Synthesis of spiropyrans as building blocks for molecular switches and dyads

Article abstract of DOI:10.1021/jo100309r

The synthesis of spiropyrans was improved significantly with use of ultrasonic radiation. To show the broad applicability of this methodology a range of spiropyrans were prepared which are equipped with iodo, hydroxyl, ethinyl, or azido groups as potential building blocks for conjugation to functional ?-systems or biopolymers. Representatively, the conjugation chemistry was demonstrated for the preparation of spiropyran conjugates with pyrene, perylene, and nile red via the lick-type cycloaddition. These molecular dyads were characterized by optical spectroscopy.

Full text of DOI:10.1021/jo100309r

pubs.acs.org/joc
corresponding merocyanines is accompanied not only by a
Synthesis of Spiropyrans As Building Blocks for
Molecular Switches and Dyads
significant structural change from a nonplanar to a planar
structure but also by a large polarity increase. Hence it is not
surprising that spiropyrans have not only been used for
organic materials but also conjugated to amino acids,8
peptides,9 proteins,10 and nucleic acids11 in order to equip
these biomolecules with the photochromic switch. Despite
the great potential of spiropyrans, however, the synthetic
accessibility of these compounds is rather limited. Herein, we
want to present an improved synthetic procedure for spiro-
pyrans that are equipped with iodo, hydroxyl, azido, or
ethinyl groups. These spiropyrans represent building blocks
that can be used for cross-linking reactions or bioconjuga-
tion to attach the photochromic compound to functional
π-systems or biopolymers, respectively. Representatively, we
demonstrate this for the preparation of spiropyran-chromo-
phore conjugates as molecular dyads via “click”-type cyclo-
addition.
Christoph Beyer and Hans-Achim Wagenknecht*
University of Regensburg, Institute for Organic Chemistry,
Universita€tsstrasse 31, 93053 Regensburg, Germany
achim.wagenknecht@chemie.uni-regensburg.de
Received February 23, 2010
As building blocks we synthesized two sets of spiropyrans
carrying either hydroxyl or iodo functionalities as reactive
groups (Scheme 1). For the first set of spiropyrans, the
alkylation of 2,3,3-trimethylindolenine (1) with 3-iodopro-
panol gave in good yield the corresponding indolium iodide 2
that carries the short C3-linker. Deprotonation of 2 with
potassium hydroxide gave 3 as colorless crystals. The stan-
dard protocol for preparation of spiropyrans, which is
refluxing 3 with 4-nitrosalicylaldehyde in EtOH, gave the
spiropyran 4a in only 16% yield after 3 h and in 54% yield
after 24 h. Longer heating caused accumulation of side
products that complicated the purification. It turned out to
be very useful to use ultrasonic radiation for 1-2 h in
EtOH12 to obtain 4a as well as the spiropyrans 4b-k in
acceptable to excellent yields ranging from 52% to 93%. We
assume that ultrasound enhances reaction rates simply by a
more intimate mixing of reagents as was observed for other
organic reactions.13 Using this significantly facilitated and
efficiently working synthetic protocol we synthesized the
second set of spiropyrans bearing an iodoalkyl linker. The
indolenine 1 was first treated with 1,3-diiodopropane, and 5
was subsequently deprotonated to the methyleneindoline 6.
With use of ultrasonic radiation, the spiropyrans 7a-f were
obtained in good yields (58-94%). This method was also
successfully applied to prepare spirooxazine 8.
The synthesis of spiropyrans was improved significantly
with use of ultrasonic radiation. To show the broad
applicability of this methodology a range of spiropyrans
were prepared which are equipped with iodo, hydroxyl,
ethinyl, or azido groups as potential building blocks for
conjugation to functional π-systems or biopolymers.
Representatively, the conjugation chemistry was demon-
strated for the preparation of spiropyran conjugates with
pyrene, perylene, and nile red via the “click”-type cyclo-
addition. These molecular dyads were characterized by
optical spectroscopy.
