Photochromism of tetrahydroindolizines. Part XIV: Synthesis of cis-fixed conjugated photochromic pyridazinopyrrolo[1,2-b]isoquinolines incorporating carbon-rich linkers

Article abstract of DOI:10.1016/j.tetlet.2014.02.078

New carbon-rich photochromic tetrahydroindolizines (THIs) bearing dihydroisoquinoline derivatives as heterocyclic bases (region B) have been synthesized via different chemical and photochemical pathways. Three alternative pathways for the synthesis of the

Full text of DOI:10.1016/j.tetlet.2014.02.078

Tetrahedron Letters 55 (2014) 2190–2196
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Photochromism of tetrahydroindolizines. Part XIV: synthesis
of cis-fixed conjugated photochromic pyridazinopyrrolo
[1,2-b]isoquinolines incorporating carbon-rich linkers
a
a
a
a
Saleh A. Ahmed a,b, , Khalid S. Khairou , Basim H. Asghar , Hussni A. Muathen , Nariman M. A. Nahas ,
⇑
Hossa F. Alshareef a
a Chemistry Department, Faculty of Applied Sciences, Umm Al-Qura University, 21955 Makkah Al-Mokarramma, Saudi Arabia
b Chemistry Department, Faculty of Science, Assiut University, 17516 Assiut, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 1 June 2013
Revised 30 January 2014
Accepted 13 February 2014
Available online 1 March 2014
New carbon-rich photochromic tetrahydroindolizines (THIs) bearing dihydroisoquinoline derivatives as
heterocyclic bases (region B) have been synthesized via different chemical and photochemical pathways.
Three alternative pathways for the synthesis of the target photochromic THI-based pyridazinopyrrol-
o[1,2-b]isoquinolines via in situ trapping with hydrazine hydrate have been established. In order to
obtain high product yields, different Sonogashira-mediated coupling reactions have been optimized.
Low temperature multichannel UV–vis and flash photolysis techniques were used to detect the photo-
chromic and kinetic properties of the synthesized system.
Keywords:
Photochromism
Tetrahydroindolizine (THI)
Linker-conjugates
Rapid system
cis-Fixed
Ó 2014 Elsevier Ltd. All rights reserved.
Kinetics
Because of the potential applications of photochromic com-
pounds in erasable optical memories and photoswitches, they have
attracted significant attention.1–10 Upon light irradiation, photo-
chromic molecules exhibit reversible color and structural changes.
Photochromic molecules can be employed to modulate various
physicochemical properties upon light irradiation, and they have
received remarkable attention for their potential applications as
photoswitches and optical memory systems.11–16 Since the pio-
neering discovery of Dürr on photochromic dihydroindolizines
(DHIs) and tetrahydroindolizines (THIs), they have been consid-
ered as very interesting photochromic families because of their
specific properties such as high photo-fatigue resistance, broad
absorption spectra in the visible region, high sensitivity to activa-
tion with light, and high photochromic reactivity.17–20 The explora-
tion of new di- and tetrahydroindolizine structures with improved
properties has received significant attention in organic materials
science.18–22 It is well known that suitable functionalization in
both regions (region A is fluorene, region B is the ester or cyano
groups, and region C is the heterocyclic base part) of the DHI skel-
eton with different substituents can modify effectively the
photochromic behavior of dihydroindolizines.23–26 The position of
the substituents is also important for fine-tuning of their optoelec-
tronic properties.20–26 So far, our related research has been mainly
focused on the effects of subsitutents on the fluorene and pyrida-
zine moieties in the dihydroindolizine photochromes.18–31
To the best of our knowledge, there are not many reports on
photochromic tetrahydroindolizines (THIs). Such molecules under-
go a photoinduced change of color in solution, solid state, and in
polymer matrices when exposed to UV irradiation or direct sun-
light, and return to their initial state when the illumination ceases,
normally via a thermal pathway. The photochromic behavior of
THIs (Fig. 1) is based on a reversible pyrroline ring-opening,
induced by light, which converts a colorless form (usually named
the ‘closed form’) into the colored form (betaine form).23,24 Few re-
ports on photochromic THIs showed that the thermal reverse reac-
tion, the 1,5-electrocyclization from the ring-open betaine to the
THI shows rates extending from milliseconds to several weeks,23,24
depending on the substituents and structure of the molecule
involved. This interesting wide range in the lifetime of the colored
form allows these molecules to find many versatile applications as
shown by DHI photochromes.30,31
In continuation of our previous work dealing with the synthesis
and properties of photochromic tetrahydroindolizines (THIs),23,24 in
this Letter, the synthesis of new, highly conjugated, photochromic
⇑
Corresponding author. Tel.: +20 882332200, +966 530435760; fax: +20
882342708.
