Synthesis and spectrokinetic studies of a new family of photochromic 2H- chromenes (= 2H-1-benzopyrans): Dimethyl 6-aryl-2,2-dimethyl-2H-chromene-7,8- dicarboxylates

Article abstract of DOI:10.1002/(SICI)1522-2675(20000315)83:3<650::AID-HLCA650>3.0.CO;2-U

A series of dimethyl 6-aryl-2,2-dimethyl-2H-chromene-7,8-dicarboxylates were synthesized, and the photochromic properties of this new family of dimethyl-2H-chromenes were studied under continuous irradiation. The presence of the methoxycarbonyl groups was shown to stabilize the colored forms. This stabilization depended on the solvent, and in two cases the formation of long-lived opened forms was observed. Under irradiation with a mercury lamp, this family of 2H-chromenes showed a strong resistance to photodegradation.

Full text of DOI:10.1002/(SICI)1522-2675(20000315)83:3<650::AID-HLCA650>3.0.CO;2-U

650
Helvetica Chimica Acta ± Vol. 83 (2000)
Synthesis and Spectrokinetic Studies of a New Family of Photochromic 2H-
Chromenes (ˆ2H-1-Benzopyrans): Dimethyl 6-Aryl-2,2-dimethyl-2H-
chromene-7,8-dicarboxylates
by Alain Maggiani, Arlette Tubul, and Pierre Brun*
Á
Â
Â
Â
Â
Â
Laboratoire de Synthese Organique Selective, GCOPL, ESA 6114, Universite de la Mediterranee, Faculte des
Sciences de Luminy, 163 Avenue de Luminy, case 901, F-13288 Marseille Cedex 9 (Phone: (33) 4-91-82-92-70;
fax: (33) 4-91-82-94-15; e-mail: brun@chimlum.univ-mrs.fr)
A series of dimethyl 6-aryl-2,2-dimethyl-2H-chromene-7,8-dicarboxylates were synthesized, and the
photochromic properties of this new family of dimethyl-2H-chromenes were studied under continuous
irradiation. The presence of the methoxycarbonyl groups was shown to stabilize the colored forms. This
stabilization depended on the solvent, and in two cases the formation of long-lived opened forms was observed.
Under irradiation with a mercury lamp, this family of 2H-chromenes showed a strong resistance to
photodegradation.
1. Introduction. ± Organic photochromic compounds have been extensively studied
during the last twenty years because of their potential applications for industrial
purposes [1 ± 4]. Among these compounds, the 2H-chromene (ˆ2H-1-benzopyran)
series was particularly investigated, as it is used in the optical industry (variable-
transmission glasses) [5]. The influence of different substituents has been studied to
establish structure-reactivity relationships [6][7]. It has been shown that the presence
of electron-withdrawing groups at the aromatic ring enhances the photochromic
properties (increase of the Aeq value, vide infra). This is particularly the case with nitro
groups. However, in this last case, the 2H-chromenes are very sensitive to photo-
degradation. It was also noted that the photochromic properties are increased (higher
Aeq value, faster fading rate) when the benzene ring of the benzopyran is replaced by a
benzo-condensed framework, such as a naphthalene or a phenanthrene ring. However,
the synthesis and the photochromic behavior of 2H-chromenes bearing electron-
withdrawing groups, such as methoxycarbonyl groups, and substituted with a freely
rotating aromatic nucleus were not reported.
We describe here the synthesis and the spectrokinetic properties of a series of
chromenes of type 1 bearing phenyl groups with different substituents and two
methoxycarbonyl groups at positions 7 and 8.

Helvetica Chimica Acta ± Vol. 83 (2000)
651
2. Results. ± The photochromic phenomenon of chromenes can be described by an
equilibrium, induced by UV irradiation, between, at least, two species (Scheme 1).
Usually, the opened form is colored while the closed one is colorless.
Scheme 1
The various chromenes used in this work were synthesized starting from the
corresponding phenol derivatives 2 which were obtained by a previously described
method [8] (Scheme 2). The chromenes 1 were then prepared via 3 by a two-step
procedure described by Mann and co-workers [9] (Table 1).
Scheme 2
a) For Ar, see Table 1
Table 1. Formation of Propargylic Ether Derivatives 3 and 2,2-Dimethyl-2H-chromenedicarboxylates 1
Ar
Product
[%]
Product
[%]
Ar
Product
[%]
Product
[%]
Ph
3a
b
c
d
e
31
91
53
38
73
86
1a
b
c
d
e
49
59
61
70
63
51
4-MeO C6H4
4-Br C6H4
4-MeCO C6H4
4-Cl C6H4
3g
h
i
j
k
58
88
82
0
1g
h
i
j
k
50
47
35
±
1-Naphthyl
2-Ph C6H4
4-Ph C6H4
2-PhO C6H4
4-PhO C6H4
4-NO2 C6H4
0
±
f
f

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Helvetica Chimica Acta ± Vol. 83 (2000)
The spectrokinetic studies were performed with a modified [10] Beckman UV
spectrophotometer. The photochromic chromene 1 in toluene, MeCN, or EtOH was
irradiated at 238 for 1.5 h under UV light with a Xe lamp (400 W). The irradiation was
then stopped and the ring-closure process (Scheme 1) monitored by recording the
decrease of the absorbance of the opened forms. The results are reported in Table 2.
