Two 1,3-Diazabicyclo[3.1.0]hex-3-enes with a 'Tripod' core

Article abstract of DOI:10.1002/hlca.201100333

The photochromic 1,3-diazabiclyclo[3.1.0]hex-3-enes 5 and 6 were synthesized from two premade tris-aldehydes and two premade aziridinyl ketones and characterized (Scheme 1). Their spectra showed structurei-photochromic behavior relationships (SPBR), which were analyzed. Copyright

Full text of DOI:10.1002/hlca.201100333

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Helvetica Chimica Acta – Vol. 95 (2012)
Two 1,3-Diazabicyclo[3.1.0]hex-3-enes with a ꢀTripodꢁ Core
by Nosrat O. Mahmoodi*a), Khalil Tabatabaeiana), and Hamzeh Kiyanib)
a) Department of Chemistry, Faculty of Sciences, University of Guilan, P.O. Box 41335-1914, Rasht, Iran
(fax: þ 98-131-3233262; e-mail: Mahmoodi@guilan.ac.ir; nosmahmoodi@gmail.com)
b) School of Chemistry, Faculty of Science, Damghan University, 36715364, Damghan, Iran
The photochromic 1,3-diazabiclyclo[3.1.0]hex-3-enes 5 and 6 were synthesized from two premade
tris-aldehydes and two premade aziridinyl ketones and characterized (Scheme 1). Their spectra showed
structureꢀphotochromic behavior relationships (SPBR), which were analyzed.
Introduction. – Photochromism is a vast field encompassing well known phenom-
ena associated with reversible transformations of photoisomers having different
absorptions upon irradiation with UV and VIS light. This phenomena is not limited to
the color or absorption spectra, as the changes are based on two different molecules
with different physical and chemical properties [1][2].
Although many types of photochromic compounds have been reported so far,
crystals that show photochromic reactions in the crystalline state are very rare [2].
Bicyclic aziridines represent a very interesting class of organic compounds, possessing
unique photochromic properties. It has been demonstrated that these compounds form
deeply colored, fairly stable materials under UV radiation. This property allows us to
consider bicyclic aziridines as possible candidates in the search for photochromic
materials [3][4]. Recently, we used a novel type of potentiometry with membrane
sensors based on 6-(4-nitrophenyl)-2,4-diphenyl-3,5-diazabicyclo[3.1.0]hex-2-ene and
6-(4-nitrophenyl)-2-phenyl-4,4-dipropyl-3,5-diazabicyclo[3.1.0]hex-2-ene for the de-
tection of SnII [5] and SrII ions [6] at trace levels in real samples, respectively.
Results and Discussion. – In continuation of prior attempts [3] in the field of 1,3-
diazabicyclo[3.1.0]hex-3-ene systems and their applications in photochromism [3][4],
we present here the photochromism and synthesis of two novel 1,3-diazabicyclo[3.1.0]-
hex-3-enes 5 and 6 from two tris-aldehydes and two aziridinyl ketones as starting
materials (Scheme 1).
Both synthesized 1,3-diazabicyclo[3.1.0]hex-3-enes 5 and 6 undergo reversible
photochromic reactions in cyclohexane, EtOH, Me2CO, and AcOEt by irradiation with
254 nm UV light and VIS light. We have also found that ꢀtripodꢁ-connected 1,3-
diazabicyclo[3.1.0]hex-3-ene systems undergo reversible photochromic reaction in the
crystalline state where also ring opening takes place. Both the AAA isomer as well as
its photogenerated BBB form possess a threefold axis of symmetry and are stable under
ambient condition, in addition the photochromic reaction could be repeated without
destruction of the crystal structures (Scheme 2).
ꢂ 2012 Verlag Helvetica Chimica Acta AG, Zꢃrich

