Practical synthesis of azobenzenophanes

Article abstract of DOI:10.1021/jo062164p

We devised a practical synthetic route to azobenzenophanes via successive Cu- and Pd-catalyzed coupling reaction of aryl hydrazide and aryl halide followed by Cu(I)-mediated oxidation reaction.

Full text of DOI:10.1021/jo062164p

to correlate the degree of steric distortion with the photochemical
as well as thermal E/Z isomerization behavior.3 Some of the
notable azobenzenophanes, prepared and used for this purpose,
are shown in Figure 1 (1a and 1b reported by Rau and co-
worker,3a,e 2a and 2b by Tamaoki and co-workers3d,g).
Synthetically, they are addressed by either annulation of
properly functionalized azobenzenes or reductive coupling of
bis(nitroarene) precursors, in general. However, neither synthetic
approach is satisfactory because of the low product yield and
functional group tolerance. For example, azobenzenophanes 2a
and 2c were prepared from bis(nitroarene) 3a and 3c in 0.13%
and 0.30% yield, respectively (Scheme 1).3f,g Synthesis of 1a
and 1b fared no better.3e
Practical Synthesis of Azobenzenophanes
Hong-Min Kang, Hee-Yeon Kim, Jin-Woo Jung,
and Cheon-Gyu Cho*
Department of Chemistry, Hanyang UniVersity,
Seoul 131-791, Korea
ccho@hanyang.ac.kr
ReceiVed October 18, 2006
Further exploitation of azobenzenophane to its full potential
thus requires more efficient synthetic methods to ensure better
availability as well as wider structural diversity. Previously, we
reported an effective two-step synthetic protocol to azobenzenes,
consisting of the Pd-catalyzed coupling reaction of aryl hy-
drazide 4 with aryl halide 5 and NBS/pyridine-mediated
oxidation reaction of the resultant diaryl hydrazide into azoben-
zene 6 (Scheme 2).4 The ineffectiveness of the current synthetic
methods prompted us to use our method for construction of
azobenzenophanes (Scheme 2).
We first studied the synthesis of [1,1](3,3′)-azobenzenophane
2a, starting with diiodide 11.5 Its Cu(I)-catalyzed coupling
reaction with NHBocNH2 provided the bis-coupling product 12
in 81% yield. Subjection of 12 into the subsequent Pd-catalyzed
coupling reaction with diiodide 11 afforded cyclic aryl hydrazide
13 in 53% yield. Oxidation of cyclic aryl hydrazide 13 into
azobenzenophane 2a was achieved with the CuI/Cs2CO3 system
with an isolated yield of 61% after silica-gel flash column
chromatography (Scheme 3).4b Oxidation with the NBS/pyridine
system was ineffective in this case, resulting in production of a
complex mixture.
[1,1′](3,3′)-Azobenzenophane 17 in which azobenzene units
are directly connected each other at the 3,3′-positions represents
the azobenzenophane member with the shortest carbon linker
ever (none!). Synthesis commenced with 3,3′-diiodo-biphenyl
14 prepared according to the literature method.6 Successive
Cu(I)- and Pd-catalyzed coupling reactions provided cyclic
hydrazide 16 in 40% overall yield from 14. Cu(I)-mediated
oxidation reaction furnished 17 in 60% isolated yield upon
column chromatography (Scheme 4).
We devised a practical synthetic route to azobenzenophanes
via successive Cu- and Pd-catalyzed coupling reaction of
aryl hydrazide and aryl halide followed by Cu(I)-mediated
oxidation reaction.