Table 2. Spectrokinetic Properties of the 2,2-Dimethyl-2H-chromenedicarboxylates 1
Ar
MeCN
EtOH
Toluene
lmaxa) [nm] kDb) [s
]
Aeq
)
lmaxa) [nm] kDb) [s
]
Aeq
)
lmaxa) [nm] kDb) [s
] Aeq )
1
c
1
c
1
c
4
4
4
4
4
4
4
1a Ph
411
405
415
406
5 ´ 10
2 ´ 10
4 ´ 10
3 ´ 10
4 ´ 10
10
4 ´ 10
2 ´ 10
,
,
,
,
0.10 411
0.05 410
0.10 421
0.09 406
2 ´ 10
0.09
0.03
0.08
0.11
420
418
419
416
8 ´ 10
10
,
,
0.09
0.15
0.09
0.20
4
4
4
4
4
b 1-Naphthyl
c 2-Ph C6H4
d 4-Ph C6H4
4 ´ 10
2 ´ 10
5 ´ 10
,
,
3 ´ 10
4
10
4
32 ´ 10
,
4
4
4
10
3 ´ 10
3 ´ 10
2 ´ 10
4
4
4
4
4
4
4
4
9 ´ 10
2 ´ 10
7 ´ 10
4 ´ 10
,
,
,
4
4
4
4
4
e 2-PhO C6H4
f 4-PhO C6H4
412
418
4 ´ 10
2 ´ 10
,
0.07 436
0.11 415
0.11 410
0.05
437
1 ´ 10
5 ´ 10
0.08
0.11
0.17
4
4
4
4
12 ´ 10
,
7 ´ 10
2 ´ 10
6 ´ 10
,
,
0.0451 422
,
,
4
4
2 ´ 10
0
10
g 4-MeO C6H4 409
0.08
0.06
0.20
420
432
437
4 ´ 10
4
3
10
10
,
4
4
4
4 ´ 10
5 ´ 10
2 ´ 10
4
4
4
4
4
h 4-Br C6H4
455
2 ´ 10
9 ´ 10
0.03 438
0.08 410
5 ´ 10
2 ´ 10
8 ´ 10
0
,
,
,
0.03
0.04
4
i 4-MeCO C6H4 437
,
2 ´ 10
4
10
a) lmax of the ꢀopened formꢁ. b) Kinetic constant(s) of the ring closure. c) Absorbance at the photostationary state.
3. Discussion. ± 3.1. Synthesis. As can be seen from Table 1, the yields of the
propargylic ether derivatives 3 are modest to good, except for the 4-chlorophenyl- and
the 4-nitrophenyl-substituted derivatives 3j and 3k. In these two cases, the poorer
reactivity of the phenolic precursors 2j and 2k can be explained by the inductive and
resonance effects of these substituents decreasing the nucleophilicity of the phenol
moiety. The yield for the subsequent cyclization step leading to the chromenes 1 is low
when an electron-attracting group is located at the 4-position (see 1i in Table 1).
3.2. Influence on the lmax of the Opened Form of 1. When toluene is replaced by the
more polar MeCN as solvent in the irradiation of 1, a hypsochromic effect is observed
on the lmax value of the opened form (see Scheme 1) when the substituent is an electron-
donating group (see 1a ± g), while no effect is observed for an electron-withdrawing
group (see 1i). Such a negative solvatochromic effect is indicative of the existence of
zwitterionic rather than quinone-like opened forms [11].
When toluene or MeCN are replaced by EtOH, the result is not so clear cut, and
positive and negative solvatochromic effects are observed, depending on the nature of
the substituent. In fact, in most cases, a hypsochromic effect is observed between the

Helvetica Chimica Acta ± Vol. 83 (2000)
653
nonpolar toluene and EtOH, while no effect or a bathochromic effect is observed
between the aprotic polar MeCN and the protic polar EtOH. This indicates that
H-bonding can also participate in the stabilization of opened forms. In a nonpolar
solvent (toluene), in which solvatation effects are not important, the Aeq value is higher
with electron-donating than with electron-withdrawing groups.
When the phenyl substituent of the parent chromene 1a is substituted by another
phenyl group, the effect on the lmax value depends on the position of the latter
substituent. Thus, in the case of the ([1,1'-biphenyl]-4-yl)-substituted compound 1d,
lmax is smaller than in the case of the parent 1a or the ([1,1'-biphenyl]-2-yl)-substituted
compound 1c. This reflects the coplanarity of the two aromatic rings of the biphenyl
moiety in the case of 1d, and thus that the two rings are conjugated. This effect on lmax is
not observed when non-conjugated substituents are introduced at the 2- or 4-position of
the phenyl substituent of the parent 1a (see 1e and 1f). The highest lmax value is
observed when a Br-atom is located at the 4-position (see 1h). Compound 1i shows a
high lmax value in aprotic solvents.
