S. C. Burdette et al.
FULL PAPER
12 h. The reaction mixture was diluted with EtOAc (10 mL) and
washed with 2 m aqueous HCl (10 mL) and saturated aqueous
NaCl (10 mL). The organic layer was dried with MgSO4 and the
solvent was removed. Column chromatography on silica (EtOAc/
hexanes, 4:6) gave the monoamide as a red solid. The monoamide
(100 mg, 0.32 mmol), picolinic acid chloride (300 mg, 2.1 mmol),
and K2CO3 (440 mg, 3.2 mmol) were combined in THF (10 mL)
and stirred at 23 °C for 24 h. The mixture was filtered, the filtrate
was collected, and the solvent was removed under vacuum. The
crude residue was purified by column chromatography on alumina
there is no effective way to disrupt the H-bonding in
AzoAMP-1 to restore transǞcis isomerization, and no
means of effectively preventing the isomerization without a
pendant pyridyl group. Whereas the simplicity of H-bond-
ing provides an attractive strategy for blocking isomeriza-
tion, tuning the strength of the interaction has proven to be
more difficult than originally hypothesized; however, these
studies support the concerted inversion mechanism of AB
photoisomerization. To inhibit photoisomerization, the
concerted inversion pathway must be energetically unfavor- (hexanes/EtOAc, 5:1) to give 6 (80 mg, 60%) as a light-orange so-
lid; m.p. Ͼ 260 °C; Rf = 0.25 (alumina; EtOAc/hexanes, 1:4). 1H
NMR (400 MHz, CDCl3): δ = 8.93 (t, J = 8.3 Hz, 2 H), 8.68 (s, 2
H), 8.34 (d, J = 7.8 Hz, 2 H), 8.16 (d, J = 8.9 Hz, 2 H), 7.94 (t, J
able and only the H-bonding in AzoAMP-1 can prevent the
aryl group distortions that are a prerequisite to isomeriza-
tion by inversion. Alternative means to toggle between a
photoactive and photoinactive states in AB derivatives are
= 8.2 Hz, 2 H), 7.6 (t, J = 7.8 Hz, 2 H), 7.56 (s, 2 H), 7.29 (s, 2
H) ppm. 13C NMR (100 MHz, CDCl3): δ = 162.2, 150.4, 148.5,
being investigated by our group.
140.8, 137.8, 137.5, 133.4, 126.8, 124.0, 122.7, 120.58, 117.57 ppm.
IR (neat): ν = 3300.2, 2920.7, 2850.9, 1682.5, 1586.3, 1568.1,
˜
1464.7, 1448.7, 1427.2, 1311.32, 1280.7, 1259.8, 1238.5, 1155.0,
1087.2, 1018.8, 997.2, 950.6, 902.1, 869.6, 790.7, 764.3, 741.2,
Experimental Section
+
700.9, 684.5 cm–1. HRMS (+ESI): m/z calcd. for C24H19N6O2
General Procedures: All reagents were purchased and used without
further purification. 2,2Ј-Diaminoazobenzene (6; DAAB) was pre-
pared according to literature procedures.[48] Dichloromethane
(CH2Cl2) and toluene were sparged with argon and dried by pass-
age through alumina-based drying columns. All chromatography
and thin-layer chromatography (TLC) were performed on silica
(200–400 mesh). TLCs were developed by using EtOAc/hexanes
mixtures. 1H and 13C NMR spectra were recorded with a 400 MHz
NMR instrument. Chemical shifts are reported in ppm relative to
tetramethylsilane (TMS). IR spectra were recorded with an FTIR
instrument and samples were analyzed neat. High-resolution mass
spectra were recorded in positive ion mode (+ESI).
423.1569; found 423.1560.
2,2Ј-Bis[N,NЈ-(2-quinoline)methyl]diaminoazobenzene (AzoAMQ,
9): DAAB (200 mg, 0.94 mmol), 2-quinolinecarbaldehyde (320 mg,
2.0 mmol), and NaBH(OAc)3 (466 mg, 2.2 mmol) were combined
in CH2Cl2 (15 mL) and stirred at 23 °C for 24 h. Water (10 mL)
was added and the organic layer was collected and dried with
MgSO4. Solvent was removed under vacuum and the residue was
purified by flash chromatography on silica (hexanes/EtOAc, 1:9) to
give 9 (260 mg, 56%) as a dark-red solid; m.p. 101–102 °C; Rf =
1
0.20 (silica; EtOAc/hexanes, 1:4). H NMR (400 MHz, CDCl3): δ
= 9.25 (t, J = 5.3 Hz, 2 H), 8.16 (d, J = 8 Hz, 2 H), 8.08 (d, J =
8 Hz, 2 H), 8.00 (dd, J = 5.9, 1.8 Hz, 2 H), 7.80 (d, J = 7.8 Hz, 2
H), 7.76 (td, J = 7.0, 1.5 Hz, 2 H), 7.56 (td, J = 7.7, 1.2 Hz, 2 H),
7.4 (d, J = 8.7 Hz, 2 H), 7.27–7.25 (m, 2 H), 6.87–6.83 (m, 4 H),
4.82 (d, J = 5.16 Hz, 2 H) ppm. 13C NMR (100 MHz, CDCl3): δ
= 158.6, 143.2, 137.5, 136.9, 131.8, 129.9, 129.2, 127.98, 127.9,
2,2Ј-Bis[N,NЈ-(2-pyridyl)ethyl]diaminoazobenzene (AzoAEP, 7):
DAAB (300 mg, 1.4 mmol) in MeOH (35 mL) was combined with
acetic acid (170 μL, 3.8 mmol) and freshly distilled 2-vinylpyridine
(260 μL, 3.8 mmol). The mixture was stirred at 65 °C for 12 h and
allowed to cool to room temperature. After removing half of the
MeOH, ice (50 g) was added and the resulting homogeneous solu-
tion was made basic (pH 10) with 1 m KOH. The product was ex-
tracted with EtOAc (3ϫ 20 mL), the organic layers were combined,
dried with MgSO4, and the solvent was removed under vacuum.