Azobenzenes have characteristic photoresponsive properties
with potential applications in the areas of nonlinear optics,
optical storage media, chemosensors, and photochemical
switches.1 Such photochemical response is exerted by reversible
changes in the molecular geometry through the photochemical
E/Z isomerization of the diazo bonds. The rates of the E/Z
isomerization reactions can be modulated by changing the
chemical structures or environment therein, although the exact
mechanistic nature is not fully understood.2 Azobenzenophanes
in which two azobenzene units are linked together in a circular
manner have additional interest as they can be used for the study
(1) (a) Willner, I.; Willner, B. In Bioorganic Photochemistry: Biological
Applications of Photochemical Switches; Morrison, H., Ed.; Wiley: New
York, 1993; Vol. 2, pp 1-110. (b) Ghosh, S.; Banthia, A. K.; Maiya, B. G.
Org. Lett. 2002, 4, 3603. (c) Wang, S.; Advincula, R. C. Org. Lett. 2001,
3, 3831. (d) DiCesare, N.; Lakowicz, J. R. Org. Lett. 2001, 3, 3891. (e)
Harvey, A. J.; Abell, A. D. Tetrahedron 2000, 56, 9763. (f) Burland,
D. M.; Miller, R. D. Walsh, C. A. Chem. ReV. 1994, 94, 31. (g) Kanis,
D. R.; Ratner, M. A.; Marks, T. J. Chem. ReV. 1994, 94, 195. (h) Ichimura,
K. Photochromism: Molecules and Systems; Durr, H., Bouas-Laurent, H.,
Eds.; Elsevier: Amsterdam, 1990; p 903. (i) Kumar, G. S.; Neckers, D. C.
Chem. ReV. 1989, 89, 1915.
(2) (a) Junge, D. M.; McGrath, D. V. J. Am. Chem. Soc. 1999, 121,
4912. (b) Stracke, A.; Wendorff, J. H.; Goldmann, D.; Janietz, D.; Stiller,
B. AdV. Mater. 2000, 12, 282. (c) Berg, R. H.; Hvilsted, S.; Ramanujam,
P. S. Nature 1996, 383, 505. (d) Rasmussen, P. H.; Ramanujam, P. S.;
Hvilsted, S.; Berg, R. H. J. Am. Chem. Soc. 1999, 121, 4738. (e) Li, S.;
McGrath, D. V. J. Am. Chem. Soc. 2000, 122, 6795. (f) Liao, L.-X.; Junge,
D. M.; McGrath, D. V. Macromolecules 2002, 35, 319. (g) Leclair, S.;
Mathew, L.; Giguere, M.; Motallebi, S.; Zhao, Y. Macromolecules 2003,
36, 9024. (h) Kim, M.-J.; Shin, B.-G.; Kim, J.-J.; Kim, D.-Y. J. Am. Chem.
Soc. 2002, 124, 3504. (i) Muraoka, T.; Kinbara, K.; Kobayashi, Y.; Aida,
T. J. Am. Chem. Soc. 2003, 125, 5612. (j) Jousselme, B.; Blanchard, P.;
Gallego-Planas, N.; Delaunay, J.; Allain, M.; Richomme, P.; Levillain, E.;
Roncali, J. J. Am. Chem. Soc. 2003, 125, 2888. (k) Renner, C.; Kusebauch,
U.; Lo¨weneck, M.; Milbradt, A. G.; Moroder, L. J. Peptide Res. 2005, 65,
4 (l) Nagamani, S. A.; Norikane, Y.; Tamaoki, N. J. Org. Chem. 2005, 70,
9304. (m) Muraoka, T.; Kinbara, K.; Aida, T. Nature 2006, 440, 512.
(3) (a) Rau, H.; Lueddecke, E. J. Am. Chem. Soc. 1982, 104, 1616. (b)
Shinkai, S.; Minami, T.; Kusano, Y.; Manabe, O. J. Am. Chem. Soc. 1983,
105, 1851. (c) Ritter, G.; Haefelinger, G.; Lueddecke, E.; Rau, H. J. Am.
Chem. Soc. 1989, 111, 4627. (d) Tamaoki, N.; Ogata, K.; Koseki, K.;
Tsuguo, Y. Tetrahedron 1990, 46, 5931. (e) Roettger, D.; Rau, H.
