One-pot synthesis of photochromic naphthopyrans in the solid state

Article abstract of DOI:10.1021/ol006038y

matrix presented p-TsOH-catalyzed condensation reactions of 1,1-diaryl-2-propyn-1-ol (1) and 2-naphthol (2) in the solid state gave 3,3-diaryl-3H-naphtho[2,1-b]pyran (6) via Claisen rearrangement. Similar reactions of 1 with 2,6-(7) and 2,7-dihydroxynaphthalenes (8) afforded naphthodipyrane derivatives 9 and 10, respectively. Bis-naphthopyran derivatives 12 were also obtained by the reaction of 1,1,6,6-tetraaryl-2,5-hexadiyn-1,6-diol (11) and 2-naphthol (2) in the solid state.

Full text of DOI:10.1021/ol006038y

ORGANIC
LETTERS
2
000
Vol. 2, No. 14
133-2134
One-Pot Synthesis of Photochromic
Naphthopyrans in the Solid State
2
,†
†
‡
‡
Koichi Tanaka,* Hiroko Aoki, Hiroyuki Hosomi, and Shigeru Ohba
Department of Applied Chemistry, Faculty of Engineering, Ehime UniVersity,
Matsuyama, Ehime 790-8577, Japan, and Department of Chemistry, Faculty of Science
and Technology, Keio UniVersity, Hiyoshi 3, Kohoku-ku, Yokohama 223-8522, Japan
tanaka@en3.ehime-u.ac.jp
Received May 9, 2000
ABSTRACT
p-TsOH-catalyzed condensation reactions of 1,1-diaryl-2-propyn-1-ol (1) and 2-naphthol (2) in the solid state gave 3,3-diaryl-3H-naphtho[2,1-
b]pyran (6) via Claisen rearrangement. Similar reactions of 1 with 2,6- (7) and 2,7-dihydroxynaphthalenes (8) afforded naphthodipyrane derivatives
9
and 10, respectively. Bis-naphthopyran derivatives 12 were also obtained by the reaction of 1,1,6,6-tetraaryl-2,5-hexadiyn-1,6-diol (11) and
2-naphthol (2) in the solid state.
Naphthopyran derivatives are of special interest as photo-
chromic compounds, which have a wide variety of applica-
tions such as ophthalmic glasses, electronic display systems,
2 2
carried out in CH Cl solution in the presence of p-TsOH
(0.1 equiv) for 1 h, 6a was produced in 39% yield.
1
optical switches, and temporary or permanent memories.
In continuation of our ongoing study on solvent-free organic
2
synthesis, we now wish to report a simple and efficient
synthetic method for various kinds of photochromic naph-
thopyrans in the solid state.
A mixture of 1,1-diphenyl-2-propyn-1-ol (1a), 2-naphthol
(2), p-TsOH (0.1 equiv), and a small amount of anhydrous
silica gel as a drying agent was well ground for 10 min at
room temperature using a mortar and pestle and was kept
for 1 h in order to complete the reaction. The reaction mixture
was chromatographed on silica gel to give 3,3-diphenyl-3H-
3
4
naphtho[2,1-b]pyran (6a) in 56% yield. Increasing the
amount of TsOH or a longer reaction time caused a decrease
in the yield of 6a, and a complex mixture of unidentified
product was produced. When the reaction of 1a and 2 was
This solid-state reaction involves the following two steps.
†
First 1,1-diphenyl-2-propyn-1-ol (1a) and 2-naphthol (2a)
Ehime University.
Keio University.
‡
(
1) Gemert, B. V. In Organic Photochromic and Thermochromic
(4) Typical procedure. A mixture of 1a (0.5 g, 2.4 mmol), 2 (0.34 g,
2.4 mmol), p-TsOH (0.046 g, 0.24 mmol), and silica gel (1.0 g) was ground
for 10 min at room temperature using a mortar and pestle, and the mixture
was kept for 1 h. The reaction mixture was chromatographed on silica gel
using toluene as eluent to give 6a (0.45 g, 56% yield, mp 160-162 °C) as
colorless needles.
Compounds; Crano, J. C., Guglielmetti, R. J., Eds.; Plenum Press: New
York, 1999.
(
2) Tanaka, K.; Toda, F. Chem. ReV. 2000, 100, 1025-1074.
(3) Gemert, B. V.; Bergomi, M.; Knowles, D. Mol. Cryst. Liq. Cryst.
1
994, 246, 67-73.
1
0.1021/ol006038y CCC: $19.00 © 2000 American Chemical Society
Published on Web 06/16/2000