3.3 Influence on the Kinetic Constants of the Ring Closure (see Scheme 1). In most
cases, we observed two kinetic constants, and in one case three constants (1d). This
means that at least two opened species are involved in the ring-closure process. The
only difference between these forms lies in the relative configuration of the conjugated
system (cis-cis-cis, cis-trans-trans, cis-trans-cis, trans-trans-trans, trans-trans-cis, etc.) [12].
As in the case of nitro groups, the presence of the two carboxylate functions on the
chromene structure decreases significantly the bleaching kinetic constants. Indeed, the
chromene analog of 1a, without the two ester groups does not exhibit any photo-
chromic properties: its fading rate is so fast that the opened form cannot be detected
under our experimental conditions. The decrease of the kinetic constants is due to the
stabilization of the opened forms by the strong electron-withdrawing effect of the ester
groups and also by an extended conjugation. Furthermore, kD for 1g in MeCN and 1i in
EtOH cannot be measured. In solution, the opened forms of these substrates are very
stable and are still colored one month after the end of irradiation. If in the case of 1i a
strong stabilization can be envisioned because of the polarity and the chelating
properties of EtOH, this is not the case for 1g; the behavior of the latter can not be
explained for the moment.
Table 2 shows that, at equilibrium (between the closed and the opened forms), the
absorbances Aeq are not very important for the compounds studied, the highest one
being 0.2 for 1d in toluene and 1i in EtOH. Usually, in the 2H-chromene series, these
Aeq values are between 0.2 and 0.7 under the conditions we use.
In the case of 1d, the equilibrium between the opened and the closed forms depends
on the nature of the irradiation source. With a Xe lamp, an Aeq of 0.2 is observed at the
equilibrium state, while on irradiation with a Hg lamp (500 W), Aeq reaches a value of
0.9. In fact, chromene 1d exhibits in the UV spectrum a lmax at a slightly lower value
(334 nm) than the value usually observed for 2,2-dimethyl-2H-chromenes (ca. 345 nm)
[13]. Thus, because of its emission spectrum, the Hg lamp is much more appropriate to
induce the opening of chromene 1d.
It must be noted that this type of irradiation with a Hg lamp is used to study the
photodegradation processes of photochromic compounds. Usually under these
conditions, degradation is observed already after 10 min of irradiation [14]. In the

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Helvetica Chimica Acta ± Vol. 83 (2000)
case of the chromene 1d, we did not observe any degradation after 1.5 h of irradiation.
Thus, 1d is particularly stable towards photodegradation.
Conclusion. ± The synthesis of a new family of 2,2-dimethyl-2H-chromenes 1 that
are substituted with an aryl and two ester groups is described. Depending on the nature
of the aryl substituent, the yields are modest to good. As compared with the
unsubstituted parent 2H-chromenes, the introduction of the aryl substituent does not
lead to important modifications of the photochromic properties. However, the
introduction of the methoxycarbonyl groups reduces the thermal bleaching constant,
thus inducing photochromic behavior or enabling the observation of permanently
colored forms. Moreover, the presence of these two functions has an effect on the
photochromic properties similar to the one of a nitro group, but leads to much more
stable compounds upon UV irradiation. It is shown that the influence of the irradiation
source is very important: a stronger absorbance is observed with a Hg lamp than with a
Xe lamp in the case of 1d.
Experimental Part
General. TLC. Merck F254 silica gel. Column chromatography Merck silica gel 60 or 60 H (for flash
chromatography (FC)). M.p.: Electrothermal-IA-9100 apparatus; in capillary tubes. LR Spectra: Perkin-Elmer-
1
297 spectrometer; CHCl3 soln.; nÄmax in cm 1. H- and 13C-NMR Spectra: Bruker-AC-250 spectrometer; at 250
and 62.2 MHz, resp., in CDCl3 soln.; chemical shifts d in ppm, coupling constants J in Hz.
Propargylic-Ether Formation: General Procedure. To a mixture of the polysubstituted arylphenol (2 mmol),
K2CO3 (4 mmol), KI (3.4 mmol), and CuI (0.04 mmol) in dry DMF (8 ml) under Ar, 3-chloro-3-methylbut-1-
yne [15] (4 mmol) is added. The mixture is stirred at 658 until no further conversion is observed by TLC. After
cooling, H2O (15 ± 20 ml) is added and the mixture extracted with CH2Cl2 (3 Â 20 ml). The combined CH2Cl2
extract is washed successively with 2n NaOH (2 Â 15 ± 20 ml), 2n HCl (2 Â 15 ± 20 ml), and H2O to neutrality,
dried (MgSO4) and evaporated. The product is purified by FC (hexane/Et2O).
