Synthesis of Novel 1,3,5-Tris(arylazo)benzenes via Pd-Catalyzed Couplings and Cu(I)-Mediated Direct Oxidations

Article abstract of DOI:10.1021/jo035720d

A series of novel 1,3,5-tris-azobenzenes were prepared from 1,3,5-trihalobenzene via Pd-catalyzed couplings of N-Boc aryl hydrazines and subsequent Cu(I)-mediated direct oxidations. The oxidation of tris-arylhydrazide provided the azobenzene as a mixture

Full text of DOI:10.1021/jo035720d

SCHEME 1. Syn th esis of Tr is-a r ylh yd r a zid e
Syn th esis of Novel
1,3,5-Tr is(a r yla zo)ben zen es via
P d -Ca ta lyzed Cou p lin gs a n d
Cu (I)-Med ia ted Dir ect Oxid a tion s
Young-Kwan Lim, Sunju Choi,† Kyung Bae Park,† and
Cheon-Gyu Cho*
Department of Chemistry, Hanyang University,
Seoul 131-791, Korea, and Radioisotope & Radiation
Application Team, HANARO Center,
KAERI, Daejon 305-301, Korea
ccho@hanyang.ac.kr
Received November 22, 2003
Abstr a ct: A series of novel 1,3,5-tris-azobenzenes were
prepared from 1,3,5-trihalobenzene via Pd-catalyzed coup-
lings of N-Boc aryl hydrazines and subsequent Cu(I)-
mediated direct oxidations. The oxidation of tris-arylhy-
drazide provided the azobenzene as a mixture of all four of
the possible E/Z-isomers; [E,E,E]-, [E,E,Z]-, [E,Z,Z]-, and
[Z,Z,Z]-1,3,5-tris-azobenzenes. A slow removal of the solvent
in the dark transformed the isomers into the all-trans,
[E,E,E]-isomer.
their characteristic properties not present in nondendritic
azobenzenes.2 A brief literature survey revealed many
examples bearing photochromic azobenzene units posi-
tioned in various places within the dendritic skeletons.
Their photochemical and mechanical behaviors would be
governed by the types of substituents present, location
of diazo-linkages as well as the shape of the molecules.
Conventional synthetic methods, primarily based on the
couplings of functionalized azobenzene moieties, exert
much restriction on the type of chemical ligation methods
due to the lability of the diazo group, hence limiting their
molecular structures and functional groups.5 We have
previously reported a new synthetic approach to various
linear azobenzenes from aryl hydrazides and aryl halides
via Pd-catalyzed couplings and subsequent direct oxida-
tions.6 Our coupling-oxidation protocol would be a
powerful alternative to the conventional methods, as the
labile diazo-linkages are realized at the final stage of the
synthesis. Prompted by the immediate applicability of our
coupling-oxidation protocol toward starburst-shaped
azobenzenes, we have studied the couplings of aryl
hydrazides with 1,3,5-trihalobenzene and subsequent
direct oxidations into the 1,3,5-tris(arylazo)benzenes. In
this account, we wish to present the details of our study
on the synthesis of various functionalized 1,3,5-tris-
(arylazo)benzenes.
Azobenzenes have received a great deal of interest for
their potential applications in the area of nonlinear
optics, optical storage media, chemosensors, and photo-
chemical switches, due to the characteristic reversible
cis-trans isomerization of the diazo linkage, causing
changes of molecular geometry under visible light.1 In
recent years, various dendritic,2 peptidic,3 and polymeric
polyazobenzenes4 have emerged as new promising pho-
tochemical material in those fields. Dendritic or star-
burst-shaped azobenzenes are of particular interest for
* Corresponding author. Phone: +82+2-2290-0936.
† KAERI.
(1) (a) Ichimura, K. Photochromism: Molecules and Systems; Durr,
H., Bouas-Laurent, H., Eds.; Elsevier: Amsterdam, 1990; p 903. (b)
Willner, I.; Willner, B. In Bioorganic Photochemistry: Biological
Applications of Photochemical Switches, Morrison, H., Ed.; Wiley: New
York, 1993; Vol. 2, pp 1-110. (c) Kumar, G. S.; Neckers, D. C. Chem.
Rev. 1989, 89, 1915. (d) Kanis, D. R.; Ratner, M. A.; Marks, T. J . Chem.
Rev. 1994, 94, 195. (e) Burland, D. M.; Miller, R. D. Walsh, C. A. Chem.