E-mail address: saleh_63@hotmail.com (S.A. Ahmed).
http://dx.doi.org/10.1016/j.tetlet.2014.02.078
0040-4039/Ó 2014 Elsevier Ltd. All rights reserved.

S. A. Ahmed et al. / Tetrahedron Letters 55 (2014) 2190–2196
2191
R5
R2
R4
R6
R5
R6
R3
R1
R1
R4
hν
N
R3
N
C
Δ
R2
B
R2
A
R2
R1
R1
THI-form (colorless)
betaine-form (colored)
Figure 1. Ring-opening upon UV irradiation and ring-closure in tetrahydroindolizine (THI) photochromes.
H
H
H
n
n
n
O
C
O
C
COCH3
COCH3
N
N
hν
Et2O
H3C
C
C
CH3
N2
Et2O
COCH3
COCH3
n
n
n
n= 0
H
n= 0
n= 1
n= 2
H
H
1a,
1b,
1c,
3a, n= 0
2a,
2b,
n= 1
3b,
n= 1
n= 2
3c,
2c, n= 2
Scheme 1. Preparation of spirocyclopropene precursors 3a–c.
H
H
H
n
n
H
n
n
X
X
X
H3COC
C
+
N
+
COCH3
COCH3
N
Δ
Et2O
24 h/RT
N
COCH3
N
+
-
COCH3
hν
COCH3
COCH3
COCH3
X
4a-d
n
n
n
H
H
n
H
H
5a-l
6a-l
5`a-l
3a-c
Scheme 2. Preparation of photochromic THIs 6a–l from spirocyclopropenes 3a–c.

2192
S. A. Ahmed et al. / Tetrahedron Letters 55 (2014) 2190–2196
tetrahydroindolizines via palladium-mediated Sonogashira cou-
pling is reported. The kinetics of the 1,5-electrocyclization to obtain
different fading rates to suit some industrial applications are the
main motivation behind this work.
tion of the pyrazoles 2a–c in low yields (23%, 29% and 36%, respec-
tively) (Scheme 1).
Photolysis of the pyrazole derivatives 2a–c was carried out in a
Schlenck30–34 photochemical reactor made from Pyrex (k >290 nm).
The source of irradiation was a high-pressure mercury lamp (HPK
125 W, Philips). Solutions to be photolyzed were flushed with dry
nitrogen for 30 min before switching on the lamp. Photolysis was
The diazo derivatives 1a–c have been prepared previously.30,31
The cycloaddition of hex-3-yne-2,5-dione to the 9-diazofluorene
derivatives 1a–c in dry ether in the dark for 24 h led to the forma-
H
H
n
n
H
n
X
X
X
NH2NH2
EtOH
hν
Δ
N
N
N
COCH3
COCH3
CH3
H3C
N
N
CH3
H3C
N
N
H
n
H
n
n
8a-l
H
7a-l
6a-l
Scheme 3. Method A for the preparation of photochromic THIs 7a–l from THIs 6a–l in ethanol at ambient temperature.
H
SiMe3
n
n
SiMe
3n
X
+
I
X
X
N
Pd(PPh3)2Cl2
CuI / Et3N
T
B
A
F
/
N
N
COCH3
COCH3
I
COCH3
COCH3
COCH3
n
COCH3
n
9a-d
H
10a-c
T
H
F
H
6a-l
SiMe3
11a-l
EtOH
Method B
EtOH
NH2NH2
Method C
NH2NH2
H
n
H
n
X
X
hν
N
Δ
N
CH3
H3C
N
N
CH3
H3C
N
N
H
7a-l
n
H
n
8a-l
Scheme 4. Methods B and C for the preparation of the targets 7a–l and 8a–l.

