Synthesis of photochromic monomers derived from 1′-(2- methacryloxyethyl)-3,3-dimethyl-2-[2H]-spirobenzopyran indoline

Article abstract of DOI:10.1081/SCC-200049808

The syntheses of five photochromic monomers derived from N- (2-methacryloxyethyl)-3′, 3′-dimethylspiro-[2H-1] benzopyrane-2,2′-indoline are reported. The preparation of these compounds involves the heterogeneous reaction between the N-(hydroxyethyl)-2,3,3- trimethylindolenonium bromide and methacryloyl chloride in a polar solvent. The esterificated salt is easily purified by crystallization in chloroform-hexane. Further condensation with the proper 2-hydroxybenzaldehyde produces the photochromic monomer in high yield. This method can also be applied in the preparation of other spiropyrane derivatives.

Full text of DOI:10.1081/SCC-200049808

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Synthesis of Photochromic
Monomers Derived from
1′‐(2‐Methacryloxyethyl)‐3,3‐Dimethyl‐2‐[2H]‐Sp
Indoline
Luis Ernesto Elizalde a , Raquel Ledezma a & Raúl G. López a
a Centro de Investigación en Química Aplicada , Saltillo, Coahuila, México
Published online: 12 Apr 2011.
To cite this article: Luis Ernesto Elizalde , Raquel Ledezma & Raúl G. López (2005) Synthesis of Photochromic
Monomers Derived from 1′‐(2‐Methacryloxyethyl)‐3,3‐Dimethyl‐2‐[2H]‐Spirobenzopyran Indoline, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 35:4,
603-610, DOI: 10.1081/SCC-200049808
To link to this article: http://dx.doi.org/10.1081/SCC-200049808
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Synthetic Communicationsw, 35: 603–610, 2005
Copyright # Taylor & Francis, Inc.
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1081/SCC-200049808
Synthesis of Photochromic Monomers
Derived from 10-(2-Methacryloxyethyl)-3,3-
Dimethyl-2-[2H]-Spirobenzopyran Indoline
´
Luis Ernesto Elizalde, Raquel Ledezma, and Raul G. Lopez
Centro de Investigacion en Quımica Aplicada, Saltillo, Coahuila, Mexico
´
´
´
´
Abstract: The syntheses of five photochromic monomers derived from N- (2-metha-
cryloxyethyl)-30, 30-dimethylspiro-[2H-1] benzopyrane-2, 20-indoline are reported. The
preparation of these compounds involves the heterogeneous reaction between the
N-(hydroxyethyl)-2,3,3-trimethylindolenonium bromide and methacryloyl chloride in
a polar solvent. The esterificated salt is easily purified by crystallization in chloro-
form-hexane. Further condensation with the proper 2-hydroxybenzaldehyde produces
the photochromic monomer in high yield. This method can also be applied in the pre-
paration of other spiropyrane derivatives.
Keywords: Photochromic monomers, spirobenzopyranes, photochromic polymers
INTRODUCTION
The preparation of functional optical materials based on compounds with
photochromic properties has become one of the more promising topics in
material sciences. These materials are used in the fabrication of several
devices such as optical memories, switches, and holograms. These systems
consist mainly of two components: the support media and the photoactive
material.
The most-employed supporting materials for these devices are polymers.
In some cases the polymers are doped with photochromic molecules.
Received in the USA 17 November 2004
Address correspondence to Luis Ernesto Elizalde, Centro de Investigacion en
´ ´
Quımica Aplicada, Blvd. Enrique Reyna # 140, Saltillo, Coahuila, Mexico. E-mail:
´
elizalde@polimex.ciqa.mx

