarins without
substituents, the introduction of electron-withdrawing substituents with p electrons

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Helvetica Chimica Acta Vol. 86 (2003)
Table 1. Spectrokinetic Properties of 6 11 under FlashÀIrradiation Conditions (25 mm in toluene at 258)
Structure
Com-
pound
Type of
annellation (closed [nm]
form)
l [nm] l1
A01
l2
A02
kD [sÀ1
]
c2
[nm]
(amplitude  106
[%])
6
5,6
321
392
500
1.2
2.60 (16)
0.05 (17)
0.02 (66)
9.0
Ref 1a) 5,6
302
354
491
441
1.05
2.20 (69)
0.02 (31)
2.6
4.9
8
5,6
0.37 590
0.26 562
0.22 49.00 (62)
0.02 (38)
Ref 2b) 5,6
330
347
429
0.11 20.00 (91)
0.03 (9)
4.2
7
6,7
6,7
328
367
445
448
3.3
2.1
597
615
1.8
1.4
13.00 (51)
0.50 (11)
0.03 (38)
3.7
10
349
72 (43)
0.82
11.90 (18)
0.29 (15)
0.04(24)
11
6.7
447
0.31 604
0.18 18.00 (52)
0.35 (13)
1.1
0.03 (35)
Ref 3c) 6,7
339
347
432
462
0.95 563
0.45
4.50 (53)
0.03 (47)
2.0
3.8
9
5,6
414
0.37
15.65 (71)
0.02 (29)
a) 3,8-Dihydro-8,8-diphenylpyrano[3,2-f][1]benzopyran-3-one.
b) 2,8-Dihydro-8,8-diphenylpyrano[2,3-f][1]-
benzopyran-2-one. c) 2,8-Dihydro-2,2-diphenylpyrano[3,2-g][1]benzopyran-8-one.

Helvetica Chimica Acta Vol. 86 (2003)
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Fig. 1. UV Absorption spectrum of compound 10 (closed form)
Fig. 2. Set of decreasing absorption spectra of compound 10 (open form) after flash irradiation
located on C(3) of the coumarin moiety (EtOCO group in compounds 6 8, COOH
group in compound 10, and carboxamide group in compound 11) led to a global and
significant bathochromic shift in the spectra of the open forms, without the loss of the
visible absorption spectral pattern.

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Helvetica Chimica Acta Vol. 86 (2003)
Table 2. Calculations of the Rate Constants of Thermal Ring Closure for Compound 10
l [nm]
A0
kD [sÀ1
]
Amplitude [%]
c2
448
2.13
72 Æ 44
8.2
 10À7
 10À7
11.9 Æ 0.7
0.29 Æ 0.03
18
15
24
0.040 Æ 0.002
615
1.471
Æ 438
5.0
12.2 Æ 0.8
0.33 Æ 0.02
0.041 Æ 0.002
18
16
28
Besides this interesting feature, the colorability intensification observed (except for
compound 11) due to the presence of the EtOCO group, particularly in compounds
with the coumarin nucleus fused in the 6,7-positions of the 2H-1-benzopyran entity, is
also noteworthy.
This effect is particularly interesting, considering the appreciable thermal instability
of all the open forms, indicated by the very fast thermal bleaching rates. Fast-bleaching
kinetics is normally accompanied by modest colorabilities, as the formation of colored
species in a reasonable yield is hindered. This improvement is apparently lost when the
ester substituent is converted to the silylated carboxamide. The loss of photochromic
properties, mainly colorability, for photochrome moieties chemically bonded to a silane
link has been addressed several times in the literature [11]. It is currently accepted that,
during irradiation, a part of the UV light energy is dissipated through the silyl link. It is
likely that the same process occurs for compound 11, leading to the poor colorability
observed in this case.