Photochromic switches have received increasing attention
due to their potential as part of optoelectronic molecular
devices,1 sensors,2 and fluorescent switches for photonic
materials,3 nanoparticles,4 and labeling of biopolymers.5
Among the structurally diverse photochromic compounds
spiropyrans6 and spirooxazines6,7 play a special role since
their photoinduced and reversible ring-opening to the
The synthesized spiropyrans 4a-k and 7a-f bear differ-
ent substitution patterns at the phenolic part, including
electron-withdrawing and -donating substituents (Table 1).
(1) For reviews see: (a) Raymo, F. M.; Tomasulo, M. Chem.;Eur. J.
2006, 12, 3186–3193. (b) Pischel, U. Angew. Chem. Int. Ed. 2007, 46, 4026–
4040.
(2) (a) Inouye, M.; Ueno, M.; Tsuchiya, K.; Nakayama, N.; Konishi, T.;
Kitao, T. J. Org. Chem. 1992, 57, 5377–5383. (b) Liu, Z.; Jiang, L.; Liang, Z.;
Gao, Y. Tetrahedron 2006, 62, 3214–3220. (c) Sakata, T.; Jackson, D. K.;
Marriott, G. J. Org. Chem. 2007, 73, 227–233.
(3) For review see: Cusido, J.; Deniz, E.; Raymo, F. M. Eur. J. Org.
Chem. 2009, 2031–2045.
(8) Sakata, T.; Yan, Y.; Marriott, G. J. Org. Chem. 2005, 70, 2009–2013.
(9) Angelini, N.; Corrias, B.; Fissi, A.; Pieroni., O.; Lenci, F. Biophys. J.
1998, 74, 2601–2610.
(10) (a) Kocer, A.; Walko, M.; Meijberg, W.; Feringa, B. L. Science 2005,
309, 755–758. (b) Hayak, A.; Liu, H.; Belfort, G. Angew. Chem., Int. Ed.
2006, 45, 4094–4098.
(4) For review see: Tian, Z.; Wu, W.; Li, A. D. Q. ChemPhysChem 2009,
10, 2577–2591.
(5) For review see: Mayer, G.; Heckel, A. Angew. Chem., Int. Ed. 2006,
45, 4900–4921.
(6) For review see: Berkovic, G.; Krongauz, V.; Weiss, V. Chem. Rev.
2000, 100, 1741–1753.
(11) (a) Asanuma, H.; Shirasuka, K.; Yoshida, T.; Takarada, T.; Liang,
X.; Komiyama, M. Chem. Lett. 2001, 30, 108–109. (b) Zhang, P.; Meng, J. B.;
Matsuura, T.; Wang, Y. M. Chin. Chem. Lett. 2002, 13, 299–302.
ꢀ
ꢀ
(12) (a) Torres, R. S.; Vazquez, S. L. A.; Gonzalez, E. A. Synth. Commun.
1995, 25, 105–110. (b) Gonzalez, E. A.; Josefina Lozano, J. Synth. Commun.
1998, 28, 4035–4041.
(7) Petersen, M. A.; Deniz, E.; Nielsen, M. B.; Sortino, S.; Raymo, F. M.
Eur. J. Org. Chem. 2009, 4333–4339.
(13) Cravotto, G.; Demetri, A.; Nano, G. M.; Palmisano, G.; Penoni, A.;
Tagliapietre, S. Eur. J. Org. Chem. 2003, 4438–4444.