´
L. E. Elizalde, R. Ledezma, and R. G. Lopez
604
The process involves the dispersion of the photoactive molecule (i.e., spiro-
benzopyrane derivatives) in a polymer matrix as a solid solution. Unfortu-
nately, after the dispersion takes place, the photochromic dye tends to
agglomerate in J or H stacks, decreasing the photoactive capacity.[1]
In other cases, the photochromic molecule can be incorporated into a polymer
chain through a covalent bond by a free radical copolymerization process, using
photochromic monomers with a vinyl, acrylate, or methacrylate moieties.
There are several methods to incorporate the acryloyl moiety into spiroben-
zopyrane photochromic molecules. Those methods involves the substitution of
the acryloyl fraction on the positions 4, 5, 7, or 8 of the benzopyrane ring[2–5]
or in the 10, 40 or 50 positions of the indoline ring (Fig. 1).[6–9] It is important
that the substituted photoactive molecule preserves its photochromic properties.
It is known that the substitution on the positions 4, 5, 7, or 8 decreases the rever-
sibility and magnitude of the ring opening-closure process. This is because the
resonance effect may be inhibited sterically in the open form (merocyanine).[10,11]
The reported synthetic process for the substitutions on the positions 40, 50 or 70
uses phenylhydrazine derivatives as starting materials, by means of Fisher metho-
dology,[12] which involves more than four steps, with the consequent purification
of the reaction products on each step during the complete synthetic method.
Zaitseva[13] reported the preparation of N-(2-hydroxyethyl)-spirobenzo-
pyrane indoline followed by esterification with methacryloyl chloride or
methacrylic acid, according to Fig. 2. Unfortunately with this methodology
low yields were obtained.[7]
In this paper, we report an alternative method for the synthesis of N-(2-
hydroxyethyl)-spirobenzopyrane indoline derivatives that can be useful for
the preparation of photochromic polymers.
EXPERIMENTAL
Materials
All organic materials and reagents were analytical grade and were used as
purchased (Aldrich, Merck) unless otherwise noted. 1H and 13C NMR
Figure 1. Spirobenzopyrane indoline photochromic molecule.

Synthesis of Photochromic Monomers
605
Figure 2. Reported methodology for the preparation of the N-(2-methacryloxyethyl)-
spirobenzopyrane indoline.
spectra were obtained using a 300 MHz Jeol-JNM-ECP300 spectrometer,
using CDCl3 as solvent and tetramethyl silane as standard, at room tempera-
ture. Routine infrared spectra were performed on a Magna Nicolet 550
Infrared Spectrometer. Elemental analyses were determined on a Perkin
Elmer 2400 Series Analyzer and UV-Vis spectra on a HP 8452 spectrometer.
The chromatograms were run on a G.C.-M.S. Hewlett packard HP-5971.
Synthesis of N-(2-hydroxyethyl)-2,3,3-trimethylindoleine Bromide (3)
A mixture of 5.59 mL (34.8 mmol) of 2,3,3-trimethylindoline, 2.47 mL
(34.9 mmol) of 2-bromo ethanol and 4.36 mL of 2-butanone were placed in
a Schlenk tube under inert atmosphere. The reaction mixture was evacuated
and frozen in liquid nitrogen temperature. Then, after reaching the room temp-
erature, the mixture was heated at 1408C for 10 h. The solid obtained was
purified by soxhlet extraction with benzene for 24 h, and then dried for 48 h
1
in vacuum. H NMR (300 MHz, DMSO d6) d: 7.81 (m, 2H), 7.73 (m, 2H),
4.71 (t, 2H, J ¼ 8 Hz), 4.23 (t, 2H, J ¼ 8 Hz), 2.21 (s, 3H), 1.7 (s, 6H). 13C
(50 MHz, DMSO d6) d: 200.75, 144.4, 143.46, 132.5, 131.56, 126.07,117.8,
60.85, 57.41, 52.85, 24.69, 12.65. FT-IR (KBr) n max 3200, 1100 cm21
.
Synthesis of N-2-methacryloxy ethyl-2,3,3-trimethylindolenine
Bromide (4)
In a 100 mL three-neck round-bottom flask equipped with magnetic stirring
and condenser were placed 5.2 g (18.9 mmol) of N-(2-hydroxyethyl)-2,3,3-tri-
methylindoline bromide and 20 mL of dry acetone. Then, 1.8 mL (19.1 mmol)
of methyl methacryloyl chloride were added, and the reaction mixture was
kept at reflux for 24 h. Then, the acetone was distilled, and the solid
obtained was dissolved in chloroform followed by precipitation in hexane.