S. A. Ahmed et al. / Tetrahedron Letters 55 (2014) 2190–2196
2193
performed in dry ether for three hours under a nitrogen atmosphere
to give the target diacetyl spirocyclopropene derivatives 3a–c in
low yields (29%, 20%, and 14%, respectively).32–34 The structures
of the diacetyl spirocyclopropenes 3a–c were established on the ba-
sis of analytical and spectroscopic data.35
Nucleophilic addition of substituted 1-aryl-3,4-dihydroisoquin-
olines 4a–d to spirocyclopropene derivatives 3a–c using the cyclo-
propene route,19–27 (Scheme 2) in dry ether at room temperature
under a dry nitrogen atmosphere in the absence of light, afforded
the new photochromic tetrahydroindolizines (THIs) 6a–l. The reac-
tion occurred through electrophilic addition of the electron-
deficient spirocyclopropene derivatives 3a–c to the nitrogen of
the N-heterocyclic isoquinoline derivatives 4a–d, which led to
ring-opening via a cyclopropyl-allyl conversion of 50a–l to the col-
ored betaines 5a–l (Scheme 2).
Subsequent ring-closure to give THIs 6a–l resulted in a partial
slow thermal 1,5-electrocyclization reverse reaction (Scheme 2),
which can be reversed upon exposure to light. The prepared THIs
6a–l showed low photostability and decomposition can occur
during purification and also on standing for a few days at ambient
temperature.19,23 The decomposition was apparent as a gradual
loss of photochromic properties. The THIs 6a–l reach the t30 value
(a decrease of 30% of the initial absorbance) within the range of
67–92 min depending on both the substituents on the fluorene
and isoquinoline moieties. In addition, compared with those THIs
bearing ester groups, the THIs under investigation showed a
decrease in the t30 values by a factor of 7–9. It was found necessary
to react them directly after work-up, with hydrazine in absolute
ethanol at room temperature for eight hours to afford cis-fixed con-
jugated photochromic THIs 7a–l (Scheme 3). The pure products
were obtained as white powders in low to moderate yields
(18–52%) after two successive column chromatographic purifica-
tions on silica gel using dichloromethane as the eluent.
A successful alternative pathway for the synthesis of the target
photochromic THIs 7a–l was achieved through palladium-medi-
ated Sonogashira coupling of THIs 9a–d with alkynes 10a–c in
the presence of palladium diphenylphosphinedichloride (5%) and
CuI/Et3N in dry THF to afford the desired photochromic trimethyl-
silyl THIs 11a–l in 23–42% yields after purification by flash chro-
matography on silica gel with CH2Cl2 as the eluent. Treatment of
THIs 11a–l with tetrabutylammonium fluoride (TBAF) in dry THF
for 12 h afforded the desilylated products 6a–l in 39–54% yields.
Rapid treatment of the THIs 6a–l with hydrazine hydrate in abso-
lute ethanol at ambient temperature for eight hours afforded the
target THIs 7a–l in 52–68% yields (Method C, Scheme 4).
Table 1
Substituent patterns, yields, and melting points of the target photochromic THIs 7a–l
synthesized by three alternative methods A–C
THI
X
n
Method
Yield (%)
mp (°C)
7a
7a
7a
7b
7b
7b
7c
7c
7c
7d
7d
7d
7e
7e
7e
7f
H
H
H
H
H
H
H
H
0
0
0
1
1
1
2
2
2
0
0
0
1
1
1
2
2
2
0
0
0
1
1
1
2
2
2
0
0
0
1
1
1
2
2
2
A
B
C
A
B
C
A
B
C
A
B
C
A
B
C
A
B
C
A
B
C
A
B
C
A
B
C
A
B
C
A
B
C
A
B
C
24
28
46
28
33
47
20
30
50
18
23
41
29
31
40
30
34
51
44
32
48
41
29
46
46
33
44
52
34
49
49
33
40
48
27
43
191
192–193
192
180
182
181–182
166–168
165–167
166–167
146
145–146
147
136
133–135
134
119
121
120
172
173
172
165
164–165
166
153
153
152
211
210
209
191
190–191
192
179
178
177–178
H
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
F
F
F
F
F
F
F
F
F
CN
CN
CN
CN
CN
CN
CN
CN
CN
7f
7f
On the other hand, deprotection of the silyl groups and reac-
tions of the acetyl groups were achieved in one step when photo-
chromic trimethylsilyl THIs 11a–l were treated with hydrazine
hydrate in ethanol for six hours to afford the desired THIs 7a–l in
40–51% yields (Method C, Table 1). Thus, rigid acetylenic bridged
THIs 7a–l could be successfully prepared as shown in Scheme 4.
