Synthesis and NMR spectroscopic characterization of some fluoro-2H-1-benzopyran derivatives

Article abstract of DOI:10.1071/CH05062

The synthesis of some new fluoro-2H-1-benzopyran derivatives utilizing a reaction between titanium phenolates and β-phenylcinnamaldehydes in toluene is reported. These compounds were characterized by NMR and UV/visible spectroscopy as well as mass spectrometry. In solution all the compounds are photochromic. Complete assignment of the ¹H and ¹³C resonances was achieved by concerted application of homonuclear (gs-COSY), proton-detected (C, H) one-bond (gs-HMQC), and long-range (gs-HMBC) heteronuclear two-dimensional chemical shift correlation experiments using a 500 MHz NMR spectrometer equipped with a cryoplatform and a 5 mm cryoprobe. The mass spectra of the different compounds were characterized by intense molecular and high fragment ions. The introduction of an atom of fluorine as a molecular probe is of interest in determining the mechanistic aspects of the photochemical process. CSIRO 2005.

Full text of DOI:10.1071/CH05062

Full Paper
CSIRO PUBLISHING
www.publish.csiro.au/journals/ajc
Aust. J. Chem. 2005, 58, 517–521
Synthesis and NMR Spectroscopic Characterization of Some
Fluoro-2H-1-Benzopyran Derivatives
Yannick Teral,A Gabriel Roubaud,B Claude Aubert,C Robert Faure,B
and Mylène CampredonA,D
A JE 2421 TRACES, Université de la Méditerranée, Faculté des Sciences de Luminy,
13298 Marseille Cedex 9, France.
B UMR-CNRS-6178, Faculté des Sciences de St Jérome, Université Paul Cézanne,
13397 Marseille Cedex 13, France.
C UPRES EA 3286, Faculté de Pharmacie de la Timone, Université de la Méditerranée,
13385 Marseille Cedex 5, France.
D Corresponding author. Email: Mylene.Campredon@luminy.univ-mrs.fr
The synthesis of some new fluoro-2H-1-benzopyran derivatives utilizing a reaction between titanium phenolates
and β-phenylcinnamaldehydes in toluene is reported.These compounds were characterized by NMR and UV/visible
spectroscopy as well as mass spectrometry. In solution all the compounds are photochromic. Complete assignment
of the 1H and 13C resonances was achieved by concerted application of homonuclear (gs-COSY), proton-detected
(C, H) one-bond (gs-HMQC), and long-range (gs-HMBC) heteronuclear two-dimensional chemical shift correlation
experiments using a 500 MHz NMR spectrometer equipped with a cryoplatform and a 5 mm cryoprobe. The mass
spectra of the different compounds were characterized by intense molecular and high fragment ions.The introduction
of an atom of fluorine as a molecular probe is of interest in determining the mechanistic aspects of the photochemical
process.
Manuscript received: 24 February 2005.
Final version: 13 May 2005.
Introduction
heteroaromatic groups in order to enhance the photochromic
properties of this series. From our perspective, the introduc-
tion of a fluorine atom may be useful in providing a molecular
probe. Moreover, these fluoro compounds are of interest
in determining the mechanistic aspects of the photochemi-
cal process.[7,8] In this paper, seven fluorobenzopyrans were
synthesized and characterized using NMR and UV/visible
spectroscopy as well as mass spectrometry.
2H-Pyran compounds are present in nature as a key unit
of natural products[1] and the benzopyran ring system is
the active constituent of natural pigments.[2] Even though
Becker et al.[3] reported on the photochromism of several
naturally occurring 2H-1-benzopyrans for the first time in
1970, only a few articles dealt with these derivatives until the
1990s. However, interest in these photochromic molecules
has since grown as a result of their commercial use in the
field of variable optical materials. Photochromic compounds
are of great interest to industry, but 2H-1-benzopyrans are
less photochromic than 2H-naphtho[1,2-b]pyrans and 3H-
naphtho[2,1-b]pyrans,[1] and the lack of interest in these
compounds arises as a result of their poor colour.[4] The
photochromic activity of these molecules is a well known
phenomenon based on UV absorption of the uncoloured
form, which can undergo isomerization after the scission
of the C O bond of the pyran moiety. This reaction is
reversible and the back isomerization to the uncoloured
form takes place by thermal or photochemical processes.
