6-Dialkylaminobenzimidazole nonlinear optical dyes

Article abstract of DOI:10.1080/00397911.2011.564342

(Chemical Equation Presented) A new 6-dialkylaminobenzimidazole nonlinear optical dye was synthesized in eight linear steps with an overall yield of 16%.

Full text of DOI:10.1080/00397911.2011.564342

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6-Dialkylaminobenzimidazole Nonlinear
Optical Dyes
Matthew C. Davis a & Thomas J. Groshens a
a Chemistry and Materials Division, Michelson Laboratory, Naval Air
Warfare Center, China Lake, California, USA
Accepted author version posted online: 31 Oct 2011.Version of
record first published: 29 May 2012.
To cite this article: Matthew C. Davis & Thomas J. Groshens (2012): 6-Dialkylaminobenzimidazole
Nonlinear Optical Dyes, Synthetic Communications: An International Journal for Rapid Communication
of Synthetic Organic Chemistry, 42:18, 2664-2675
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Synthetic Communications1, 42: 2664–2675, 2012
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2011.564342
6-DIALKYLAMINOBENZIMIDAZOLE NONLINEAR
OPTICAL DYES
Matthew C. Davis and Thomas J. Groshens
Chemistry and Materials Division, Michelson Laboratory,
Naval Air Warfare Center, China Lake, California, USA
GRAPHICAL ABSTRACT
Abstract A new 6-dialkylaminobenzimidazole nonlinear optical dye was synthesized in eight
linear steps with an overall yield of 16%.
Keywords Benzimidazole; chromophore; nonlinear optical
INTRODUCTION
As part of a program to discover new organic nonlinear optical dyes for
electrooptic devices,[1] three polymethine, ‘‘push–pull’’ dyes (1–3) based on a benzimi-
dazole ring system were synthesized (Fig. 1). These dyes are composed of one to three
olefin linkages between the electron donor di-n-butylaminophenyl group and the elec-
tron acceptor at each end of the molecule. The electron acceptors used to complete the
dyes were 2-dicyanomethylene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran (TCF)[2]
and 2,4-bis(trichloromethyl)-6-methyl-1,3,5-triazine (TMT).[3,4]
The synthesis started by selective nucleophilic aromatic substitution of 2,4-
difluoronitrobenzene with isobutylamine to give 4 (Scheme 1).[5–9] The second fluor-
ine atom was then displaced by dibutylamine to give intermediate 5. Single-crystal
x-ray analysis of 5 proved the desired sequence of fluorine substitution was the case
(Fig. 2). The nitro group of 5 was reduced by catalytic hydrogenation, and the oxi-
datively sensitive triaminobenzene 6 was immediately reacted with trimethyl ortho-
formate to form the benzimidazole 7.[10] The latter reaction would not take place
without the presence of a small amount of catalyst, p-toluenesulfonic acid. Lithiation
followed by formylation of 7 was accomplished at ꢀ78 ꢁC to give the aldehyde 8 in
Received December 30, 2010.
This article is not subject to U.S. copyright laws.
Address correspondence to Matthew C. Davis, Chemistry and Materials Division, Michelson
Laboratory, Naval Air Warfare Center, China Lake, CA 93555, USA. E-mail: matthew.davis@navy.mil
2664

6-DIALKYLAMINOBENZIMIDAZOLE
2665
Figure 1. Structures of dyes synthesized.
excellent yield.[11–14] Aldol condensation of aldehyde 8 with isophorone gave the
ketone 9.
Reaction of ketone 9 with lithioacetonitrile[15–17] at ꢀ78 ꢁC with a crucial
quench at this temperature[18] gave the tertiary alcohol 10 as a mixture of diastereo-
mers (Scheme 2). Dehydration of 10 with hot acetic acid gave the unsaturated nitrile
11 as a mixture of geometric isomers in good yield.[19] Unfortunately, all attempts to
reduce nitrile 11 to aldehyde 12 using diisobutylaluminum hydride (DIBAL) at
ꢀ78 ꢁC were unsuccessful. Although esters have been reduced successfully with
DIBAL, or even lithium aluminum hydride, in the presence of a benzimidazole,[20,21]
a literature survey found that this heterocycle typically undergoes reductive cleavage
with these reagents.[22–24] Thus, ketone 9 was reacted with the lithium imine anion of
N-cyclohexylacetimine, which after aqueous acid hydrolysis gave the desired alde-
hyde 12. To complete the syntheses, condensation of aldehydes 8 and 12 with either
Scheme 1. Synthesis of benzimidazole template.