Dimethyl 4-[(1,1-Dimethylprop-2-ynyl)oxy][1,1'-biphenyl]-2,3-dicarboxylate (3a): IR (CHCl3): 1719, 1739
(CˆO); 2386 (CꢀC); 3300 (ꢀCH). 1H-NMR: 1.59 (s, 6 H); 2.58 (s, 1 H); 3.51 (s, 3 H); 3.81 (s, 3 H); 7.17 ± 7.76
(m, 7 H). 13C-NMR: 29.69 (q); 29.69 (q); 52.53 (q); 52.69 (q); 72.94 (s); 73.91 (d); 86.13 (s); 122.03 (d); 122.13
(s); 126.96 (s); 127.71 (d); 127.71 (d); 128.55 (d); 128.55 (d); 132.30 (d); 132.47 (d); 135.59 (s); 140.15 (s); 152.96
(s); 167.33 (s); 168.50 (s). Anal. calc. for C21H20O5 (352.38): C 71.51, H 5.67; found: C 71.39, H 5.94.
Dimethyl 3-[(1,1-Dimethylprop-2-ynyl)oxy]-6-(naphthalen-1-yl)benzene-1,2-dicarboxylate (3b): IR
(CHCl3): 1725, 1735 (CˆO); 2395 (CꢀC); 3300 (CꢀCH). 1H-NMR: 1.56 (s, 3 H); 1.58 (s, 3 H); 2.55
(s, 1 H); 3.09 (s, 3 H); 3.73 (s, 3 H); 7.09 ± 7.32 (m, 6 H); 7.44 (d, J ˆ 8.0, 1 H); 7.65 (d, J ˆ 8.6, 1 H); 7.73 (d, J ˆ
8.0, 1 H). 13C-NMR: 29.50 (q); 29.79 (q); 52.19 (q); 52.61 (q); 73.79 (s); 75.02 (d); 86.00 (s); 121.79 (d); 122.09
(s); 125.26 (d); 125.90 (d); 126.36 (d); 126.92 (d); 127.20 (s); 128.16 (d); 128.38 (d); 132.16 (s); 133.11 (s); 133.51
(d); 133.58 (d); 134.08 (s); 137.86 (s); 153.19 (s); 167.37 (s); 167.57 (s). Anal. calc. for C25H22O5 (402.44): C 74.54,
H 5.47; found: C 74.73, H 5.50.
Dimethyl 4-[(1,1-Dimethylprop-2-ynyl)oxy][1,1':2',1''-terphenyl]-2,3-dicarboxylate (3c): IR (CHCl3): 1725,
1738 (CˆO); 2326 (CꢀC); 3300 (CꢀCH). 1H-NMR: 1.52 (s, 6 H); 2.47 (s, 1 H); 3.45 (s, 3 H); 3.77 (s, 3 H); 6.83
(d, J ˆ 8.6, 1 H); 7.12 ± 7.35 (m, 9 H); 7.44 (d, J ˆ 8.6, 1 H). 13C-NMR: 29.30 (q); 29.86 (q); 52.47 (q); 52.62 (q);
73.95 (s); 74.56 (d); 86.17 (s); 121.98 (d); 125.51 (s); 126.92 (d); 127.26 (d); 128.20 (d); 128.20 (d); 128.75 (d);
129.94 (d); 129.94 (d); 130.19 (d); 130.47 (d); 132.58 (s); 133.83 (d); 135.85 (s); 138.63 (s); 140.84 (s); 141.04 (s);
152.50 (s); 167.41 (s); 167.93 (s). Anal. calc. for C27H24O5 (428.48): C 75.61, H 5.60; found: C 75.76, H 5.64.
Dimethyl 4-[(1,1-Dimethylprop-2-ynyl)oxy][1,1':4',1''-terphenyl]-2,3-dicarboxylate (3d): IR (CHCl3): 1728,
1733 (CˆO); 2350 (CꢀC); 3300 (CꢀCH). 1H-NMR: 1.61 (s, 6 H); 2.57 (s, 1 H); 3.53 (s, 3 H); 3.81 (s, 3 H);
7.24 ± 7.40 (m, 6 H); 7.54 (d, J ˆ 8.2, 2 H); 7.55 (d, J ˆ 7.9, 2 H); 7.74 (d, J ˆ 8.7, 1 H). 13C-NMR: 29.59 (q); 29.59
(q); 52.49 (q); 52.57 (q); 73.83 (s); 74.65 (d); 86.02 (s); 121.95 (d); 126.93 (s); 127.14 (d); 127.14 (d); 127.20 (d);
127.20 (d); 127.58 (s); 128.87 (d); 128.87 (d); 128.98 (d); 128.98 (d); 132.16 (s); 132.35 (d); 135.02 (s); 138.99 (s);
140.35 (d); 140.68 (s); 152.92 (s); 166.92 (s); 168.41 (s). Anal. calc. for C27H24O5 (428.48): C 75.61, H 5.60; found:
C 75.81, H 5.77.