Several groups interested in the commercialization of pho-
tochromic plastic ophthalmic lenses have modified the parent
compound in an attempt to provide molecules with appropri-
ate properties and have patented[5,6] 2H-1-benzopyrans with
Results
We have synthesized 2,2-diphenyl-6-fluoro-, 2,2-di(4-fluoro-
phenyl)-6-fluoro-, 2,2-di(4-fluorophenyl)-6-methyl-, 2,2-
di(4-fluorophenyl)-6-methoxy-, 2,2-di(4-fluorophenyl)-5,7-
dimethyl-, 2,2-di(4-fluorophenyl)-7,8-dimethoxy-, and 2,2-
di(3-trifluoromethylphenyl)-7,8-dimethoxy-2H-benzopyran
1–7. These compounds have the general structure shown in
Scheme 1.
These fluoro-2H-1-benzopyran derivatives have been syn-
thesized in three steps from readily available starting mate-
rials. We have followed the most convenient synthetic route
towards benzopyrans, namely one that involves a reaction
between titanium phenolates and β-phenylcinnamaldehydes
in toluene. The overall synthetic route to compounds 1–7 is
outlined in Scheme 2.
© CSIRO 2005
10.1071/CH05062
0004-9425/05/070517

518
Y. Teral et al.
Propargyl alcohols A–C were prepared as outlined in
mixture, which was subsequently heated at reflux for three
hours while the reaction was monitored by thin-layer chro-
matography (TLC). The reaction mixture was subsequently
hydrolyzed using a KOH solution (2 M) and filtered. The
aqueous phase was further extracted with diethyl ether. The
combined organic extracts were dried (Na2SO4), filtered, and
concentrated under vacuum. The resultant yellow oil was
purified by chromatography (0–5% diethyl ether in pentane)
to afford, after evaporation of the eluent and pentane recrys-
tallization, compounds 1–5 as white powders and compounds
6 and 7 as yellow powders. The results are summarized in
Table 3 along with the wavelength maxima of the coloured
forms in toluene at 20◦C.
Scheme 2. To a solution of sodium acetylide (solution in
xylenes, 30 mL, 10 equiv.) in freshly distilled tetrahydro-
furan (THF) (250 mL) at −10◦C was added dropwise a
solution of the ketone (11.0 mmol) in THF (100 mL). Upon
complete addition, the mixture was allowed to warm to
room temperature, the reaction mixture was poured into
ice/water, and the two phases were separated. The organic
phase was washed with saturated aqueous ammonium chlo-
ride solution (100 mL), while the aqueous phase was further
extracted with diethyl ether (3 × 100 mL). The combined
organic extracts were dried (Na2SO4), filtered, and concen-
trated under vacuum. The xylenes were then removed by
azeotropic distillation of a methanol/xylene mixture. Chro-
matography (0–5% diethyl ether in pentane) afforded the
alcohol A as a white powder (88% yield), mp 78◦C. Com-
pounds B and C were obtained as yellow oils in 75 and 79%
yields, respectively, as reported in Table 1.
The yields obtained were in accordance with previous
work.[11] Formation of compound 8 was not achieved because
the C-alkylation step was probably inhibited as a result of the
(–I) effect on the aromatic ring of the trifluoromethyl group
(Scheme 3).[12]
Precursors A, B, and C then gave rise to aldehydes
D, E, and F upon Meyer–Schuster rearrangement[10] (1,3-
migration) under acidic catalysis (H2SO4). To a solution of
propargyl alcohol in dioxan was added a solution of sulfu-
ric acid (2.5 mL H2SO4/2.5 mL H2O). The mixture was then
heated at reflux for five minutes. The yields (see Table 2) for
this step were generally high and the crude products were
often sufficiently pure as to be used directly in the formation
of the benzopyran.