´
L. E. Elizalde, R. Ledezma, and R. G. Lopez
606
The product was recovered after filtration yielding 88%, 1H NMR (300 MHz,
CDCl3) d: 7.87 (m, 2H), 7.65 (m, 2H), 5.86 (s, 1H), 5.72 (s, 1H), 5.23 (t, 2H,
J ¼ 6 Hz), 4.86 (t, 2H, 6Hz), 3.12 (s, 3H), 1.82 (s, 3H), 1.80 (s, 3H). 13C
(50MHz, CDCl3) d: 197.91, 178.70, 141.60, 141.18, 130.11, 129.93,
129.55, 127.45, 123.16, 115.86, 58.60, 51.84, 42.25, 23.41, 18.28, 16.97.
FT-IR (KBr Film) n max 1719, 1160 cm21
.
General Procedure for Preparation of Derivatives of
N-(2-Methacryloxyethyl)-30, 30-dimethylspiro-[2H-1]
Benzopyrane-2,20-indoline 2 (a–e)
A mixture of 1.56 g (9.36 mmol) of 2-hydroxy-5-nitrobenzaldehyde, 3.14 g
(9.36 mmol) of N-(2-methacryloxyethyl)-2,3,3-trimethylindolenine bromide,
2 mL (14.7 mmol) of triethylamine and 25 mL of distilled ethanol was
placed in a three-neck round-bottom flask and heated under reflux for 12 h.
Then, the reaction mixture was rotoevaporated and the residue redissolved
in 50 mL of chloroform and extracted with 20 mL of aqueous solution of
10% sodium hydroxide. The precipitate was recovered and washed with
cold ethanol and then recrystallized in ethanol.
Spectroscopic Properties of N-(2-Methacryloxyethyl)-30,30-
dimethylspiro-[2H-1] Benzopyrane-2,20-indoline 2a
1H NMR (300 MHz, CDCl3) d: 7.09 (m, 2H), 7.07 (m, 2H), 7.01 (m, 2H),
6.83 (d, 1H, J ¼ 12 Hz), 6.81 (m, 1H), 6.68 (d, 1H, J ¼ 8 Hz), 6.09 (d, 1H,
J ¼ 1.5 Hz), 5.69 (d, 1H, J ¼ 12 Hz), 5.56 (d, 1H, J ¼ 1.5 Hz), 4.28 (t, 2H,
J ¼ 6.5 Hz), 3.53 (m, 2H), 1.93 (s, 3H), 1.309 (s, 3H), 1.15 (s, 3H). 13C
(50 MHz, CDCl3) d: 167.40, 154.26, 147.36, 136.52, 129.97, 129.62,
126.94, 125.88, 121.91, 119.71, 118.38, 115.26, 106.65, 104.64, 63.27,
52.50, 42.72, 30.85, 20.41, 18.73. E.I.-M.S. D.I.P. m/z, (intensity, %)
159 (100), 375 (4). FT-IR (KBr Film) n max 1718, 1160 cm21. Anal Calcd
for C24H25NO3: C, 76.8%; H, 6.7 %; N, 3.7% Found C, 75.85%; H, 7.01%;
N, 3.40%.
Spectroscopic Properties of N-(2-Methacryloxyethyl)-30,30-
dimethylspiro-[2H-1] Benzopyrane-6-methyl-2,20-indoline 2b
1H NMR (300 MHz, CDCl3) d: 7.25 (m, 2H), 7.05 (m, 2H), 7.95 (d, 1H,
J ¼ 7 Hz), 6.83 (d, 1H, J ¼ 10.5 Hz), 6.75 (d, 1H, J ¼ 7 Hz), 6.54 (d,
1H, J ¼ 8 Hz), 6.09 (d, 1H, 1.5 Hz), 5.77 (d, 1H, 10.5 Hz), 5.48 (d, 1H,
J ¼ 1.5 Hz), 4.28 (t, 2H J ¼ 6.5 Hz), 3.53 (m, 2H), 2.25 (s, 3H),