Helvetica Chimica Acta – Vol. 95 (2012)
Scheme 1. Synthetic Route to 5 and 6
537
The changes in the absorption spectra of ꢀtripodꢁ-linked 1,3-diazabicyclo[3.1.0]hex-
3-enes 5 and 6 in EtOH under irradiation with 254 nm light are shown in Fig. 1. In
general, the absorption of the ring-closed form appears at a shorter wavelength, while
the absorption of the ring-open form takes place at a longer wavelength. When AAA-5
was irradiated, two new absorption bands appeared at 258 and 410 nm, respectively,
corresponding to BBB-5. A similar result was obtained when AAA-6 was irradiated at
254 nm; the two new absorption bands appeared at 251and 375 nm, respectively, which
are ascribed to BBB-6. When solid state samples were left in the dark at room
temperature, the color faded slowly. This behavior is similar to that observed in solution
and indicates clearly that ꢀtripodꢁ-linked 1,3-diazabicyclo[3.1.0]hex-3-enes also behave
similar in the crystalline state on irradiation.
In other attempts, we synthesized for the first time 1,3-diazabicyclo[3.1.0]hex-3-ene
7a – 7m under solvent-free conditions in much shorter reaction times. In this case, the
reaction was completed after 1 – 12 h instead of 4 – 7 d as reported previously (Fig. 2,
Table) [3c – 3g]. A color change in the reaction mixture from orange to blue or greenish
blue was characteristic for product formation.
Our studies indicate that compounds 5 – 7 in their solid state undergo very low
fatigue on irradiation (they can be recycled many times without loss of performance) as
compared to their behavior in solution. The described solvent-free procedure for the
synthesis of 7 provides a ready access to a variety of these compounds. The colorless
isomers 8A and 9A, after remaining for 0 – 15 s under ordinary room light, changed

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Scheme 2. Photochromic Reactions of 1,3-Diazabicyclo[3.1.0]hex-3-enes 5 and 6 with a Tripod Core
color. Compound 8A with a pyridin-2-yl group changed from colorless to deep green
(8B photoisomer), while compound 9A with a pyridin-3-yl group changed from
colorless to deep blue (9B photoisomer; Fig. 3). There are principally two isomers
possible for either 8B or 9B, the depicted (E)-form being more stable than its isomeric
(Z)-form with a pendant arm (Fig. 4) [7].
The authors thank the Research Council of the University of Guilan for support of this study.

Helvetica Chimica Acta – Vol. 95 (2012)
539
Fig. 1. Change in the UV/VIS absorption spectra of 5 (left) and 6 (right) upon irradiation with 254 nm
light in EtOH solutions (c ¼ 2 · 10ꢀ5 m)
Fig. 2. 1,3-Diazobicyclo[3.1.0]hex-3-enes 7a – 7m, synthesized under solvent-free conditions
Table. Synthesis of 1,3-Diazabicyclo[3.1.0]hex-3-enes 7 under Solvent-Free Conditions
7a)
R1
R2
Time [h]
Yield [%]b)
M.p. [8]
a
b
c
d
e
f
g
h
i
Me
iPr
Et
Me
iPr
Me
iBu
0.5
2
4
4
5
97
93
94
90
88
95
96
95
87
85
89
94
88
181 – 182
136 – 137
140 – 138
148 – 147
165 – 164
153 – 152
172 – 170
141 – 140
170 – 169
168 – 167
170 – 171
180 – 181
189 – 190
Me
(CH2)4
(CH2)5
4
2
Ph
H
H
H
H
H
H
H
2-thienyl
furan-2-yl
2-OHC6H4
3-OHC6H4
4-OHC6H4
14
11
13
11
9
j
k
l
m
4-OH,3-MeOC6H3
12
a) Compounds (A form) determined by IR and 1H- and 13C-NMR spectroscopy. b) Yield of isolated
product.
Experimental Part
General. Column chromatography (CC): silica gel (SiO2; mesh 200 – 300). TLC: SiO2 plates. M.p.:
Mettler-Fpc5 apparatus; uncorrected. Absorption spectra: spectra in the range 200 – 800 nm (EtOH, c ¼
1.0 · 10ꢀ4 mol dmꢀ3) as well as the positions of lAmax (in nm) for the initial A form and of lBmax (in nm) for
the photoinduced B form were measured with a Shimadzu-UV-2100 spectrophotometer; the photo-