Rev. 1994, 94, 31 (f) Schlingmann, G.; Milne, L.; Carter, G. T.
Tetrahedron 1998, 54, 13013. (g) Harvey, A. J .; Abell, A. D. Tetrahedron
2000, 56, 9763. (h) Wang, S.; Advincula, R. C. Org. Lett. 2001, 3, 3831.
(i) DiCesare, N.; Lakowicz, J . R. Org. Lett. 2001, 3, 3891. (j) Sunazuka,
T.; Handa, M.; Nagai, K.; Shirahata, T.; Harigaya, Y.; Otoguro, K.;
Kuwajima, I.; Omura, S. Org. Lett. 2002, 4, 367. (k) J ousselme, B.;
Blanchard, P.; Gallego-Planas, N.; Delaunay, J .; Allain, M.; Richomme,
P.; Levillain, E.; Roncali, J . J . Am. Chem. Soc. 2003, 125, 2888. (l)
Muraoka, T.; Kinbara, K.; Kobayashi, Y.; Aida, T. J . Am. Chem. Soc.
2003, 125, 5612. (m) Saiki, Y.; Sugiura, H.; Nakamura, K.; Yamaguchi,
M.; Hoshi, T.; Anzai, J .-i. J . Am. Chem. Soc. 2003, 125, 9268. (n) Lee,
D. H.; Im, J . H,; Son, S. U.; Chung, Y. K.; Hong, J .-I. J . Am. Chem.
Soc. 2003, 125, 7752.
(2) (a) J unge, D. M.; McGrath, D. V. J . Am. Chem. Soc. 1999, 121,
4912. (b) Stracke, A.; Wendorff, J . H.; Goldmann, D.; J anietz, D.; Stiller,
B. Adv. Mater. 2000, 12, 282.
(3) (a) Berg, R. H.; Hvilsted, S.; Ramanujam, P. S. Nature 1996,
383, 505. (b) Rasmussen, P. H.; Ramanujam, P. S.; Hvilsted, S.; Berg,
R. H. J . Am. Chem. Soc. 1999, 121, 4738. (c) Li, S.; McGrath, D. V. J .
Am. Chem. Soc. 2000, 122, 6795. (d) Liao, L.-X.; J unge, D. M.; McGrath,
D. V. Macromolecules 2002, 35, 319.
The required tris(arylhydrazido)benzenes can be pre-
pared through the two possible routes as depicted in
Scheme 1, where the hydrazides A and B are isomeric
each other with respect to the location of the Boc group.
Route A turned out to be ineffective as the Cu(I)-
catalyzed coupling of tert-butyl carbazate with 1,3,5-
tribromobenzene did not proceed as smoothly as we
hoped.7 Attempted couplings provided a complex mixture
(5) (a) The Chemistry of Synthetic Dyes; Venkataraman, K., Ed.;
Academic Press: New York, 1970; Vols. 1-7. (b) Hegarty, A. F. In The
Chemistry of Diazonium and Diazo Groups, Patai, S., Ed.; Wiley: New
York, 1978; Part 2, p 545. (c) Gordon, P. F.; Gregory, P. Organic
Chemistry in Colour; Springer: New York, 1983; p 95. (d) Szele, I.;
Zollinger, H. Top. Curr. Chem. 1983, 112, 1. (e) Zollinger, H. Color
Chemistry; VCH: New York, 1987; p 85. (f) Davey, M. H.; Lee, V. Y.;
Miller, R. D.; Marks, T. J . J . Org. Chem. 1999, 64, 4976.
(6) Lim, Y.-K.; Lee, K.-S.; Cho, C.-G. Org. Lett. 2003, 5, 979.
(7) (a) Ganjian, I.; Basile, D. V. Anal. Biochem. 1997, 246, 152. (b)
Ghisletta, M.; J alett, H.-P.; Gerfin, T.; Gramlich, V.; Hegetschweiler,
K. Helv. Chim. Acta 1992, 75, 2233.
(4) (a) Leclair, S.; Mathew, L.; Giguere, M.; Motallebi, S.; Zhao, Y.
Macromolecules 2003, 36, 9024. (b) Kim, M.-J .; Shin, B.-G.; Kim, J .-
J .; Kim, D.-Y. J . Am. Chem. Soc. 2002, 124, 3504.