One can notice also the appearance of several rate constants (2 to 4) for the thermal
fading of the new compounds. This phenomenon is probably due to the stabilization of
different s-trans and s-cis open-form isomers during the photochromic process of such
systems. Compounds 7, 10, and 11, which are derived from compound Ref 3 by different
substitutions at C(3), have a similar kinetics behavior. Indeed, except the very fast rate
constant in compound 10 (72 sÀ1), these three compounds behave similarly with three
corresponding rate constants, which are of the same order of magnitude. It is likely that,
in 7 and 11, the fourth fastest component is not detected in our experimental conditions,
due to poor amplitude, which falls within the flash excitation. On the other hand, the
unsubstituted compound Ref 3 is clearly different from those substituted at C(3) both
in the thermal fading, which can only be described in the reference compound by a two-
step decay, and in the spectroscopic characteristics (ca. 430 vs. ca. 450 nm).
Compound 9 was synthesized in order to minimize the influence of the coumarin
moiety in the thermal instability of the open forms. Compared to the reference 2H-
chromenes, no improvement in photochromic behavior was achieved through the
fusion of an additional benzene ring between the coumarin and the 2H-1-benzopyran
moieties.
3. Conclusions.
Four new hetero-[6,7]-annellated 2H-chromenes have been
synthesized in a series for which very few compounds are known in the literature.

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The synthesis of 2H-chromenes fused with a pyranone ring possessing an ester
substituent was achieved by standard methods. This kind of substitution opens the
possibility of further modifications in the molecules and constitutes a potentially
interesting way to bind covalently photochromic molecules to convenient polymeric
matrices. No loss of the relevant spectral features was observed, and the new
compounds exhibit a marked intensification in the coloration efficiency. The
conversion of the ester group to a silylated carboxamide group led, however, to a
significant decrease in the colorability.
Experimental Part
1. General. Petroleum ether: b.p. 40 608. Column chromatography (CC): silica gel 60 (70 230 mesh).
M.p.: uncorrected. UV Spectra: in EtOH on a JASCO 7850; lmax (log e [dm3 ¥ molÀ1 ¥ cmÀ1]) in nm. FT-IR
1
Spectra: Bomem, MB Series; in cmÀ1. H-NMR Spectra: in CDCl3 (if not stated otherwise) on a Varian Unity
Plus (300 MHz); l in ppm rel. to Me4Si (ˆ0 ppm), J in Hz; assignments were based on irradiation experiments.
13C-NMR Spectra: in CDCl3 on a Varian Unity Plus (75.4MHz). MS: AutoSpecE Spectrometer; m/z (%).
Elemental analyses: LECO 932 CHNS Analyzer. HR-FABMS: VG AutoSpec M spectrometer.
2. Spectrokinetics Measurements. For the determination at 258 of l1 and l2, A01 and A02, and kD 25 mm of 6
11 in toluene were used. The flash photolysis apparatus was coupled to a Warner and Swasey rapid spectrometer,
to allow recording of absorption spectra of the colored forms in the visible 400 700-nm range (acquisition time:
1 ms, repetitively: 1.25 ms) [12][13]. Flashes (duration: 50 ms) were generated by two Xe tubes with a quartz
envelope. The energy of the flashes was 60 J for the whole polychromatic emission spectrum. For measurements,
thermostated (258) 100-mm cells were used. The light from the analysis lamp (50 W, quartz-iodine) was filtered
with a Schott GG400 high-pass filter. In a preliminary experiment, both the visible absorption spectrum, and l1
and l2 of the open forms were determined. In a second experiment, the initial absorbances A01 and A02 were
measured, followed by the decrease in absorbance with time. The rate constants were calculated with a multi-
exponential model designed to minimize the c2 (residual quadratic error). The c2 for each fitting is reported in
Table 1.
