Synthesis of carbonyl dyes from 1-hydroxy-2-acetonaphthone and 2-fluorobenzophenone

Article abstract of DOI:10.1002/jhet.434

(Chemical Equation Presented) The reaction between 1-hydroxy-2- acetonaphthone and 2-fluorobenzophenone in basic medium afforded two diastereoisomeric carbonyl dyes whose structures were unambiguously established using spectroscopic methods. A mechanism for the formation of these dyes involving a base-catalysed addition followed by dehydration and intramolecular aromatic nucleofilic substitution is proposed.

Full text of DOI:10.1002/jhet.434

September 2010
Synthesis of Carbonyl Dyes from 1-Hydroxy-2-Acetonaphthone
and 2-Fluorobenzophenone
1123
Paulo J. Coelho,* Isabel C. Fernandes, and Luis M. Carvalho
´ ´
Centro de Quımica-Vila Real, Universidade de Tras-os-Montes e Alto Douro, 5001-801 Vila Real,
Portugal
*E-mail: pcoelho@utad.pt
Received December 17, 2009
DOI 10.1002/jhet.434
Published online 16 July 2010 in Wiley Online Library (wileyonlinelibrary.com).
The reaction between 1-hydroxy-2-acetonaphthone and 2-fluorobenzophenone in basic medium
afforded two diastereoisomeric carbonyl dyes whose structures were unambiguously established using
spectroscopic methods. A mechanism for the formation of these dyes involving a base-catalysed addi-
tion followed by dehydration and intramolecular aromatic nucleofilic substitution is proposed.
J. Heterocyclic Chem., 47, 1123 (2010).
INTRODUCTION
RESULTS AND DISCUSSION
Reaction between 1-hydroxy-2-acetonaphthone 1 and
benzophenone 2 in the presence of sodium tert-butoxide
is known to produce, after acid treatment, mainly 2,2-
diphenylnaphthopyran-4-one 4, a useful compound in
the synthesis of photochromic naphthopyrans [1,2]. The
reaction involves a base-catalysed addition of 1 to 2 fol-
lowed by dehydration that provides the yellow interme-
diate 3. Then the acid catalyzed intramolecular 1,4-addi-
tion of the phenolic hydroxyl group to the a,b-conju-
gated ketone produces the diphenylnaphthopyran-4-one
4 (Scheme 1) [3]. This low yielding reaction (56%)
requires an excess of base and ketone and is thus far
limited to diarylketones [4–6].
To improve the yield and understand how this dye is
formed, we re-investigated this reaction and found out
that, in fact, two different dyes are formed after the first
step of the reaction between 1 and 5 (t-BuOK in toluene
under reflux). NH4Cl(aq) hydrolysis of the basic reaction
mixture afforded a yellow dye 7 (less polar, 63% yield)
as well as a small amount of the already known dye 6
(more polar, 7% yield) (Scheme 2).
Spectroscopic characterization of the new yellow dye
7 using DEPT, COSY, HMBC, HSQC provided the
complete assignment of all proton and carbon resonan-
ces and showed that this compound is a diastereoisomer
of the previously isolated dye 6 (Table 1). Long-range
CAH correlations in the HMBC spectrum established
the connectivity between all atoms and are shown in
Figure 1.
Recently, we have reported that the reaction between
1 and 2-fluorobenzophenone 5 in the presence of 5
equivalents of potassium tert-butoxide in toluene under
reflux, followed by reflux in AcOH/HCl gives rise to a
small amount of a blue dye (5.7%). Spectroscopic char-
acterization using high-resolution NMR techniques
established the highly conjugated structure 6 for this
product [7].
The spectroscopic data for compounds 7 and 6 are
quite similar. Both exhibit the same molecular formula
1