2752 J. Org. Chem. 2010, 75, 2752–2755
Published on Web 03/24/2010
DOI: 10.1021/jo100309r
r
2010 American Chemical Society

Beyer and Wagenknecht
JOCNote
SCHEME 1. Synthesis of Spiropyran Building Blocks 4a-k and
7a-f and the Spirooxazine 8a
TABLE 1. Substituents and Yields of Spiropyrans 4a-k and 7a-f
R1
R2
R3
yield (%)
4a
4b
4c
4d
4e
4f
4g
4h
4i
NO2
H
Cl
OCH3
Br
CtCH
CtCH
Br
NO2
Br
H
NO2
Cl
Br
Br
NO2
CtCH
H
H
H
H
H
H
H
H
H
H
OCH3
H
H
H
H
H
H
H
H
H
H
Br
H
OCH3
H
OCH3
OCH3
H
H
H
Br
OCH3
OCH3
H
84
87
78
54
93
68
75
52
83
76
82
94
74
83
80
68
58
4j
4k
7a
7b
7c
7d
7e
7f
FIGURE 1. UV/vis absorption of the merocyanines 4a-k (100 μM
in EtOH, after irradiation at λ = 312 nm, for R1, R2, and R3 see
Table 1).
aFor R1, R2, and R3 see Table 1.
SCHEME 2. Synthesis of Spiropyran Dyads 10a-c
Accordingly, the photocoloration properties which were
measured immediately after saturation of the merocya-
nines by irradiation at 312 nm differ quite significantly
(Figure 1). As expected, the spiropyrans 4a and 4i, bearing
a nitro group as R1, showed the strongest extinction of the
merocyanine at 549 or 568 nm, respectively. Moreover, we
confirmed representatively for compounds 4a and 4h the
reversibility of the photoinduced switching (see the Support-
ing Information).
Representatively, we tested with spiropyran 7a the appli-
cability of the synthesized building blocks. The Huisgen-
Meldal-Sharpless “click” chemistry14-16 was chosen as a
facile methodology for the preparation of the chromophore-
spiropyran conjugates 10a-c as molecular dyads. Surpris-
ingly, the application of this reaction has rarely been applied
for spiropyran conjugation.17 The spiropyran 7a was first
converted to the corresponding azide 9, which was further
(14) Huisgen, R. Angew. Chem., Int. Ed. 1962, 2, 565–598.
(15) Tornoe, C. W.; Christensen, C.; Meldal, M. J. Org. Chem. 2002, 67,
3057–3064.
(16) Lewis, W. G.; Green, L. G.; Grynszpan, F.; Radic, Z.; Carlier, P. R.;
Taylor, P.; Finn, M. G.; Sharpless, K. B. Angew. Chem., Int. Ed. 2002, 41,
1053–1057.
(17) (a) Binder, W. H.; Sachsenhofer, R.; Straif, C. J.; Zirbs, R. J. Mater.
Chem. 2007, 17, 2125–2132. (b) Zhang, Q.; Ning, Z.; Yan, Y.; Qian, S.; Tian,
H. Macromol. Rapid Commun. 2008, 29, 193–201.
reacted in the Cu(I)-catalyzed cycloaddition to the conju-
gates 10a-c, bearing pyrene, perylene, or nile red as chro-
mophores, in excellent yields (84-91%) (Scheme 2).
J. Org. Chem. Vol. 75, No. 8, 2010 2753

Beyer and Wagenknecht
JOCNote
conjugation to functional π-systems or to biopolymers.
Representatively, we have shown this for the preparation
of spiropyran-chromophore conjugates as molecular dyads
via the “click”-type cycloaddition. Due to their photoswitch-
able energy transfer properties the dyads 10a-c represent
promising photochromic compounds.
Experimental Section
1-(3-Hydroxypropyl)-2,3,3-trimethyl-3H-indolium Iodide (2).
Freshly distilled 1 (1.5 mL, 9.34 mmol) was dissolved in CHCl3
(17 mL) and degassed. 3-Iodo-1-propanol (1.00 g, 10.4 mmol)
was added and the solution was refluxed for 24 h. The mixture
was cooled to rt, the solvent was evaporated, and the oil was
washed with petroleum ether and triturated with Et2O to afford
1
2 as a purple solid (3.224 g, 99%). H NMR (DMSO-d6, 300
FIGURE 2. UV/vis absorption spectra of 10a-c (100 μM in EtOH)
after irradiation at 312 nm (solid lines, Mc) and after irradiation at
590 nm (dashed lines, Sp).