Flash chromatography on silica (EtOAc/hexanes, 1:9) gave 7
(380 mg, 64%) as a dark-red solid; m.p. 152–153 °C; Rf = 0.20 (sil-
ica; EtOAc/hexanes, 1:5). 1H NMR (400 MHz, CDCl3): δ = 8.58
(d, J = 5.0 Hz, 2 H), 8.28 (s, 1 H), 7.59 (t, J = 6.8 Hz, 4 H), 7.28–
7.19 (m, 5 H), 6.87 (d, J = 8.6 Hz, 2 H), 6.75 (t, J = 8.0 Hz, 2 H),
3.73 (t, J = 6.7 Hz, 4 H), 3.21 (t, J = 6.7 Hz, 4 H) ppm. 13C NMR
(100 MHz, CDCl3): δ = 159.0, 150.4, 143.9, 137.1, 131.8, 127.5,
127.6, 126.5, 119.6, 116.5, 112.4, 49.5 ppm. IR (neat): ν = 3253.7,
˜
3070.1, 2833.1, 1604.2, 1552.2, 1497.0, 1438.5, 1421.0, 1386.8,
1347.2, 1310.9, 1247.7, 1194.7, 1151.4, 1130.5, 1109.8, 1082.8,
1046.3, 964.3, 938.4, 811.2, 770.1, 753.43, 738.3 cm–1. HRMS
+
(+ESI): m/z calcd. for C32H27N6 495.2297; found 495.2338.
2,2Ј-Bis[N,NЈ-(2-benzyl)methyl]diaminoazobenzene (AzoAMB, 10):
DAAB (100 mg, 0.47 mmol), benzaldehyde (96 μL, 0.94 mmol),
and NaBH(OAc)3 (250 mg, 1.2 mmol) were combined in CH2Cl2
(15 mL) and stirred at 23 °C for 24 h. The reaction was quenched
by adding water (10 mL), the organic layer was separated, dried
with MgSO4, and the solvent was removed under vacuum. Flash
chromatography on silica (EtOAc/hexanes, 1:19) gave 10 (140 mg,
76%) as a bright-orange solid; m.p. 133–135 °C; Rf = 0.35 (silica;
123.4, 116.5, 112.2, 43.0, 38.0 ppm. IR (neat): ν = 3323.9, 3070.2,
˜
3006.4, 2926.5, 1595.0, 1566.4, 1504.0, 1472.5, 1433.1, 1363.6,
1318.9, 1308.1, 1287.3, 1246.9, 1210.9, 1172.9, 1144.8, 1113.8,
1095.0, 1075.7, 1042.5, 1002.5, 994.0, 880.8, 856.6, 834.0, 794.2,
1
EtOAc/hexanes, 1:4). H NMR (400 MHz, CDCl3): δ = 8.57 (s, 2
H), 7.61 (dd, J = 8.0, 1.3 Hz, 2 H), 7.41–7.30 (m, 10 H), 7.23 (t, J
= 7.6 Hz, 2 H), 6.78–6.74 (m, 4 H), 4.49 (s, 4 H) ppm. 13C NMR
(100 MHz, CDCl3): δ = 143.3, 139.0, 136.7, 131.7, 128.9, 127.9,
+
768.8, 736.6 cm–1. HRMS (+ESI): m/z calcd. for C26H26N6
423.2297; found 423.2279.
127.5, 127.5, 116.5, 112.4, 47.4 ppm. IR (neat): ν = 3234.8, 3064.0,
˜
2,2Ј-Bis[N,NЈ-(2-picolinamide)]diaminoazobenzene (AzoAP, 8): A
suspension of picolinic acid (240 mg, 2.0 mmol) in CH2Cl2 (7 mL)
was cooled to 0 °C and N-methylmorpholine (220 μL, 2.0 mmol)
and benzotriazol-1-yl-oxytripyrrolidinophosphonium hexafluoro-
phosphate (PyBOP, 520 mg, 1.0 mmol) were added. The reaction
mixture was warmed to room temperature and stirred for an ad-
ditional 12 h. The reaction mixture was treated with a solution of
DAAB (210 mg, 1.0 mmol) in DMF (5 mL) and stirred for another
3034.1, 2874.9, 2839.9, 1886.4, 1680.7, 1606.8, 1558.2, 1503.5,
1458.6, 1449.2, 1419.7, 1363.1, 1327.8, 1315.1, 1303.0, 1239.4,
1221.1, 1201.2, 1152.1, 1124.8, 1082.2, 1066.0, 1043.3, 1028.2,
932.2, 908.0, 870.3, 844.3, 831.4, 778.8, 733.6, 696.4 cm–1. HRMS
+
(+ESI): m/z calcd. for C26H24N4 393.2079; found 393.2048.
2,2Ј-Bis[N,NЈ-(2-furanyl)methyl]diaminoazobenzene (AzoAMF, 11):
DAAB (300 mg, 1.4 mmol), 2-furaldaldehyde (300 mg, 3.1 mmol),
4800
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Eur. J. Org. Chem. 2013, 4794–4803