Helvetica Chimica Acta ± Vol. 83 (2000)
655
Dimethyl 4-[(1,1-Dimethylprop-2-ynyl)oxy]-2'-phenoxy[1,1'-diphenyl]-2,3-dicarboxylate (3e): IR (CHCl3):
1724, 1735 (CˆO); 2333 (CꢀC); 3300 (ꢀCH). 1H-NMR: 1.47 (s, 6 H); 2.49 (s, 1 H); 3.43 (s, 3 H); 3.69 (s, 3 H);
6.71 ± 6.84 (m, 4 H); 6.97 ± 7.18 (m, 6 H); 7.62 (d, J ˆ 8.6, 1 H). 13C-NMR: 28.48 (q); 30.50 (q); 51.12 (q); 53.36
(q); 72.78 (s); 73.60 (d); 86.35 (s); 117.21 (d); 117.21 (d); 119.81 (d); 122.52 (d); 123.12 (d); 124.35 (d); 125.02
(d); 127.57 (s); 128.37 (d); 128.37 (d); 130.85 (d); 131.72 (d); 131.90 (s); 131.97 (s); 134.40 (s); 152.75 (s); 153.76
(s); 157.19 (s); 167.37 (s); 167.41 (s). Anal. calc. for C27H24O6 (444.48): C 72.89, H 5.40; found: C 73.13, H 5.38.
Dimethyl 4-[(1,1-Dimethylprop-2-ynyl)oxy]-4'-phenoxy[1,1'-biphenyl]-2,3-dicarboxylate (3f): IR (CHCl3):
1720, 1735 (CˆO); 2325 (Cꢀ); 3300 (ꢀCH). 1H-NMR: 1.37 (s, 6 H); 2.55 (s, 1 H); 3.51 (s, 3 H); 3.76 (s, 3 H);
6.87 ± 7.03 (m, 5 H); 7.12 ± 7.26 (m, 5 H); 7.69 (d, J ˆ 8.6, 1 H). 13C-NMR: 29.27 (q); 29.27 (q); 51.35 (q); 53.68
(q); 72.57 (s); 73.80 (d); 86.07 (s); 117.30 (d); 118.13 (d); 118.13 (d); 119.84 (s); 120.70 (d); 120.70 (d); 125.06
(d); 126.93 (s); 128.68 (s); 131.15 (d); 131.15 (d); 132.25 (d); 132.25 (d); 134.82 (s); 134.88 (d); 152.85 (s); 157.07
(s); 157.19 (s); 167.22 (s); 168.45 (s). Anal. calc. for C27H24O6 (444.48): C 72.89, H 5.40; found: C 73.11, H 5.46.
Dimethyl 4-[(1,1-Dimethylprop-2-ynyl)oxy]-4'-methoxy[1,1'-biphenyl]-2,3-dicarboxylate (3g): IR (CHCl3):
1722, 1736 (CˆO); 2321 (CꢀC); 3300 (ꢀCH). 1H-NMR: 1.58 (s, 6 H); 2.57 (s, 1 H); 3.52 (s, 3 H); 3.73 (s, 3 H);
3.78 (s, 3 H); 6.83 (d, J ˆ 8.7, 2 H); 7.14 (d, J ˆ 8.7, 2 H); 7.26 (d, J ˆ 8.6, 1 H); 7.69 (d, J ˆ 8.6, 1 H). 13C-NMR:
29.32 (q); 29.32 (q); 52.23 (q); 52.30 (q); 55.16 (q); 73.55 (s); 74.39 (d); 85.83 (s); 113.69 (d); 113.69 (d); 121.77
(d); 126.52 (s); 129.32 (d); 129.32 (d); 131.90 (s); 132.10 (d); 132.15 (s); 134.87 (s); 152.32 (s); 159.01 (s); 167.00
(s); 168.33 (s). Anal. calc. for C22H22O6 (382.41): C 69.03, H 5.75; found: C 69.15, H 5.82.
Dimethyl 4'-Bromo-4-[(1,1-dimethylprop-2-ynyl)oxy][1,1'-biphenyl]-2,3-dicarboxylate (3h): IR (CHCl3):
1725, 1735 (CˆO); 2392 (CꢀC); 3300 (ꢀCH). 1H-NMR: 1.60 (s, 6 H); 2.58 (s, 1 H); 3.53 (s, 3 H); 3.81 (s, 3 H);
7.10 (d, J ˆ 8.4, 2 H); 7.30 (d, J ˆ 8.7, 1 H); 7.44 (d, J ˆ 8.4, 2 H); 7.73 (d, J ˆ 8.7, 1 H). 13C-NMR: 29.34 (q); 29.34
(q); 52.35 (q); 52.41 (q); 73.63 (s); 74.55 (d); 85.65 (s); 121.69 (d); 121.73 (s); 126.77 (s); 129.89 (d); 129.79 (d);
131.38 (d); 131.38 (d); 131.77 (s); 131.96 (d); 133.92 (s); 138.77 (s); 152.92 (s); 166.84 (s); 167.85 (s). Anal. calc.
for C21H19BrO5 (431.88): C 58.43, H 4.40; found: C 58.28, H 4.66.