2666
M. C. DAVIS AND T. J. GROSHENS
Figure 2. X-ray structure of 5.
TCF or TMT acceptors gave the dyes 1–3 (Scheme 3). Although the aldehydes 8 and
12 were mixtures of E and Z isomers, the dye products 1 and 2 were shown to have
exclusively E alkene geometry by proton nuclear magnetic resonance spectroscopy.[25]
Scheme 2. Homologation of ketone 9.

6-DIALKYLAMINOBENZIMIDAZOLE
2667
Scheme 3. Completion of dye syntheses.
EXPERIMENTAL
The melting points were collected on a Mel-Temp II from Laboratory Devices
(Holliston, MA) and are not corrected. All NMR data were collected on a Bruker
Avance II 300-MHz spectrometer (1H at 300 MHz, 13C at 75 MHz, 19F at
282 MHz). Nuclear magnetic resonance data (free-induction decays) were processed
using NUTS software from Acorn NMR (Livermore, CA). All spectra are referenced
to solvent, tetramethylsilane or fluorotrichloromethane (in the case of 19F). The
ultraviolet–visible absorbance spectra for the dyes were obtained with a Cary 5
NIR-vis-UV spectrophotometer and quartz cuvettes. Elemental analyses were
performed by Atlantic Microlab, Inc. (Norcross, GA). Piperidinium acetate,[25]
N-cyclohexylacetimine,[25] and the TCF[2] acceptor were prepared according to litera-
ture procedures. All other reagents were obtained commercially and used as received.
N-iso-Butyl-2-nitro-5-fluoroaniline (4)
A 500-mL, round-bottomed flask equipped with magnetic stirring bar and ther-
mometer was charged with 57.85 g 2,4-difluoronitrobenzene (0.36 mol), 40.44 g TEA
(0.4 mol, 1.1 equiv), and 40 mL H2O. The mixture was stirred in an ice bath while
29.3 g iso-butylamine and (39.6 mL, 0.4 mol, 1.1 equiv) was added over 2 h, keeping
the internal temperature below 50 ꢁC. After stirring at rt for 2 h, the reaction was com-
plete by thin-layer chromatography (TLC). Ether (200 mL) was added, and the phases
were separated. The organic layer was washed with 100 mL H2O followed by 100 mL
brine. After drying over anhydrous MgSO4, the volatiles were rotary evaporated, leav-
ing the crude product as an orange oil. Reduced pressure distillation (1 torr) gave
76.13 g of the title compound in analytically pure form (94%). dH (CDCl3): 8.28 (bs,
NH), 8.20 (dd, J ¼ 9.4 and 6.1 Hz, 1H), 6.47 (dd, J ¼ 11.6 and 2.5 Hz, 1H), 6.34 (m,
1H), 3.08 (dd, J ¼ 7.0 and 5.3 Hz, 2H), 2.02 (hept, J ¼ 6.7 Hz, 1H), 1.06 (d, J ¼ 6.7 Hz,
Hz, 6H); dC (CDCl3): 169.49, 166.09, 147.94 (d, JCF ¼ 13.3 Hz), 130.19 (d,
JCF ¼ 12.5 Hz), 128.99, 130.93 (d, JCF ¼ 25.1 Hz), 99.46 (d, JCF ¼ 27.0 Hz), 51.11,
28.02, 20.51; dF (CDCl3): ꢀ100.1. Elemental analysis calculated for C10H13FN2O2:
C, 56.60; H, 6.17; N, 13.20. Found: C, 56.79; H, 6.19; N, 13.29.
N-iso-Butyl-2-nitro-5-(di-n-butylamino)aniline (5)
A 1-L, round-bottomed flask equipped with magnetic stirbar and reflux con-
denser was charged with 70.5 g 4 (333 mmol), 128.7 g dibutylamine (0.99 mmol, 3

2668
M. C. DAVIS AND T. J. GROSHENS
equiv), 45 g anhydrous K2CO3, and 100 mL N,N-dimethylacetamide (DMAC). The
1
mixture was refluxed for 18 h when the reaction was complete by H NMR. Water
(100 mL) was added, and while stirring the product spontaneously crystallized from
the upper layer of dibutylamine. The mixture was filtered through a coarse-porosity
glass frit to give 95.6 g of the title compound as a bright yellow, microcrystalline
powder (89%). The solid could be further purified by recrystallization from hexanes.