are condensed to give propargyl ether (3a) in the presence
of p-TsOH. In the second step Claisen rearrangement of 3a
occurred to give 4a, and finally naphthopynan 6a was
obtained via cyclization of quinodimethane (5a). Similar
treatment of 1b-1f with 2 gave the corresponding naphtho-
pyrans (6b-6f) in the yields of 30-63%. (Table 1)
Table 2. One-Pot Synthesis of Naphthopyrans in the Solid
State
entry
product
yield, %
mp (°C)
1
2
3
4
5
6
7
9a
9e
9f
10a
12a
12g
12f
17
13
12
27
61
41
57
272-275
231-234
>300
228-231
289-291
241-243
297-299
Table 1. One-Pot Synthesis of Naphthopyrans in the Solid
State
entry
product
yield, %
mp (°C)
1
2
3
4
5
6
6a
6b
6c
6d
6e
6f
56
56
30
58
63
44
160-162
156-160
188-192
154-157
122-124
197-200
of the new bis-naphthopyran derivatives (12) are now under
investigation.
Naphthodipyran derivatives 9 and 10 were also prepared
efficiently by a solid-solid reaction between 1 and 2,6- (7)
and 2,7-dihydroxynaphthalenes (8). For example, when a
mixture of 1a, 7, p-TsOH (0.1 equiv), and a small amount
of silica gel was well ground for 10 min at room temperature
in the solid state, naphthodipyran 9a was obtained after
chromatographic separation in 17% yield, which is higher
5
than that previously reported. Similarly, 9b, 9c, and 10a
were obtained in 13, 12, and 27% yields, respectively. When
Figure 1. Ortep drawing of 12a with 50% probability displacement
ellipsoids. The molecule has a crystallographic 2-fold rotational
axis. The dihedral angle between the two naphthyl rings is 56.4-
(
1)° and the torsion angle around the central C-C bond (Cnaph
-
C-C-Cnaph) is -44.5(5)°.
In conclusion, we have developed a simple and efficient
one-pot synthesis of various kinds of photochromic naph-
thopyranes in the solid state. This provides an environment-
friendly solventless method, avoiding the use of halogenated
hydrocarbon solvents such as dichloromethane.
OL006038Y
the reaction of 2 with 1,1,6,6-tetraaryl-2,5-hexadiyne-1,6-
diol (11) was carried out, novel bis-naphthopyran derivatives
(
6) Selected spectral data for 12a: IR (Nujol) 1622 cm-1; λmax (CHCl3)
1
2
42 nm (ꢀ 78700), 319 nm (ꢀ 7000), 356 nm (ꢀ 8300); H NMR (CDCl3)
1
3
δ 8.03 (d, J ) 9.0 Hz, 2H), 7.70-7.06 (m, 30H), 6.15 (s, 2H); C NMR
CDCl3)δ 152.6, 144.6, 143.8, 135.9, 131.1, 130.2, 129.5, 128.4, 128.1,
28.0, 127.9, 127.8, 127.6, 127.5, 127.4, 126.9, 126.5, 126.0, 123.3, 118.8,
12 were obtained. For example, a mixture of 11a, 2, p-TsOH
(
1
(0.1 equiv), and a small amount of silica gel was well ground
for 10 min at room temperature using a mortar and pestle
and was kept for 1 h. The reaction mixture was chromato-
graphed on silica gel to give bis-naphthopyran derivative 12a
in 61% yield. Similarly, 12g and 12f were obtained in 41
and 57% yields, respectively. The structure of 12a was
116.8, 82.3. Anal. Calcd for C50H34O2: C, 90.06; H, 5.14. Found: C, 90.28;
H, 5.24.
(
7) X-ray Data for 12a. C50H34O2; Mr ) 666.82; monoclinic, C2/c; a
) 25.261(5), b ) 9.112(3), and c ) 17.539(3) Å, â ) 115.95(1)°; V )
630(1) Å ; Z ) 4; Dx ) 1.220 g cm ; µ(Mo KR) ) 0.073 mm ; 298 K.
3
-3
-1
3
Structure refinement with TEXSAN; all H atom parameters refined; final
R ) 0.044 for 2995 observed reflections. Crystallographic data (without
structure factors) have been deposited with the Cambridge Crystallographic
Data Centre as supplementary publication no. CCDC-143884. Copies of
the data can be obtained, free of charge, on application to CCDC, 12 Union
Road, Cambridge CB2 1EZ, U.K. (fax +44 1223 336033 or e-mail
deposit@ccdc.cam.ac.uk).
6
determined by spectral data and finally by X-ray crystal
7
structure analysis (Figure 1). The photochromic properties
(5) Knowles, D. B.; Gemert, B. V. U.S. Pat. 1995, 5,464,567.
2134
Org. Lett., Vol. 2, No. 14, 2000