The benzopyran derivatives were subsequently syn-
thesized as follows. A solution of tetraethylorthotitanate
(10 mmol in 10 mL) in toluene (10 mL) was gently added
under an atmosphere of nitrogen to the phenolic compound
(10 mmol) in anhydrous toluene (50 mL) at room tempera-
ture and the ethanol was removed by azeotropic distillation
of a toluene/ethanol mixture. The mixture was then allowed
to cool to room temperature. The α,β-ethylenic compound
(10 mmol) in anhydrous toluene (80 mL) was added to the
As a follow-on to these results, unsuccessful attempts were
made to synthesize trifluoromethylpyrans using a bromo-
aromaticringandtrifluoromethylcopperreagents, asreported
by Carr et al.[13] and Urata and Fuchikami.[14] This latter
approach may be successful if iodopyran derivatives, which
are known to be more reactive than their bromo analogues,
are used.
1
For compounds 1–7 (Scheme 2), assignment of the H
and 13C chemical shifts of the phenyl ring protons and car-
bons on the basis of nJC,F and nJF,F coupling constants and
signal intensities was found to be trivial. However, even in
1
the 500 MHz H NMR spectra, on the basis of the multi-
plet pattern and the magnitude of the splitting, the proton
resonances of the benzo[2,1-b]pyran skeleton were charac-
teristic first-order spin systems which were no longer able
Table 1. Propargyl alcohol yields
ꢀ
ꢀ
Product
R3
R3
R4
R4
Yield [%]
A
B
C
H
H
CF3
H
H
CF3
H
F
H
H
F
H
88[9]
75
79
R4Ј R3Ј
R4Ј R3Ј
2Ј
3
5Ј
R5
R6
4
R5
R6
h␯
1
6؅ 1؅
2
4a
6؆ 1؆
O
⌬, h␯
O8a
2؆
2
Table 2. Aldehyde yields
5؆
R8 R7
R8 R7
ꢀ
ꢀ
R4Љ R3Љ
Product
R3
R3
R4
R4
Yield [%]
R4Љ R3Љ
Photomerocyanine
D
E
F
H
H
CF3
H
H
CF3
H
F
H
H
F
H
100
100
85
Scheme 1. Photochromic equilibrium and numbering system for
2H-benzopyran compounds 1–7.
R5
R4Ј
R3Ј
R4Ј
R3Ј
R4Ј
R3Ј
R4Ј R3Ј
HO
R6, Ti(OEt)4
R5
R7
R8 R7
C6H5CH3, 110ЊC
(a) NaC2H, THF, Ϫ5ЊC to RT
(b) NH4Cl, H2O
H2SO4, Dioxan
O
O
R6
OH
⌬
H
O
R8
R4Љ R3Љ
1–7
R4Љ R3Љ
R4Љ R3Љ
R4Љ R3Љ
A–C
D–F
Scheme 2.

Synthesis and Characterization of Some Fluoro-2H-1-Benzopyran Derivatives
519
[17]
1
to be assigned. Therefore, complete assignment of the H
para-fluorine atoms causes no appreciable shift in λmax,
and 13C resonances was achieved by concerted application
of homonuclear (gs-COSY), proton-detected (C, H) one-
bond (gs-HMQC), and long-range (gs-HMBC) heteronuclear
two-dimensional chemical shift correlation experiments. All
the CHn groups were unambiguously characterized from
the analysis of long-range correlation responses over two
while the presence of two CF3 groups in the meta-position
leaves λmax unchanged. As would be expected from previous
reports, the presence of an electron-donating group in the
six-position induced a red shift (ꢀλ 76 nm).[4] On the other
hand, electron-donating groups such as methoxy at the R7-
and R8-positions had little effect.
3
and three bonds (2J and J couplings) using the gs-HMBC
The photochromic properties of compound 4 are promis-
ing and very similar to those of the 8ꢀ-methoxyspiro
(fluorenenaphtho[2,1-b]pyran)[16] and spiro(3H-naphtho
[2,1-b]pyran-3,9ꢀ-[9H]-thioxanthene),[18] which are included
for comparison in Table 4.
sequence. To illustrate this strategy, significant long-range
1H–13C connectivities observed in the gs-HMBC spectrum
for compound 3 are shown in Scheme 4 (the arrows always
link a proton to a carbon).