10.1021/jo035720d CCC: $27.50 © 2004 American Chemical Society
Published on Web 02/28/2004
J . Org. Chem. 2004, 69, 2603-2606
2603

TABLE 1. Cou p lin gs of Va r iou s N-Boc Ar yl Hyd r a zin es
w ith Tr ibr om oben zen e
TABLE 2. Cu (I)-Med ia ted Dir ect Oxid a tion s of Tr is-a r yl
Hyd r a zid es in to Tr is-a zoben zen es
entry
1
time (h)
product
yield (%)
entry
R
time (h)
product
yield (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
R ) H
2
2
2
3
3
2
3
2
2
3
2
2
2
2a
2b
2c
2d
2e
2f
2g
2h
2i
98
98
91
86
99
77
93
90
99
99
99
99
94
1
2
3
4
5
6
7
8
9
10
11
12
13
H
p-Me
p-OMe
p-tBu
p-Ph
3
2
3
2
3
0.5
2
2
1.5
2
3a
3b
3c
3d
3e
3f
3g
3h
3i
64
80
52
64
74
trace
74
trace
42
71
R ) p-Me
R ) p-OMe
R ) p-tBu
R ) p-Ph
R ) p-NO2
R ) p-CO2Me
R ) p-COMe
R ) p-CN
R ) p-COPh
R ) o-OMe
R ) p-n-hexyl
R ) p-n-dodecyl
p-NO2
p-CO2Me
p-COMe
p-CN
p-COPh
o-OMe
2j
2k
2l
3j
3k
3l
3
2
2
63
74
68
p-n-hexyl
p-n-dodecyl
2m
3m
SCHEME 2. Cu (I)-Med ia ted Dir ect Oxid a tion s of
Bis-Boc-d ia r yl Hyd r a zin es to Azoben zen es
A set of subsequent control experiments yielded the
optimized conditions, allowing the generation of various
1,3,5-tris(arylazo)benzenes from tris(arylhydrazido)ben-
zenes (Table 2).10 In all cases, the oxidations provided
all possible cis/trans isomers; [E,E,E]-, [E,E,Z]-, [E,Z,Z]-
, and [Z,Z,Z]-1,3,5-tris(arylazo)benzenes. The ratio of four
E/Z isomers were determined to be 70:20:7:3 by isolation
with silica gel chromatography in the case of 3a . We also
found that the E/Z isomers converse into the [E,E,E]-
isomer upon slow removal of the solvents in the dark.
The yields reported are the values after the isomeriza-
tion. Incompatible were the ones bearing NO2 or COMe
groups (entries 6 and 8) due to the their thermal
instability. Running the oxidations at lower temperatures
indeed provided the corresponding 1,3,5-tris(arylazo)-
benzenes, but at much slower rates (20-30% conversion
after 7 days). The isolated pure [E,E,E] isomers are
photochemically stable when they are in the solid phase
but rapidly undergo cis-trans photoisomerization in
solution to provide a mixture of all four E/Z isomers when
exposed to the lights. A slow removal of the solvent in
the dark again transformed the isomers back into the
all-trans, [E,E,E]-isomer.
In summary, we have shown that various functional-
ized 1,3,5-tris(arylazo)benzenes can be readily prepared
from 1,3,5-trihalobenzene via Pd-catalyzed couplings with
N-Boc aryl hydrazines and subsequent Cu(I)-mediated
direct oxidations. Our new protocol would allow a precise
integration of azobenzene units into the target molecules
for the generation of new functional poly-azobenzenes
with various intentions. We are currently investigating
the applications of 1,3,5-tris-azobenzenes, 3l or 3m , in
particular, as new holographic grating materials. A
further extension of our method to the synthesis of
of products, some of which resulted from the couplings
at -NH2 rather than the desired -NHBoc site. No
significant improvement was observed with more reactive
1,3,5-triiodobenzene.8 Meanwhile, N-Boc aryl hydrazines
were well coupled with 1,3,5-triiodobenzene as well as
1,3,5-tribromobenzene under the Pd(OAc)2/P(t-Bu)3 cata-
lyst system to provide the corresponding tris(arylhydrazi-
do)benzenes in good to excellent yields (route B). In this
case, the aryl substituent would exert a steric hindrance
to prevent the coupling reactions from taking place at
the -NH2 side. Table 1 summarizes the results on the
coupling reactions of various substituted aryl hydrazides
with 1,3,5-tribromobenzene.
