Maleimides designed for self-assembly and reactivity on graphene

Article abstract of DOI:10.3390/molecules201018856

Two new maleimide derivatives have been synthesized, prone to self-assemble and react with graphene as dienophiles. Both compounds bear a long alkyl chain on the carbon-carbon double bond position 3. The maleimide 1 bears a second alkyl chain at the nitro

Full text of DOI:10.3390/molecules201018856

Molecules 2015, 20, 18856-18869; doi:10.3390/molecules201018856
OPEN ACCESS
molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Maleimides Designed for Self-Assembly and Reactivity
on Graphene
Cristina Mattioli † and André Gourdon †,*
NanoSciences Group, Centre d’Elaboration de Matériaux et d’Etudes Structurales,
Centre National de la Recherche Scientifique, CEMES-CNRS, 29 rue Jeanne Marvig,
BP 94347, 31055, Toulouse Cedex 4, France; E-Mail: cristinamattioli7@gmail.com
†
These authors contributed equally to this work.
* Author to whom correspondence should be addressed; E-Mail: andre.gourdon@cemes.fr;
Tel.: +33-562-257-859; Fax: +33-562-257-999.
Academic Editor: Derek J. McPhee
Received: 26 August 2015 / Accepted: 13 October 2015 / Published: 16 October 2015
Abstract: Two new maleimide derivatives have been synthesized, prone to self-assemble and
react with graphene as dienophiles. Both compounds bear a long alkyl chain on the carbon-carbon
double bond position 3. The maleimide 1 bears a second alkyl chain at the nitrogen, while in
compound 2, three maleimide functionalities are linked to a triethynylbenzene core.
Keywords: maleimides; Diels-Alder; graphene
1. Introduction
Chemical functionalization of graphene is essential [1] for future practical applications of this attractive
material and it has been recently shown that its peculiar electronic structure allows it to react both as a
diene or a dienophile in Diels-Alder reaction, thus permitting a large variety of additions in relatively mild
conditions [2]. Current work in progress involves the [2 + 2] and [2 + 4] cycloadditions of several maleimides
with graphene on silicon carbide surfaces or with graphene flakes supported on silicon dioxide.
In this context, we recently synthesized the derivatives 1 and 2 where the dienophile groups are
functionalized maleimides.
Maleimides are a class of substrates arousing interest in many fields of application. Some derivatives
possess anticancer, antifungal, herbicidal, or pesticidal properties [3]. The most interesting type of reactivity

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is shown in Diels-Alder reactions [4,5], as dipolarophiles in 1,3-dipolar cycloadditions [6] or in Michael
additions. In particular, the high affinity towards the thiolic functions of the amino acid cysteine, renders
the maleimide core as a nice platform for protein recognition [7,8] or for the labelling with fluorescent
units [9]. The same maleimide backbone can show fluorescence properties, if bearing phenyl-substituents
on the carbon-carbon double bond [10,11]. Other applications see the employment of maleimides as curing
agents in epoxy resins [12] or reagents for radicalar polymerizations [13], as well as “active” chemical
functionalities in polymers, allowing for further attachment of different moieties through thio-ene [14,15]
or Diels-Alder reaction [16].
The first maleimide derivative of the series, 1, bears two alkyl chains –C12H25 directly connected to the
core at positions 1 and 3 (Figure 1). The position 4 is functionalized with a –CH3 group, deriving from the
particular synthetic strategy that was adopted. The presence of the two long alkyl chains should favour
the adsorption of the molecule on the surface, by establishment of CH-π interactions. At the same time,
1 is designed to allow a self-organization of the molecules in linear features on the graphene surface.
The second derivative, 2, presents a slightly more complex structure. The maleimide reactive groups are
born by a triethynylbenzene platform. This kind of aromatic core is chosen for two reasons: (1) it favors
the molecular adsorption on the surface thanks to π-π interactions; (2) it allows the tuning of reactive
sites density on the surface by varying the length of the phenyl-ethynyl spacers. The maleimide groups
are functionalized in position 4 by a –CH3 group, in position 3 by a –C12H25 alkyl chain and in position 1
by a –C3H6 chain, connecting it to the aromatic platform by an ether bond. The C3H6 chain is adopted in
order to guarantee to the maleimide core enough flexibility such as to adapt the correct geometrical
conformation upon Diels-Alder reaction. The role of the alkyl chain –C12H25 is to promote the adsorption
on the surface by establishment of CH-π interactions.
Figure 1. Functionalized maleimides 1 and 2.