MHz) δ 8.01-7.91 (m, 1 H), 7.90-7.81 (m, 1 H), 7.67-7.57 (m, 2
H), 4.56 (t, 2 H, J = 6.9 Hz), 3.55 (t, 2 H, J = 5.5 Hz), 2.87 (s, 3
H), 2.11-1.97 (m, 2 H), 1.54 (s, 6 H); 13C NMR (DMSO-d6, 75
MHz) δ 196.4, 141.7, 141.0, 129.2, 128.8, 123.4, 115.4, 57.8, 54.1,
45.7, 29.6, 21.8, 14.3, 5.4; MS (ESI, DCM/MeOH þ 10 mmol/L
NH4Ac) m/z (%) 218.0 (100) [Mþ].
(S)-3,4,10,10a-Tetrahydro-10,10,10a-trimethyl-2H-[1,3]oxaz-
ino[3,2-a]indole (3). 2 (3.09 g, 8.97 mmol) was suspended in
degassed water (53 mL), finely ground KOH (1.23 g, 21.85 mmol)
was added, and the mixture was stirred at rt for 2 h. CH2Cl2
(50 mL) was added and the mixture was stirred for 30 min. The
aqueous layer was separated and extracted with CH2Cl2 (2 ꢀ
45 mL). The combined organic layers were washed with brine
and water, then dried over Na2SO4. The solvent was evapor-
aterd. The residue was dried under vacuum and purified by flash
chromatography on silica gel (petroleum ether:EtOAc 4:1 to
1:1) to afford 3 as colorless crystals (0.84 g, 43%). Rf 0.47
(hexane:EtOAc 4:1); 1H NMR (600 MHz, CDCl3) δ 7.13 (t, 1 H,
J = 7.7 Hz, CH-C3), 7.08 (d, 1 H, J = 7.3 Hz, CH-C5), 6.81 (t,
1 H, J = 7.2 Hz, CH-C4), 6.59 (d, 1 H, J = 7.8 Hz, CH-C2),
4.08 (dt, 1 H, J = 2.6, 12.4 Hz, CH2-C9), 3.72 (dd, 1 H, J = 5.2,
11.8 Hz, CH2-C9), 3.66 (dd, 1 H, J = 4.6, 14.6 Hz, CH2-C11),
3.54 (m, 1 H, CH2-C11), 2.02-1.92 (m, 1 H, CH2-C10), 1.56
(s, 3 H, CH3-C14), 1.30 (s, 3 H, CH3-C12), 1.20 (d, 1 H, J =
13.4 Hz, CH2-C10), 1.07 (s, 3 H, CH3-C13); 13C NMR
(150 MHz, CDCl3) δ 148.1 (C1), 139.2 (C6), 127.2 (C3), 122.0
(C5), 119.2 (C4), 108.6 (C2), 98.3 (C8), 61.0 (C9), 48.0 (C7), 39.1
(C11), 26.7 (C13), 21.7 (C10), 18.6 (C12), 13.0 (C14); HRMS
(EI-MS) calcd for C14H19NO [Mþ] 217.1467, found 217.1472.
General Procedure for Synthesis of 4a-k. To a degassed
solution of 3 (0.1 M for 4a and 4h, 0.06 M for 4b-g and 4i-k)
in dry EtOH was added the salicylaldehyde (1.0 equiv). The
mixture was sonicated at 35 kHz. EtOH was evaporated. The
residue was taken up in CH2Cl2, washed with water, and dried
over Na2SO4. The solvent was evaporated and dried under
vacuum. The crude product was purified by flash chromatog-
raphy on silica gel. For details for 4a-k see the Supporting
Information.