Mp 60–62 ꢁC. dH (CDCl3): 8.59 (t, J ¼ 4.7 Hz, NH), 8.04 (d, J ¼ 9.8 Hz, 1H), 6.04
(dd, J ¼ 9.5 and 2.6 Hz, 1H), 5.61 (d, J ¼ 2.9 Hz, 1H), 3.33 (dd, J ¼ 9.9 and 6.7 Hz,
4H), 3.05 (dd, J ¼ 6.8 and 5.4 Hz, 2H), 2.03 (hept, J ¼ 6.9 Hz, 1H), 1.61 (pent,
J ¼ 7.2 Hz, 4H), 1.38 (hex, J ¼ 7.8 Hz, 4H), 1.04 (d, J ¼ 6.8 Hz, 6H), 0.98 (t,
J ¼ 7.3 Hz, 6H); dC (CDCl3): 153.82, 148.35, 129.46, 123.14, 103.14, 90.49, 51.22,
50.89, 29.79, 27.98, 20.71, 20.47, 14.07. Elemental analysis calculated for
C18H31N3O2: C, 67.25; H, 9.72; N, 13.07. Found: C, 67.42; H, 9.71; N, 13.07.
2-iso-Butylamino-4-(di-n-butylamino)aniline (6)
A mixture of 52.25 g 5 (40 mmol), 2 g 5% Pd=C, and 700 mL EtOH containing
3 mL HOAc was hydrogenated (50 psi) on a Parr apparatus for 5 h. The reaction
mixture was taken off the hydrogenation apparatus and protected with N2 as far
as possible, as the product develops a purple color when exposed to air. After filter-
ing through diatomaceous earth to remove the catalyst, the mixture was rotary
evaporated, leaving 47 g of the crude product as a brownish oil (99%). No further
purification was performed before use in the next step, and the molecule was too
oxidatively sensitive to give accurate combustion analyses. dH (DMSO): 6.43
(d, J ¼ 8.1 Hz, 1H), 5.90 (d, J ¼ 2.6 Hz, 1H), 5.85 (dd, J ¼ 8.4 and 2.7 Hz, 1H),
4.37 (t, J ¼ 5.5 Hz, NH), 3.85 (bs, NH2), 3.05 (t, J ¼ 7.5 Hz, 4H), 2.83 (t, J ¼
6.0 Hz, 2H), 1.88 (hept, J ¼ 6.8 Hz, 1H), 1.43 (m, 4H), 1.30 (m, 4H), 0.95 (d, J ¼
6.6 Hz, 6H), 0.89 (t, J ¼ 7.2 Hz, 6H); dC (DMSO): 142.21, 137.89, 125.73, 116.15,
102.87, 98.58, 51.54, 51.38, 29.29, 27.19, 20.45, 19.82, 13.80.
6-(Di-n-butylamino)-1-iso-butyl-1H-benzimidazole (7)
A 250-mL, round-bottomed flask equipped with magnetic stirbar and N2 bub-
bler was charged with 47 g 6 (39 mmol), 179 mL DMAC, 25.6 g trimethyl orthofor-
mate (59 mmol, 1.5 equiv), and 700 mg of p-toluenesulfonic acid monohydrate
(1 mmol, 2.5 mol%). The mixture was heated to 80 ꢁC for 1 h. After this time, the
reaction was complete by NMR. The mixture was partitioned between 500 mL
Et2O and 500 mL H2O. The organic layer was separated and washed with 300 mL
saturated aqueous NaHCO3 and finally 500 mL brine. After drying the organic layer
over anhydrous MgSO4, the solvent was rotary evaporated, leaving a thick dark oil.
The crude product was distilled at reduced pressure (0.1 torr) to give 47.76 g of the
title compound as a viscous, pale yellow oil (97%). dH (CDCl3): 7.65 (s, 1H), 7.60
(d, J ¼ 8.7 Hz, 1H), 6.76 (dd, J ¼ 9.0 and 2.2 Hz, 1H), 6.49 (d, J ¼ 2.3 Hz, 1H),
3.86 (d, J ¼ 7.1 Hz, 2H), 3.31 (t, J ¼ 7.6 Hz, 4H), 2.21 (hept, J ¼ 7.1 Hz, 1H), 1.60
(pent, J ¼ 7.1 Hz, 4H), 1.38 (hex, J ¼ 7.6 Hz, 4H), 1.00–0.93 (m, 12H); dC (CDCl3):
145.92, 141.59, 135.85, 135.72, 120.55, 110.55, 92.57, 52.49, 51.99, 29.60, 29.15,

6-DIALKYLAMINOBENZIMIDAZOLE
2669
20.59, 20.41, 14.16. Elemental analysis calculated for C19H31N3: C, 75.70; H, 10.36;
N, 13.94. Found: C, 75.45; H, 10.46; N, 14.03.