Dimethyl 4'-Acetyl-4-[(1,1-dimethylprop-2-ynyl)oxy][1,1'-biphenyl]-2,3-dicarboxylate (3i): IR (CHCl3):
1705 (CˆO, ketone); 1723, 1734 (CˆO, esters); 2351 (CꢀC); 3300 (ꢀCH). 1H-NMR: 1.60 (s, 6 H); 2.55
(s, 3 H); 2.60 (s, 1 H); 3.51 (s, 3 H); 3.80 (s, 3 H); 7.29 (d, J ˆ 8.6, 1 H); 7.31 (d, J ˆ 8.4, 2 H); 7.76 (d, J ˆ 8.6,
1 H); 7.90 (d, J ˆ 8.4, 2 H). 13C-NMR: 26.66 (q); 29.41 (q); 29.41 (q); 52.44 (q); 52.50 (q); 73.74 (s); 74.76 (d);
85.64 (s); 121.70 (d); 127.00 (s); 128.40 (d); 128.40 (d); 128.57 (d); 128.57 (d); 131.81 (s); 132.00 (d); 134.08 (s);
136.00 (s); 144.80 (s); 153.26 (s); 166.88 (s); 167.79 (s); 197.68 (s). Anal. calc. for C23H22O6 (394.42): C 69.98,
H 5.58; found: C 70.13, H 5.39.
Dimethyl 2,2-Dimethyl-2H-chromene-7,8-dicarboxylate (ˆ Dimethyl 2,2-Dimethyl-2H-1-benzopyran-7,8-
dicarboxylate) Formation: General Procedure. To a soln. of the dicarboxylate 3 (1 mmol) in dry DMF (5 ml),
N,N-dimethylaniline (0.05 ml) is added. The mixture is stirred under Ar at 140 ± 1458 overnight. After cooling,
the mixture is poured into H2O (10 ± 15 ml) and extracted with CH2Cl2 (3 Â 10 ± 15 ml). The combined extract is
washed successively with 2n NaOH (2 Â 5 ml), 2n HCl (2 Â 5 ml), and H2O to neutrality, dried (MgSO4), and
evaporated. The product is purified by FC (hexane/Et2O).
Dimethyl 2,2-Dimethyl-6-phenyl-2H-chromene-7,8-dicarboxylate (1a): IR (CHCl3): 1725, 1735 (CˆO).
1H-NMR: 1.40 (s, 6 H); 3.49 (s, 3 H); 3.82 (s, 3 H); 5.71 (d, J ˆ 9.9, 1 H); 6.27 (d, J ˆ 9.9, 1 H); 6.97 (s, 1 H);
7.18 ± 7.33 (m, 5 H). 13C-NMR: 27.84 (q); 27.84 (q); 52.09 (q); 52.33 (q); 121.13 (d); 122.07 (s); 123.60 (d); 127.21
(d); 127.84 (s); 128.14 (s); 128.16 (d); 128.16 (d); 129.33 (d); 129.33 (d); 131.01 (s); 133.61 (d); 133.66 (s); 139.85
(s); 149.92 (s); 166.61 (s); 168.10 (s). Anal. calc. for C21H20O5 (352.38): C 71.51, H 5.67; found: C 71.86, H 5.82.
Dimethyl 2,2-Dimethyl-6-(naphthalen-1-yl)-2H-chromene-7,8-dicarboxylate (1b): M.p. 1718. IR (CHCl3):
1725, 1735 (CˆO). 1H-NMR: 1.42 (s, 3 H); 1.44 (s, 3 H); 3.16 (s, 3 H); 3.81 (s, 3 H); 5.69 (d, J ˆ 9.9, 1 H); 6.22
(d, J ˆ 9.9, 1 H); 6.95 (s, 1 H); 7.16 ± 7.39 (m, 4 H); 7.54 (d, J ˆ 8.2, 1 H); 7.71 ± 7.79 (m, 2 H). 13C-NMR: 27.94
(q); 28.03 (q); 51.92 (q); 52.44 (q); 77.58 (s); 121.14 (d); 121.90 (s); 123.73 (s); 125.04 (d); 125.74 (d); 125.80 (d);
126.05 (d); 126.63 (d); 127.80 (d); 128.12 (d); 130.39 (d); 131.77 (s); 132.06 (s); 132.37 (s); 133.36 (s); 133.88 (d);
137.80 (s); 150.09 (s); 166.87 (s); 167.30 (s). Anal. calc. for C25H22O5 (402.44): C 74.54, H 5.47; found: C 74.54,
H 5.68.
Dimethyl 6-([1,1'-Biphenyl]-2-yl)-2,2-dimethyl-2H-chromene-7,8-dicarboxylate (1c): IR (CHCl3): 1725 and
1738 (CˆO). 1H-NMR: 1.32 (s, 6 H); 3.44 (s, 3 H); 3.78 (s, 3 H); 5.59 (d, J ˆ 9.8, 1 H); 5.99 (d, J ˆ 9.8, 1 H); 6.53
(s, 1 H); 7.12 ± 7.34 (m, 9 H). 13C-NMR: 27.78 (q); 27.97 (q); 52.26 (q); 52.50 (q); 77.54 (s); 121.39 (d); 123.52 (s);
126.84 (d); 127.14 (d); 127.97 (d); 128.13 (d); 128.87 (d); 129.81 (d); 129.81 (d); 130.23 (d); 130.23 (d); 130.34
(d); 131.16 (d); 131.57 (s); 133.66 (s); 133.98 (s); 138.63 (s); 140.75 (s); 141.03 (s); 149.63 (s); 166.97 (s); 167.78
(s). Anal. calc. for C27H24O5 (428.48): C 75.61, H 5.60; found: C 75.72, H 5.60.