The three products obtained from the different pathways showed
the same analytical and spectroscopic data as well as the same
melting points and mixed melting points (Table 1). The chemical
structures of all the synthesized THIs were confirmed on the bases
of spectroscopic and analytical methods.36
7g
7g
7g
7h
7h
7h
7i
7i
7i
7j
7j
7j
7k
7k
7k
7l
7l
7l
The electronic spectra of the newly synthesized THIs 6a–l and
7a–l were measured in dichloromethane at a concentration of
1 ꢀ 10ꢁ5 mol/L at 23 °C using a UV–vis spectrophotometer. All
the THIs showed yellow color in both the solid state and in dichlo-
romethane (Table 2). The intensities (log
e) of these bands were
found to be between 4.01 and 4.46 depending on the number of
Table 2
Absorption spectral data of THIs 6a–l and 7a–l and their corresponding betaines 5a–l and 8a–l, and their kinetic data (monitored by UV–vis-spectrophotometry at ambient
temperature for betaines 5a–l and at ꢁ30 °C for betaines 8a–l) in CH2Cl2 (c = 1 ꢀ 10ꢁ5 mol/L)
THI/
Betaine
kmax (THI)
[nm]
kmax (betaine)
[nm]
Color of
betaine
t1/2 (s)
Betaine
THI/
Betaine
kmax (THI)
[nm]
kmax (betaine)
[nm]
Color of
betaine
t1/2 (ms)
Betaine
6a/5a
6b/5b
6c/5c
6d/5d
6e/5e
6f/5f
6g/5g
6h/5h
6i/5i
389
388
395
387
386
392
394
389
390
391
394
395
528
532
536
526
528
531
533
538
537
542
544
545
Red
Red
Red–violet
Red
Red
210
235
246
7a/8a
7b/8b
7c/8c
7d/8d
7e/8e
7f/8f
7g/8g
7h/8h
7i/8i
386
387
398
385
386
386
385
356
388
391
391
392
443, 628
446, 630
447, 630
346, 638
346, 640
447, 650
440, 623
441, 628
441, 630
450, 625
448, 628
443, 632
Blue
Blue
Blue
Blue
Blue
Blue-green
Blue
Blue
Blue
30
37
46
96
106
117
79
88
97
1245
1394
1463
968
1007
1120
1369
1527
1798
Red
Red
Red–violet
Red–violet
Red–violet
Red–violet
Red–violet
6j/5j
6k/5k
6l/5l
7j/8j
7k/8k
7l/8l
Blue
Blue
Blue
119
102
130

2194
S. A. Ahmed et al. / Tetrahedron Letters 55 (2014) 2190–2196
alkyne groups and substitution on the isoquinoline moiety. The
absorptions of THIs 6a–l and 7a–l were observed in the far UV-
region and showed absorption maxima between 387 and 395 nm
(Figs. 2 and 3, Table 2). This absorption is dependent on the num-
ber of phenylethyne (n) substituents on the fluorene (region A). As
established previously,26–34 these absorption bands can be as-
Furthermore, a noticeable bathochromic shift of about 2–6 nm
was observed upon increasing the number of bridged phenyl acety-
lenic groups from n = 0 to n = 3, with no dependency on the substi-
tuted or non-substituted isoquinoline moiety. This may be
attributed to the increasing aromaticity of the fluorene unit conju-
gated with the aromatic phenyl rings through the bridged acetylenic
bond. Additional spectroscopic data on the UV–vis measurements of
the colored betaines under investigation are listed in Table 2.