6-(Di-n-butylamino)-1-iso-butyl-1H-benzimidazole-2-
carboxaldehyde (8)
A 250-mL, round-bottomed flask equipped with magnetic stirring bar, 25-mL
addition funnel, and N2 bubbler was charged with 2.86 g (9.5 mmol) 7 and 50 mL
anhydrous THF. The mixture was stirred in a dry ice=acetone bath. The addition
funnel was charged with 7.6 mL 2.5 M butyllithium in hexanes (19 mmol, 2 equiv)
which was added dropwise in 10 min. After the addition, the mixture was allowed
to warm to -20 ꢁC and held at this temperature for 30 min. The mixture was then
cooled back down with the dry ice=acetone bath before 2.08 g anhydrous dimethyl-
formamide (DMF; 28.5 mmol, 3 equiv) was added dropwise over 10 min. After stir-
ring for 30 min, the cooling bath was removed and the mixture was allowed to warm
to rt over 2 h. Water (100 mL) was added along with 30 mL saturated aqueous
NH4Cl. After stirring for 30 min, the mixture was extracted with three 50-mL
portions of Et2O. The organic phases were collected and washed with 25 mL H2O
followed by 25 mL brine. The organic phase was dried over anhydrous MgSO4
and rotary evaporated to 2.9 g of an orange oil (95%), which slowly crystallized to
a low-melting, yellow solid. No further purification was necessary for the subsequent
step. dH (CDCl3): 9.92 (s, 1H), 7.69 (d, J ¼ 9.2 Hz, 1H), 6.87 (dd, J ¼ 9.2 and 2.3 Hz,
1H), 6.31 (d, J ¼ 2.3 Hz, 1H), 4.32 (d, J ¼ 7.2 Hz, 2H), 3.37 (t, J ¼ 7.7 Hz, 4H), 2.23
(hept, J ¼ 7.2 Hz, 1H), 1.63 (pent, J ¼ 7.2 Hz, 4H), 1.40 (hext, J ¼ 7.7 Hz, 4H), 0.99 (t,
J ¼ 7.2 Hz, 6H), 0.95 (d, J ¼ 6.7 Hz, 6H); dC (CDCl3): 183.41, 148.35, 145.48, 139.48,
135.66, 123.04, 113.35, 89.76, 51.68, 51.66, 29.76, 29.59, 20.57, 20.35, 14.17. Elemen-
tal analysis calculated for C20H31N3O: C, 72.91; H, 9.48; N, 12.75. Found: C, 72.78;
H, 9.52; N, 12.68.
(E)-3-(2-(6-(Di-n-butylamino)-1-iso-butyl-1H-benzimidazole-
2-yl)vinyl)-5,5-dimethylcyclohex-2-enone Hydrate (9)
A 50-mL, round-bottomed flask equipped with a magnetic stirring bar was
charged with 3.0 g 8 (9.1 mmol), 1.38 g isophorone (10 mmol, 1.1 equiv), and 20 mL
EtOH. In one portion, a solution of 200 mg NaOH (5 mmol) in 0.5 mL H2O was
added, and the mixture was heated to reflux for 25 min. After this time, the reaction
was complete by TLC. Water (20 mL) was added, causing a red precipitate to form.
The mixture was filtered on a medium-porosity glass frit to give the title compound
in crude form as a brick red powder. Recrystallization from heptane gave 2.8 g of the
title compound as bright red needles (70%). Mp 114–116 ꢁC. dH (CDCl3): 7.63 (d,
J ¼ 15.4 Hz, 1H), 7.58 (d, J ¼ 9.2 Hz, 1H), 6.88 (d, J ¼ 15.4 Hz, 1H), 6.78 (dd,
J ¼ 8.7 and 1.9 Hz, 1H), 6.37 (d, J ¼ 1.4 Hz, 1H), 6.22 (s, 1H), 3.95 (d, J ¼ 6.8 Hz,
2H), 3.34 (t, J ¼ 7.7 Hz, 4H), 2.46 (s, 2H), 2.34 (s, 2H), 2.21 (hept, J ¼ 7.2 Hz, 1H),
1.62 (pent, J ¼ 7.7 Hz, 4H), 1.40 (hex, J ¼ 7.7 Hz, 4H), 1.14 (s, 6H), 1.06–0.92 (m,
12H); dC (CDCl3): 200.19, 153.76, 147.59, 146.34, 137.81, 135.63, 134.42, 128.34,
120.46, 119.61, 111.72, 91.34, 51.85, 51.68, 50.94, 39.44, 33.62, 29.92, 29.68, 28.74,

2670
M. C. DAVIS AND T. J. GROSHENS
20.69, 20.62, 14.21. Elemental analysis calculated for C29H43N3O ꢂ 0.75 H2O: C,
75.13; H, 9.60; N, 9.07. Found: C, 75.02; H, 9.81; N, 8.90.