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Fig. 3. Colorless isomers 8A (left) and 9A (right) after remaining for 0 – 15 s under ordinary room light
Fig. 4. The MOPAC drawing for either 8B or 9B indicates the (E)-form as a more stable isomer compared
to the (Z)-form
induced open form B was generated upon UV irradiation (Hg low-pressure lamp (DRSh-260) þ UV-
transmitting glass filters), and reversion to the initial A form was achieved upon either storage in the dark
for 1 – 7 d or by heating at 80 – 908 for 4 – 5 min. IR Spectra (KBr): Shimadzu-IR-470 spectrophotometer;
˜n in cmꢀ1. NMR Spectra: Bruker-DRX 500 MHz (1H) instrument and Bruker-DRX-125-Avance (13C)
spectrometer; d in ppm with the solvent as internal standard (CDCl3 at d 7.26, (D6)DMSO at d 2.50), J in
Hz.
4,4’,4’’-[1,3,5-Triazine-2,4,6-triyltris(oxy)]tris[benzaldehyde] (3) was synthesized according to [8].
Yield 69.5%. White solid. M.p. 175 – 1768. IR: 3090w, 2850m, 1718vs, 1600s, 1570vs, 1370vs, 1210s, 1180m,
1
1100w, 810s, 760m, 690m. H-NMR (CDCl3): 7.30 (d, J ¼ 8.5, 6 H); 7.90 (d, J ¼ 8.6, 6 H); 9.98 (s, 3 H).
2,2’,2’’-[1,3,5-Triazine-2,4,6-triyltris(oxy-4,1-phenylene)]tris[6-(4-nitrophenyl)-4-phenyl-1,3-diazabi-
cyclo[3.1.0]hex-3-ene] (5). To the soln. of 3 (1 mmol, 0.44 g) and aziridinyl ketone 1 (3 mmol, 0.81 g) in
dry EtOH (7 ml) was added NH4OAc (14 mmol, 1.08 g) at r.t. The mixture was stirred for 4 d at r.t. On
cooling in a refrigerator, a precipitate was formed. The precipitate was collected by filtration, washed
with small portions of EtOH, and dried. CC (SiO2, hexane/AcOEt 5 :1) gave 5 (72%). Yellow solid.
Closed form 48%. M.p. 186 – 1878. IR: 3080w, 3020w, 1600m, 1560s, 1520s, 1480m, 1440m, 1370vs, 1340s,

