Synthesis and characterization of novel triazenes from the reaction of the cyclic aminal 1,3,6,8-tetraazatricyclo[4.3.1.13,8]undecane (TATU) with diazonium ions

Article abstract of DOI:10.1016/j.tetlet.2010.02.174

The reaction of the cyclic aminal 1,3,6,8-tetraazatricyclo[4.3.1.1^3,8]undecane (TATU, 4) with diazonium salts resulted in the formation of a new series of bis-triazenes, namely 3,8-bis[(4-methoxyphenyl)diazenyl]-1,3,6,8-tetraazabicyclo[4.3.1]decane 6a, 3,8-bis[(2-methoxyphenyl)diazenyl]-1,3,6,8-tetraazabicyclo[4.3.1]decane 6b, 3,8-bis(p-tolyldiazenyl)-1,3,6,8-tetraazabicyclo[4.3.1]decane 6c. When aniline derived diazonium salt 5d was coupled with TATU, 3,8-bis(phenyldiazenyl)-1,3,6,8-tetraazabicyclo[4.3.1]decane 6d and bis[1,5-bis-((E)-phenyldiazenyl)-1,3,5-triazepan-3-yl]methane 7 were obtained. These compounds were characterized by HR-MS, ¹H and ¹³C NMR and 2D-NMR. Additionally, the structure of compound 7 was confirmed by X-ray crystallography.

Full text of DOI:10.1016/j.tetlet.2010.02.174

Tetrahedron Letters 51 (2010) 2500–2504
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Synthesis and characterization of novel triazenes from the reaction of the cyclic
aminal 1,3,6,8-tetraazatricyclo[4.3.1.13,8]undecane (TATU) with diazonium ions
*
Augusto Rivera , Diego González-Salas
Departamento de Química, Universidad Nacional de Colombia, Ciudad Universitaria, Carrera 30 No. 45-03, Bogotá D.C., Colombia
a r t i c l e i n f o
a b s t r a c t
The reaction of the cyclic aminal 1,3,6,8-tetraazatricyclo[4.3.1.13,8]undecane (TATU, 4) with diazonium
salts resulted in the formation of a new series of bis-triazenes, namely 3,8-bis[(4-methoxyphenyl)diaze-
nyl]-1,3,6,8-tetraazabicyclo[4.3.1]decane 6a, 3,8-bis[(2-methoxyphenyl)diazenyl]-1,3,6,8-tetraazabicy-
clo[4.3.1]decane 6b, 3,8-bis(p-tolyldiazenyl)-1,3,6,8-tetraazabicyclo[4.3.1]decane 6c. When aniline
derived diazonium salt 5d was coupled with TATU, 3,8-bis(phenyldiazenyl)-1,3,6,8-tetraazabicy-
clo[4.3.1]decane 6d and bis[1,5-bis-((E)-phenyldiazenyl)-1,3,5-triazepan-3-yl]methane 7 were obtained.
These compounds were characterized by HR-MS, 1H and 13C NMR and 2D-NMR. Additionally, the struc-
ture of compound 7 was confirmed by X-ray crystallography.
Article history:
Received 22 January 2010
Revised 25 February 2010
Accepted 26 February 2010
Available online 3 March 2010
Ó 2010 Elsevier Ltd. All rights reserved.