J. Photochem. Photobiol. A: Chem. 1996, 101, 205. (f) Norikane, Y.;
Kitamoto, K.; Tamaoki, N. Org. Lett. 2002, 4, 3907. (g) Norikane, Y.;
Kitamoto, K.; Tamaoki, N. J. Org. Chem. 2003, 68, 8291. (i) Ciminelli,
C.; Granucci, G.; Persico, M. J. Chem. Phys. 2005, 123, 174317. (j)
Rajakumar, P.; Senthilkumar, B.; Srinivasan, K. Aust. J. Chem. 2006, 59,
75.
(4) (a) Lim, Y.-K.; Lee, K.-S.; Cho, C.-G. Org. Lett. 2003, 5, 979. (b)
Lim, Y.-K.; Choi, S.; Park, K.-B.; Cho, C.-G. J. Org. Chem. 2004, 69,
2603. (c) Kim, K.-Y.; Shin, J.-T.; Lee, K.-S.; Cho, C.-G. Tetrahedron Lett.
2004, 45, 117.
(5) Prepared from 3,3′-diaminodiphenylmethane under Sandmeyer condi-
tions: 68% yield.
(6) Inoue, A.; Kitagawa, K.; Shinokubo, H.; Oshima, K. Tetrahedron
2000, 56, 9601.
10.1021/jo062164p CCC: $37.00 © 2007 American Chemical Society
Published on Web 12/14/2006
J. Org. Chem. 2007, 72, 679-682
679

SCHEME 4. Synthesis of 17
FIGURE 1. Representative azobenzenophanes.
SCHEME 5
SCHEME 1. Synthesis of 2a and 2c
SCHEME 2
SCHEME 6
SCHEME 3. Synthesis of Azobenzenophane 2a
product 20 was obtained in 45% yield. Subsequent Cu(I)-
catalyzed homocoupling followed by Cu(I)-mediated oxidation
reaction provided azobenzenophane 2c in 31% overall yield
from 20.
With the same reaction sequence azobenzenophane bearing
ketal groups 26 was prepared from diiodide 238 (Scheme 6).
Protection of the ketone group proved to be essential because
the unprotected form of 26 resulted in formation of a complex
product mixture under the oxidation conditions. Installation of
BocNHNH2 followed by the coupling reaction with 23 provided
bis-hydrazide 25 in good overall yield. After oxidation, azoben-
Synthesis of [1,1′](3,3′)-azobenzenophane with ethylene link-
age 2c required slight modification of the strategy because the
Cu(I)-catalyzed coupling reaction of 187 with BocNHNH2
produced not only the desired bis-coupling product 19 but also
mono-hydrazide 20 and cyclic hydrazide 21 in isolated yields
of 21%, 37%, and 13%, respectively. No significant improve-
ment in the total yield or product ratio was observed even with
excess BocNHNH2 (up to 10 equiv) in the coupling reaction
and/or prolonged reaction time (Scheme 5). With careful control
of BocNHNH2 equivalents and reaction time, monocoupling
(7) Prepared from m-bromo-benzyl bromide via the Fe-mediated coupling
reaction under the conditions reported: 79% yield. Vogtle, F.; Eisen, N.;
Franken, S.; Bullesbach, P.; Puff, H. J. Org. Chem. 1987, 52, 5560.
(8) 3,3′-Diiodobenzophenone: Lulinski, P.; Skulski, L. Bull. Chem. Soc.
Jpn. 2000, 73, 951.