3. Synthesis. General Procedure for the Synthesis of Coumarins 2a 2c. A mixture of dihydroxybenzalde-
hyde (5.00 g, 36.2 mmol), diethyl malonate (7.12 ml, 47.0 mmol), and EtOH (50 ml) was placed in a round-
bottom flask, and a few drops of piperidine and glacial AcOH were added. After 4, 5, and 4 h reflux for 2a, 2b,
2c, resp., the soln. was cooled, and H2O (50 ml) was added. The precipitate was collected by filtration, washed
with a soln. of EtOH (40 ml) and H2O (60 ml), and air-dried.
Ethyl 6-hydroxy-2-oxo-2H-[1]benzopyran-3-carboxylate (2a). Yellow solid (93%), M.p. 188 1908
(EtOH). FT-IR: 3331, 1748 (CˆO), 1672 (CˆO). 1H-NMR: 1.42 (t, J ˆ 7.2, EtO); 4.42 (q, J ˆ 7.2, EtO);
5.18 (s, OH); 7.03 (d, J ˆ 2.7, HÀC(5)); 7.15 7.18 (dd, J ˆ 2.7, 9, HÀC(7)); 7.24 7.32 ( m, HÀC(8)); 8.44
(s, HÀC(4)).
Ethyl 7-hydroxy-2-oxo-2H-[1]benzopyran-3-carboxylate (2b). Light yellow solid (71%), M.p. 171 1728
1
(EtOH). FT-IR: 3552, 3471, 3333, 1741 (CˆO), 1681 (CˆO). H-NMR ((D6)acetone): 1.37 (t, J ˆ 7.2, EtO);
4.35 (q, J ˆ 7.2, EtO); 6.81 (d, J ˆ 2.4, HÀC(8)); 6.93 6.97 (dd, J ˆ 2.1, 8.4, H-C(6)); 7.75 (d, J ˆ 8.4, HÀC(5));
8.63 (s, HÀC(4)); the signal due to OH was not observed.
Ethyl 8-hydroxy-2-oxo-2H-[1]benzopyran-3-carboxylate (2c). Light yellow, fluffy crystals (69%). M.p.
178 1818 (EtOH). FT-IR: 3306, 1747 (CˆO), 1696 (CˆO). 1H-NMR ((D6)acetone): 1.35 (t, J ˆ 7.2, EtO);
4.38 (q, J ˆ 7.2, EtO); 7.20 7.36 (m, HÀC(5), HÀC(6), HÀC(7)); 8.63 (s, HÀC(4)); 9.30 (br. s, OH).
2,7-Dihydroxynaphthalene-1-carbaldehyde (4): A soln. of BBr3 in CH2Cl2 (14ml) was gradually added by
syringe to a CH2Cl2 soln. (10 ml) of 2,7-dimethoxynaphthalene-1-carbaldehyde (3; 1.00 g, 4.63 mmol), cooled at
À 558, and maintained under an inert atmosphere. The mixture was left at r.t. with stirring for 24h. The soln. was
treated with H2O (40 ml), extracted with Et2O (3 Â 20 ml), and the org. layers were combined and dried
(Na2SO4). Solvent evaporation gave a brown solid, which was purified by CC (light petroleum/Et2O) to give 4
(52%). Yellow crystals. M.p. 198 2008 [14]. FT-IR (nujol): 3460 to 3097 (wide band), 1613. 1H-NMR
((D6)DMSO): 6.90 6.98 (m, J ˆ 8.7, HÀC(3), HÀC(6)); 7.69 (d, J ˆ 8.7, HÀC(4) or HÀC(5)); 7.95 (d, J ˆ 9.3,
HÀC(5) or HÀC(4)); 8.32 (d, J ˆ 2.1, HÀC(8)); 10 (br. s, HOÀC(7), exchanged with D2O); 10.69 (s, CHO);
11.71 (s, HOÀC(2), exchanged with D2O).