Triazenes are a unique class of polyazo compounds containing
three consecutive nitrogen atoms with a double bond between
N1 and N2 (R–N1 = N2–N3–R0R00). The two most widely utilized
methods for the synthesis of triazenes are the coupling of aryl dia-
zonium salts to primary or secondary amines and the addition of
organometallic reagents to alkyl azides.1 Triazenes have been used
for many purposes, such as anticancer agents,2 as coupling part-
ners in combinatorial chemistry,3 as protecting groups for amines
in organic synthesis4 and in the formation of novel heterocycles.5
Vaughan reported on the reaction of diazonium salts with
formaldehyde/ethylenediamine mixtures to afford the cage-like
bis-triazenes of type 3,8-di-[2-aryl-1-azenyl]-1,3,6,8-tetraazabicy-
clo[4.4.1]undecane 1.6 The formation of the bis-triazene 1 was
attributed to the coupling of the diazonium ion to the aminal cage
1,3,6,8-tetraazatricyclo[4.4.1.13,8]dodecane (TATD, 2), which is
formed in situ from the condensation of ethylenediamine and
formaldehyde.6 Alternatively, a similar reaction of diazonium salts
with either hexamethylenetetramine (urotropine) or an aqueous
mixtures of ammonia-formaldehyde affords 3,7-bis(arylazo)
-1,3,5,7-tetraazabicyclo[3.3.1]nonanes 3.7 We recently communi-
cated an efficient one-pot synthesis of the aminal cage 1,3,6,8-tet-
raazatricyclo[4.3.1.13,8]undecane (TATU, 4).8 While TATD has been
the subject of much theoretical and experimental investigation,9
TATU has been less extensively studied.10 As a part of our contin-
uing studies on the reactions of macrocyclic aminals, we planned
to investigate the reaction of TATU and diazonium ions, applying
Vaughan’s methodology.6
N
N
N
N
N
Ar
N
N
Ar
N
N
N
N
N
1
2
N
Ar
N
N
N
N
N
N
N
Ar
3
Following the literature procedure,6 the reaction of TATU and
diazonium salts 5a–b afforded complex mixtures, from which were
unable to isolate the expected bis-triazenes 6a–d. On one hand,
when diazonium salts with electron-withdrawing groups such as
p-nitro or p-bromine were used the triazenes 1 and 3 were the ma-
jor recognizable products. These results prompted us to examine
the mode of reaction of this the aminal cage 4 with the diazonium
ions.
Since cyclic aminals such as TATU 4 undergo facile Brönsted
acid-catalyzed ring cleavage, we reasoned that the reaction with
diazonium salts failed due to the low pH of the medium.11 Thus,
on the basis of the work developed by Vaughan’s group12 we ex-
plored different reaction conditions by varying the pH. The opti-
mized conditions include the careful addition of an aqueous
solution of the appropriate diazonium salt13 to a saturated sodium
carbonate solution of TATU over 20 min. After the reaction stirred
for approximately 30 min, the resulting precipitate was isolated by
vacuum filtration, washed with water, dried, and purified by
* Corresponding author. Tel.: +57 1 3165000x14464; fax: +57 1 3165220.
E-mail address: ariverau@unal.edu.co (A. Rivera).
0040-4039/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2010.02.174

A. Rivera, D. González-Salas / Tetrahedron Letters 51 (2010) 2500–2504
2501
recrystallization to afford a new type of bis-triazenes, namely 3,8-
di(2-aryl-1-azenyl)-1,3,6,8-tetrazabyciclo[4.3.1]decanes
6a–d.14
equivalent CH2 geminal protons and to establish the nature of
the conformational structure of this bicyclic system. The foregoing
correlations led to the conclusion that the preferred conformation
of a 1,3,6,8-tetraazabicyclo[4.3.1]decane system is a chair–chair
conformation (Fig. 1).
This method works well with electron-rich diazonium salts but
failed with electron-poor salts. In addition, when the diazonium
salt derivate of aniline 5d was used, the desired triazene 6d was
obtained, along with the unexpected compound bis-[1,5-bis-((E)-
phenyldiazenyl)-1,3,5-triazepan-3-yl]methane 7.
At ambient temperature, the 13C NMR spectra of compounds
6a–d in CDCl3 showed resonances for each aryl group in the aro-
matic region. The aliphatic region exhibited singlets due to methyl
groups (for 6a–c) but lacked some methylene signals or displayed
peaks that were low or broad. The 13C chemical shifts for these car-
bons were obtained from cross sections of 2D heteronuclear
{1H–13C} HSQC or HMQC spectra. We believe that the lacking of
these signals is due to an equilibrium of the rotamers arising from
restricted rotation around the N2–N3 bond of the triazene.16 This
hypothesis was confirmed by the analysis of 1H and 13C NMR spec-
tra at low temperatures in CDCl3. When the temperature of the
solution of 6a in CDCl3 was lowered, the signals in the aliphatic re-
gion of the spectrum broadened and partially resolved at 213 K.