680 J. Org. Chem., Vol. 72, No. 2, 2007

SCHEME 7
room temperature and partitioned into H2O and ether. The separated
organic solution was dried over MgSO4, filtered, concentrated, and
purified by column chromatography to give 35 mg of 2a (61%
1
yield). H NMR (400 MHz, CDCl3) δ 8.17 (s, 4H), 7.66 (d, J )
7.7 Hz, 4H), 7.39 (t, J ) 7.7 Hz, 4H), 7.35 (d, J ) 7.7 Hz, 4H),
4.19 (s, 4H). 13C NMR (100 MHz, CDCl3) δ 153.7, 140.9, 131.1,
129.2, 126.0, 118.9, 40.2. FTIR (CH2Cl2) 2956, 2923, 1726, 1595,
1462, 1272, 1121, 1073 cm-1. HRMS (M + 1)+ calcd for C26H21N4
389.1766, found 389.1770.
15. 74% yield. 1H NMR (400 MHz, CDCl3) δ 7.71 (s, 2H) 7.46-
7.31 (m, 6H), 4.48 (bs, 4H), 1.53(s, 18H). 13C NMR (100 MHz,
CDCl3) δ 155.1, 143.4, 141.1, 128.4, 123.4, 122.3, 122.2, 81.9,
28.3. FTIR (CH2Cl2) 3340, 2977, 2931, 1699, 1600, 1576, 1368,
1340, 1255 cm-1. HRMS (M + Na)+ calcd for C22H30N4NaO4
437.2165, found 437.2155.
1
16. 54% yield. H NMR (400 MHz, CDCl3) δ 7.88 (bs, 2H),
7.43-7.33 (m, 8H), 7.25 (t, J ) 7.6 Hz, 2H) 7.08 (dd, J ) 8.0, 1.2
Hz, 2H), 6.84 (dd, J ) 8.0, 2.0 Hz, 2H), 6.49 (bs, 2H), 1.34 (s,
18H). 13C NMR (100 MHz, CDCl3) δ 154.2, 149.0, 144.4, 143.4,
142.5, 128.6, 128.1, 124.5, 123.5, 123.2, 120.0, 116.0, 113.9, 82.3,
28.2. FTIR (CH2Cl2) 3305, 2977, 2928, 2854, 1699, 1607, 1582,
1482, 1368, 1328, 1255, 1152 cm-1. HRMS (M + Na)+ calcd for
C34H36N4NaO4 587.2634, found 587.2634.
zenophane 26 was obtained in 47% isolated yield. Unfortunately,
the ketal protecting groups in 26 are too robust to be unmasked
under the conditions not affecting the azo groups (Scheme 6).
Azobenzenophane 30 bearing a hydroxyl group at the
methylene linker was then prepared as a surrogate by following
the route in Scheme 7.
In summary, we devised a new synthetic approach to
azobenzenophane, consisting of Cu- and/or Pd-catalyzed cou-
pling reaction of aryl hydrazide and aryl halide and Cu(I)-
mediated oxidation reaction of the resultant cyclic aryl hy-
drazide. This new strategy would readily provide various other
structurally and functionally useful cyclic azobenzenes for
further exploitation of their interesting photochemical properties
to full potential.
17. 60% yield. 1H NMR (400 MHz, CDCl3) δ 7.30 (td, J ) 8.0,
0.6 Hz, 4H), 7.10 (ddd, J ) 8.0, 2.0, 1.2 Hz, 4H), 7.00 (ddd, J )
8.0, 2.0, 1.2 Hz, 4H), 6.51 (t, J ) 1.6 Hz, 4H). 13C NMR (100
MHz, CDCl3) δ 153.7, 139.3, 129.8, 124.7, 120.1, 119.7. FTIR
(CH2Cl2) 2959, 2921, 2851, 1739, 1706, 1593, 1569, 1466, 1261,
1162, 1090, 1024 cm-1. No parent ion peak was observed due to
the decomposition.
1
19. 21% yield. H NMR (400 MHz, CDCl3) δ 7.33-7.28 (m,
4H), 7.20 (t, J ) 7.6 Hz, 2H), 6.95 (d, J ) 8.0 Hz, 2H), 4.44 (bs,
4H), 2.91 (s, 4H), 1.51 (s, 18H). 13C NMR (100 MHz, CDCl3) δ
155.2, 143.1, 141.9, 128.1, 124.8, 123.5, 121.1, 81.7, 37.9, 28.3.