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2. Results and Discussion
2.1. Maleimide 1
From a retrosynthetic point of view, 1 can be disconnected to the alkyl-functionalized maleic anhydride
3 and 1-dodecylamine (Scheme 1).
Scheme 1. Retrosynthetic analysis for the maleimide derivative 1.
Different disconnections can be envisaged for the alkyl-functionalized maleic anhydride 3. The synthesis
of this kind of derivatives has largely been studied in the literature, due to their interesting biological
activity [17]. The reported disconnection (Scheme 2) appeared the most interesting to us and was already
employed by Argade et al. for the synthesis of “Chaetomellic Anhydride A” [18].
Scheme 2. Retrosynthetic analysis for the anhydride derivative 3.
The strategy leads to disconnect the anhydride 3 directly to maleic anhydride and 2-bromo-tetradecanoic-
acid. All the synthetic steps could be performed in a one-pot fashion (Scheme 3).
Scheme 3. Synthesis of the alkyl-functionalized maleic anhydride 3. Conditions: (a) oxalyl
chloride (1.6 eq.), DMF cat., dry toluene, 20 °C, 2 h; (b) 2-aminopyridine (1 eq.), triethylamine
(1 eq.), dry diethyl ether, 20 °C, 3 h; (c) tert-butanol, 82 °C, 18 h; (d) maleic anhydride (1 eq.),
sodium acetate (1 eq.), acetic acid, 120 °C, 5 h. Yield over the four steps: 27%.

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In a first step (Scheme 3a), 2-bromo-tetradecanoic-acid was activated to an acyl chloride, by employing
an excess of oxalyl chloride, in dry toluene at room temperature for 2 h, under an argon atmosphere. The
product was obtained as a yellow oil after evaporation of the solvent and was employed without any
purification in the following step. The second step (Scheme 3b) consisted in a nucleophilic acyl substitution
by 2-aminopyridine. The reaction was done in dry diethyl ether at room temperature for 3 h, employing
triethylamine as a base. Product 5 was obtained as a yellow solid after solvent evaporation under reduced
pressure and employed without any purification in the following step. In the third step (Scheme 3c), the
derivative 5 was cyclized to product 6 by stirring under reflux of tert-butanol for 18 h. 6, obtained as a
dark thick oil after solvent evaporation, was employed for the following reaction without any purification.
The last step (Scheme 3d) consisted in reacting 6 with maleic anhydride, in presence of one equivalent
of sodium acetate, in refluxing acetic acid for 5 h. The proposed mechanism (Scheme 4) for this last step
is similar to the one described by Bauman et al. for the similar synthesis of dimethylmaleic anhydride [19].
The proton in alpha to the carbonyl group of 6 is made particularly acidic by the presence of the quaternary
nitrogen substituent. In the employed conditions, it is possible to assume that the protonated and
deprotonated forms are in equilibrium: the so formed carbanion a can act as a Michael donor and attack
maleic anhydride in position 3, to give an adduct b that after a sequence of reactions (β-elimination, ring
opening and decarboxylation) yields the 1-pyridine-3-dodecyl-4-methyl functionalized maleimide d.
Hydrolysis in the acidic environment followed by cyclization leads to the desired 3-dodecyl-4-methyl
maleic anhydride 3.
Scheme 4. Mechanism of formation of the functionalized maleic anhydride 3 from
compound 6.
The product 3 could be isolated by silica gel column chromatography (eluent petroleum ether/diethyl
ether 9:1) as a yellow oil, with a yield over four steps of 27%.
The alkyl functionalized maleic anhydride 3 was reacted with 1-dodecylamine to yield the maleimide
1 (Scheme 5).