The resulting tris(arylhydrazido)benzenes (2a -m ),
however, did not give the desired 1,3,5-tris(arylazo)-
benzenes under the conditions that were successfully
employed for the oxidation of monodiaryl hydrazides.6 We
isolated instead several products including the ones
resulted from the brominations at the nitrogen and/or
aryl groups. Unlike the cases with diaryl hydrazides, the
tert-butyl groups in this trisubstituted system might be
too hindered for the oxidations to proceed. While we were
studying the Cu(I)-catalyzed coupling reactions of aryl
hydrazides with aryl halides, we have learned that bis-
Boc diaryl hydrazines can be directly oxidized into the
azobenzenes when heated at 110 °C in the presence of
Cu(I) and a base (Scheme 2).9
(10) Compounds 3a and 3f have been prepared from 1,3,5-(NO2)3-
benzene in three steps with overall yields of less than 2% through the
formation of 1,3,5-tris(aci-nitro)benzene followed by the diazo-couplings
with the corresponding aryl diarzonium salts and denitrations. Severin,
T.; Hufnagel, J .; Temme, H.-L. Chem. Ber. 1968, 101, 2468.
(8) Kwong, F. Y.; Klapars, A.; Buchwald, S. L. Org. Lett. 2002, 4,
581.
(9) Kim, K.-Y.; Shin, J .-T.; Lee, K.-S.; Cho, C.-G. Tetrahedron Lett.
2004, 45, 117.
2604 J . Org. Chem., Vol. 69, No. 7, 2004

2h : 1H NMR (400 MHz, CDCl3) δ 7.81 (d, J ) 8.8 Hz, 6H),
7.56 (d, J ) 8.8 Hz, 6H), 6.48 (bs, 3H), 5.73 (s, 3H), 2.55 (s, 9H),
1.34 (s, 27H); 13C NMR (100 MHz, CDCl3) δ 196.6, 152.9, 149.8,
146.5, 132.5, 128.8, 120.3, 90.8, 83.1, 28.0, 26.5; FT-IR (CHCl3)
3335, 2984, 1725, 1682, 1604, 1328, 1273, 1156 cm-1; HRMS
(FAB) m/z (M + 1)+ calcd for C45H55N6O9 823.4031, found
823.4061.
multigeneration dendrimers and cyclic polyazobenzenes
is also underway.
Exp er im en ta l Section
N′-[3,5-Bis(N-ter t-bu toxyca r bon yl-N′-p h en ylh yd r a zin o)-
p h en yl]-N-p h en ylh yd r a zin eca r boxylic Acid ter t-Bu tyl Es-
ter (2a ). To a flask were charged 2.150 g (10.3 mmol) of phenyl
hydrazide (1a ), 0.325 g (1.0 mmol) of 1,3,5-tri-bromobenzene,
0.035 g (15 mol %) of Pd(OAc)2, 0.095 mL of P(t-Bu)3 (15 mol %)
dissolved in hexane, 3.360 g of Cs2CO3, and 10 mL of anhydrous
toluene at rt. The resulting mixture was stirred for 30 min at rt
and heated at 110 °C. After 2 h, the reaction mixture was cooled,
concentrated, and chromatographed (hexanes/EtOAc ) 7:1) to
afford 0.708 g of the product 2a in 98% yield: 1H NMR (400 MHz,
CDCl3) δ 7.43 (d, J ) 8.4 Hz, 6H), 7.21 (dd, J ) 8.4, 7.2 Hz, 6H),
7.03 (t, J ) 7.2 Hz, 3H), 6.43 (bs, 3H), 5.81 (s, 3H), 1.32 (s, 27H);
13C NMR (100 MHz, CDCl3) δ 153.6, 150.1, 142.5, 128.1, 124.2,
121.8, 90.7, 82.0, 28.1; FT-IR (CHCl3) 3350, 2980, 1714, 1620,
1495, 1347, 1308, 1156 cm-1; HRMS (FAB) m/z (M + 1)+ calcd
for C39H49N6O6 697.3714, found 697.3687.
2i: 1H NMR (400 MHz, CDCl3) δ 7.64 (d, J ) 8.8 Hz, 6H),
7.52-7.49 (m, 6H), 6.50 (bs, 3H), 5.69 (s, 3H), 1.33 (s, 27H); 13
C
NMR (100 MHz, CDCl3) δ 152.6, 149.6, 146.2, 132.3, 120.6, 118.6,
106.8, 90.7, 83.5, 27.9; FT-IR (CHCl3) 3334, 2980, 2228, 1720,
1602, 1499, 1322, 1302, 1152 cm-1; HRMS (FAB) m/z (M + 1)+
calcd for C42H46N9O6 772.3571, found 772.3569.