Helvetica Chimica Acta – Vol. 95 (2012)
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1
1260m, 1230m, 1160m, 1080m, 1040m, 1020w, 765m, 740m, 690s. H-NMR (CDCl3; closed form 48%):
2.47 (s, 3 H); 3.77 (s, 3 H); 6.72 (s, 3 H); 7.05 – 7.14 (m, 6 H); 7.16 – 7.22 (m, 6 H); 7.40 (d, J ¼ 7.3, 6 H);
7.46 – 7.59 (m, 9 H); 7.95 (br. s, 6 H); 8.16 (d, J ¼ 8.0, 6 H). 13C-NMR (CDCl3): 42.2; 58.2; 96.1; 121.9;
124.1; 127.8; 128.6; 128.9; 129.3; 131.9; 132.3; 139.3; 145.7; 147.8; 151.5; 171.0; 174.0.
Irradiation of the EtOH soln. of 5 with UV light converted it to the open green form (open form
52%). UV/VIS (EtOH): 210 and 250 before irradiation, and 210, 255 and 415 after irradiation. 1H-NMR
(CDCl3; open form BBB-5): 2.72 (s, 3 H); 3.72 (s, 3 H); 6.20 (s, 3 H); 7.46 – 7.59 (m, 27 H); 7.95 (br. s,
6 H); 8.20 (d, J ¼ 8.2, 6 H). 13C-NMR (CDCl3): 48.3; 57.3; 97.2; 121.9; 124.2; 127.7; 128.5; 129.1; 129.34;
131.7; 132.4; 137.0; 145.8; 147.9; 151.8; 170.4; 174.0.
3,3’,3’’-[1,3,5-Triazine-2,4,6-triyltris(oxy)]tris[benzaldehyde] (4) was synthesized according to [8].
Yield 78%. White solid. M.p. 225 – 2268. IR: 3390w, 3080w, 3020w, 2820m, 2710m, 1695s, 1590s, 1560vs,
1480m, 1450m, 1370vs, 1270m, 1220vs, 1150m, 1130m, 1080m, 805s, 760m, 690m, 640m. 1H-NMR
(CDCl3): 7.34 (d, J ¼ 7.4, 3 H); 7.48 (t, J ¼ 7.3, 3 H); 7.58 (s, 3 H); 7.69 (d, J ¼ 6.93, 3 H); 9.93 (s, 3 H).
13C-NMR (CDCl3): 122.0; 127.7; 128.3; 129.2; 130.7; 138.1; 152.3; 173.7; 191.2.
2,2’,2’’-[1,3,5-Triazine-2,4,6-triyltris(oxy-3,1-phenylene)]tris[6-(3-nitrophenyl)-4-phenyl-1,3-diazabi-
cyclo[3.1.0]hex-3-ene] (6). As described for 5, with 4 and aziridinyl ketone 2: 70% of 6. Yellow solid.
Closed form 46%. M.p. 181 – 1828. IR: 3080w, 3020w, 1595m, 1560s, 1518s, 1480m, 1440m, 1370vs, 1340s,
1
1260m, 1225s, 1150m, 1080m, 1040m, 1020m, 765m, 740m, 690m. H-NMR (CDCl3; closed form 46%):
2.48 (s, 3 H); 3.71 (s, 3 H); 6.72 (s, 3 H); 7.05 – 7.13 (m, 6 H); 7.29 – 7.53 (m, 24 H); 7.94 (br. s, 6 H); 8.02 –
8.07 (m, 6 H). 13C-NMR (CDCl3): 41.9; 57.9; 95.9; 121.1; 121.7; 121.9; 122.9; 125.5; 128.9; 129.1; 129.3;
129.8; 129.9; 131.9; 133.0; 133.3; 140.7; 148.9; 152.1; 170.9; 174.0.
Irradiation of the EtOH soln. of 6 with UV light converted it to the open pale green form (open form
54%). UV/VIS (EtOH): 210, 246 and 272 before irradiation, and 210, 252 and 382 after irradiation.
1H-NMR (CDCl3): 2.77 (s, 3 H); 3.71 (s, 3 H); 6.20 (s, 3 H); 7.29 – 7.53 (m, 21 H); 7.94 (br. s, 6 H); 8.13 (s,
3 H); 8.19 (s, 3 H). 13C-NMR (CDCl3): 48.0; 57.0; 97.1; 121.2; 121.8; 121.9; 123.1; 125.0; 128.9; 129.1;
129.3; 129.9; 130.1; 131.8; 132.3; 133.3; 140.5; 148.9; 152.1; 171.2; 174.0.
Synthesis of 7a – 7m: General Procedure. A mixture of aziridinyl ketone 1 or 2 (268 mg, 1 mmol),
aldehyde or ketone (1 mmol), and NH4OAc (750 mg, 10 mmol) was vigorously stirred at r.t. for 1 – 12 h.
During this time, the color of the mixture gradually changed. After completion of the reaction, the solid
compounds were purified by either prep. TLC or CC (AcOEt/petroleum ether 3 :1) and recrystallized
from 96% EtOH yielding the desired compounds. In some cases (7a – 7j), the final product was
recrystallized from 96% EtOH without preceding chromatography.
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Received August 21, 2011