T.-F. Tan et al. / Tetrahedron 62 (2006) 4900–4906
4905
3. Experimental
4
1
0
0
0
.2
.8
.4
.0
3.1. General procedure for the synthesis of 2,2-diaryl-
naphthopyrans (entries 1–6)
The target compounds 1–6 were prepared in moderate
yields through reactions of Grignard reagents with naph-
thopyran biones in dry tetrahydrofuran (THF) instead of
1
8–20
toluene.
Prepared Grignard reagent (10 mmol) in diethyl ether was
added to naphthopyran bione (5 mmol, synthesized as
described in the literature ) in dry THF under reflux.
6
18
19,20
The mixtures were stirred until no starting materials
remained in TLC. The reaction mixture was then cooled to
room temperature and ethyl ether was added to extract the
organic layer. The organic phases were combined, and dried
with anhydrous magnesium sulfate. Solvent evaporation
gave a crude product, which was purified by a silica-gel col-
umn chromatography using petroleum ether/ethyl ether as
eluent. Recrystallization from ethanol or acetone gave a crys-
talline material.
0
200
400
600
800
Time (sec.)
Figure 12. The absorption changes at the lmax of 4 (lmax ¼486 nm, 2 wt %
loading) and 6 (lmax¼463 nm, 2 wt % loading) in PMMA films under con-
tinuous UV–vis irradiation with a 400 W high-pressure mercury lamp.
irradiation in a 40-time cycle. The absorbances at lmax were
zero before UV irradiation (ring-closed form), but they were
different after UV irradiation (ring-opened form). On grad-
ual increase of cycle times, the absorbances at lmax were
gradually decreased after UV irradiation (ring-opened
form). A plot of the absorbance against the cycle times
was made as shown in Figure 13. The fatigue resistance
was examined after 280-cycle irradiation of UV–vis. As
shown in Figure 13, the fatigue resistance of compound 4
was examined and recorded. After 280-cycle UV–vis irradi-
ation, the absorbance at maximum wavelength was kept in
3
.1.1. 2,2-Bis(3-trifluoro methylphenyl)-3H-naphtho[2,1-
ꢀ
1
b]pyran (1). Yield: 46%. Mp: 103–104 C. H NMR: d 6.21
d, 1H, J¼6.6 Hz), 7.14–7.43 (m, 14H), 7.75 (d, 1H,
(
ꢁ
1
J¼6.0 Hz). IR (KBr): 1622, 1510 (C]C) cm , 1330,
ꢁ1
+
1224 (C–F) cm . EIMS: m/z 471 (M ). Anal. Calcd for
C H F O: C, 68.94; H, 3.40. Found: C, 68.70; H, 3.41.
27 16
6
3
.1.2. 2,2-Bis(4-tertiary butylphenyl)-3H-naphtho[2,1-
ꢀ
1
b]pyran (2). Yield: 36%. Mp: 194–195 C. H NMR:
d 1.27 (s, 18H), 6.28 (d, 1H, J¼6.6 Hz), 7.20–7.72 (m,
9
9.1% of that of first irradiation in open ring form. As it
1
4H), 7.93 (d, 1H, J¼5.4 Hz). IR (KBr): 2962, 1463, 1361
was extrapolated to 1000 cycles, the absorbance of maxi-
mum wavelength after UV–vis irradiation would be kept
in 96.9% of that of first irradiation in open ring form
ꢁ
1
+
(C]C) cm . EIMS: m/z 447 (M ). Anal. Calcd for
C H O: C, 88.79; H, 7.62. Found: C, 88.51; H, 7.61.
3
3 34
n
(
A¼A (1ꢁX ) , where n: cycle times, A : the original absorp-
0
0
3
.1.3. 2,2-Bis(4-sulfur methylphenyl)-3H-naphtho[2,1-
ꢀ
tion intensity; X: the variational absorption intensity). It was
shown that 2,2-diarylnaphthopyrans exhibited excellent sta-
bility. The useful lifetime of the photochromic films is of ut-
most importance to its commercial success.
1
b]pyran (3). Yield: 36%. Mp: 142–143 C. H NMR:
d 2.43 (s, 6H), 6.17 (d, 1H, J¼6.6 Hz), 7.14–7.71 (m,
1
4H), 7.93 (d, 1H, J¼5.6 Hz). IR (KBr): 1618, 1510
ꢁ1
+
(C]C) cm . EIMS: m/z 427 (M ). Anal. Calcd for
C H OS : C, 76.06; H, 5.16. Found: C, 76.28; H, 5.14.
2
7
22
2
3
b]pyran (4). Yield: 23%. Mp: 94–95 C. H NMR: d 2.77
.1.4. 2,2-Bis(2,4-dimethoxyphenyl)-3H-naphtho[2,1-
ꢀ
1
1
0
0
0
.2
.8
.4
.0
(
(
(
s, 6H), 2.84 (s, 6H), 6.45 (d, 1H, J¼6.8 Hz), 7.00–7.11
m, 12H), 7.91 (d, 1H, J¼5.8 Hz). IR (KBr): 1608, 1501
ꢁ
1
+
C]C) cm . EIMS: m/z 455 (M ). Anal. Calcd for
C H O : C, 76.65; H, 5.73. Found: C, 76.43; H, 5.72.
29 26 5
3.1.5. 2,2-Bis(3-fluoro-4-methoxyphenyl)-3H-naphtho[2,1-
b]pyran (5). Yield: 41%. Mp: 132–134 C. H NMR: d 3.85
ꢀ
1
(
1
s, 6H), 6.12 (d, 1H, J¼6.4 Hz), 6.96–7.71 (m, 12H), 7.95 (d,
ꢁ1
H, J¼5.4 Hz). IR (KBr): 1621, 1514 (C]C) cm . EIMS:
+
m/z 431 (M ). Anal. Calcd for C H F O : C, 75.34; H,
27 20 2 3
4.65. Found: C, 75.20; H, 4.64.
3
.1.6. 2,2-Bis(3-chloro-4-methoxyphenyl)-3H-naphtho[2,1-
ꢀ
1
0
5
10
15
20
25
30
b]pyran (6). Yield: 32%. Mp: 107–108 C. H NMR: d 3.84
(s, 6H), 6.11 (d, 1H, J¼9.8 Hz), 6.86–7.68 (m, 12H), 7.94 (d,
Times of cycle (x10)
ꢁ1
1
H, J¼8.4 Hz). IR (KBr): 1631, 1498 (C]C) cm . EIMS:
Figure 13. Photoinduced absorption changes for compound 4 in PMMA
film at lmax; photoirradiation started at each point of with visible light,
finished at the point of B and started with UV light.
+
m/z 463 (M ). Anal. Calcd for C H O Cl : C, 69.98; H,
27 20 3 2
4.32. Found: C, 69.96; H, 4.31.