The reaction mechanism for the formation of 3,8-bis-(2-aryl-1-
diazenyl)-1,3,6,8-tetraazabicyclo[4.3.1]decane 6a–d is believed to
occur by the route shown in Scheme 1, which is analogous to the
previously reported mechanism for the formation of 1 and 3.7,17
However, under these reaction conditions, the predominant
All compounds have been completely characterized by 1H and
13C NMR, melting point, and HR-MS. When necessary, COSY, HMQC
or HSQC, HMBC and NOESY experiments were conducted and all
results are consistent with the proposed formulations. Further-
more, the structure of tetrakis-triazene 7 was unequivocally con-
firmed by X-ray crystallography.
The bis-triazenes 6a–d contain bicyclic structures with a seven-
membered ring bridged to a six-membered ring and the structures
are unsymmetrical. Additionally, the compounds present an unu-
sual type of chirality, where the geometrical rigidity (similar to
Tröger’s bases15) and nonplanar structure have created a chiral
environment for geminal protons or N-substituted groups (i.e.,
for CH2 of the NCH2CH2N group). This results in diastereomers
(the non-equivalence of geminal protons), which causes the
assignments of these protons to become complicated. In this con-
text, a NOESY was conducted to unambiguously assign the non-
4.31 ppm
3.89 ppm
3.29 ppm
4.52 ppm
4.51 ppm
5.01 ppm
3.39 ppm
5.21 ppm
4.03 ppm
Figure 1. Selected key 6a NOESY correlations.
N
N
N
+N2Ar
N+
N
N
:
N
N
N
N
N
5a-d
N
4
N
N
+
ArN2
Ar
N
N
Ar
Ar
p-methoxy
5a
HO-
OH
o-methoxy
p-methyl
Ph
5b
8
5c
5d
N
N
N
Ar
N
N
N
N
N
N
N
Ar
-CH2(OH)2
N+
N
N
N
N
Ar
OH
6a-d
N
HO-
Ar
Scheme 1. Synthetic pathway for 3,8-bis-(2-aryl-1-diazenyl)-1,3,6,8-tetraazabicyclo[4.3.1]decanes 6.

2502
A. Rivera, D. González-Salas / Tetrahedron Letters 51 (2010) 2500–2504
Table 1
7.26 (120.7)
Selected bond lengths (Å) and bond angles (°) for 7
N
N
N
N
Bond lengths (Å)
Bond angles (°)
N
N
7.19 (128.8)
7.08 (126.0)
N1–N2
N2–N3
N4–N5
N5–N6
N9–N10
N10–N11
N12–N13
N13–N14
1.3352(17)
1.2716(17)
1.3361(18)
1.2673(18)
1.3490(19)
1.273(2)
N2–N1–C28
N2–N1–C25
C28–N1–C25
N5–N4–C27
N5–N4–C26
C27–N4–C26
N10–N9–C31
N10–N9–C30
C30–N9–C31
N13–N12–C32
N13–N12–C33
C32–N12–C33
C27–N7–C28
C27–N7–C29
C28–N7–C29
C30–N8–C33
C30–N8–C29
C33–N8–C29
113.87(12)
120.57(13)
124.82(12)
115.74(12)
121.92(13)
118.76(13)
117.62(16)
113.74(13)
126.47(15)
124.6(4)
N
N
3.34 (63.1)
N
5.04 (70.6)
N
1.359(4)
1.264(3)
N
N
N
N
4.11 (43.4)
Figure 2. 1H NMR (13C) ppm spectroscopic data for 7 in CDCl3.
110.5(3)
119.5(4)
114.34(12)
112.55(12)
112.85(12)
113.35(12)
112.88(12)
112.69(12)
species in the basic solution is TATU 4. The reaction sequence is ini-
tiated by attack on the electrophilic diazonium ion by one of the
two equivalent nitrogen atoms in TATU 4 that have the most sp3
character.10b Next, nucleophilic attack at the adjacent methylene
by the hydroxyl group results in the formation of hemiaminal 8.