3’-(2-(6-(Di-n-butylamino)-1-iso-butyl-1H-benzimidazole-
2-yl)vinyl)-5’,5’-dimethylcyclohex-2’-ene-1’-hydroxyacetonitrile (10)
A 500-mL, round-bottomed flask equipped with magnetic stirring bar, addition
funnel, and N2 bubbler was charged with 4.43 g anhydrous MeCN (108 mmol, 5
equiv) and 40 mL anhydrous THF. The solution was cooled in a dry ice acetone
bath. The addition funnel was charged with 37.8 mL 2.3 M hexyllithium in hexanes
(87 mmol, 4 equiv), which was then added dropwise over 30 min. A precipitate
formed during this time. A clean addition funnel containing a solution of 9.74 g 9
(22 mmol) in 20 mL anhydrous THF was attached, which was added dropwise over
15 min. The reaction mixture was stirred another 30 min in the cooling bath. Then,
10 mL saturated aqueous NH4Cl was added dropwise, and the cooling bath was
removed. After stirring at rt for 2 h, the reaction mixture was diluted with 250 mL
H2O and extracted with EtOAc (3 ꢃ 100 mL). The organic extracts were collected
and washed again with 250 mL H2O followed by 250 mL brine. After drying over
anhydrous MgSO4, the solvent was rotary evaporated, leaving a yellow-orange solid.
Recrystallization from heptane gave the title compound as pale yellow leaflets (9 g,
85%). Mp 125–127 ꢁC. dH (CDCl3): 7.50 (d, J ¼ 8.2 Hz, 1H), 7.47 (d, J ¼ 15.6 Hz,
1H), 6.69 (d, J ¼ 8.9 Hz, 1H), 6.45 (d, J ¼ 15.6 Hz, 1H), 6.32 (bs, 1H), 5.92 (s, 1H),
3.83 (d, J ¼ 7.4 Hz, 2H), 3.60 (bs, 1 OH), 3.24 (t, J ¼ 7.4 Hz, 4H), 2.5 (d, J ¼ 16.3,
1H), 2.4 (d, J ¼ 16.3 Hz, 1H), 2.20–1.91 (m, 3H), 1.89 (d, J ¼ 13.7 Hz, 1H), 1.66 (d,
J ¼ 13.7 Hz, 1H), 1.52 (m, 4H), 1.38–1.20 (m, 4H), 1.04 (d, J ¼ 7.2 Hz, 6H),
0.96–0.75 (m, 12H); dC (CDCl3): 148.47, 145.87, 137.93, 137.82, 137.12, 134.10,
132.54, 119.49, 117.45, 113.85, 111.58, 92.13, 69.57, 63.18, 52.06, 50.94, 47.83,
38.48, 33.09, 32.99, 32.11, 31.84, 31.77, 31.28, 30.54, 30.22, 29.88, 29.84, 29.76,
29.57, 29.54, 27.73, 25.63, 22.87, 22.83, 22.81, 20.64, 20.58, 14.27, 14.17. Elemental
analysis calculated for C31H46N4O: C, 75.87; H, 9.45; N, 11.42. Found: C, 75.87;
H, 9.25; N, 11.65.
(E and Z)-3-(2-(6-(Di-n-butylamino)-1-iso-butyl-1H-benzimidazole-
2-yl)vinyl)-5,5-dimethylcyclohex-2-enylidene)acetonitrile (11)
A 250-mL, round-bottomed flask equipped with magnetic stirring bar and
reflux condenser was charged with 9 g 10 (18 mmol) and 75 mL glacial HOAc. The
mixture was refluxed for 2 h whereby the reaction was complete by TLC. Rotary
evaporation of the HOAc gave the crude product as a red oil. Recrystallization from
hexanes gave the title compound as garnet-colored crystals (7.6 g, 90%). Mp
114–116 ꢁC. dH (CDCl3): 7.59 (d, J ¼ 15.5 Hz, 1H), 7.52 (d, J ¼ 9.1 Hz, 1H), 6.84
(s, 1H), 6.71 (d, J ¼ 8.4 Hz, 1H), 6.60 (d, J ¼ 15.5 Hz, 1H), 6.32 (bs, 1H), 4.95 (s,
1H), 3.86 (d, J ¼ 7.8 Hz, 2H), 3.26 (t, J ¼ 7.8 Hz, 4H), 2.29–2.03 (m, 5H), 1.54 (pent,
J ¼ 6.5 Hz, 4H), 1.31 (hext, J ¼ 7.1 Hz, 4H), 0.99–0.85 (m, 18H); dC (CDCl3): 157.10,
148.32, 146.12, 144.07, 137.55, 135.99, 126.93, 120.13, 117.15, 116.52, 111.63, 93.64,
91.58, 51.98, 50.93, 44.72, 39.15, 31.42, 29.85, 29.56, 28.29, 20.66, 20.58, 14.16.