FTIR (CH2Cl2) 3335, 2977, 2930, 2860, 1698, 1606, 1488, 1453,
1368, 1340, 1254, 1165, 1060 cm-1. HRMS (M + Na)+ calcd for
C24H34N4NaO4 465.2478, found 465.2466.
Experimental Section
12. To a sealed tube were added 200 mg (0.48 mmol) of 11,
188 mg (3.0 equiv) of tert-butyl carbazate, 464 mg (3.0 equiv) of
Cs2CO3, CuI (1.0 equiv), 1,10-phenanthroline (1.0 equiv), and DMF
(5 mL) under Ar atmosphere. After 8 h at 80 °C, the reaction
mixture was cooled to room temperature, diluted with ether, and
washed with H2O. The organic solution was dried over MgSO4,
filtered, concentrated, and purified by column chromatography to
20. 1H NMR (400 MHz, CDCl3) δ 7.32-7.06 (m, 7H), 6.89 (d,
J ) 7.2 Hz, 1H), 4.43 (bs, 2H), 2.87 (s, 4H), 1.50 (s, 9H). 13C
NMR (100 MHz, CDCl3) δ 154.9, 143.8, 142.9, 141.1, 131.3, 129.7,
128.9, 128.0, 126.9, 124.5, 123.2, 122.2, 121.0, 81.7, 37.7, 37.8,
28.4. FTIR (CH2Cl2) 3337, 2977, 2930, 2861, 1698, 1598, 1488,
1475, 1368, 1341, 1293, 1254, 1070 cm-1. HRMS (M + Na)+ calcd
for C19H23BrN2NaO2 413.0841, found 413.0840.
1
give 167 mg of 12 (81% yield). H NMR (400 MHz, CDCl3) δ
7.30-7.20 (m, 6H), 6.94 (d, J ) 8.0 Hz, 2H), 4.41 (bs, 4H), 3.96
(s, 2H), 1.46 (s, 18H). 13C NMR (100 MHz, CDCl3) δ 155.0, 143.0,
140.8, 128.1, 125.1, 124.0, 121.1, 81.7, 41.9, 28.4. FTIR (CH2Cl2)
3339, 2976, 2925, 2853, 1709, 1602, 1488, 1453, 1368, 1254, 1151
cm-1. HRMS (M + Na)+ calcd for C23H32N4NaO4 451.2321, found
451.2312.
1
22. 42% yield. H NMR (400 MHz, CDCl3) δ 7.38 (d, J ) 7.2
Hz, 2H), 7.19 (t, J ) 7.6 Hz, 2H), 6.99 (t, J ) 7.6 Hz, 2H), 6.94-
6.90 (m, 4H), 6.50-6.42 (m, 6H), 6.13 (bs, 2H), 2.86 (d, J ) 6.0
Hz, 4H), 2.81 (d, J ) 6.8 Hz, 4H), 1.33 (s, 18H). 13C NMR (100
MHz, CDCl3) δ 153.8, 148.1, 142.3, 142.0, 141.7, 128.6, 128.0,
124.5, 122.1, 121.4, 119.3, 112.6, 111.0, 82.0, 37.9, 37.6, 28.2.
FTIR (CH2Cl2) 3301, 3054, 2978, 2932, 1692, 1608, 1527, 1488,
1454, 1369, 1306, 1159 cm-1. HRMS (M + Na)+ calcd for
C38H44N4NaO4 643.3260, found 643.3272.
13. To a flask were added 112 mg (0.26 mmol) of 11, 115 mg
(0.26 mmol) of 12, 262 mg (3.0 equiv) of Cs2CO3, 6 mg (10 mol
%) of Pd(OAc)2, 0.08 mL (10 mol %) of P(t-Bu)3 dissolved in
hexane, and 100 mL of anhydrous toluene under Ar atmosphere.