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Helvetica Chimica Acta Vol. 86 (2003)
Ethyl 9-Hydroxy-3-oxo-3H-benzo[f][1]benzopyran-2-carboxylate (5). A mixture of 4 (0.500 g, 2.66 mmol),
diethyl malonate (2.30 ml, 5.30 mmol), DMSO (10 ml), piperidine (3 ml), and glacial AcOH (1 ml) was heated
under reflux for 3 h at 508. After cooling, H2O (5 ml) was added. The precipitate was collected by filtration and
washed with a soln. of EtOH, to give 5 (80%). Yellow solid. M.p. 244 2468. FT-IR (nujol) 3516, 1738 (CˆO),
1
1682 (CˆO), 1631. H-NMR: 1.46 (t, J ˆ 7.2, EtO); 4.48 (q, J ˆ 7.2, EtO); 6.22 (br. s, OH); 7.20 (dd, J ˆ 2.7, 9,
HÀC(8)); 7.30 (d, J ˆ 9, HÀC(5)); 7.66 (d, J ˆ 2.7, HÀC(10)); 7.83 (d, J ˆ 9, HÀC(7)); 8.01 (d, J ˆ 9, HÀC(6));
‡
‡
9.24( s, HÀC(1)). MS: 285 (1.18, [M ‡ 1] ), 284(100, M ), 256 (7), 239 (54), 228 (30), 210 (15), 212 (50), 184
‡
(23), 155 (44), 126 (20), 77 (6). HR-MS: 284.068474 (M , C27H21O5; calc. 284.068231).
General Procedure for the Synthesis of 6 9. TsOH (0.154g, 0.89 mmol) and hydroxycoumarin (1.00 g,
6.17 mmol) were added to a soln. of 1,1-diphenylprop-2-yn-1-ol (1.91 g, 9.26 mmol) in 50 ml of dry MeCN (for 6
and 9) or dry toluene (for 7 and 8). The suspension was refluxed for ca. 48 h under Ar, and, after cooling, it was
treated with H2O and extracted with CHCl3 (4 Â 30 ml). The combined org. layers were washed with 10%
NaOH soln. (4 Â 30 ml) and dried (Na2SO4). Solvent evaporation gave a yellow oil, which was purified by CC
(petroleum ether/Et2O).
Ethyl 3,8-Dihydro-3-oxo-8,8-diphenylpyrano[3,2-f][1]benzopyran-2-carboxylate (6). Light yellow solid
(20%). M.p. 192 1938. UV: lmax 391.5 (4513), 321.5 (4264), 266.5 (4744). FT-IR (nujol): 1756 (CˆO), 1739
(CˆO), 1694. 1H-NMR: 1.40 (t, J ˆ 7, EtO); 4.42 (q, J ˆ 7, EtO); 7.56 (d, J ˆ 10, HÀC(9)); 7.08 (d, J ˆ 10,
HÀC(10)); 7.12 7.50 (m, HÀC(5), HÀC(6)); 7.24 7.44 ( m, 10 arom. H, Ph); 8.78 (s, HÀC(1)). 13C-NMR:
14.22 (Me); 62.06 (CH2O); 82.77 (C(8)); 113.52; 117.05 (C(5) or C(6)); 117.66 (C(9) or C(10)); 117.96; 118.30;
123.50 (C(5) or C(6)); 126.87 (Ph); 127.93 (Ph); 128.26 (Ph); 132.68 (C(9) or C(10)); 143.6; 143.8 (C(1));
148.84; 150.18; 156.56 (CˆO); 163.37 (CˆO). The signals for C(5), C(6), C(9), and C(10) were assigned by
‡
‡
‡
HETCOR. MS: 425 (1.24, [M ‡ 1] ), 424 (75, M ), 379 (7, [M À OEt] ), 368 (16), 348 (22), 347 (100, [M À
‡
‡
Ph] ), 310 (18). HR-MS: 424.131777 (M , C27H20O5; calc. 424.131074).