6-DIALKYLAMINOBENZIMIDAZOLE
2671
Elemental analysis calculated for C31H44N4: C, 78.77; H, 9.38; N, 11.85. Found: C,
78.59; H, 9.20; N, 11.79.
(E and Z)-3-(2-(6-(Di-n-butylamino)-1-iso-butyl-1H-benzimidazole-
2-yl)vinyl)-5,5-dimethylcyclohex-2-enylidene)acetaldehyde (12)
A 500-mL, round-bottomed flask equipped with magnetic stirring bar was
charged with 100 mL Et2O and 1.88 g diisopropylamine (19 mmol, 2.1 equiv). The
mixture was cooled in an ice bath, and 8.09 mL 2.3 M hexyllithium (19 mmol, 2.1
equiv) in hexanes was added by syringe. After stirring 10 min, the mixture was cooled
to ꢀ78ꢁC, and 2.32 g N-cyclohexylacetimine (19 mmol, 2.1 equiv) was added drop-
wise over 15 min. After stirring for 1 h, a solution of 3.97 g 9 (9 mmol) in 20 mL anhy-
drous THF was added over 20 min. After the addition, the cooling bath was
removed, and the mixture was stirred at rt for 3 h. The mixture was cooled in an
ice bath, and 2.32 g HOAc was added dropwise in 5 min followed by a solution of
2.34 g oxalic acid dihydrate in 100 mL H2O. The mixture was stirred at rt overnight.
The organic phase was separated and washed with 100 mL H2O followed by 100 mL
brine. After drying over anhydrous MgSO4, the solvent was rotary evaporated, leav-
ing a red oil. Silica-gel chromatography (25% EtOAc in hexanes) gave 2.44 g of the
title compound as a dark red semisolid. The oil was triturated with hexanes to give
the product as a brick-red powder (58%) which is a 70:30 mixture of E/Z geometric
isomers based on NMR. Mp 104–106 ꢁC. dH (CDCl3): 10.22 (d, J ¼ 8.3 Hz, 1H,
trans), 10.08 (d, J ¼ 8.3 Hz, 1H, cis), 7.66 (d, J ¼ 15.3 Hz, 1H, trans), 7.62 (d,
J ¼ 15.6 Hz, 1H, cis), 7.57 (d, J ¼ 8.9 Hz, 1H), 7.38 (s, 1H), 6.78 (dd, J ¼ 9.2 and
2.2 Hz, 1H), 6.68 (d, J ¼ 15.6 Hz, 1H, trans), 6.66 (d, J ¼ 15.6 Hz, 1H, cis), 6.47 (s,
1H, cis), 6.38 (s, 1H, trans), 5.97 (d, J ¼ 8.4 Hz, 1H, cis), 5.77 (d, J ¼ 8.4 Hz, 1H,
trans), 3.93 (d, J ¼ 7.2 Hz, 2H), 3.33 (t, J ¼ 8.1 Hz, 4H), 2.69 (s, 1H), 2.31 (mult,
3H), 2.21 (hex, J ¼ 5.9 Hz, 1H), 1.62 (pent, J ¼ 6.8 Hz, 4H), 1.39 (hex, J ¼ 7.5 Hz,
4H), 1.08 (s, 6H, cis), 1.06 (s, 6H, trans), 1.00 (d, J ¼ 6.5 Hz, 6H), 0.98 (t, J ¼ 7.3 Hz,
Hz, 6H); dC (CDCl3): 190.84, 189.70, 155.65, 155.48, 148.32, 146.02, 144.49, 144.35,
137.61, 136.23, 135.29, 132.52, 128.19, 126.40, 124.97, 120.08, 120.03, 116.29, 116.08,
111.47, 91.48, 51.88, 50.87, 46.17, 39.37, 39.12, 38.96, 31.39, 31.28, 29.84, 29.60,
28.59, 28.46, 20.69, 20.60, 14.22. Elemental analysis calculated for C31H45N3O: C,
78.27; H, 9.53; N, 8.83. Found: C, 78.50; H, 9.79; N, 8.69.