1-(3-Iodopropyl)-2,3,3-trimethylindolinium Iodide (5). Freshly
distilled 1 (30 mL, 186.9 mmol) was dissolved in MeCN (40 mL)
and degassed. Freshly distilled 1,3-diiodopropane (75 mL,
653 mmol) was added, and the reaction mixture was refluxed
for 48 h. After cooling the solid was filtered off, washed with
MeCN and CHCl3 (2ꢀ), and dried in a vacuum to yield 5 as a
pale gray-yellow solid (65.7 g, 77%). 1H NMR (DMSO-d6,
400 MHz) δ 8.02-7.94 (m, 1 H, arom., C8-H), 7.88-7.80 (m,
1 H, arom., C5-H), 7.69-7.59 (m, 2 H, arom., C6/7-H), 4.48 (t,
2 H, N-CH2), 3.43 (t, 2 H, I-CH2), 2.86 (s, 3 H, C2-Me), 2.41
(m, 2 H, CH2-propyl), 1.55 (s, 6 H, C3-Me); 13C NMR
(DMSO-d6, 100 MHz) δ 197.3 (Cquat), 141.8 (Cquat), 141.1
(Cquat), 129.4 (C6), 128.9 (C7), 123.5 (C5), 115.2 (C8), 54.2
(Cquat), 48.4 (N-CH2), 31.0 (CH2-propyl), 22.0, 14.3
FIGURE 3. Fluorescence spectra of 10a-c (100 μM in EtOH) after
irradiation at 312 nm (solid lines, Mc) and after irradiation at
590 nm (dashed lines, Sp); λexc = 355 nm (10a), 413 nm (10b),
545 nm (10c). The dotted lines represent the spectra that are corrected
by the differences in optical density at the excitation wavelength.
The UV/vis absorption of the spiropyran conjugates
10a-c (Figure 2) after irradiation at 590 nm display exclu-
sively the spiropyran isomer and the additional chromo-
phore by the characteristic bands at ∼350 (pyrene in 10a),
∼425 (perylene in 10b), and ∼550 nm (nile red in 10c). After
irradiation at 312 nm, the merocyanine forms of all three
dyads show an additional absorption at ∼560 nm. If the
dyads are excited at their characteristic wavelength (10a:
355 nm; 10b: 413 nm; 10c: 545 nm) the fluorescence (Figure 3)
is quenched by the merocyanine, which is even more obvious
if the data are corrected by the optical densities at the
excitation wavelength. The latter result indicates an energy
transfer process from the chromophore to the merocyanine
that makes these switches interesting candidates for func-
tional π-systems. The efficiency of this process increases
from dyad 10a over 10b to 10c due to the enhanced spectral
overlap. In 10c, however, the nile red cannot be excited
selectively because the merocyanine absorbs in the same
range. Dyad 10a shows a small emission at ∼650 nm pro-
bably due to an exciplex.
In conclusion we have demonstrated an improved and
easily applicable synthetic methodology to assemble spiro-
pyrans 4a-k, 7a-f, 8, and 9 that are equipped with iodo,
hydroxyl, azido, or ethinyl groups as building blocks for
2754 J. Org. Chem. Vol. 75, No. 8, 2010

Beyer and Wagenknecht
JOCNote
(C2-Me), 2.2 (I-CH2); MS (ESI, DCM/MeOH þ 10 mmol/L
NH4Ac) m/z (%) 327.8 (100) [Mþ].
10-(3-Azidopropyl)-10,30-dihydro-30,30-dimethyl-6-nitrospiro-
[2H-1-benzopyran-2,20[2H]-indole] (9). 7a (1.58 g, 3.31 mmol)
was dissolved in dry DMF (62 mL), NaN3 (877 mg, 13.49 mmol)
was added, and the mixture was stirred in the dark at rt for 19 h.