On the other hand, irradiation of the target THIs 7a–l at ambient
temperature did not afford the colored betaines 8a–l, and no pho-
tochromic properties were evident. This can be attributed to the
1,5-electrocyclic reaction to THIs 7a–l. This phenomenon moti-
vated us to study further the conditions for obtaining the photo-
chromic properties of this class of THI system. Thus, the colored
betaines 8a–l were analyzed using an FT–UV–vis photospectrome-
ter after irradiation of the THIs 7a–l at low temperature (ꢁ30 °C).
The blue to blue–green colored betaines showed two absorption
maxima around 440–450 and 620–750 nm depending on the sub-
situtents on both fluorene and isoquinoline regions (Fig. 3).
The kinetics of the thermal 1,5-electrocyclization of betaines
5a–l were studied by using multichannel FT–UV–vis spectropho-
tometry (Fig. 4). The kinetic measurements showed that the
signed to the locally excited
p–
p⁄-transition (LE) located in the
butadienyl-vinyl-amine chromophores29–34 of the THIs 6a–l and
7a–l (Table 2).
Irradiation of THIs 6a–l with ultraviolet light for two minutes
with an approximate 7 cm distance between the light and the
probe, led to ring-opened betaines 5a–l (Fig. 2). The colored betaine
forms 5a–l varied from red to red–violet in CH2Cl2 (concentration of
1 ꢀ 10ꢁ5 mol/L) at room temperature because of their slower 1,5-
electrocyclization, which refers to the stabilization of the charged
zwitterionic betaines. All the absorption maxima of the colored
betaines 5a–l were found to be in the visible region and lie between
528 (betaines 5a,e) and 545 nm (betaine 5l). The UV–vis spectra of
the colored betaines containing a cyano-substituted isoquinoline,
as in THIs 5j–l, exhibit a red–violet color and were shifted batho-
chromically by about 17 nm compared with non-substituted
betaine 5a. This can be attributed to the electron-attracting prop-
erty of the cyano group.
0.9
389 nm
1.4
0.8
538 nm
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0.7
531 nm
t= 0 sec
0.6
THI 6b
392 nm
40 sec
-------- Betaine 5b
0.5
0.4
t = 440 sec
0.3
0.2
0.1
350
400
450
500
550
600
650
700
Wavelength (nm)
350
400
450
500
550
600
650
700
750
Wavelength (nm)
Figure 4. Kinetics of the thermal fading of the 1,5-electrocyclization of betaine 6h
to THI 5h (cycle time = 40 s, and run time = 440 s) in CH2Cl2 (c = 1 ꢀ 10ꢁ4 mol/L) at
25 °C.
Figure 2. UV–vis spectra of photochromic THI 6f and the corresponding betaine 5f
in dichloromethane at ambient temperature (c = 1 ꢀ 10ꢁ5 mol/L).
1.6
1.2
1.0
0.8
0.6
0.4
0.2
0.0
391 nm
446 nm
391 nm
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
t = 0 sec
1sec
t = 8 sec
623 nm
450 nm
625 nm
350 400 450 500 550 600 650 700 750 800 850
350 400 450 500 550 600 650 700 750
Wavelength (nm)
Wavelength (nm)
Figure 5. FT–UV–vis kinetics of the thermal fading of the 1,5-electrocyclization of
betaine 8e to THI 7e (cycle time = 1 s, and run time = 8 s) in CH2Cl2 (c = 1 ꢀ 105 mol/
L) at ꢁ30 °C.
Figure 3. UV–vis spectra of photochromic THI 7j at ambient temperature and the
corresponding betaine 8j at ꢁ30 °C in dichloromethane (c = 1 ꢀ 10ꢁ5 mol/L).

S. A. Ahmed et al. / Tetrahedron Letters 55 (2014) 2190–2196
2195
Figure 6. Flash photolysis of THI 7f for determination of the absorption maxima and half-life time of betaine 8f in dichloromethane at 23 °C (c = 1 ꢀ 10ꢁ5 mol/L).
half-lives of the colored betaines 5a–l were in the second domain
between 210 and 1798 s (Table 2, Fig. 4).
Acknowledgment
A highly pronounced increase in the half-lives of the betaines
with a methyl substituted isoquinoline (5d,e,f) by approximately
a factor of six was observed compared with the half-lives of the
betaines 5a–c bearing a non-substituted isoquinoline. This in-
crease in the half-lives may be attributed to the stabilization of
the electrostatic charges on the betaines by the electron-donating
methyl group.