(E)-2-(3-Cyano-4-(3-(3-((E)-2-(6-(di-n-butylamino)-1-iso-butyl-1H-
benzimidazole-2-yl))vinyl)-5,5-dimethylcyclohex-2-enylidene)prop-
1-enyl)-5,5-dimethylfuran-2(5H)-ylidene)malononitrile (1)
A 250-mL, round-bottomed flask equipped with magnetic stirring bar was
charged with 4.14 g 12 (8.7 mmol), 1.3 g TCF acceptor (6.5 mmol, 0.75 equiv), and
50 mL CH2Cl2. After all the solids dissolved, 940 mg piperidinium acetate (6.5 mmol,
0.75 equiv) was added in one portion. The mixture quickly became dark green and
viscous and was stirred at rt for 1 h. The solvent was rotary evaporated, leaving a
crude black oil. This residue was suspended in 40 mL EtOH, whereupon the product
precipitated. The mixture was filtered on a medium-porosity glass frit, and the filter
cake washed twice with 10-mL portions of EtOH. After air-drying on the frit, 2.3 g of

2672
M. C. DAVIS AND T. J. GROSHENS
the title compound (54%) was obtained analytically pure as a dark purple powder.
kmax ¼ 672 nm (toluene). dH (CDCl3): 7.98 (dd, J ¼ 15.0 and 12.0 Hz, 1H), 7.71 (bs,
1H), 7.52 (d, J ¼ 9.5 Hz, 1H), 6.72 (d, J ¼ 8.7 Hz, 1H), 6.58 (d, J ¼ 15.0 Hz, 1H),
6.52 (s, 1H), 6.36 (d, J ¼ 12.6 Hz, 1H), 6.28 (s, 1H), 6.22 (d, J ¼ 15.0 Hz, 1H), 3.89
(d, J ¼ 7.7 Hz, 2H), 3.29 (t, J ¼ 7.7 Hz, 4H), 2.38 (s, 2H), 2.30 (s, 2H), 2.14 (pent,
J ¼ 6.4 Hz, 1H), 1.62 (s, 6H), 1.55 (m, 4H), 1.32 (hext, J ¼ 7.7 Hz, 4H), 1.01 (s, 6H),
0.94 (d, J ¼ 6.6 Hz, 6H), 0.91 (t, J ¼ 7.3 Hz, 6H); dC (CDCl3): 176.10, 173.29, 153.33,
148.39, 146.24, 145.56, 143.54, 137.95, 135.83, 135.40, 133.56, 129.79, 120.21, 117.10,
116.94, 112.47, 111.85, 111.67, 111.62, 97.24, 95.59, 91.18, 56.19, 51.82, 50.87, 39.89,
39.29, 31.59, 29.89, 29.68, 28.69, 26.51, 20.73, 20.70, 20.63, 14.23. Elemental analysis
calculated for C42H52N6O: C, 76.79; H, 7.98; N, 12.79. Found: C, 76.58; H, 8.00; N,
12.57.
2,4-Bis(trichloromethyl)-6-methyl-1,3,5-triazine (TMT)
A 100-mL, round-bottomed flasked was charged with 10 g trichloroacetonitrile
(6.9 mL, 69 mmol, 2.1 equiv), 1.35 g MeCN (33 mmol), and 4.7 g boron trifluoride
etherate (33 mmol). The mixture was cooled in an ice bath and saturated with HCl(g)
for 15 min. The mixture was stoppered and allowed to stand for 2 days. The solid
mixture was partitioned between H2O and Et2O. The organic phase was rotary eva-
porated, and the remaining residue was recrystallized from EtOH, giving the title
compound as a white, microcrystalline powder (6 g, 55%). Mp 93–96 ꢁC (lit.[26]
96–97 ꢁC); dH (CDCl3): 2.97 (s); dC (CDCl3): 181.38, 174.89, 94.79, 26.31. Elemental
analysis calculated for C6H3Cl6N3: C, 21.85; H, 0.92; N, 12.74. Found: C, 21.89; H,
0.86; N, 12.72.