After attack on the diazonium ion by the hemiaminalic nitrogen,
one molecule of formaldehyde hydrate is eliminated, affording
the observed bis-triazenes 6a–d.
Only one report exists on the direct synthesis of tetrakis-triaz-
enes.18 We now report that compound 7, a novel tetrakis-triazene,
has been isolated from the reaction of the cyclic aminal TATU 4
with a diazonium salt 5d. We also present the X-ray crystal struc-
ture of 7 here. This new tetrakis-triazene 7 was isolated by crystal-
lization in CHCl3/EtOH as an amorphous solid. The simplicity of 1H
NMR spectra indicated that the molecule is highly symmetric. The
cross-peak in the HMQC two dimensional spectrum was taken into
account when assigning 13C NMR signals (Fig. 2). The 1H NMR spec-
trum exhibits three signals in the aliphatic region with relative
intensities of 8:8:2. The more shielded aminal hydrogen at
3.34 ppm exists as a singlet and corresponds to the two hydrogen
atoms of the methylene bridge between the two rings of the tria-
zepane. Another singlet at 4.11 ppm corresponds to the protons
of the ethylene moiety of the triazepane. An eight-proton singlet
at 5.04 ppm was assigned to the equivalent methylene groups
(NCH2N) in the triazepane rings. These signals show a cross-peak
in the HMQC contour plot with the signal at 63.1, 43.3 and
70.6 ppm, respectively, in the carbon domain. HR-MS (m/z 630.
2940) suggested a molecular formula of C33H38N14
.
Crystals suitable for X-ray analysis were readily grown in ethyl
acetate. The structure of 7 was unambiguously determined by X-
ray crystallography (Fig. 3)19 and selected bonds lengths and an-
gles are given in Table 1. In concordance with reported data,20 Fig-
ure 3 shows that the configuration around the N@N bonds (e.g.,
N2–N3 or N5–N6) are ‘anti’ and these bonds are significantly short-
er (ca. 1.27 Å) than the N–N bonds (e.g., N1–N2 or N4–N5) (ca.
1.34 Å). Other notable features of the structure in Figure 3 include
bond angles around N1, N4, N9 and N12, which are close to sp2-
P
hybridization [
a
ffi 360°]. In contrast, the bond angles around
the nitrogen atom bridge (N7 and N8) are close to an sp3 geometry
P
[
a
= 339.7° around N7, and 338.9° around N8].
As shown in Scheme 2 the formation of 7 could be explained by
the coupling of the diazonium salt 5d to 3,30-methylenebis-1,3,5-
Figure 3. Molecular structure of 7. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres.

A. Rivera, D. González-Salas / Tetrahedron Letters 51 (2010) 2500–2504
2503
HO
OH
N
Ar
Ar
N
N
N
N
NH
N
N
N
N
+N2Ar
N
Ar
12
+
N
+N2Ar
N
N
N
HO
N
N
N
4
N
N
HO
11
Ar
OH
10
OH
N
N
N
N
N
N
+
4ArN2
N
N
N
N
N
N
N
N
N
7
- CH2(OH)2
4
OH
N
HO
Scheme 2. Proposed pathway for bis[1,5-bis-((E)-phenyldiazenyl)-1,3,5-triazepan-3-yl]methane 7 formation.
N
N
- CH2(OH)2
10
OH
9
12. (a) Moser, S.; Church, R.; Peori, M. B.; Vaughan, K. Can. J. Chem. 2005, 83, 1071–
1083; (b) Moser, S. L.; Vaughan, K. Can. J. Chem. 2004, 82, 1725–1735; (c)
Tingley, R.; Peori, M. B.; Church, R.; Vaughan, K. Can. J. Chem. 2005, 83, 1799–
1807.
triazabicyclo[3.2.1]octane 9. Alternatively, we speculated that the
more nucleophilic nitrogen (most sp3 character)10b atoms in TATU
4 simultaneously attack two molecules of the diazonium salt 5d to
form 11. This macrocycle then undergoes intramolecular nucleo-
philic attack to yield 10 and open chain by-products, such as 12,
which we have not been able to isolate. Finally, the formation of
compound 9 can be explained by the reaction of imidazolidine-
1,3-diyldimethanol 10 with TATU 4.