The solvent was evaporated. The residue was dried under
vacuum and purified by flash chromatography on silica gel
(CH2Cl2) to yield 9 as a golden foam (1.08 g, 83%). Rf 0.82
(CH2Cl2); 1H NMR (400 MHz, CDCl3) δ 8.01 (m, 2 H), 7.20 (dt,
1 H, J = 1.3, 7.7 Hz), 7.10 (dd, 1 H, J = 0.9, 7.3 Hz), 6.94 (d, 1 H,
J = 10.3 Hz), 6.90 (dt, 1 H, J = 0.9, 7.5 Hz), 6.75 (d, 1 H, J =
8.4 Hz), 6.60 (d, 1 H, J = 7.8 Hz), 5.86 (d, 1 H, J = 10.4 Hz),
3.39-3.18 (m, 4 H), 2.01-1.90 (m, 1 H), 1.88-1.75 (m, 1 H),
1.29 (s, 3 H), 1.19 (s, 3 H); 13C NMR (100 MHz, CDCl3) δ 159.4,
146.8, 141.1, 136.0, 128.4, 127.8, 125.9, 122.8, 121.8, 121.6,
119.8, 118.4, 115.5, 106.7, 106.6, 52.6, 49.0, 40.8, 28.1, 25.9,
19.9; HRMS (PI-EI) calcd for C21H21N5O3 [Mþ•] 391.1644,
found 391.1644.
1-(3-Iodopropyl)-3,3-dimethyl-2-methyleneindoline (6). 5 (212
mg, 0.47 mmol) was suspended in degassed water (56 mL) and
finely ground NaOH (559 mg, 14.0 mmol) was added. The
mixture was heated at 80 °C for 15 min and cooled to rt, then
Et2O (60 mL) was added, with stirring for 1 h, and extracted with
Et2O and CH2Cl2 (2 ꢀ 20 mL). The organic layers were washed
with water, combined, and dried over Na2SO4. The solvents
were evaporated to yield 6 as a pale pink solid (139 mg, 91%). 1H
NMR (300 MHz) δ 7.18-7.08 (m, 2 H), 6.83-6.61 (m, 2 H), 3.93
(dd, 2 H, J = 1.9, 22.2 Hz), 3.63 (t, 2 H, J = 6.8 Hz), 3.23 (t, 2 H,
J = 6.7 Hz), 2.21 (quint, 2 H, J = 6.8 Hz), 1.35 (s, 6 H); 13C
NMR (75 MHz) δ 161.5 (Cquat), 145.7 (Cquat), 137.5 (Cquat),
127.6 (þ, CH), 122.0 (þ, CH), 118.7 (þ, CH), 105.3 (þ, CH),
104.1 (þ, CH3), 87.5 (þ, CH3), 73.8 (-, CH2), 44.3 (Cquat), 42.6
(-, CH2), 30.1 (-, CH2), 3.6 (-, CH2); MS (EI, 70 eV) m/z (%)
184.0 (100) [(M - HI - CH3)þ•], 198.9 (42) [(M - HI)þ•], 327.0
(9) [Mþ•].
General Procedure for Synthesis of 7a-f. Under degassed
conditions freshly prepared 6 was dissolved in dry EtOH
(0.1 M). Salicylaldehyde (1.0 equiv) was added, and the mixture
was sonicated at 35 kHz. The solvent was evaporated, and the
remaining residue was taken up in CH2Cl2, washed with water,
and dried over MgSO4. The solvent was evaporated. The raw
product was dried under vacuum and purified with flash chro-
matography on silica gel. For details for 7a-f see the Supporting
Information.