After 36 h at 110 °C, the reaction mixture was cooled to room
temperature and filtered through a plug of Celite. The filtrate was
concentrated and chromatographed to give 85 mg of 13 (53% yield).
1H NMR (400 MHz, CDCl3) δ 7.46 (d, J ) 8.0 Hz, 2H), 7.25-
7.18 (m, 4H), 7.11 (t, J ) 7.6 Hz, 2H), 7.00 (d, J ) 8.0 Hz, 2H),
6.78 (d, J ) 8.0 Hz, 2H), 6.58 (dd, J ) 8.0, 1.6 Hz, 2H), 6.41 (s,
2H), 6.25 (s, 2H), 3.88 (s, 2H), 3.75 (s, 2H), 1.33 (s, 18H). 13C
NMR (100 MHz, CDCl3) δ 153.8, 148.3, 142.9, 142.6, 141.6, 128.9,
128.3, 124.8, 121.6, 121.0, 119.2, 112.4, 111.6, 82.1, 42.2, 42.1,
28.0. FTIR (CH2Cl2) 3336, 2977, 2925, 2852, 1713, 1606, 1449,
1368, 1252, 1156 cm-1. HRMS (M + Na)+ calcd for C36H40N4-
NaO4 615.2947, found 615.2948.
1
2c. 74% yield. H NMR (400 MHz, CDCl3) δ 7.52-7.49 (m,
4H), 7.40 (t, J ) 3.6 Hz, 4H), 7.33 (t, J ) 7.6 Hz, 4H), 7.27-7.24
(m, 4H), 3.12 (s, 8H). 13C NMR (100 MHz, CDCl3) δ 152.1, 141.2,
131.1, 128.9, 124.2, 120.0, 35.9. FTIR (CH2Cl2) 2925, 2863, 1600,
1478, 1450, 1441, 1354, 1309, 1244, 1144, 1076 cm-1. HRMS (M
+ 1)+ calcd for C28H25N4 417.2079, found 417.2072.
1
23. Prepared from 27. H NMR (400 MHz, CDCl3) δ 7.88 (t,
J ) 1.6 Hz, 2H), 7.62 (ddd, J ) 7.6, 1.6, 1.2 Hz, 2H), 7.42 (td, J
) 7.6, 1.2 Hz, 2H), 7.04 (t, J ) 7.6 Hz, 2H), 4.03 (s, 4H). 13C
NMR (100 MHz, CDCl3) δ 143.9, 137.3, 134.8, 130.0, 128.0, 125.4,
94.3, 65.0. FTIR (CH2Cl2) 3058, 2955, 2888, 1663, 1566, 1469,
1415, 1251 cm-1. HRMS (M + 1)+ calcd for C15H13I2O2 478.9005,
found 478.9015.
2a. To a sealed tube were charged 87 mg (0.15 mmol) of 13, 66
mg (2.4 equiv) of CuI, 150 mg (3.0 equiv) of Cs2CO3, and 3 mL
of DMF. After 72 h at 140 °C, the reaction mixture was cooled to
J. Org. Chem, Vol. 72, No. 2, 2007 681

1
24. 62% yield. H NMR (400 MHz, CDCl3) δ 7.62 (bs, 2H),
127.0, 95.2, 75.7, 21.9. FTIR (CH2Cl2) 3056, 2922, 1744, 1584,
1568, 1467, 1425, 1371, 1228, 1178, 1065, 1023 cm-1. HRMS (M
+ Na)+ calcd for C15H12I2NaO2 500.8825, found 500.8827.