and similar patterns in the Mass spectra and in the H
and 13C NMR spectra. The main differences between
these two diastereoisomeric dyes in the NMR spectra
were the chemical shifts of protons H-30 found at 6.04
(s) for dye 7 and at 9.12 (s) for dye 6 and the chemical
shift of the carbonyls found at 195.36 ppm for 7 and at
183.58 ppm for 6. The NOESY spectrum showed an im-
portant correlation between H-30and H-3 for compound
7, which was not observed for compound 6 and thus
establishes a Z-configuration for the double bond
between carbons 2 and 20 of dye 7.
Scheme 1. Synthesis of 2,2-diphenylnaphthopyran-4-one 4.
C
V
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P. J. Coelho, I. C. Fernandes, and L. M. Carvalho
Vol 47
Scheme 2. Synthesis of dyes 6 and 7.
The UV-vis spectra of these two dyes are very differ-
molecular nucleophilic aromatic substitution would lead
to the two diastereoisomeric dyes 6 and 7 (Scheme 3)
[8,9].
ent. While the blue dye 6 exhibits a large band in the
visible spectrum with a maximum at 538 nm (e 1.1 ꢀ
104), a sub-maximum at 577 nm (e 1.1 ꢀ 104), and two
shoulders at 504 nm (e 0.83 ꢀ 104) and 630 nm (e 0.50
ꢀ 104), the yellow dye 7 presents a maximum at 394
nm (e 0.74 ꢀ 104) (Figure 2). The lower kmax for dye 7
suggests a less efficient conjugation that may be due to
the repulsion between the oxygen atoms at C-20 and C-1
that would led to a less planar structure of this
Z-isomer.
Although both dyes were formed under basic condi-
tions, a small amount of the blue dye 6 was also formed
when the yellow dye 7 was refluxed in acid medium
(AcOH/HCl). This can be explained through an acid cat-
alyzed isomerization of 7 to 6 (Scheme 4).
EXPERIMENTAL
The formation of both dyes under basic medium led
us to propose the following mechanism: subsequent to
the base-catalyzed addition between 1 and 5, proton
transfer and dehydration would form the phenolate A,
which might adopt two configurations, that upon intra-
The reagents were obtained from Aldrich and were used as
supplied. Solvents were of analytical grade. The reactions
were monitored by thin-layer chromatography on aluminum
plates precoated with Merck silica gel 60 F254 (0.25 mm).
Melting point was determined in capillary tubes and are
Table 1
NMR spectral data for dyes 6 and 7.
Dye 6
Dye 7
Atom
1H (J in Hz)
13C
1H (J in Hz)
13C
1
2
183.58, s
111.21, s
123.18, d
119.53, d
137.78, s
127.25, d
131.84, d
126.38, d
126.90, d
132.59, s
162.44, s
120.74, d
150.14, s
121.38, s
126.47, d
124.81, d
132.03, d
117.12, d
153.34, s
136.05, s
128.77, d
128.98, d
129.54, d
195.36, s
113.96, s
124.59, d
118,11, d
137.28, s
127.35, d
130.04, d
125.77, d
124.35, d
125.18, s
163.54, s
124.15, d
147.72, s
126.59, s
128.18, d
123.96, d
131.20, d
115.50, d
148.52, s
140.28, s
128.58, db
127.86, db
129.70, d
3
7.66, d (9.6)
6.73, d (9.6)
7.80, d (8.8)
4
4a
7.25a
5
6
7.42, d (7.6)
ꢁ7.55a
7.74, d (8.0)
7.62, ddd (1.3,6.9, 8.0)
7.51, ddd (1.0,7.0, 8.0)
8.45, d (8.0)
7
7.36, dd (7.5; 8.0)
8.34, d (8.0)
8
8a
20
30
9.12, s
7.48, s
40
40a
50
ꢁ7.55a
7.25, dd (7.5; 7.6)
ꢁ7.58a
7.10a
7.15, d (8.9)
7.20a
60
70
800
ꢁ7.51a
7.05a
800a
1
200 and 600
300 and 500
400
ꢁ7.52a
ꢁ7.62a
ꢁ7.52a
7.45a
7.45a
7.40a
All 1H-13C connectivities were assigned by HMBC and HSQC and the multiplicities were determined by DEPT experiments.
a Approximate central values due to overlapped signals.
b The values may be interchanged.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