2j: 1H NMR (400 MHz, CDCl3) δ 7.75-7.72 (m, 12H), 7.64
(d, J ) 8.8 Hz, 6H), 7.57-7.53 (m, 3H), 7.46-7.42 (m, 6H), 6.43
(bs, 3H), 5.80 (s, 3H), 1.36 (s, 27H); 13C NMR (100 MHz, CDCl3)
δ 195.0, 153.0, 149.8, 146.2, 137.4, 132.5, 131.9, 130.5, 129.5,
127.5, 120.1, 90.4, 82.8, 27.9; FT-IR (CHCl3) 3335, 2980, 1725,
1659, 1601, 1328, 1281, 1156 cm-1; HRMS (FAB) m/z (M + 1)+
calcd for C60H61N6O9 1009.4500, found 1009.4489.
2k : 1H NMR (400 MHz, CDCl3) δ 7.35-7.32 (m, 3H), 7.19-
7.15 (m, 3H), 6.87-6.81 (m, 6H), 6.36 (bs, 3H), 6.03 (s, 3H), 3.84
(s 9H), 1.35 (s, 27H); 13C NMR (100 MHz, CDCl3) δ 155.7, 154.1,
149.5, 131.4, 128.7, 129.2, 120.3, 111.3, 91.2, 81.0, 55.5, 28.2;
The following compounds 2b-m were prepared by using the
same procedure as described for 2a .
N′-[3,5-Bis(N′-ter t-bu toxyca r bon yl-N-p-tolylh yd r a zin o)-
p h en yl]-N-p-tolylh yd r a zin eca r boxylic a cid ter t-bu tyl ester
(2b): 1H NMR (400 MHz, CDCl3) δ 7.30 (d, J ) 8.4 Hz, 6H),
7.01 (d, J ) 8.4 Hz, 6H), 6.39 (bs, 3H), 5.79 (s, 3H), 2.28 (s, 9H),
1.33 (s, 27H); 13C NMR (100 MHz, CDCl3) δ 153.8, 150.2, 140.1,
133.8, 128.8, 122.0, 90.8, 91.8, 28.2, 21.0; FT-IR (CHCl3) 3343,
2980, 1713, 1616, 1510, 1336, 1160 cm-1; HRMS (FAB) m/z (M
+ 1)+ calcd for C42H55N6O6 739.4183, found 739.4199.
N′-[3,5-Bis(N′-ter t-bu toxycar bon yl-N′-(4-m eth oxyph en yl)-
h ydr azin o)ph en yl]-N-(4-m eth oxyph en yl)h ydr azin ecar box-
ylic a cid ter t-bu tyl ester (2c): 1H NMR (400 MHz, CDCl3) δ
7.33 (d, J ) 8.4 Hz, 6H), 6.78-6.74 (m, 6H), 6.29 (bs, 3H), 5.82
(s, 3H), 3.79 (s, 9H), 1.35 (s, 27H); 13C NMR (100 MHz, CDCl3)
δ 156.2, 153.9, 150.0, 135.8, 123.7, 113.3, 90.7, 81.6, 55.3, 28.2;
FT-IR (CHCl3) 3340, 2976, 1710, 1620, 1507, 1339, 1251, 1156
cm-1; HRMS (FAB) m/z (M + 1)+ calcd for C42H55N6O9 787.4031,
found 787.4001.
N′-{3,5-Bis[N-ter t-bu toxycar bon yl-N-(4-ter t-bu tylph en yl)-
h yd r a zin o]p h en yl}-N-(4-ter t-b u t ylp h en yl)h yd r a zin eca r -
boxylic a cid ter t-bu tyl ester (2d ): 1H NMR (400 MHz, CDCl3)
δ 7.38 (d, J ) 8.8 Hz, 6H), 7.27-7.24 (m, 6H), 6.26 (bs, 3H),
5.83 (s, 3H), 1.34 (s, 27H), 1.29 (s, 27H); 13C NMR (100 MHz,
CDCl3) δ 153.8, 150.2, 147.0, 139.9, 125.1, 121.4, 90.9, 81.9, 34.4,
31.5, 28.2; FT-IR (CHCl3) 3343, 2965, 1718, 1616, 1515, 1371,
1335, 1160 cm-1; HRMS (FAB) m/z (M + 1)+ calcd for C51H73N6O6
865.5592, found 865.5578.