Synthesis of Photochromic Monomers
607
1.96 (s, 3H), 1.24 (s, 3H), 1.17 (s, 3H). 13C (50 MHz, CDCl3) d: 167.40,
152.11, 147.42, 136.59, 130.51, 129.68, 127.73, 127.33, 121.92, 119.38,
118.38, 115.07, 106.67, 104.71, 63.39, 52.51, 42.82, 26.30, 20.89, 20.53,
18.85. E.I.-M.S. D.I.P. m/z, (intensity, %) 159 (100), 389 (12), FT-IR (KBr
Film) n max 1718, 1160, 815, 743 cm21. Anal Calcd for C25H27NO3: C,
77.1%; H, 7.0%; N, 3.6% Found C, 76.10%; H, 7.34%; N, 3.15%.
Spectroscopic Properties of N-(2-Methacryloxyethyl)-30,30-
dimethylspiro-[2H-1] Benzopyrane-6-nitro-2,20-indoline 2c
1H NMR (300 MHz, CDCl3) d: 8.05 (m, 2H), 7.45 (m, 2H), 7.15 (d, 1H,
J ¼ 7 Hz), 6.92 (d, 1H, J ¼ 12 Hz), 6.87 (d, 1H, J ¼ 7 Hz), 6.79 (d,
1H, J ¼ 8 Hz), 6.16 (1H, J ¼ 1.5 Hz), 5.81 (d, 1H, 12 Hz), 5.51 (d, 1H,
J ¼ 1.5 Hz), 4.54 (t, 2H, J ¼ 6.45 Hz), 3.53 (m, 2H), 1.96 (s, 3H),
1.24 (s, 3H), 1.17 (s, 3H). 13C (50 MHz, CDCl3) d: 167.3, 159.53, 146.81,
141.25, 136.22, 135.85, 128.47, 128.03, 126.13, 122.95, 121.98, 120.12,
118.61, 115.75, 106.96, 62.90, 53.10, 42.73, 26.18, 20.17, 18.70. E.I.-M.S
D.I.P. m/z, (intensity, %) 159 (100), 420 (28). FT-IR (KBr Film) n max
1718, 1518, 1163, 953, 746 cm21. Anal Calcd for C24H24N2O5: C, 68.6%;
H 5.8%; N, 6.7%, Found C, 68.58%; H, 5.93%; N, 6.41%. M.P. 848C
Spectroscopic Properties of N-(2-Methacryloxyethyl)-30,30-
dimethylspiro-[2H-1] Benzopyrane-6-chloro-2,20-indoline 2d
1H NMR (300 MHz, CDCl3) d: 7.45 (m, 2H), 7.35 (m, 2H), 7.05 (d, 1H,
J ¼ 7 Hz), 6.93 (d, 1H, J ¼ 10.5 Hz), 6.85 (d, 1H, J ¼ 7 Hz), 6.64 (d,
1H, J ¼ 8 Hz), 6.09 (d, 1H, 1.5 Hz), 5.77 (d, 1H, 10.5 Hz), 5.48 (d, 1H,
J ¼ 1.5 Hz), 4.28 (t, 2H J ¼ 6.5 Hz), 3.53 (m, 2H), 1.96 (s, 3H),
1.24 (s, 3H), 1.17 (s, 3H). 13C (50 MHz, CDCl3) d: 167.3, 152.76, 147.14,
136.27, 135.25, 131.47, 129.67, 128.68, 127.81, 122.95, 121.98, 120.12,
116.57, 106.71, 104.98, 89.75, 63.13, 52.66, 42.69, 26.19, 20.31, 18.69.
E.I.-M.S. D.I.P. m/z, (intensity, %) 159 (100), 409 (14), 411 (4), FT-IR
(KBr Film) n max 1718, 1162, 965, 744 cm21. Anal Calcd for
C24H24ClNO3: C, 70.3%; H 5.9%; Cl, 8.6%; N, 3.4% Found C, 69.12%; H,
5.90%; N, 3.10%. M.P. 768C
Spectroscopic Properties of N-(2-Methacryloxyethyl)-30,30-
dimethylspiro-[2H-1] Benzopyrane-6-bromo-2,20-indoline 2e
1H NMR (300 MHz, CDCl3) d: 7.41 (m, 2H), 7.35 (m, 2H), 7.05 (d, 1H,
J ¼ 7 Hz), 6.90 (d, 1H, J ¼ 10.5 Hz), 6.65 (d, 1H, J ¼ 7 Hz), 6.45 (d,
1H, J ¼ 8 Hz), 6.09 (d, 1H, 1.5 Hz), 5.80 (d, 1H, 10.5 Hz), 5.48 (d, 1H,