There are few papers reported in the literature on mass
spectrometric studies of chromene derivatives.[15,16] In our
study, mass spectra of the different compounds were always
characterized by intense molecular ions. Fragmentation path-
ways, such as the loss of a radical (77 Da) or neutral (78 Da)
phenyl group in compound 1, the loss of a fluorophenyl
group (95 or 96 Da) in compounds 2–6, and the loss of a tri-
fluoromethylphenyl group (149 or 150 Da) in compound 7,
are common. This leads to the detection of the following
A preliminary study has already been conducted[19,20] on
compound 4, while some fatigue resistance tests will be the
subject of a following investigation.
Conclusions
A series of new photochromic compounds of the ben-
zopyran family that contain fluoro substituents have been
1
prepared. Total H and 13C NMR assignments were elabo-
high fragment ions: [M − ϕ)]+•, compound 1; [M − ϕF]+•
,
rated by concerted application of homonuclear (gs-COSY),
proton-detected (C, H) one-bond (gs-HMQC), and long-
range (gs-HMBC) heteronuclear two-dimensional chemical
shift correlation experiments. The mass spectra of the differ-
ent compounds were characterized by intense molecular and
high fragment ions. The photochromic properties were sen-
sitive to substituents on the pyranic ring, but the introduction
of two para-fluorine atoms caused little shift in λmax, while
the presence of two CF3 groups in the meta-position left λmax
unchanged.
compounds 2–6; and [M − ϕCF3]+•, compound 7. In ben-
zopyrans 1 and 2, in which R6 = F, loss of 19 Da is the result
of a loss of the fluorine atom on the pyranic ring by homolytic
cleavage. In benzopyrans 3–7, the loss of 15 Da is due to the
loss of a methyl group by homolytic cleavage. In benzopyrans
4, 6, and 7, the loss of 31 Da results from methoxy loss.
The spectroscopic data presented inTable 3 lists the wave-
length maxima of the coloured forms in toluene at 20◦C. It
is noteworthy that only the photomerocyanine of compound
4 shows a strong absorption at 485 nm. These observations
indicate that substituents on the phenyl groups can have
substantial effects on colour, but the introduction of two
Kinetic studies under UV irradiation are in progress in
order to determine the mechanistic aspects of the photochem-
ical process.
Table 3. Yields and spectroscopic data for benzopyran derivatives
ꢀ
ꢀ
ꢀ
ꢀ
Compound R3 = R3 R4 = R4 R5
R6
R7
R8
Yield [%] λmax [nm]
1
2
3
4
5
6
7
8
H
H
H
H
H
H
CF3
H
H
F
F
F
F
F
H
H
H
H
H
H
CH3
H
H
F
F
H
H
H
H
H
H
H
H
H
30
22
34
31
37
20
22
0
414
411–456w
413
489s
400
400–497w
401–499w
–
CH3
OCH3
H
H
H
CH3
OCH3 OCH3
OCH3 OCH3
H
CF3
H
H
OEt
OEt
R
EtO
O
Ti
H
F
F
O
O
R
H
R
OTi(OEt)3
H
R
O
CH3
CF3
CF3
R ϭ C6H5
Scheme 3. Inhibition of C-alkylation.
Scheme 4. Significant HMBC correlations observed for compound 3.

520
Y. Teral et al.
Table 4. Comparative spectroscopic data for benzopyrans and spiropyrans
Compound
Structure
2,2-Di(4-fluorophenyl)-6-
methoxy-2H-benzopyran 4
8ꢀ-Methoxyspiro(fluorene-
naphtho[2,1-b]pyran)
Spiro(3H-naphtho[2,1-b]pyran-
3,9ꢀ-[9H]-thioxanthene)
F
O
OCH3
OCH3
O
S
O
F
λmax [nm] in toluene
489
485
490
Experimental
phase was further extracted with diethyl ether. The combined organic
extracts were dried (Na2SO4), filtered, and concentrated under vac-
uum. The resultant yellow oil was obtained and purified by column
chromatography (silica, 0–5% diethyl ether in pentane).