N-Bip h en yl-4-yl-N′-[3,5-b is(N′-b ip h en yl-4-yl-N′-ter t-b u -
toxyca r bon ylh yd r a zin o)p h en yl]h yd r a zin eca r boxylic a cid
ter t-bu tyl ester (2e): 1H NMR (400 MHz, CDCl3) δ 7.53-7.42
(m, 18H), 7.37-7.33 (m, 6H), 7.29-7.25 (m, 3H), 6.53 (bs, 3H),
5.87 (s, 3H), 1.36 (s, 27H); 13C NMR (100 MHz, CDCl3) δ 153.6,
150.1, 141.8, 140.3, 136.9, 128.5, 126.8, 126.74, 126.65, 122.0,
90.7, 82.2, 28.2; FT-IR (CHCl3) 3347, 2980, 1721, 1612, 1487,
1336, 1156 cm-1; HRMS (FAB) m/z (M + 1)+ calcd for C57H61N6O6
925.4653, found 925.4620.
N′-{3,5-Bis[N-ter t-bu toxyca r bon yl-N′-(4-n itr op h en yl)h y-
d r a zin o]p h en yl}-N-(4-n it r op h en yl)h yd r a zin eca r b oxylic
a cid ter t-bu tyl ester (2f): 1H NMR (400 MHz, CDCl3) δ 8.12-
8.03 (m, 6H), 7.72-7.68 (m, 6H), 6.36 (bs, 3H), 5.70 (s, 3H), 1.36
(s, 27H); 13C NMR (100 MHz, CDCl3) δ 152.5, 149.5, 147.9, 143.0,
124.1, 120.0, 90.8, 83.8, 27.9; FT-IR (CHCl3) 3351, 2984, 1725,
1593, 1519, 1942, 1916, 1156 cm-1; HRMS (FAB) m/z (M + 1)+
calcd for C39H46N9O12 832.3266, found 832.3280.
FT-IR (CHCl3) 3347, 2980, 1721, 1616, 1503, 1343, 1160 cm-1
;
HRMS (FAB) m/z (M + 1)+ calcd for C42H55N6O9 787.4031, found
787.4033.
2l: 1H NMR (400 MHz, CDCl3) δ 7.33 (d, J ) 8.4 Hz, 6H),
7.03 (d, J ) 8.4 Hz, 6H), 6.29 (bs, 3H), 5.82 (s, 3H), 2.54 (t, J )
8.0 Hz 6H), 1.62-1.53 (m, 6H), 1.39-1.23 (m, 18H), 1.34 (s, 27H),
0.88 (t, J ) 6.8 Hz, 9H); 13C NMR (100 MHz, CDCl3) δ 153.8,
150.2, 140.2, 138.9, 128.1, 121.8, 90.9, 81.8, 35.4, 31.8, 31.5, 29.1,
28.2, 22.7, 14.2; FT-IR (CHCl3) 3346, 2929, 1716, 1615, 1510,
1334, 1159 cm-1; HRMS (FAB) m/z (M+1)+ calcd for C57H85N6O6
949.6531, found 949.6520.
2m : 1H NMR (400 MHz, CDCl3) δ 7.33 (d, J ) 8.4 Hz, 6H),
7.02 (d, J ) 8.4 Hz, 6H), 6.32 (bs, 3H), 5.82 (s, 3H), 2.53 (t, J )
8.0 Hz, 6H), 1.58-1.55 (m, 6H), 1.37 - 1.25 (m, 54H), 1.33 (s,
27H), 0.87 (t, J ) 6.8 Hz, 9H); 13C NMR (100 MHz, CDCl3) δ
153.8, 150.2, 140.2, 138.9, 128.1, 121.9, 90.8, 81.8, 35.4, 32.0,
31.6, 29.8 (2C), 29.7 (2C), 29.6 (2C), 29.4, 28.2, 22.8, 14.2; FT-
IR (CHCl3) 3346, 2929, 2855, 1716, 1619, 1510, 1334, 1159 cm-1
;
HRMS (FAB) m/z (M + 1)+ calcd for C75H121N6O6 1201.9348,
found 1201.9369.