Ethyl 2-Oxo-8,8-diphenyl-2H,8H-pyrano[3,2-g][1]benzopyran-3-carboxylate (7). Light brown solid (26%),
M.p. 171 1728. UV: lmax (log e) 366.4 (4512), 328.5 (4264), 266.5 (4744). FT-IR: 1770, 1715. 1H-NMR: 1.40
(t, J ˆ 7, EtO); 4.39 (q, J ˆ 7, EtO); 6.29 (d, J ˆ 10, HÀC(7)); 6.67 (d, J ˆ 10, HÀC(6)); 6.88 (s, HÀC(10)); 7.24
(s, HÀC(5)); 7.28 7.42 (m, 10 arom. H, Ph); 8.44 (s, HÀC(4)). 13C-NMR: 14.19 (Me); 61.65 (CH2O); 84.38
(C(8)); 104.26 (CH); 112.24; 114.35; 118.78; 121.28 (CH); 126.80 (CH); 128.01 (CH); 128.32 (CH); 129.67
‡
(CH); 143.63; 148.63 (CH); 156.81; 157.07; 158.56 (CˆO); 163.29 (CˆO). MS: 425 (30, [M ‡ 1] ), 424
‡
‡
‡
‡
(100, M ), 396 (1, [M À CO] ), 379 (7, [M À OEt] ), 348 (20), 347 (86, [M À Ph] ), 319 (3). Anal. Calc. for
C27H20O5: C 76.42, H 4.72; found C 76.37, H 4.94.
Ethyl 2-Oxo-8,8-diphenyl-2H,8H-pyrano[2,3-f][1]benzopyran-3-carboxylate (8). Off white solid (12%).
1
M.p. 185 1868 (EtOH). UV: lmax 354.0 (4929), 290.5 (4830), 264.5 (4848). FT-IR: 1771, 1717. H-NMR: 1.40
(t, J ˆ 7, EtO); 4.40 (q, J ˆ 7, EtO); 6.29 (d, J ˆ 10, HÀC(9)); 6.92 (d, J ˆ 8.4, HÀC(6)); 7.20 (d, J ˆ 10,
HÀC(10)); 7.28 7.44 (m, 10 arom. H and HÀC(5)); 8.45 (s, HÀC(4). 13C-NMR: 14.19 (Me); 61.63 (CH2O);
84.31 (C(8)); 108.99; 112.06; 113.89; 114.35 (CH); 115.80 (CH); 126.86 (CH); 128.13 (CH); 128.27 (CH); 129.07
(CH); 130.18 (CH); 143.67; 149.20 (CH); 151.55; 156.67; 157.91 (CˆO); 163.25 (CˆO). MS: 424 (9), 347 (8),
279 (5), 149 (23), 119 (24), 107 (73), 106 (100), 91 (30), 79 (43), 77 (34). Anal. calc. for C27H20O5: C 76.42, H
4.72; found: C 76.36, H 4.69.
Ethyl 3-Oxo-10,10-diphenyl-3H,10H-pyrano[2',3':7,8]naphtho[2,1-b]pyran-2-carboxylate (9). Red-brown
solid (40%). M.p. 232 2348. UV: lmax 413.5 (3439), 264.0 (4604). FT-IR (nujol): 1752, 1694. 1H-NMR: 1.50
(t, J ˆ 7.2, EtO); 4.48 (q, J ˆ 7.2, EtO); 6.31 (d, J ˆ 9.6, HÀC(11)); 7.23 (d, J ˆ 9.6, HÀC(12)); 7.24 7.40
(m, 6 arom. H, HÀC(5), HÀC(8)); 7.50 7.58 (m, 4arom. H, Ph); 7.74 ( d, J ˆ 8.7, HÀC(6)); 7.94( d, J ˆ 9,
HÀC(7)); 9.36 (s, HÀC(1)). 13C-NMR: 14.24 (Me); 61.85 (CH2O); 82.72 (C(10)); 122.02; 113.65; 114.34 (CH);
115.51; 118.32 (CH); 123.41 (CH); 126.36; 126.91 (Ph); 127.09 (CH); 127.81 (Ph); 128.17 (Ph); 131.57(CH);
‡
136.75 (CH); 143.82 (CH); 148.19 (CH); 154.67; 156.47; 157.91(CˆO); 163.58 (CˆO). MS: 476 (18, [M ‡ 2] ),
‡
‡
‡
475 (52, [M ‡ 1] ), 474 (23, M ), 429 (6). HR-MS: 475.154622 ([M ‡ 1] , C31H22O5; calc. 475.154549).