Materials
CompoundsweresynthesizedinaccordancewithScheme2.Allreagents
wereobtainedfromAldrichandwereusedassupplied. Reactionsolvents
were predried and distilled immediately before use. Dichloromethane
was distilled from phosphorous pentoxide, while THF was predried
over potassium hydroxide and distilled from sodium benzophenone.
Flash column chromatography was carried out using Merck 60 silica
gel (0.063–0.200 nm) using solvents as supplied.
2,2-Diphenyl-6-fluoro-2H-benzopyran 1
Compound 1[26] was obtained as a white powder. The solid was
recrystallized from pentane, mp 115–116◦C. δH (CDCl3) 6.27 (1H, d, J
9.8, H3), 6.60 (1H, d, J 9.8, H4), 6.75 (1H, dd, J 8.4 and 2.9, H5), 6.83
(1H, dd, J 8.6 and 2.9, H7), 6.89 (1H, dd, J 8.7 and 4.7, H8), 7.30 (2H, t,
J 8.0, H4ꢀ), 7.36 (4H, t, J 7.9, H3ꢀ), 7.45 (4H, d, J 7.9, H2ꢀ). δC (CDCl3)
82.4 (C2), 112.6 (d, J 23.8, C5), 115.6 (d, J 23.1, C7), 117.4 (d, J 8.0,
C8), 122.1 (d, J 8.0, C4a), 122.8 (C4), 126.9 (C2ꢀ), 127.6 (C4ꢀ), 128.1
(C3ꢀ), 130.4 (C3), 144.4 (C1ꢀ), 148.3 (C1a), 157.3 (d, J 238.5, C6). m/z
(70 eV) 302 (61%, M+•), 283 (4), 225 (100).
Instrumentation
The compounds were characterized by NMR and UV/visible spec-
troscopy, as well as mass spectrometry.
NMR spectra were recorded in CDCl3 solutions at 300 K using
a Bruker Avance DRX 500 spectrometer equipped with a Bruker
CryoPlatform and a 5 mm cryo TXI probe. The temperature of the
probe and preamplifier was 30 K. Chemical shifts were referenced to
CDCl3:δH 7.25 ppm, δC 77.1 ppm.[21] Fortwo-dimensionalexperiments
Bruker microprograms using gradient selection (gs) were applied. The
gs-COSY spectra[22] were obtained with an F2 spectral width of 10 ppm
in 2 K data points for 256 t1 increments and sine-bell windows in both
dimensions. The gs-HMQC spectra[23] resulted from a 256 × 1024 data
matrix size with 2–16 scans per t1, depending on the sample concentra-
tion, an inter-pulse delay of 3.2 ms, and a 5 : 3 : 4 gradient combination.
The gs-HMBC spectra[24] were measured using a pulse sequence opti-
mized on 3J aromatic couplings (inter-pulse delay for the evolution of
long-range couplings: 50 ms) and the same gradient ratio as described
for the HMQC experiments. In this way, direct responses (1J couplings)
were not completely removed.
The visible absorption spectra of photomerocyanines were recorded
for 10−4 M photochromic solutions in spectroscopic grade toluene
in 10 mm quartz cells using a Beckman DU 7500 diode array
spectrometer.[25] Samples were irradiated with a Xe lamp at 20◦C and
400W m2.
Mass spectrometry was performed with a Hewlett Packard 5987
mass spectrometer operating in electron impact (70 eV) mode using a
direct insertion probe interface. The direct probe temperature for analy-
sis was programmed from 50 to 200◦C at 30◦C min−1 and the ion source
was held at 200◦C.
2,2-Di(4-fluorophenyl)-6-fluoro-2H-benzopyran 2
Compound 2[20] was obtained as a white powder. The solid was
recrystallized from pentane, mp 122.5–124◦C. δH (CDCl3) 6.16 (1H, d,
J 9.8, H3), 6.60 (1H, d, J 9.8, H4), 6.76 (1H, dd, J 8.9 and 2.0, H5),
6.83 (2H, m, H5 and H7), 7.03 (4H, t, J 8.8, H3ꢀ), 7.39 (4H, dd, J 8.8
and 5.5, H2ꢀ). δC (CDCl3) 81.8 (C2), 112.7 (d, J 23.8, C5), 115.0 (d, J
21.4, C3ꢀ), 115.8 (d, J 23.3, C7), 117.4 (d, J 7.9, C8), 121.9 (d, J 8.2,
C4a), 123.2 (C4), 128.7 (d, J 8.2, C2ꢀ), 129.9 (C3), 140.0 (C1ꢀ), 147.9
(C1a), 157.4 (d, J 238.6, C6), 162.1 (d, J 247.2, C4ꢀ). m/z (70 eV) 338
(51%, M+•), 319 (7), 243 (100).