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Scheme 5. Synthesis of the maleimide derivative 1: (a) 1-dodecylamine, ZnBr2, HMDS, dry
toluene, 80 °C, 19 h, 89%.
The employed conditions were adapted to our case from those suggested by Reddy et al. for similar
compounds. The anhydride ring was opened by the carbonyl addition of 1-dodecylamine, in toluene at
room temperature. After taking the mixture to 80 °C, the Lewis acid zinc dibromide was added, followed
by hexamethyldisilazane and the mixture was then refluxed for 19 h, to afford the cyclized maleimide
with 89% yield. Although the mechanism of the amic acid cyclization is not yet clearly defined, it is
assumed to consist in a Lewis acid/ HMDS promoted sylilation of an intermediate amic acid to a labile
trimethylsilyl ester, followed by subsequent thermal deoxysilylation [20]. It is interesting to notice that
the cyclization reaction by more “standard” conditions [17] (i.e., refluxing in acetic anhydride in the
presence of sodium acetate), was unsuccessful in this particular case and only the starting reagent was
1
recovered. The product was obtained as yellow oil. The 2D H-NMR characterizations confirmed the
disubstitution by the two –C12H25 alkyl chains with in particular the chemical shifts N-CH2 at 3.44 ppm
and C=C–CH2 at 2.35 ppm.
2.2. Maleimide 2
Among the different retrosynthetic paths that can be envisaged, we choose to adopt the one based on
the formation of the maleimide bond at the end of the synthesis, by reacting the amine-nitrogen atoms of
the precursor 7 with the formerly prepared functionalized maleic anhydride 3 (Scheme 6). The precursor
7 could be obtained by deprotection of the product obtained by coupling 1,3,5-triethynylbenzene and the
compound 9.
Scheme 6. Retrosynthetic analysis for the maleimide 2.

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2.2.1. Synthesis of 9
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Tert-butyl 3-bromopropylcarbamate was synthesized by a literature procedure [21]. The second step
consisted in the O-alkylation of p-iodophenol with tert-butyl 3-bromopropylcarbamate. p-Iodophenol
was deprotonated by cesium carbonate in acetonitrile at 65 °C; the as-generated nucleophile was then
alkylated in a SN2 reaction, promoted by sodium iodide [22]. Product 9 was obtained with an 83% yield
as a yellow solid after column chromatography on silica gel (Scheme 7).
Scheme 7. Synthesis of the precursor 9: (a) NaOH, Boc2O, H2O/THF, 0 °C–22 °C, 5 h, 90%;
(b) p-iodophenol, Cs2CO3, NaI, dry CH3CN, 65 °C, 5 h, 83%.
2.2.2. Synthesis of 7
Compound 8 was obtained by Sonogashira cross coupling between 1,3,5-triethynylbenzene [23,24] and
the precursor 9 (Scheme 8a). The reagents were stirred in dry tetrahydrofuran/diethylamine, in the presence
of bis(triphenylphosphine) palladium(II) dichloride (2% per alkyne) and copper iodide (0.8% per alkyne)
as catalyst. The reaction temperature was optimized at 45 °C and the reaction time to 4 h. The moderate
warming allowed to speed up the reaction, in particular the palladium C-I insertion step, unfavored by
the presence of the electron donor substituent in para to the iodine on 9. Under these conditions, the
product 8 was obtained after a simple column chromatography (cyclohexane/ethyl acetate 6:4) with a 48%
yield as a light yellow solid. Alternative conditions, such as: tetrahydrofuran/triethylamine as solvents,
copper iodide (2.7% per alkyne) and tetrakis(triphenylphosphine)palladium(0) (1.3% per alkyne) as
catalyst, at room temperature (22 °C) for 18 h, allowed as well to obtain 8, but the yields were slightly
lower and less reproducible (ranging from 24% to 48%) and the purification more difficult. In the following
step (Scheme 8b), the tert-butyloxycarbonyl (Boc) protecting group was removed to generate the
free-amine 7.
A solution of 8 in N,N-dimethylformamide (0.04 M) was irradiated with microwaves at a power of
230 Watts, adjusting the microwave reactor parameters such as to keep the reaction temperature at 180 °C
for 10 min (Scheme 8b) [25,26]. In these conditions, the Boc decomposition was quite rapid and 7 could
be recovered quantitatively as a brown thick oil, showing only a partial solubility in dimethylsulfoxide.
Due to the high polar character of the molecule, related to the presence of the free amines, it was not
possible to carry on a chromatographic purification, but the product was just treated with petroleum ether
in order to remove some non-polar impurities. Likely, the deprotection mechanism in the presence of
N,N-dimethylformamide, could be related to the solvent decomposition in formic acid and dimethylamine,
at high temperatures (Scheme 9) [27]. The as-generated dimethylamine is the nucleophilic species attacking

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the Boc carbonyl, determining the formation of a urea group, that then thermally decomposes to finally
yield the free amines.
Scheme 8. Synthesis of the precursor 7: (a) 9, Pd(PPh3)2Cl2 (6%), CuI (2.3%), dry
THF/Et2NH, 45 °C, 4 h, 48%; (b) µW (230 W), DMF, 180 °C, 10 min, 100%.
Scheme 9. Proposed mechanism for the Boc thermal decomposition.
We tested also a standard deprotection procedure in acidic medium. 8 was dissolved in a solution 4 M
of hydrochloric acid in tetrahydrofuran and the reaction run at 0 °C for 10 min then at 22 °C for 30 min.
The product could be recovered after basic work up, by extraction with ethyl acetate with yields going
up to 75%. However, the extraction procedure suffered from lack of reproducibility and many difficulties
were encountered in the recovery of 7, probably due to its insolubility in ethyl acetate. Another problem
that we had to deal with was the cleavage of the phenolic-ether bond that can be promoted in these
conditions [28], leading to the recovery of the only alkyl chain moiety.