S. A. Ahmed is highly indebted to Prof. Dr. Jochen Mattay, Uni-
versity of Bielefeld, Germany and Prof. Dr. Watson Lees, Florida
International University, USA for carrying out the spectroscopic
measurements and for their helpful discussions and revision on
this work. Many thanks are due to the Alexander von Humboldt
foundation (AvH) and Umm Al-Qura University for financial sup-
port of this work.
An increase in the half-lives of the betaines by increasing the
number acetylenic bridges from one to three in the fluorene part
was recorded. This may be attributed to the bulky sterically hin-
dered phenyl rings substituted on the fluorene moiety. On the
other hand, low temperature FT–UV–vis (ꢁ30 °C) and flash photol-
ysis techniques were used for detection of both the absorption
maxima and the half-lives of the betaine forms 8a–l (Figs. 5 and
6). The half lives were found to be in the millisecond domain and
were between 30–130 ms. The rapid 1,5-electrocyclization sug-
gested that the betaine structure exists only in a cis-fixed form
and cyclized back thermally from this form to the THI skeleton.
The pronounced tuning of the absorption maxima and the kinetic
properties by changing the substitution in the fluorene region, as
well as in the dihydroisoquinoline region, should help this family
of compounds to find many applications, particularly in the area
of molecular electronics.
References and notes
1. (a) Bouas-Laurent, H.; Dürr, H. Pure Appl. Chem. 2001, 73, 639–665; (b) Dorion,
G. H.; Wiebe, A. F. Photochromism; Focal Press: New York, 1970;
(c)Photochromism; Brown, G. H., Ed.; Wiley: New York, 1971; (d) Dürr, H.;
Bouas-Laurent, H. Photochromism: Molecules and Systems; Elsevier: Amsterdam,
1990; (e) Crano, G. C.; Guglielmetti, R. Organic Photochromic and Thermochromic
Compounds; Plenum Press: New York, 1999; (f) McArdle, C. B. Applied
Photochromic Polymer Systems; Blackie: Glasgow, 1992; (g) Irie, M. Photo-
Reactive Materials for Ultrahigh Density Optical Memory; Elsevier: Amsterdam,
1994.
2. (a) Guglielmeti, R.; Samat, A. Proceedings of the First International Symposium on
Organic Photochromism, Molecular Crystals and Liquid Crystals, 1994, 246.; (b)
Irie, M. In Molecular Switches; Feringa, B. L., Ed.; Wiley-VCH: Weinheim, 2001;
pp 37–60; (c) Iri, M. In Organic Photochromic and Thermochromic Compounds;
Crano, J. C., Gugielmetti, R. J., Eds.; Plenum Press: New York, 1999; Vol. 1, pp
207–221.
3. (a) Gorodetsky, B.; Branda, N. Adv. Funct. Mater. 2007, 17, 786; (b) Roberts, M.
N.; Carling, C. J.; Nagle, J. K.; Branda, N.; Wolf, M. O. J. Am. Chem. Soc. 2009, 131,
16644.
In conclusion, carbon-rich molecules based on photochromic
tetrahydroindolizines (THIs) have been successfully synthesized
via Sonogashira coupling reactions. The coupling reactions
between fluorenes (region A) and acetylenic bridges in addition
to substitution on the dihydroisoquinolines (region B) resulted in
target molecules with extended photochromism. Interesting
photochromic properties have been observed by tuning the chem-
ical structure of the photochromic THI by changing the number of
acetylenic bridges in the fluorene part and the substitution on the
isoquinoline region. This pronounced influence of the substituents
in both regions A and C showed strong effects on the UV–vis
absorptions of DHIs and betaines, as well as their kinetic properties
(half-lives). The cis-fixed betaine forms with 1,5-electrocyclization
were confirmed using FT–UV–vis and flash photolysis measure-
ments. These broad spectrum photochromic properties of the
new THIs and their corresponding betaines should aid in finding
suitable applications for these materials.