In conclusion, we have demonstrated that the use of a basic
medium provides a mild and effective method for the coupling of
diazonium ions with TATU 4. The successful synthesis of bis-triaz-
enes 6a–d and tetrakis-triazene 7 provides an alternative method
for the preparation of bis-triazenes and paves the way for the prep-
aration of these types of compounds from cyclic aminals.
13. Rondestvedt, C. S.; Davis, S. J. J. Org. Chem. 1957, 22, 200–203.
14. 3,8-Bis-[(4-methoxyphenyl)diazenyl]-1,3,6,8-tetraazabicyclo [4.3.1]decane (6a):
yield 55%, mp 122–123 °C. 1H NMR (400 MHz, CDCl3): d 7.21 (d, J = 8.76 Hz,
2H), 7.15 (d, J = 8.64 Hz, 2H), 6.75 (d, J = 8.88 Hz, 2H), 6.71 (d, J = 8.76 Hz, 2H),
5.34 (d, J = 13.08 Hz, 1H), 5.21 (d, J = 13.07 Hz, 1H), 5.15 (d, J = 13.63 Hz, 1H),
5.01 (d, J = 13.89 Hz, 1H), 4.52 (d, J = 13.24 Hz, 1H), 4.51 (d, J = 13.24 Hz, 1H),
4.31 (d, J = 14.04 Hz, 1H), 4.03 (m, 1H), 3.89 (d, J = 14.08 Hz, 1H), 3.85 (m, 1H),
3.77 (s, 6H), 3.39 (m, 1H), 3.29 (m, 1H). 13C NMR (100 MHz, CDCl3): d 158.2,
157.8, 144.3, 143.9, 121.8, 121.7, 113.8, 73.7, 70.6, 66.9, 66.0, 55.4, 55.4, 50.4,
47.3. HR-EIMS m/z: calcd for C20H26N8O2: 410.4732, found: 410.2162. 3,8-Bis-
[(2-methoxyphenyl)diazenyl]-1,3,6,8-tetraazabicyclo[4.3.1]decane (6b): yield
48%, mp 107–110 °C. 1H NMR (400 MHz, CDCl3): d 7.18 (d, J = 7.0 Hz, 1H),
7.08 (d, J = 8.2 Hz, 1H), 7.04 (d, J = 8.2 Hz, 1H), 6.95 (d, J = 7.1 Hz, 1H), 6.85 (d,
J = 7.9 Hz, 2H), 6.79 (t, J = 6.7 Hz, 1H), 6.63 (t, J = 6.9 Hz, 1H), 5.40 (d, J = 10.8 Hz,
1H), 5.26 (d, J = 13.5 Hz, 2H), 5.02 (d, J = 14.0 Hz, 1H), 4.62 (d, J = 12.0 Hz, 1H),
4.59 (d, J = 12.0 Hz, 1H), 4.32 (d, J = 14.0 Hz, 1H), 4.07 (t, J = 11.7 Hz, 1H), 3.90
(d, J = 12.0 Hz, 1H), 3.90 (m, 1H), 3.84 (s, 3H), 3.76 (s, 3H), 3.46 (d, J = 14.9 Hz,
1H), 3.33 (t, J = 12.3 Hz, 1H). 13C NMR (100 MHz, CDCl3): d 153.2, 153.1, 140.2,
139.7, 127.1, 126.6, 120.8, 120.7, 119.2, 118.8, 112.0, 111.8, 73.9, 71.3, 66.0
(broad), 56.1, 50.2, 47.7. HR-EIMS m/z: calcd for C20H26N8O2: 410.4732, found:
410.2168. 3,8-Bis(p-tolyldiazenyl)-1,3,6,8-tetraazabicyclo[4.3.1]decane (6c):
yield 60%, mp 104–105 °C. 1H NMR (400 MHz, CDCl3): d 7.16 (d, J = 8.04 Hz,