Molecules 2015, 20
2.2.3. Synthesis of 2
18863
The tri-amine 7 was condensed with the maleic anhydride 3 to yield the tri-maleimide 2 (Scheme 10).
The reaction was carried out analogously to the synthesis of the functionalized maleimide 1.
The anhydride 3 cycle was at first opened by reacting it in an acyl nucleophilic substitution with the
amine nitrogens of 7, in toluene. Due to the insolubility of 7 in toluene, a solution of the anhydride 3 in
toluene was added to the flask containing the thick oil 7 and the mixture was warmed at 111 °C for 16 h.
With this procedure, 7 could be brought in solution as its derived carbamic acid, which was then cyclized
to 2 by employing the system ZnBr2/HMDS described above. The compound 2 could then be recovered
by two column chromatography purifications on silica gel (hexane/ethyl acetate 6:4; then hexane/diethyl
ether 95:5, followed by diethyl ether 100%) with a 20% yield. The identity and purity of the product
were confirmed by 1H-NMR spectroscopy and high-resolution mass spectrometry. The global yield over
the five steps from 3-bromopropylamine hydrobromide was 5%.
Scheme 10. Synthesis of the tri-maleimide 2: (i) 3, dry toluene, 111 °C, 16 h; (ii) ZnBr2,
HMDS, 80 °C, 5 h, then 22 °C, 11 h, 20%.
In summary, we have developed the syntheses of two maleimide derivatives designed for
self-assembly on graphene and Diels-Alder cycloadditions with this material in order to carry out
controlled functionalization in mild conditions. The strategy that we adopted consisted in the synthesis
of the alkyl-functionalized anhydride precursor and its successive reaction with the amine precursor for
the generation of the maleimide core. Current work involves transfers on graphene surfaces in ultra-high
vacuum, imaging of self-assembled monolayers by Scanning Tunneling Microscopy and tip-induced
controlled activation of cycloadditions.

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3. Experimental Section
General Information
1,3,5-Tris[(trimethylsilyl)ethynyl)benzene and 1,3,5-tri-ethynylbenzene were synthesized by literature
procedures from the references [23,24]. Tert-butyl 3-bromopropylcarbamate was synthesized by a
literature procedure [17]. Solvents were dried over molecular sieves prior to use. Dry DMF was from
Acros Organics (Morris Plains, NJ, USA) or Sigma Aldrich (St. Louis, MO, USA). THF was distilled on
sodium/benzophenone. Flash column chromatography was performed by using silica gel (60 Å pore size,
40–63 µm Merck, Kenilworth, NJ, USA). The reactions were monitored by thin layer chromatography
(TLC) on silica gel-coated plates (Merck 60 F254). Detection was performed by using UV light and by
charring the plate at ca. 200 °C, after dipping it in an ethanolic solution of potassium permanganate.
13
The yields refer to chromatographically and spectroscopically (1H-NMR and C-NMR) homogeneous
materials, unless otherwise stated. The NMR spectroscopic data were recorded with Bruker Avance
300/400/500 MHz (Bruker, Fremont, CA, USA) instruments and were calibrated by using the residual
undeuterated solvent as an internal reference (CDCl3 at δH = 7.26 ppm, δC = 77.16 ppm, CD2Cl2 at
δH = 5.33 ppm, δC = 53.84 ppm). Chemical shifts are reported in parts per million (ppm) on the δ scale
and coupling constants (J) are in Hertz (Hz). The abbreviations used to describe the multiplicities are
s = singlet, bs = broad singlet, d = doublet, t = triplet, dd = doublet of doublets, q = quintuplet, m = multiplet.
Mass spectra were recorded at the Service Commune de Spectrometrie de Masse of University Paul
Sabatier (Toulouse 3), Toulouse (France). Elemental analyses were done by the Service d’Analyse de l’ICSN
(Paris, France). Microwave heating was carried out in closed vials with a CEM-Discovery monomode
microwave apparatus under the specified conditions (power, temperature, time).
2-Bromo-tetradecanoic-chloride (4): In an oven dried three neck flask, under an atmosphere of argon,
13 mL (3.31 g, 26.08 mmol) of a 2 M solution of oxalyl chloride in dichloromethane were added to a
solution of 5 g (16.3 mmol) of 2-bromotetradecanoic acid in 80 mL of dry toluene, followed by a drop
of dimethylformamide. The mixture was stirred for 2 h at room temperature, and then the solvent was
removed under reduced pressure to give 4 as a yellow oil. The product was used for the following
reaction without any further purification.
2-Bromo-N-(pyridin-2-yl) tetradecanamide (5): To a solution of 2-aminopyridine (1.53 g, 16.3 mmol)
and dry triethylamine (2.27 g, 16.3 mmol) in dry ether (100 mL) at room temperature under argon, was
added the chloride 4 (5.3 g, 16.3 mmol) in dry ether (30 mL) in a dropwise fashion over a period of 20 min
under vigorous stirring. The reaction mixture was further stirred for 3 h at R.T. (20 °C) and the solvent
removed under vacuum. The product (a yellow solid) was used for the following reaction without any
further purification.
3-Dodecyl-2-oxo-2,3-dihydro-1H-imidazo [1,2-a] pyridin-4-ium Bromide (6): The total residue (5) was
dissolved in 100 mL of tert-butanol and warmed at reflux (82 °C) for 18 h. The solvent was removed under
reduced pressure, giving an orange oil that was used for the following step without any purification.