(E)-2,4-Bis(trichloromethyl)-6-(3-(3-((E)-2-(6-(di-n-butylamino)-1-iso-
butyl-1H-benzimidazole-2-yl))vinyl)-5,5-dimethylcyclohex-2-
enylidene)prop-1-enyl)-1,3,5-triazine (2)
A 200-mL, round-bottomed flask equipped with magnetic stirring bar and
reflux condenser was charged with 1.26 g 12 (2.7 mmol), 0.87 g TMT (2.7 mmol, 1
equiv), and 50 mL CH2Cl2. In one portion, 0.38 g piperidinium acetate (2.7 mmol,
1 equiv) was added, and the mixture was refluxed for 30 min. The mixture was cooled
to rt and rotary evaporated, leaving a dark semisolid. Trituration of the residue with
25 mL EtOH gave a dark precipitate. The mixture was filtered on a medium-porosity
glass fritted filter funnel. After air-drying on the frit, the title compound was
obtained as a dark purple, microcrystalline powder. Recrystallization from i-PrOH
gave the title compound as fine black, iridescent needles (61%). kmax ¼ 436 nm
(CH2Cl2). dH (CDCl3): 8.37 (dd, J ¼ 14.7 and 14.2 Hz, 1H), 7.74 (bs, 1H), 7.55 (d,
J ¼ 8.6 Hz, 1H), 6.78–6.67 (m, 2H), 6.58–6.39 (m, 3H), 6.29 (s, 1H), 3.89 (d, J ¼
6.4 Hz, 2H), 3.27 (t, J ¼ 7.8 Hz, 4H), 2.43 (s, 2H), 2.25 (s, 2H), 2.16 (hept, J ¼ 7.1 Hz,
Hz, 1H), 1.55 (m, 4H), 1.32 (hext, J ¼ 7.2 Hz, 4H), 1.03 (s, 6H), 0.95 (d, J ¼ 6.7 Hz,
6H), 0.91 (t, J ¼ 7.3 Hz, 6H); dC (CDCl3): 174.98, 174.58, 148.80, 148.60, 146.12,
142.71, 141.79, 137.35, 134.58, 129.13, 127.00, 119.66, 114.17, 111.62, 95.33, 77.45,
51.93, 50.94, 39.53, 39.22, 31.21, 29.83, 29.59, 28.72, 20.71, 20.61, 14.23. Elemental

6-DIALKYLAMINOBENZIMIDAZOLE
2673
analysis calculated for C37H46Cl6N6: C, 56.43; H, 5.89; N, 10.67. Found: C, 55.80; H,
5.97; N, 10.44.
(E)-2-(3-Cyano-4-(2-(6-(di-n-butylamino)-1-iso-butyl-1H-
benzimidazole-2-yl))vinyl)-5,5-dimethylfuran-2(5H)-
ylidene)malononitrile (3)
A 50-mL, round-bottomed flask equipped with magnetic stirring bar charged
with 1.16 g 8 (3.5 mmol), 697 mmol TCF acceptor (3.5 mmol, 1 equiv), 500 mg
(3.5 mmol, 1 equiv), and 10 mL EtOH was refluxed for 30 min. After cooling, the pre-
cipitate was filtered on a medium-porosity glass frit to give metallic-green needles
from EtOH (1 g, 59%). Mp 239–241 ꢁC. kmax ¼ 559 nm (CH2Cl2). dH (CDCl3): 8.31
(d, J ¼ 15.0 Hz, 1H), 7.61 (d, J ¼ 9.3 Hz, 1H), 7.25 (d, J ¼ 15.5 Hz, 1H), 6.89 (dd,
J ¼ 9.5 and 2.1 Hz, 1H), 6.25 (d, J ¼ 2.1 Hz, 1H), 3.99 (d, J ¼ 8.0 Hz, 2H), 3.39 (t,
J ¼ 8.0 Hz, 4H), 2.21 (pent, J ¼ 7.0 Hz, 1H), 1.71 (s, 6H), 1.64 (m, 4H), 1.41 (hext,
J ¼ 7.4 Hz, 4H), 1.01 (d, J ¼ 6.2 Hz, 6H), 0.99 (t, J ¼ 7.4 Hz, 6H); dC (CDCl3):
176.30, 172.76, 148.17, 145.46, 139.62, 138.16, 130.82, 121.94, 114.87, 114.52,
112.72, 112.34, 111.56, 98.18, 95.01, 89.28, 77.44, 51.72, 51.34, 30.48, 29.75, 25.91,
20.59, 20.57, 14.18. Elemental analysis calculated for C31H38N6O ꢂ 0.5 EtOH: C,
72.01; H, 7.74; N, 15.75. Found: C, 72.22; H, 7.94; N, 15.41.
X-Ray Structure Determination of 5
CCDC 805891 (5) contains the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif, by e-mailing
data_request@ccdc.cam.ac.uk, or by contacting CCDC 12 Union Road, Cambridge
CB2 1EZ, UK; fax: þ44 1223 336033.
ACKNOWLEDGMENTS
Thanks go to Geoffrey A. Lindsay (NAWCWD) for advice and encourage-
ment throughout the course of this work and to Hakan Go¨ker (Ankara University)
for kindly providing ref. 23.
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