2-Oxo-8,8-diphenyl-2H,8H-pyrano[3,2-g][1]benzopyran-3-carboxylic Acid (10). 1m NaOH (0.36 ml,
0.354mmol) was added under stirring to a soln. of compound 7 (0.100 g, 0.236 mmol) in EtOH (10 ml) at r.t.
After stirring for 3 h, the mixture was cooled in an ice-water bath and acidified to pH 3 with 5m HCl. After
storage in the cold for 2 h, the precipitate was collected on a filter, washed thoroughly with H2O, and air-dried to
yield a light brown solid (40%). M.p. 180 1838. UV: lmax 349.0 (4179), 263.5 (51514). FT-IR (nujol): 1949, 1759.
1H-NMR: 6.35 (d, J ˆ 10, HÀC(7)); 6.72 (d, J ˆ 10, HÀC(6)); 6.98 (s, HÀC(10)); 7.30 7.43 (m, 10 arom. H,
HÀC(5)); 8.79 (s, HÀC(4)); 12.20 (br. s, OH). 13C-NMR: 85.01 (C(8)); 104.70 (CH); 111.07; 112.93; 120.05;
120.92 (CH); 126.83 (CH); 127.58 (CH); 128.23 (CH); 128.45 (CH); 130.60 (CH); 143.31; 150.90 (CH); 156.51;

Helvetica Chimica Acta Vol. 86 (2003)
3253
‡
‡
‡
159.87; 163.05 (CˆO); 164.27 (CˆO). MS: 398 (28, [M ‡ 2] ), 397 (100, [M ‡ 1] ), 396 (45, M ), 380 (16), 379
‡
(54), 319 (17). HR-MS: 397.108271 ([M ‡ 1] , C25H16O5; calc. 397.107599).
2-Oxo-8,8-diphenyl-N-[(3-trimethoxysilyl)propyl]-2H,8H-pyrano[3,2-g][1]benzopyran-7-carboxamide
(11). Compound 10 (39.6 mg, 0.100 mmol) was dissolved in CHCl3 (5 ml), and Et3N (0.015 ml, 0.10 mmol) was
added. The mixture was stirred and cooled to À 58 and ClCOOEt (0.010 ml, 0.10 mmol) was added. The mixture
was kept at À 58 for 30 min (3-aminopropyl)trimethoxysilane (0.017 ml, 0.10 mmol) was added, and the stirring
was kept overnight at r.t. The mixture was extracted with H2O, and the org. layer was collected and dried
(MgSO4). Solvent evaporation gave a yellow oil (89%). FT-IR (nujol): 2273, 1761, 1713. 1H-NMR: 8.80 (t, J ˆ
5.7, NH); 8.77 (s, HÀC(4)); 7.41 7.27 (m, 10 arom. H, HÀC(5)); 6.91 (s, HÀC(10)); 6.69 (d, J ˆ 9.9, HÀC(6));
6.30 (d, J ˆ 9.9, HÀC(7)); 3.58 (s, MeO); 3.48 3.41 (m, CH2N); 1.77 1.70 (m, CH2); 0.75 0.68 (m, CH2Si).
‡
HR-MS: 558.19222 ([M ‡ 1] , C31H31O7NSi; calc. 558.194806).
We are grateful to FCT (Portugal×s Foundation for Science and Technology) for financial support through
project Praxis XXI /P/QUI/10021 and to Miss Elisa Pinto for NMR and mass spectra, and elemental analyses.
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Received May 5, 2003