Supplementary material
Figure 1. UV-vis spectra of compounds 1-3, before irradiation.a
a
b
c
a
a = compound 1. b = compound 2. c = compound 3.
Figure 2. Kinetics of cyclization of compounds 1-3 in toluenea
a
a
b
c
a
a= compound 1. b= compound 2. c= compound 3.
Figure 3. Kinetics of ring-opening of compounds 1-3 in toluenea
a
b
c
a
a= compound 1. b= compound 2. c= compound 3.
Synthesis of photochromic compounds.
The identity of all compounds described below was confirmed by NMR and HR-MS spectrocopy.
Details of all the spectroscopical data are given in the main section.
2.2.1 Synthesis of 3-iodo-2-methylbenzothiophene, 4:
2-methylbenzothiophene (3g = 20.3 mmol), iodine (2.7 g = 10.2 mmol), H5IO6 (0.92 g = 4.1 mmol)
and a mixture of HAcO:H2O:H2SO4 100:20:3 (74 ml) were placed in a 100 ml round bottomed
flask. The mixture was protected from light and vigorously stirred for 3 hours (the progress of
reaction was followed by TLC). Then, enough 10% sodium bisulfite aqueous solution was added,
until decoloration was observed. The mixture was filtered, and the solid washed with water,
greenish crystals were obtained. The crude compound was treated with methanol/water at boiling
temperature, upon crystallization a white solid was obtained (47% yield).
2.2.2 Synthesis of (3,3,4,4,5,5-hexafluorocyclopent-1-en-1,2-diyl)bis(2-methyl-1-benzotiophene), 1:
548 mg of 4 (2 mmol), 3ml of anhydrous THF, and 2.4 mmol of n-BuLi (1.6M in hexane) were
added to a 10 ml round bottomed flask, capped with a septa and filled with Ar, placed in a bath at 78ºC. The mixture was stirred for 1 hour, and C5F8 (1.2 mmol) was added. After 1 hour at -78ºC, the
mix was allowed to reach r. t., and quenched with 1M HCl solution, (placing the flask in a water/ice
bath). The mixture was extracted with ethyl acetate (thrice) and washed with water, saturated
sodium bicarbonate solution and water, respectively. By distillation at reduced pressure, and
purification of the residue through a silica-gel column (eluting with hexane) a white solid was
obtained ( 49 % yield).
2.2.3 Synthesis of 6-methoxybenzothiophene, 5:
2.5 g of K2CO3, 18 ml of acetone and 2 ml (15.5 mmol) of benzenethiol were placed into a 25 ml
round bottomed flask. 2.7 ml ( 17.9 mmol) of bromoacetaldehyde diethyl acetal was added slowly,
with vigorous stirring. The mixture was stirred for 17 h at r.t., then was filtered, and the solid
washed with acetone, adding the washing liquid to the solution. By distillation of the solvent at
reduced pressure a liquid was obtained (1.91 g, 7.44 mmol). The liquid was dissolved in CH2Cl2
(150 ml) and 1.2 ml of boron trifluoride diethyl ether solvate (BF3.Et2O, 9.7 mmol), dissolved in
CH2Cl2 (15 ml) were added very slowly. The mix was left 30 min with stirring, at r. t. After
distillation of the solvent a liquid was obtained (85% of yield), and upon silica-gel column
purification (eluting with hexane:AcOEt) a colorless liquid was obtained (61% net yield).
Synthesis of 2-methyl-6-methoxybenzothiophene, 6:
2g of 5 ( 12.2 mmol) in anhydrous THF (20 ml) and 14.6 mmol of n-BuLi (1.6 M in hexane) were
added into a 50 ml round bottomed flask capped with a septa and filled with Ar. The mixture was
left 30 min with stirring at -20ºC and 1.15 ml of MeI (18.3 mmol) was added. The mixture was
allowed to reach r.t. and quenched with aqueous 1M HCl solution. The solution was extracted with
ethyl acetate (thrice), washed with water, with saturated NaHCO3 solution and with water,
respectively, dried with anhydrous Na2SO4, and the solvent was removed under reduced pressure.
The residue was purified by silica-gel column eluting with hexane, a colorless liquid, 6, was
obtained (90% yield).
Synthesis of 3-iodo-2-methyl-6-methoxybenzothiophene, 7:
Compound 6 was iodinated by the same procedure followed for the synthesis of 4, starting from 2 g
of 6 (11.2 mmol), 1.3 g of I2 (5.1 mmol), 510 mg of H5IO6 (2.2 mmol) and 105 ml of
HAcO:H2O:H2SO4 100:20:3. Upon cristalization with MeOH:H2O, a white solid was obtained (ca
40 % yield).
Synthesis of 3-(3,3,4,4,5,5-heptafluorocyclopent-1-en-1-yl)-2-methyl-1-benzothiophene, 8:
Compound 8 was synthesized by the same procedure followed for the synthesis of 1, starting from
5 g of 4 (18.2 mmol), 300 ml of anhydrous diethylether, 20.1 mmol of n-BuLi (1.6 M in hexane),
and using 1.6 ml of C5F8 (27 mmol). The crude product was purified by silica-gel column (eluting
with hexane), obtaining a white solid (80% yield).
Synthesis of 3-[3,3,4,4,5,5-hexafluoro-2-(2-metilbenzothien-3-yl)cyclopent-1-en-1-yl]-2-methyl-6methoxy-1-benzothiophene, 2:
150 mg of 7 (0.49mmol) in anhydrous THF (2 ml) was put into a 10 ml round bottomed flask,
capped with a septa and filled with Ar. The flask was placed in a bath at -78ºC and 0.5 mmol of n-
BuLi (1.6 M in hexane) was added. After stirring the mix for 1 hour at -78ºC, 140 mg of 8 ( 0.41
mmol) in 1 ml of anhydrous THF were added. The mixture was left 1 hour at -78ºC, then it was
allowed to reach r.t. Upon quenching with aqueous 1M HCl solution (20 ml) the mixture was
extracted with ethyl acetate (thrice) and washed with water, with saturated aqueous solution of
NaHCO3, and with water, respectively. The solvent was removed at reduced pressure, and the
residue was purified by silica-gel column (eluting with hexane-ethyl acetate). Upon precipitation
with n-hexane, the product was obtained as a white solid (63% yield), that turns red by exposure at
254 nm UV light.
Synthesis of 3-[3,3,4,4,5,5-hexafluoro-2-(2-metilbenzothien-3-yl)cyclopent-1-en-1-yl]-2-methyl-6methoxy-7-nitro-1-benzothiophene 3:
Nitration of 2 was achieved by the following procedure: 100 mg of 2 (0.2 mmol) were placed. 3.5
ml of glacial acetic acid and 0.5 ml of distilled anhydride acetic were placed into a 10 ml round
bottomed flask. The mixture was placed in a water/ice bath with vigorous stirring, and 0.1 ml of
fumming nitric acid (aprox 2.1 mmol) were added slowly. The flask was placed in a water bath at
8ºC. The progress of the reacción was followed by silica TLC (using hexane:ethyl acetate 4:1 as
eluent). Nearly 1 hour was needed to complete the reaction. The mixture was flushed to an
Erlenmeyer flask containing water (20 ml) in a water/ice bath. A yellow precipitate appeared. The
mixture was extracted with CH2Cl2 (thrice) and washed with water firstly, with saturated NaHCO3
aqueous solution, and finally with water. The organic solution was dried with anhydrous sodium
sulfate, filtered and the solvent was removed at reduced pressure. The resulting residue was purified
by silica column, eluting with hexane: ethyl acetate mixtures, a yellow solid was obtained (60 %
yield).