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35. For example, the 1H NMR (400 MHz, CDCl3) of the spirocyclopropene precursor
3b showed the following signals: d 7.89 (d, J = 1.82 Hz, 2H, CH-arom.), 7.80 (d,
J = 1.32 Hz, 2H, CH-arom.), 7.55 (d, J = 8.9 Hz, 2H, CH-arom.); 7.61 (dd, J = 8.9,
2.2 Hz, 4H, CH-arom.), 7.48 (dd, J = 8.9, 2.3 Hz, 4H, CH-arom.), 4.02 (s, 2H, CH-
acetylenic), 2.32 (s, 6H, 2CH3) 13C NMR (400 MHz, CDCl3) of 3a 182.9 (2C@O),
147.5 (2C), 142.2 (2C), 139.7 (2C), 135.2 (2CH), 132.5 (8CH), 129.8 (2CH), 127.4
(2CH), 123.8 (4C), 122.7 (2C), 95.2 (2C), 90.3 (2C), 83.5 (2C), 81.6 (2CH), 49.8
(C-spiro), 31.1(2CH3) ; IR (KBr):
m = 3028–3092 (C–H, arom.), 2900–2967 (C–H,
aliph.), 2252 (acetylenic bond), 1742 (30–C@O), 1708 (CO–CH3), 1670 (20–
C@O), 1530 (C@C), 1442, 1398, 1278, 1126, 1071, 947, 861, 746 cmꢁ1; HR-MS
m/e (%) 522.16 [M+] (100.0%), 523.17 (44.4%), 524.17 (16.7%), 525,17 (1.4%)
Elemental analysis for 3a (C39H22O2, 522.16): C, 89.63; H, 4.24; Found: C,
89.81; H, 4.14.
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36. For example the 1H NMR (400 MHz, CDCl3) of THI 7k showed the following
signals: d 7.93 (d, J = 8.1 Hz, 2H, CH-arom.), 7.72 (d, J = 1.32 Hz, 2H, CH-arom.),
7.69 (d, J = 8.1 Hz, 2H, CH-arom.), 7.63 (d, 7.8, 2H, CH-arom.), 7.62 (dd, J = 8.9,
2.2 Hz, 4H, CH-arom.), 7.53 (dd, J = 9.9, 2.6 Hz, 4H, CH-arom.), 7.41 (d,
J = 7.8 Hz, 2H, CH-arom.), 7.37 (dd, J = 8.1, 1.9 Hz, 2H, CH-arom.), 7.20 (dd,
J = 8.1, 1.9 Hz, 2H, CH-arom.), 4.35 (s, 2H, acetylenic CH); 3.44 (t, J = 2.3 Hz, 2H,
CH2), 2.95 (t, J = 2.3 Hz, 2H, CH2); 2.40 (s, 3H, CH3); 1.39 (s, 3H, CH3) ppm; 13C
NMR (400 MHz, CDCl3) of THI 7k showed the following signals: d 158.2 (C);
146.20 (C); 144.9 (C); 143.4 (C); 142.2 (2C); 141.0 (2C); 119.2 (C); 135.9 (C);
135.7 (C); 134.3 (2CH); 132.7 (2CH); 130.9 (9CH); 129.4 (2CH); 128.3 (2CH);
127.8 (2CH); 126.9 (2CH); 125.8 (2CH); 122.7 (4C); 121.5 (2C); 119.4 (2C); 92.5
(2C); 88.9 (2C); 86.0 (C); 82.7 (2C); 80.4 (2CH); 46.4 (CH2); 31.9 (CH2); 21.7
(CH3); 19.7 (CH3) ; IR (KBr):
m = 3030–3059 (C–H, arom.), 2965–2998 (C–H,
aliph.), 2242 (acetylenic bond), 2215 (CN), 1741 (30–C@O), 1712 (CO–CH3),
1687 (20–C@O), 1637 (C@N), 1523 (C@C), 1421, 1387, 1282, 1174, 1071, 938,
874, 758 cmꢁ1; HR-MS m/e (%) 750.28 [M+] (100.0%), 750.28 (61.7%), 750.22
(18.1%), 753.20 (2.9%); Elemental analysis for THI 7k (C55H34N4): C, 87.97; H,
4.56; N, 7.46; Found: C, 87.69; H, 4.62; N, 7.31.
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