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L. E. Elizalde, R. Ledezma, and R. G. Lopez
608
J ¼ 1.5 Hz), 4.32 (t, 2H J ¼ 6.5 Hz), 3.53 (m, 2H), 1.96 (s, 3H), 1.24 (s, 3H),
1.17 (s, 3H). 13C (50 MHz, CDCl3) d: 167.23, 157.33, 148.81, 141.25,
136.32, 132.55, 128.61, 127.83, 125.94, 121.92, 121.06, 120.48, 119.64,
117.07, 106.71, 63.05, 52.61, 42.61, 26.10, 20.19, 18.57. E.I.-M.S. D.I.P.
m/z, (intensity, %) 159 (100), 453 (20), 445 (20). FT-IR (KBr Film) n max
1718, 1163, 814, 744 cm21. Anal Calcd for C24H24BrNO3: C, 63.4%; H
5.3%; Br, 17.6%; N, 3.1% Found C, 62.42%; H, 5.41%, Br, 17.90%; N,
2.96%. M.P. 838C
RESULTS AND DISCUSSION
In our experimental work, we observed that substitution over the N atom in the
indoline fraction resulted in monomers with better photochromic properties.
These monomers are also named T monomers. Our synthetic approach is
showed on Fig. 3. In this scheme, the synthesis begins with the alkylation
of the 2,3,3-trimethylindolenine with a proper alpha-omega halohydroxyalkyl
derivative, followed by the heterogeneous esterification with methacryloyl
chloride.
We prepared the 2,3,3-trimethylindolenine according to the Nakazaki
procedure[14] by reacting phenylhydrazine and 3-methyl-2-butanone in
Figure 3. Preparation of the N-(2-methacryloxyethyl)-spirobenzopyrane indoline.

Synthesis of Photochromic Monomers
609
toluene as solvent, followed by cyclation with zinc chloride. Purification with
liquid chromatography yielded 85% of 2,3,3-trimethylindolenine.
The alkylation reaction was carried out in a sealed Schlenk tube with
2-bromoethanol, and 2-butanone as solvent. The first attempts yielded only
25% of the alkylated product. This reaction was optimized by an experimental
design using a 23 factorial strategy. It was found that the reaction of the 2,3,3-
trimethylindolenine with 2-bromoethanol at 1:1 molar ratio in 8 M concen-
tration in 2-butanone at 1408C for 10 h produce N-(2-hydroxyethyl)-2,3,3-tri-
mehtylindolenine bromide in an almost quantitative yield (98%).
We obtained the N-(methacryloxyethyl)-2,3,3-trimethylindolenine bro-
mide (4) by direct esterification of the bromide salt (3) with methacryloyl chlo-
ride in acetone using dimethyl amino pyridine as catalyst for 24 h at 608C. The
main feature of this reaction is its simplicity. The purification process can be
performed by dissolving the solid residue of the reaction mixture in chloro-
form, where the starting materials (3) are not soluble, and further precipitation
in hexane. The esterificated indolenine bromide salt was recovered in 88%
yield. The NMR of the product in chloroform showed the characteristic
singlet signals at 5.86 and 5.72 ppm for the vinyl protons of the methacryloxy
moiety. Also a pair of triplets at 5.23 and 4.86 ppm confirms the ethyl substi-
tution on the indolenine.
Preliminary work showed that the N-(methacryloxyethyl)-2,3,3-trimethyl-
indolenine bromide can also be obtained from trans-esterification of the
bromide salt (3) with methylmethacrylate in toluene using dibutyltin as
catalyst.
The photochromic monomers were obtained by reaction of the N-(meth-
acryloxyethyl)-2,3,3-trimethylindolenine bromide (4) with the proper substi-
tuted 2-hydroxy benzaldehyde and triethylamine in the molar ratio 1:1:3
respectively in ethanol. All molecules were obtained in good yields,
purified by liquid chromatography and characterized by spectroscopic tech-
niques. The yield obtained is shown on Table 1.
The NMR of the photochromic monomers showed for the N-(methacryl-
oxyethyl) derivative, a triplet signal at 4.28 ppm for the methylene linked to
Table 1. Yields obtained for the photochromic
monomers
Molecule
R
Yield (%)
2a
2b
2c
2d
2e
H
CH3
NO2
Cl
76
80
92
86
90
Br

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L. E. Elizalde, R. Ledezma, and R. G. Lopez
610
the oxygen atom and a multiplet at 3.53 ppm for the diasterotopic methylene
protons attached to the nitrogen in the indoline ring.
Due to the simplicity, good yields. and purity of the molecules obtained,
we believe that this methodology can contribute in the development of the
photoactive materials. Additionally, this methodology can be applicable to
the preparation of the other spiroindoline photochromic molecules such as
sipirooxazines.
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