2H), 7.10 (d, J = 7.84 Hz, 2H), 7.02 (d, J = 8.12 Hz, 2H), 6.99 (d, J = 8.00 Hz, 2H),
5.34 (d, J = 12.96 Hz, 1H), 5.24 (d, J = 12.76 Hz, 1H), 5.15 (d, J = 13.44 Hz, 1H),
5.03 (d, J = 13.80 Hz, 1H), 4.54 (d, J = 10.08 Hz, 1H), 4.51 (d, J = 12.06 Hz, 1H),
4.31 (d, J = 14.04 Hz, 1H), 3.99 (m, 1H), 3.92 (m, 1H), 3.88 (d, J = 14.00 Hz, 1H),
3.37 (m. 1H), 3.31 (m, 1H), 2.29 (s, 6H). 13C NMR (100 MHz, CDCl3): d 148.2,
147.8, 135.9, 135.3, 129.2, 129.2, 120.6, 120.6, 74.0(not obs), 70.4(not obs),
66.5(not obs), 50.2(not obs), 47.3(not obs), 21.0, 21.0. HR-EIMS m/z: calcd for
C20H26N8: 378.4744, found: 378.2124. 3,8-Bis(phenyldiazenyl)-1,3,6,8-
tetraazabicyclo[4.3.1]decane (6d): yield 36%, mp 134–136 °C. 1H NMR
(400 MHz, CDCl3): d 7.17 (m, 10H), 5.37 (m, 1H), 5.29 (m, 1H), 5.22 (d,
J = 14.04 Hz, 1H), 5.03 (d, J = 13.84 Hz, 1H), 4.58 (d, J = 11.72 Hz, 1H), 4.55 (d,
J = 12.8 Hz, 1H), 4.34 (d, J = 14.08 Hz, 1H), 4.02 (m, 1H), 3.90 (d, J = 14.04 Hz,
1H), 3.82 (m, 1H), 3.45 (m, 1H), 3.31 (m, 1H). 13C NMR (100 MHz, CDCl3): d
150.5, 150.0, 128.6, 126.2, 125.7, 120.8, 120.8, 74.0, 71.0, 65.9(not obs), 50.3,
47.4. HR-EIMS m/z: calcd for C18H22N8: 350.4212, found: 350.1985. Bis-[1,5-bis-
((E)-phenyldiazenyl)-1,3,5-triazepan-3-yl]methane (7): yield 32%, mp 195–
Acknowledgments
We acknowledge to División de Investigaciones Bogotá (DIB),
and Departamento de Química, Universidad Nacional de Colombia.
D.G.-S. thanks COLCIENCIAS for a fellowship.
References and notes
1. Kimball, D. B.; Haley, M. M. Angew. Chem., Int. Ed. 2002, 41, 3338–3351.
2. (a) Wanner, M. J.; Koch, M.; Koomen, G.-J. J. Med. Chem. 2004, 47, 6875–6883;
(b) Gadjeva, V. G. Int. J. Pharm. 2002, 247, 39–45.
3. Bräse, S. Acc. Chem. Res. 2004, 37, 805–816.
4. (a) Lazny, R.; Sienkiewics, M.; Bräse, S. Tetrahedron 2001, 57, 5825–5832; (b)
Gross, M. L.; Blank, D. H.; Welch, W. M. J. Org. Chem. 1993, 58, 2104–2109.
5. Wirschun, W.; Winkler, M.; Lutz, K.; Jochims, J. C. J. Chem. Soc., Perkin Trans. 1
1998, 1755–1761.
6. Vaughan, K. Org. Prep. Proced. Int. 2001, 33(1), 59–74.
7. Singer, R. D.; Vaughan, K.; Hooper, D. L. Can. J. Chem. 1986, 64, 1567–1572.
8. Rivera, A.; Núñez, M. E.; Morales-Ríos, S.; Joseph-Nathan, P. Tetrahedron Lett.
2004, 45, 7563–7565.