3a : To a sealed tube were charged 50 mg (0.07 mmol) of 2a ,
55 mg (0.29 mmol) of CuI, 94 mg (0.29 mmol) of Cs2CO3, and 1
mL of anhydrous DMF at room temperature. After 3 h at 140
°C, the reaction mixture was cooled and chromatographed
(hexanes/EtOAc ) 9:1) to furnish 18 mg of tris-azobenzenes (as
a mixture of four isomers, 64% of total yield), which were
isomerized to 3a upon slow removal of the solvent in the dark:
1H NMR (400 MHz, CDCl3) δ 8.58 (s, 3H), 8.02-7.80 (m, 6H),
7.58-7.50 (m, 9H); 13C NMR (100 MHz, CDCl3) δ 153.8, 152.3,
131.6, 129.2, 123.2, 118.9; FT-IR (CHCl3) 2922, 1604, 1503, 1421,
1152 cm-1; HRMS (FAB) m/z (M + 1)+ calcd for C24H19N6
391.1671, found 391.1622.
The following compounds 3b-m were prepared by using the
same procedure as described for 3a .
3b: 1H NMR (400 MHz, CDCl3) δ 8.51 (s, 3H), 7.90 (d, J )
8.4 Hz, 6H), 7.33 (d, J ) 8.0 Hz, 6H), 2.54 (s, 9H); 13C NMR
(100 MHz, CDCl3) δ 153.8, 150.4, 142.1, 129.7, 123.1, 118.3, 21.7;
FT-IR (CHCl3) 2965, 2922, 1600, 1269, 1094 cm-1; HRMS (FAB)
m/z (M + 1)+ calcd for C27H25N6 433.2145, found 433.2132.
3c: 1H NMR (400 MHz, CDCl3) δ 8.45 (s, 3H), 7.99 (d, J )
8.8 Hz, 6H), 7.03 (d, J ) 8.8 Hz, 6H), 3.90 (s, 9H); 13C NMR
(100 MHz, CDCl3) δ 162.2, 153.8, 146.7, 125.0, 117.8, 114.2, 55.7;
FT-IR (CHCl3) 2926, 1601, 1503, 1258, 1145, 1027 cm-1; HRMS
(FAB) m/z (M + 1)+ calcd for C27H25N6O3 481.1988, found
481.1980.
3d : 1H NMR (400 MHz, CDCl3) δ 8.53 (s, 3H), 7.94 (d, J )
8.4 Hz, 6H), 7.56 (d, J ) 8.4 Hz, 6H), 1.40 (s, 27H); 13C NMR
(100 MHz, CDCl3) δ 155.1, 153.8, 150.3, 126.0, 122.8, 118.3, 35.2,
31.4; FT-IR (CHCl3) 2965, 2867, 1604, 1503, 1464, 1269, 1109
2g: 1H NMR (400 MHz, CDCl3) δ 7.87 (d, J ) 8.8 Hz, 6H),
7.52 (d, J ) 8.8 Hz, 6H), 6.58 (bs, 3H), 5.73 (s, 3H), 3.88 (s, 9H),
1.32 (s, 27H); 13C NMR (100 MHz, CDCl3) δ 166.3, 153.0, 149.8,
146.4, 129.8, 125.3, 120.3, 90.7, 82.9, 51.9, 28.0; FT-IR (CHCl3)
3339, 2979, 1720, 1605, 1320, 1279, 1155, 1112 cm-1; HRMS
(FAB) m/z (M + 1)+ calcd for C45H55N6O12 871.3878, found
871.3845.
J . Org. Chem, Vol. 69, No. 7, 2004 2605

cm-1; HRMS (FAB) m/z (M + 1)+ calcd for C36H43N6 559.3549,
found 559.3549.
2965, 2922, 1558, 1402, 1270, 1094 cm-1; HRMS (FAB) m/z (M
+ 1)+ calcd for C27H25N6O3 481.1988, found 481.1990.
3l: 1H NMR (400 MHz, CDCl3) δ 8.51 (s, 3H), 7.91 (d, J ) 8.4
Hz, 6H), 7.34 (d, J ) 8.4 Hz, 6H), 2.70 (t, J ) 7.6 Hz, 6H), 1.71-
1.64 (m, 6H), 1.41-1.25 (m, 18H), 0.90 (t, J ) 6.8 Hz, 9H; 13C
NMR (100 MHz, CDCl3) δ 153.8, 150.6, 147.1, 129.1, 123.1, 118.7,
36.1, 31.8, 31.4, 29.1, 22.7, 14.2; FT-IR (CHCl3) 2960, 2929, 2859,
1603, 1459, 1155 cm-1; HRMS (FAB) m/z (M + 1)+ calcd for
C42H55N6 643.4488, found 644.4478.