2,2-Di(4-fluorophenyl)-6-methyl-2H-benzopyran 3
Compound 3 was obtained as a white powder. The solid was recrys-
tallized from pentane, mp 136–137◦C. δH (CDCl3) 2.22 (3H, s, CH3),
6.06 (1H, d, J 9.8, H3), 6.59 (1H, d, J 9.8, H4), 6.79 (1H, d, J 8.2, H8),
6.83 (1H, br s, H5), 6.93 (1H, dd, J 8.1 and 1.4, H7), 7.00 (4H, t, J 8.7,
H3ꢀ), 7.37 (4H, dd, J 8.8 and 5.4, H2ꢀ). δC (CDCl3) 20.6 (CH3), 81.7
(C2), 115.1 (d, J 21.5, C3ꢀ), 116.3 (C8), 120.9 (C4a), 124.0 (C4), 127.2
(C5), 128.6 (C3), 128.9 (d, J 8.2, C2ꢀ), 130.3 (C7), 130.8 (C6), 140.7
(C1ꢀ), 150.0 (C1a), 162.2 (d, J 247.0, C4ꢀ). m/z (70 eV) 334 (46%, M+•),
319 (6), 239 (100).
2,2-Di(4-fluorophenyl)-6-methoxy-2H-benzopyran 4
Melting points were measured using an Electrothermal 9100
apparatus.
Compound 4 was obtained as a white powder. The solid was recrys-
tallized from pentane, mp 152–153.5◦C. δH (CDCl3) 3.73 (3H, s,
OCH3), 6.13 (1H, d, J 9.8, H3), 6.60 (1H, d, J 2.9, H5), 6.61 (1H,
d, J 9.8, H4), 6.71 (1H, dd, J 8.8 and 2.9, H7), 6.85 (1H, d, J 8.8, H8),
7.01 (4H, t, J 8.7, H3ꢀ), 7.40 (4H, dd, J 8.8 and 5.4, H2ꢀ). δC (CDCl3)
55.7 (OCH3), 81.7 (C2), 111.7 (C5), 115.09 (C7), 115.14 (d, J 21.4,
C3ꢀ), 117.3 (C8), 121.8 (C4a), 124.1 (C4), 128.9 (d, J 8.2, C2ꢀ), 129.6
(C3), 140.6 (C1ꢀ), 146.1 (C1a), 154.3 (C6), 162.2 (d, J 246.8, C4ꢀ). m/z
(70 eV) 350 (100%, M+•), 335 (3), 319 (7), 255 (98).
General Synthesis Procedure
A solution of tetraethylorthotitanate (10 mmol in 10 mL) in toluene
was added under an atmosphere of nitrogen to the phenolic compound
(10 mmol in 50 mL) in anhydrous toluene at room temperature. The
ethanol was then removed by azeotropic distillation of a toluene/ethanol
mixture, and the reaction was allowed to cool to room temperature. The
cinnamaldehyde compound (10 mmol in 80 mL) in anhydrous toluene
was added to the mixture, which was subsequently heated at reflux for
3 h, while the reaction was monitored by TLC. The reaction mixture
was hydrolyzed using a KOH solution (2 M) and filtered. The aqueous
2,2-Di(4-fluorophenyl)-5,7-dimethyl-2H-benzopyran 5
Compound 5 was obtained as a white powder. The solid was recrys-
tallized from pentane, mp 140.5–141◦C. δH (CDCl3) 2.34 (3H, s,

Synthesis and Characterization of Some Fluoro-2H-1-Benzopyran Derivatives
521
7-CH3), 2.37 (3H, s, 5-CH3), 6.16 (1H, d, J 9.9, H3), 6.65 (1H, br
s, H6), 6.75 (1H, br s, H8), 6.90 (1H, d, J 9.9, H4), 7.10 (4H, t, J 8.6,
H3ꢀ), 7.51 (4H, dd, J 8.5 and 5.4, H2ꢀ). δC (CDCl3) 18.2 (5-CH3), 21.4
(7-CH3), 81.1 (C2), 115.0 (d, J 21.3, C3ꢀ), 115.1 (C8), 117.0 (C4a),
120.9 (C4), 124.2 (C6), 127.1 (C3), 128.8 (d, J 8.1, C2ꢀ), 134.2 (C5),
139.5 (C7), 140.9 (d, J 2.6, C1ꢀ), 152.3 (C1a), 162.1 (d, J 246.6, C4ꢀ).