9. (a) Rivera, A.; Gallo, G.; Gayón, M. E.; Joseph-Nathan, P. Synth. Commun. 1993,
23, 2921–2929; (b) Rivera, A.; Torres, O. L.; Leitón, J. D.; Morales-Ríos, M. S.;
Joseph-Nathan, P. Synth. Commun. 2002, 32, 1407–1414; (c) Rivera, A.;
Maldonado, M.; Núñez, M.; Joseph-Nathan, P. Heterocycl. Commun. 2004, 10,
77–80.
10. (a) Rivera, A.; Núñez, M. E.; Avella, E.; Ríos-Motta, J. Tetrahedron Lett. 2008, 49,
2154–2158; (b) Rivera, A.; González-Salas, D.; Ríos-Motta, J.; Hernández-
Barragán, A.; Joseph-Nathan, P. J. Mol. Struct. 2007, 837, 142–147.
11. Duhamel, L. In The Chemistry of Functional Groups, Suppl. D; Patai, S., Rappoport,
Z., Eds.; Wiley-Interscience: Chichester, 1983; pp 721–811. Chapter 20.
197 °C. 1H NMR (400 MHz, CDCl3):
d 7.26 (d, J = 6.92 Hz, 8H), 7.19 (t,
J = 7.72 Hz, 8H), 7.08 (t, J = 7.20 Hz, 4H), 5.04 (s, 8H), 4.11 (s, 8H), 3.34 (s,
2H). 13C NMR (100 MHz, CDCl3): d 150.0, 128.8, 126.0, 120.7, 70.6 (no obs.),
63.1 (not obs), 43.3 (not obs). HR-EIMS m/z: calcd for C33H38N14: 630.7492,
found: 630.2940.
15. (a) Sergeyev, S. Helv. Chim. Acta 2009, 92, 415–444; (b) Wilen, S. H.; Qi, J. Z.;
Williard, P. G. J. Org. Chem. 1991, 56, 485–487.
16. (a) Barra, M.; Srivastava, S.; Brockman, E. J. Phys. Org. Chem. 2004, 17, 1057–
1060; (b) Fu, J.; Lau, K.; Barra, M. J. Org. Chem. 2009, 74, 1770–1773.
17. Peori, M. B.; Vaughan, K.; Hooper, D. J. Org. Chem. 1998, 7437–7444.
18. Clarke, J. D.; Vaughan, K.; Bertolasi, V. Can. J. Chem. 2006, 84, 1280–1289.

2504
A. Rivera, D. González-Salas / Tetrahedron Letters 51 (2010) 2500–2504
19. Crystal data for compound 7, C33H38N14, were collected using a Bruker Appex-II
diffractometer at 100 K, Mr = 630.77, triclinic, P1, a = 10.8032(7) Å,
b = 13.3808(7) Å, c = 13.4206(7) Å, V = 1643.27(18) Å3, Z = 2, Dx = 1.275 g/cm3,
with the Cambridge Crystallographic Data Centre as supplementary
publication number CCDC 751350. Copies of these data can be obtained, free
of charge, on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax:
+44(0) 1223 336033 or email: deposit@ccdc.cam.ac.uk).
X-ray source Mo K
a (radiation), k = 0.7107 Å, F(0 0 0) = 668, colourless prism
0.44 Â 0.32 Â 0.18 mm. The structure solution was obtained by direct methods
and was refined with anisotropic thermal parameters using full-matrix least
squares procedures on F2 to give R = 0.043, wR = 0.116 for 5991 independent
observed reflections and 458 parameters. Crystallographic data (excluding
structure factors) for the given structure in this Letter have been deposited
20. (a) Little, V. R.; Jenkins, H.; Vaughan, K. J. Chem. Crystallogr. 2008, 38, 447–452;
(b) Tingley, R.; Bertolasy, V.; Vaughan, K. J. Chem. Crystallogr. 2006, 36, 831–
839; (c) Karadayl, N.; Cakmak, S.; Odabasoglu, M.; Büyükgüngor, O. Acta
Crystallogr., Sect. C 2005, 61, o303–o305.