3m : 1H NMR (400 MHz, CDCl3) δ 8.51 (s, 3H), 7.92 (d, J )
8.4 Hz, 6H), 7.34 (d, J ) 8.4 Hz, 6H), 2.70 (t, J ) 7.6 Hz, 6H),
1.69-1.64 (m, 6H), 1.34-1.18 (m, 54H), 1.88 (t, J ) 7.2 Hz, 9H;
13C NMR (100 MHz, CDCl3) δ 153.8, 150.6, 147.1, 129.1, 123.1,
123.0, 118.3, 36.1, 32.0, 31.4, 29.81, 29.78, 29.75, 29.69, 29.6,
29.5, 29.4, 22.8, 14.3; FT-IR (CHCl3) 2962, 2929, 2855, 1462,
1262 cm-1; HRMS (FAB) m/z (M + 1)+ calcd for C60H91N6
895.7305, found 895.7290.
3e: 1H NMR (400 MHz, CDCl3) δ 8.61 (s, 3H), 8.11-8.08 (m,
6H), 7.80-7.77 (m, 6H), 7.69-7.67 (m, 6H), 7.50-7.46 (m, 6H),
7.42-7.38 (m, 3H); 13C NMR (100 MHz, CDCl3) δ 153.9, 151.4,
144.2, 139.9, 128.8, 127.9, 127.8, 127.1, 123.7, 118.8; FT-IR
(CHCl3) 2926, 1601, 1408, 1265, 1156 cm-1; HRMS (FAB) m/z
(M + 1)+ calcd for C42H31N6 619.2610, found 619.2607.
3g: 1H NMR (400 MHz, CDCl3) δ 8.65 (s, 3H), 8.23 (d, J )
8.4 Hz, 6H), 8.05 (d, J ) 8.4 Hz, 6H), 3.98 (s, 9H); 13C NMR
(100 MHz, CDCl3) δ 166.2, 154.5, 153.6, 132.4, 130.6, 122.9,
119.7, 52.5; FT-IR (CHCl3) 2920, 1730, 1603, 1432, 1279, 1108
cm-1; HRMS (FAB) m/z (M + 1)+ calcd for C30H25N6O6 565.1836,
found 565.1839.
3i: 1H NMR (400 MHz, CDCl3) δ 8.68 (s, 3H), 8.09 (d, J ) 8.4
Hz, 6H), 7.87 (d, J ) 8.4 Hz, 6H); 13C NMR (100 MHz, CDCl3)
δ 153.8, 153.4, 133.3, 123.6, 120.2, 118.1, 114.9; FT-IR (CHCl3)
2926, 2856, 2227.1, 1737, 1596, 1262 cm-1. No mass data
available due to the decomposition.
Ack n ow led gm en t. This work was supported by the
Nuclear R&D Program of the Ministry of Science and
Technology (MOST). L.Y.K. acknowledges the financial
support from the BK 21 Program.
3j: 1H NMR (400 MHz, CDCl3) δ 8.69 (s, 3H), 8.11 (d, J ) 8.4
Hz, 6H), 7.99 (d, J ) 8.4 Hz, 6H), 7.86-7.84 (m, 6H), 7.65-7.61
(m, 3H), 7.54-7.50 (m, 6H); 13C NMR (100 MHz, CDCl3) δ 195.6,
154.0, 153.7, 139.8, 137.1, 132.7, 131.0, 130.0, 128.3, 122.9, 119.7;
FT-IR (CHCl3) 2926, 1663, 1601, 1449, 1308, 1281 cm-1; HRMS
(FAB) m/z (M + 1)+ calcd for C45H31N6O3 703.2458, found
703.2456.
Su p p or tin g In for m a tion Ava ila ble: Spectral data of
unreported N-Boc aryl hydrazines, 1,3,5-tris(arylhydrazido)-
benzenes, and 1,3,5-tris-(arylazo)benzenes. This material is
available free of charge via the Internet at http://pubs.acs.org.
3k : 1H NMR (400 MHz, CDCl3) δ 8.44 (s, 3H), 7.66-7.64 (m,
3H), 7.42-7.38 (m, 3H), 7.04 (d, J ) 8.0 Hz, 3H), 7.00-6.93 (m,
3H), 3.98 (s, 9H); 13C NMR (100 MHz, CDCl3) δ 157.1, 154.2,
142.0, 132.9, 120.7, 118.8, 117.0, 112.8, 56.4; FT-IR (CHCl3)
J O035720D
2606 J . Org. Chem., Vol. 69, No. 7, 2004