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Dimethyl 6-([1,1'-Biphenyl]-4-yl)-2,2-dimethyl-2H-chromene-7,8-dicarboxylate (1d). M.p. 1808. IR
(CHCl3): 1728, 1733 (CˆO). 1H-NMR: 1.41 (s, 6 H); 3.53 (s, 3 H); 3.83 (s, 3 H); 5.72 (d, J ˆ 9.9, 1 H); 6.28
(d, J ˆ 9.9, 1 H); 7.01 (s, 1 H); 7.27 ± 7.41 (m, 5 H); 7.52 ± 7.57 (m, 4 H). 13C-NMR: 28.29 (q); 29.57 (q); 52.58 (q);
52.75 (q); 77.50 (s); 121.56 (d); 124.08 (s); 127.27 (d); 127.27 (d); 127.39 (d); 127.39 (d); 127.73 (d); 127.81 (s);
129.05 (d); 129.05 (d); 129.15 (d); 129.15 (d); 129.75 (d); 133.12 (s); 133.63 (s); 134.06 (d); 139.37 (s); 140.42 (s);
140.97 (s); 150.44 (s); 167.01 (s); 168.55 (s). Anal. calc. for C27H24O5 (428.48): C 75.61, H 5.60; found: C 75.64,
H 5.76.
Dimethyl 2,2-Dimethyl-6-(2-phenoxyphenyl)-2H-chromene-7,8-dicarboxylate (1e): M.p. 1118. IR (CHCl3):
1724, 1735 (CˆO). 1H-NMR: 1.33 (s, 6 H); 3.44 (s, 3 H); 3.78 (s, 3 H); 5.59 (d, J ˆ 9.8, 1 H); 5.95 (d, J ˆ 9.8,
1 H); 6.53 (s, 1 H); 6.99 ± 7.35 (m, 9 H). 13C-NMR: 27.62 (q); 27.82 (q); 52.12 (q); 52.36 (q); 77.38 (s); 121.24 (d);
121.72 (s); 123.38 (s); 126.69 (d); 126.99 (d); 127.82 (d); 127.98 (d); 127.98 (d); 129.66 (d); 129.66 (d); 103.07 (d);
130.19 (d); 130.66 (d); 131.41 (s); 133.51 (d); 133.84 (s); 138.47 (s); 140.58 (s); 140.87 (s); 149.48 (s); 166.83 (s);
167.64 (s). Anal. calc. for C27H24O6 (444.48): C 72.89, H 5.40; found: C 72.91, H 5.53.
Dimethyl 2,2-Dimethyl-6-(4-phenoxyphenyl)-2H-chromene-7,8-dicarboxylate (1f): IR (CHCl3): 1720, 1735
1
(CˆO). H-NMR: 1.37 (s, 6 H); 3.51 (s, 3 H); 3.79 (s, 3 H); 5.67 (d, J ˆ 9.9, 1 H); 6.22 (d, J ˆ 9.9, 1 H); 6.87 ±
7.27 (m, 10 H). 13C-NMR: 27.98 (q); 27.98 (q); 52.27 (q); 52.46 (q); 77.70 (s); 118.47 (d); 118.47 (d); 119.19 (d);
119.19 (d); 121.25 (d); 121.58 (s); 123.56 (d); 123.79 (s); 129.48 (d); 129.73 (d); 129.73 (d); 129.88 (d); 129.88 (d);
131.20 (s); 133.08 (s); 133.80 (d); 134.98 (s); 150.04 (s); 156.87 (s); 157.06 (s); 166.71 (s); 168.25 (s). Anal. calc.
for C27H24O6 (444.48): C 72.89, H 5.40; found: C 72.98, H 5.45.
Dimethyl 2,2-Dimethyl-6-(4-methoxyphenyl)-2H-chromene-7,8-dicarboxylate (1g): IR (CHCl3): 1722, 1736
(CˆO). 1H-NMR: 1.37 (s, 6 H); 3.51 (s, 3 H); 3.72 (s, 3 H); 3.79 (s, 3 H); 5.67 (d, J ˆ 9.9, 1 H); 6.23 (d, J ˆ 9.9,
1 H); 6.80 (d, J ˆ 8.6, 2 H); 6.92 (s, 1 H); 7.11 (d, J ˆ 8.6, 2 H). 13C-NMR: 28.10 (q); 28.10 (q); 52.45 (q); 52.62
(q); 55.46 (q); 77.73 (s); 113.94 (d); 113.94 (d); 121.48 (d); 121.58 (s); 123.90 (s); 129.59 (d); 129.71 (d); 131.31
(s); 132.56 (s); 133.52 (s); 133.88 (d); 149.99 (s); 159.21 (s); 166.94 (s); 168.61 (s). Anal. calc. for C22H22O6
(431.41): C 69.03, H 5.75; found: C 69.15, H 5.67.