7.43-7.25 (m, 6H), 4.42 (bs, 4H), 4.05 (s, 4H), 1.45 (s, 18H). 13
C
NMR (100 MHz, CDCl3) δ 155.1, 142.9, 142.0, 127.9, 122.8, 122.3,
121.3, 109.0, 81.7, 64.8, 28.2. FTIR (CH2Cl2) 3339, 2924, 2852,
1695, 1605, 1484, 1369, 1334, 1254, 1150, 1060 cm-1. HRMS
(M + Na)+ calcd for C25H34N4NaO6 509.2376, found 509.2363.
1
29. 59% yield. H NMR (400 MHz, CDCl3) δ 7.46 (d, J ) 7.7
Hz, 2H), 7.21 (t, J ) 7.7 Hz, 2H), 7.18-7.14 (m, 4H), 7.01 (d,
J ) 7.3 Hz, 2H), 6.91 (d, J ) 7.3 Hz, 2H), 6.69 (s, 1H), 6.65 (dd,
J ) 8.1 Hz, 1.8 Hz, 2H), 6.54 (s, 2H), 6.29 (s, 2H), 3.90 (s, 2H),
2.05 (s, 3H), 1.33 (s, 18H). 13C NMR (100 MHz, CDCl3) δ 170.4,
154.4, 149.0, 143.5, 142.4, 142.3, 129.8, 129.1, 125.7, 121.7, 120.3,
120.0, 113.9, 110.8, 82.9, 77.3, 42.6, 28.7, 21.8. FTIR (CH2Cl2)
3342, 3050, 2974, 2922, 1703, 1610, 1478, 1450, 1370, 1262, 1148
cm-1. HRMS (M + Na)+ calcd for C38H42N4NaO6 673.3002, found
673.3001.
30. To a sealed tube were charged 69 mg (0.11 mmol) of 29, 49
mg (0.25 mmol) of CuI, 83 mg (0.25 mmol) of Cs2CO3, and 2.1
mL of DMF. After 12 h at 120 ˚C the reaction mixture was
quenched with H2O and extracted with ether. The organic solution
was dried over MgSO4, filtered, concentrated, and purified by
column chromatography. The purified azobenzenophane was then
dissolved in 2 mL of dry THF and cooled to 0 °C. To this solution
was added LiAlH4 (6 mg, 0.16 mmol) suspended in 1.5 mL of THF
at 0 °C. After 10 min at 0 °C, the reaction mixture was quenched
with KOH (aq) and extracted with ether. The organic solution was
dried over MgSO4, filtered, concentrated, and purified by column
chromatography to give 18 mg of 30 (42% yield over two steps).
1H NMR (400 MHz, CDCl3) δ 8.35 (t, J ) 1.8 Hz, 2H), 8.19 (s,
2H), 7.73 (d, J ) 8.1 Hz, 2H), 7.67 (td, J ) 7.3 Hz, 1.8 Hz, 2H),
7.56 (d, J ) 7.3 Hz, 2H), 7.43 (t, J ) 7.7 Hz, 2H), 7.40-7.36 (m,
4H), 6.04 (s, 1H), 4.25 (d, J ) 15.4 Hz, 1H), 4.13 (d, J ) 15.4 Hz,
1H), 2.57 (bs, 1H). 13C NMR (100 MHz, CDCl3) δ 154.2, 154.2,
144.6, 141.6, 131.8, 129.9, 129.8, 129.1, 126.6, 124.9, 121.2, 119.6,
75.8, 41.0. FTIR (CH2Cl2) 3394, 3055, 2920, 2852, 1595, 1476,
1436, 1261, 1145 cm-1. HRMS (M)+ calcd for C26H20N4O
404.1637, found 404.1638.
1
25. 51% yield. H NMR (400 MHz, CDCl3) δ 7.52-7.14 (m,
12H), 6.75 (bs, 2H), 6.68-6.53 (m, 2H), 6.30 (bs, 2H), 4.00 (s,
4H), 3.92 (s, 4H), 1.35 (s, 18H). 13C NMR (100 MHz, CDCl3) δ
153.7, 147.9, 143.9, 143.0, 142.7, 128.9, 128.1, 121.8, 121.3, 118.9,
118.6, 113.4, 110.0, 109.2, 109.1, 82.3, 64.8, 64.7, 28.0. FTIR (CH2-
Cl2) 3331, 3058, 2979, 2892, 1714, 1607, 1478, 1443, 1369, 1321,
1254, 1152, 1087 cm-1. HRMS (M + Na)+ calcd for C40H44N4-
NaO8 731.3057, found 731.3063.