m/z (70 eV) 348 (42%, M+•), 333 (8), 253 (100).
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2,2-Di(4-fluorophenyl)-7,8-dimethoxy-2H-benzopyran 6
Compound 6 was obtained as a yellow powder. The solid was
recrystallized from pentane, mp 117–117.5◦C. δH (CDCl3) 3.83 (3H,
s, 8-OCH3), 3.84 (3H, s, 7-OCH3), 6.01 (1H, d, J 9.7, H3), 6.46
(1H, d, J 8.3, H6), 6.61 (1H, d, J 9.7, H4), 6.75 (1H, d, J 8.3,
H5), 7.02 (4H, t, J 8.5, H3ꢀ), 7.45 (4H, dd, J 8.5 and 5.4, H2ꢀ).
δC (CDCl3) 55.9 (7-OCH3), 61.1 (8-OCH3), 81.8 (C2), 104.6 (C6),
114.9 (d, J 21.4, C3ꢀ), 116.0 (C4a), 121.1 (C5), 123.7 (C4), 126.4
(C3), 128.7 (d, J 13.1, C2ꢀ), 137.5 (C8), 140.4 (d, J 3.1, C1ꢀ), 145.3
(C1a), 154.0 (C7), 162.1 (d, J 246.7, C4ꢀ). m/z (70 eV) 380 (100%,
M
+•), 365 (15), 349 (12), 285 (78).
2,2-Di(3-trifluoromethylphenyl)-7,8-dimethoxy-
2H-benzopyran 7
Compound 7 was obtained as a yellow powder. The solid was
recrystallized from pentane, mp 100–101◦C. δH (CDCl3) 3.84 (3H, s,
7-OCH3), 3.87 (3H, s, 8-OCH3), 6.05 (1H, d, J 9.7, H3), 6.48
(1H, d, J 8.4, H6), 6.69 (1H, d, J 9.7, H4), 6.78 (1H, d, J 8.4,
H5), 7.47 (1H, t, J 7.7, H5ꢀ), 7.56 (1H, br d, J 7.6, H4ꢀ), 7.66
(1H, br d, J 7.7, H6ꢀ), 7.80 (1H, br s, H2ꢀ). δC (CDCl3) 55.9
(7-OCH3), 61.2 (8-OCH3), 81.8 (C2), 104.8 (C6), 115.7 (C4a), 121.4
(C5), 123.6 (q, J 3.9, C2ꢀ), 123.9 (q, J 272.7, CF3), 124.69 (q, J 7.6,
C4ꢀ), 124.71 (C4), 125.0 (C3), 128.9 (C5ꢀ), 130.3 (C6ꢀ), 130.6 (q, J 32.4,
C3ꢀ), 137.6 (C8), 145.1 (C1ꢀ), 145.3 (C1a), 154.3 (C7). m/z (70 eV) 480
(71%, M+•), 465 (8), 449 (8), 335 (100).
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doi:10.1016/S0040-4039(02)02513-3
Acknowledgments
[21] H. Günther, La Spectroscopie de RMN 1994, p. 60 (Masson:
Paris).
We thank Dr J. C. Arnall-Culliford for helpful discussions.
[22] R. E. Hurd, J. Magn. Reson. 1990, 87, 422.
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