Dimethyl 6-(4-Bromophenyl)-2,2-dimethyl-2H-chromene-7,8-dicarboxylate (1h): M.p. 1418. IR (CHCl3):
1725, 1735 (CˆO). 1H-NMR: 1.4 (s, 6 H); 3.52 (s, 3 H); 3.81 (s, 3 H); 5.72 (d, J ˆ 9.9, 1 H); 6.25 (d, J ˆ 9.9, 1 H);
6.90 (s, 1 H); 7.07 (d, J ˆ 8.4, 2 H); 7.42 (d, J ˆ 8.4, 2 H). 13C-NMR: 27.95 (q); 27.95 (q); 52.36 (q); 52.51 (q);
77.74 (s); 121.06 (d); 121.63 (s); 122.42 (s); 123.88 (s); 129.21 (d); 129.67 (s); 129.97 (d); 129.97 (d); 131.40 (d);
131.40 (d); 132.48 (s); 133.94 (d); 139.01 (s); 150.29 (s); 166.57 (s); 167.91 (s). Anal. calc. for C21H19BrO5
(431.88): C 58.43, H 4.40; found: C 58.49, H 4.46.
Dimethyl 6-(4-Acetylphenyl)-2,2-dimethyl-2H-chromene-7,8-dicarboxylate (1i): M.p. 1168. IR (CHCl3):
1705 (CˆO, ketone); 1723, 1734 (CˆO, esters). 1H-NMR: 1.41 (s, 6 H); 2.55 (s, 3 H); 3.51 (s, 3 H); 3.83 (s, 3 H);
5.73 (d, J ˆ 9.8, 1 H); 6.27 (d, J ˆ 9.8, 1 H); 6.95 (s, 1 H); 7.30 (d, J ˆ 8.2, 2 H); 7.89 (d, J ˆ 8.2, 2 H). 13C-NMR:
26.88 (q); 28.19 (q); 28.19 (q); 52.57 (q); 52.73 (q); 78.06 (s); 121.23 (d); 122.15 (s); 124.16 (s); 128.58 (d); 128.58
(d); 128.78 (d); 128.78 (d); 129.33 (d); 130.86 (s); 132.88 (s); 134.24 (d); 136.15 (s); 145.24 (s); 150.75 (s); 167.95
(s); 168.00 (s); 197.95 (s). Anal. calc. for C23H22O6 (394.42): C 69.98, H 5.58; found: C 70.04, H 5.62.
Spectrokinetics Studies. For the spectrokinetic studies, a Beckman UV spectrophotometer modified as
previously described [10] is used. A 5 ´ 10 4m soln. of the photochromic compound in toluene, MeCN, or EtOH is
irradiated for ca. 1.5 h under UV light at 238 with a Xe lamp at a flux of 400 W/m2. The irradiation is then
stopped and the ring-closure process monitored by recording the decrease of the absorbance A of the opened
forms. A Hg lamp (500 W) is also used. The data are analyzed with Grafit ꢂ software, which divides the
experimental curve into mono-, bi-, or tri-exponential graphs and calculates the corresponding kinetic constants.
REFERENCES
[1] M. Inouye, K. Kim, T. Kitao, J. Am. Chem. Soc. 1992, 114, 778.
[2] H. Dürr, H. Bouas-Laurent, C. Kranz, H. Kilburg, S. Bossman, B. Braun, K. P. Janzen, E. Blasius, J. Phys.
Chem. 1992, 5, 689.
[3] ꢀApplied Photochromism Polymer Systemsꢁ, Ed. G. McArdle, Blackie, London, 1992.
[4] ꢀOrganic and Thermochromic Compoundsꢁ, Eds. J. C. Crano, R. Guglielmetti, Kluwer Academic/Plenum
Publisher, New York, 1998 ± 1999, Vol. 1 and 2.
Â
[5] J.-L. Pozzo, R. Guglielmetti, A. Samat, V. Lokshin, G. Harie, to ESSILOR Int., U.S. Pat. 5,604,280, 1997.
Â
[6] G. Harie, A. Samat, R. Guglielmetti, D. Dekeukeleire, W. Saeyens, I. Van Parys, Tetrahedron Lett. 1997, 38,
3075.
[7] J.-L. Pozzo, A. Samat, R. Guglielmetti, R. Dubest, J. Aubard, Helv. Chim. Acta 1997, 80, 725.

Helvetica Chimica Acta ± Vol. 83 (2000)
657
[8] A. Maggiani, A. Tubul, P. Brun, Synthesis 1997, 631.
[9] D. Bell, M. R. Davies, G. R. Geen, I. S. Mann, Synthesis 1995, 707.
Â
[10] B. Luccioni-Houze, M. Campredon, R. Guglielmetti, G. Giusti, Mol. Cryst. Liq. Cryst. 1997, 297, 161.
[11] C. Reichardt, ꢀSolvent Effects in Organic Chemistryꢁ, Verlag Chemie, Weinheim, 1979.
[12] S. Nakamura, K. Uchida, A. Murakami, M. Irie, J. Org. Chem. 1993, 58, 5543.
[13] J.-L. Pozzo, Thesis, Marseille-Luminy, 1994.
[14] C. Salemi-Delvaux, Thesis, Marseille-Luminy, 1995.
[15] G. F. Hennion, A. P. Boiselle, J. Org. Chem. 1961, 26, 725.
Received October 1, 1999