Synthesis of Dyads 10a-c. To a solution of 9 (10a: 182 mg,
0.47 mmol; 10b: 76 mg, 0.21 mmol; 10c: 27 mg, 0.07 mmol) in 3:1
DMF:water (10a: 24 mL; 10b: 20 mL, 10c: 6 mL) were added 1-
ethynylpyrene (105 mg, 0.46 mmol)/3-ethynylperylene (56 mg,
0.20 mmol)/ethynyl nile red (18 mg, 0.05 mmol), CuSO4 5H2O
3
(10a: 17 mg, 0.07 mmol; 10b: 8 mg, 0.03 mmol; 10c: 2.6 mg,
0.01 mmol), tris[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl]amine
(10a: 12 mg, 0.02 mmol; 10b: 7 mg, 0.01 mmol; 10c: 2.0 mg,
0.01 mmol), and (þ)-sodium L-ascorbate (10a: 27 mg, 0.14 mmol;
10b: 14 mg, 0.07 mmol; 10c: 4.2 mg, 0.02 mmol). The mixture was
stirred at rt (∼24 h), diluted with EtOAc, and washed with brine
and water. The aqueous phase was again extracted with CH2Cl2.
The combined organic layers were dried over Na2SO4 and evapo-
rated. The crude product was purified by flash chromatography
on silica gel (CH2Cl2:MeOH 10a: 200:1 to 100:1; 10b: 1000:1 to
20:1; 10c: 300:1 to 70:1) to afford 10a as a pale green foam (262 mg,
91%), 10b as a yellow solid (123 mg, 91%), or 10c as a pink
solid (32.3 mg, 84%). For details for 10a-c see the Supporting
Information.
10-(3-Iodopropyl)-10,30-dihydro-30.30-dimethylspiro[3H]naphth-
[2,1-b][1,4]oxazine (8). Freshly prepared 6 (348 mg, 1.06 mmol)
was dissolved in dry EtOH (12 mL) and degassed. 1-Nitroso-2-
naphthol (203 mg, 1.17 mmol) was added, and the mixture was
sonicated for 2 h. The solvent was evaporated. The residue was
dried under vacuum and purified by flash chromatography on
silica gel (CH2Cl2 to CH2Cl2:MeOH 200:1) to yield 8 as a yellow
powder (126 mg, 25%). Rf 0.60 (CH2Cl2); 1H NMR (600 MHz,
CDCl3) δ 8.55 (d, 1 H, J = 8.4 Hz), 7.78-7.72 (m, 2 H), 7.68 (d,
1 H, J = 8.9 Hz), 7.58 (ddd, 1 H, J = 1.1, 6.9, 8.3 Hz), 7.40 (ddd,
1 H, J = 1.2, 6.9, 8.1 Hz), 7.22 (dt, 1 H, J = 1.2, 7.7 Hz), 7.09
(dd, 1 H, J = 1.0, 7.3 Hz), 7.00 (d, 1 H, J = 8.9 Hz), 6.90 (dt, 1 H,
J = 0.7, 7.4 Hz), 6.67 (d, 1 H, J = 7.8 Hz), 3.42-3.22 (m, 2 H),
3.20-3.09 (m, 2 H), 2.30-2.08 (m, 2 H), 1.35 (s, 3 H), 1.34 (s,
3 H); 13C NMR (150 MHz, CDCl3) δ 151.0, 146.7, 143.7, 135.6,
130.8, 130.4, 129.3, 128.0, 127.8, 127.2, 124.2, 122.7, 121.8,
121.5, 119.8, 116.8, 106.9, 98.9, 52.1, 44.9, 32.5, 25.3, 21.0, 2.8;
Acknowledgment. This work was supported by the
Deutsche Forschungsgemeinschaft and the University of
Regensburg.
Supporting Information Available: Experimental proce-
1
dures, data and images of H/13C NMR spectra, MS analysis
for 2, 3, 4a-k, 5, 6, 7a-f, 8, 9, 10a-c, and crystallographic data
of 3. This material is available free of charge via the Internet at
http://pubs.acs.org.
MS (ESI) m/z (%) 482.9 (100) [MHþ], 524.0 (16) [MHþ
MeCN].
þ
J. Org. Chem. Vol. 75, No. 8, 2010 2755