1
26. 47% yield. H NMR (400 MHz, CDCl3) δ 8.47 (t, J ) 1.6
Hz, 4H), 7.74-7.70 (m, 8H), 7.41 (t, J ) 7.6 Hz, 4H), 4.24 (s,
8H). 13C NMR (100 MHz, CDCl3) δ 153.1, 142.9, 128.7, 126.6,
124.7, 120.8, 108.3, 65.3. FTIR (CH2Cl2) 2958, 2924, 2894, 2852,
1653, 1475, 1421, 1261, 1178, 1154, 1095, 1020 cm-1. HRMS
(M + 1)+ calcd for C30H24N4NaO4 527.1695, found 527.1696.
28. To a flame-dried 100 mL round-bottomed flask charged with
27 (1.07 g, 2.5 mmol) and 7 mL of dry THF was added NaBH4
(0.11 g, 3.0 mmol) dissolved in 1.5 mL of THF slowly over 10
min at 0 °C. After addition, the mixture was warmed to room
temperature and stirred for 1 h before quenching with H2O. The
reaction mixture was extracted with ether. The combined organic
solution was dried over MgSO4, filtered, concentrated, and purified
by column chromatography to give 1.05 g of the corresponding
1
alcohol (98% yield). H NMR (400 MHz, CDCl3) δ 7.72 (t, J )
1.6 Hz, 2H), 7.61 (td, J ) 7.7 Hz, 1.6 Hz, 2H), 7.28 (d, J ) 7.7
Hz, 2H), 7.06 (t, J ) 7.7 Hz, 2H), 5.67 (d, J ) 3.3 Hz, 1H), 2.37
(d, J ) 3.3 Hz, 1H). 13C NMR (100 MHz, CDCl3) δ 145.2, 136.8,
135.3, 130.3, 125.7, 94.6, 74.5. FTIR (CH2Cl2) 3374, 2158, 1647,
1582, 1562, 1464, 1419, 1174 cm-1. HRMS (M)+ calcd for
C13H10I2O 435.8821, found 435.8815. To a flame-dried 10 mL
round-bottomed flask charged with the alcohol (3.0 mmol), and
acetic anhydride (6.0 mmol) in 15 mL of anhydrous CHCl3 was
added H2SO4 (4.5 mmol) at 0 °C. After addition, the reaction
mixture was warmed to room temperature, stirred for 20 min, and
quenched with H2O. The product was extracted with CH2Cl2, dried
over MgSO4, filtered, concentrated, and chromatographed to give
Acknowledgment. This work was supported by grant R01-
2006-000-11283-0 from the Basic Research Program of the
Korea Science & Engineering Foundation. K.H.M. and K.H.Y.
thank the BK21 fellowship.
Supporting Information Available: Spectral data for all
unknown azobenzenophanes. This material is available free of
charge via the Internet at http://pubs.acs.org.
1
1.41 g of 28 (92% yield). H NMR (400 MHz, CDCl3) δ 7.67 (t,
J ) 1.5 Hz, 2H), 7.63 (td, J ) 7.7 Hz, 1.5 Hz, 2H), 7.27 (d, J )
7.7 Hz, 2H), 7.08 (t, J ) 7.7 Hz, 2H), 6.70 (s, 1H), 2.17 (s, 3H).
13C NMR (100 MHz, CDCl3) δ 170.3, 142.5, 138.0, 136.5, 131.0,
JO062164P
682 J. Org. Chem., Vol. 72, No. 2, 2007