September 2010
Synthesis of Carbonyl Dyes from 1-Hydroxy-2-acetonaphthone
and 2-Fluorobenzophenone
1125
Figure 2. UV/vis spectra of compounds 6 and 7 (3.1 ꢀ 10ꢂ5 M,
Figure 1. Long-range CAH correlations obtained from HMBC for dye
7.
CH2Cl2).
uncorrected. The new compounds were determined to be
>95% pure by 1H NMR spectroscopy. UV-Vis spectra were
recorded on a CARY 50 Varian spectrophotometer. IR spectra
were obtained on a Perkin-Elmer FTIR 1600 spectrometer
using KBr disks (wavenumbers in cmꢂ1). Electronic impact
mass spectra were measured on a AutoSpecE spectrometer.
The 1H and 13C NMR spectra were recorded at 298 K in
for another 40 min. The dark red solution was hydrolyzed with
NH4Cl (aq) and then extracted with Et2O (3 ꢀ 20 mL). The
organic extracts were dried over anhydrous Na2SO4 and evapo-
rated leaving a deep red residue, which was purified by col-
umn chromatography (2–10% ethyl acetate/petroleum ether)
over silica gel. Two compounds were isolated: 7, 0.220 g
(63%) and 6, 0.025 g (7%).
1
CDCl3 using a Bruker ARX400 spectrometer (at 400.13 for H
and 100.62 MHz for 13C). Chemical shifts (d) are reported in
ppm and coupling constants (J) in Hz. Resonance multiplicities
for 13C were established via the acquisition of DEPT spectra.
Heteronuclear 1H-13C HSQC and HMBC experiments were
carried out using standard procedures.
(2Z)-2-(40-phenyl-2H-chromen-20-ylidene)naphthalene-1(2H)-
one (7). This compound was obtained as a yellow powder, mp
130ꢃC dec. IR: 3060, 3026, 2976, 1620, 1594, 1569, 1450, 1320,
1
1254, 1203, 1059. For H NMR and 13C NMR data see Table 1.
MS: m/z (%): 348 (75), 331 (12), 291 (8), 271 (14), 170 (100).
Exact mass for C25H16O2: 348.1150; Found 348.1146.
(2E)-2-(40-phenyl-2H-chromen-20-ylidene)naphthalene-1
(2H)-one (6). This compound was obtained as blue needles,
mp 155–158ꢃC. IR: 3050, 2923, 2852, 1624, 1593, 1541,
1505, 1468, 1371, 1315, 1273, 1235, 955, 923. For 1H NMR
General procedure for the synthesis of dyes (6) and
(7). 1-Hydroxy-2-acetonaphthone 1 (0.186 g, 1.0 mmol) and
potassium tert-butoxide (0.336 g, 3 mmol) in toluene (15 mL)
were refluxed for 20 min. 2-Fluorobenzophenone 2 (0.400 g,
2.0 mmol) was added and the reaction mixture was refluxed
Scheme 3. Mechanism for the formation of dyes 6 and 7 from 1-hydroxy-2-acetonaphthone 1 and 2-fluorobenzophenone 5.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

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P. J. Coelho, I. C. Fernandes, and L. M. Carvalho
Vol 47
Scheme 4. Acid catalysed isomerization of dye 7 to dye 6.
and 13C NMR data see Table 1. MS: m/z (%): 348 (100), 331
(25), 289 (10), 271 (40). Exact mass for C25H16O2: 348.1150;
Found 348.1148.
Guglielmetti, R., Eds.; Plenum Press: New York, 1998; Vol. 1, p
111.
[3] Coelho, P. J.; Carvalho, L. M.; Vermeersch, G.; Delbaere,
S. Tetrahedron 2009, 65, 5369.
Acknowledgment. We thank FCT (Portugal’s Foundation for
Science and Technology) for financial support through project
PTDC/QUI/66012/2006.
[4] Cottam, J.; Livingstone, R. J Chem Soc 1964, 5228.
[5] Kabbe, H. D.; Widdig, A. Angew Chem Int Ed Engl 1982,
21, 247.
[6] Nelly, S. E.; Vanderplas, B. C. J Org Chem 1991, 56, 1325.
[7] Coelho, P. J.; Carvalho, L. M. Dyes Pigm 2008, 78, 173.
REFERENCES AND NOTES
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[2] Van Gemert, B. In Organic Photochromic and Thermo-
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DOI 10.1002/jhet