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3-Dodecyl-4-methylfuran-2,5-dione (3): The residue 6 was reacted with maleic anhydride (1.60 g,
16.3 mmol) in the presence of sodium acetate (1.34 g, 16.3 mmol) in 98% acetic acid (100 mL), under
reflux (120 °C) for 5 h under constant stirring. Acetic acid was then removed under vacuum and the
residue dissolved in ether. The ether layer was washed with water (2 × 100 mL), brine (100 mL) and dried
over magnesium sulphate. The product 3 was obtained as a yellow oil after column chromatography on
silica gel (eluent petroleum ether/diethyl ether 9:1, Rf = 0.53), with a 27% yield (over 4 steps). 1H-NMR
(500 MHz, CDCl3): δ (ppm) 2.45 (t, J = 7.5 Hz, 2H, C=C–CH2), 2.07 (s, 3H, C=C–CH3), 1.5–1.6 (m, 2H,
CH2–CH2 ), 1.2–1.3 (m, 18H, CH2 (chain)), 0.87 (t, J = 7 Hz, 3H, CH3 terminal).13C-NMR (125 MHz,
CDCl3): δ (ppm) 164, 166.2, 145.1, 140.8, 32.2, 30.0, 29.9, 29.8, 29.7, 29.5, 24.8, 23.0, 14.5, 9.9. MS
+
(DCI/NH3 ): m/z = 298 [M + NH4]+. Elemental Analysis: %C 72.70 %H 9.70 %O 17.60 (found for
C17H28O3) vs. %C 72.82 %H 10.06 %O 17.12 (calculated for C17H28O3).
1,3-Didodecyl-4-methyl-1H-pyrrole-2,5-dione (1): To a stirred solution of anhydride 3 (0.770 g, 2.7 mmol)
in dry toluene (20 mL) at R.T. (22 °C), a solution of 1-dodecylamine (0.5 g, 2.7 mmol) in dry toluene
(10 mL) was added dropwise. The resulting suspension was stirred for one hour, and then zinc bromide
(0.61 g, 2.7 mmol) was added in one portion. While the resulting reaction mixture was heated at 80 °C,
a solution of hexamethyldisilazane (0.66 g, 0.86 mL, 4.1 mmol) in 10 mL of dry toluene was added drop
by drop, and then the mixture was refluxed for 19 h. The reaction mixture was cooled to RT and poured
into 0.5 N HCl (20 mL). The aqueous phase was extracted with ethyl acetate (3 × 30 mL). The combined
organic extracts were dried over anhydrous magnesium sulphate. The solution was concentrated under
reduced pressure and the residue purified by silica gel chromatography (Petroleum ether/diethyl ether
95:5), to afford the product as a yellow oil with a 89% yield.1H-NMR (500 MHz, CDCl3): δ (ppm) 3.44
(t, J = 7.5 Hz, 2H, N–CH2), 2.35 (t, J = 7.5 Hz, 2H, C=C–CH2), 1.94 (s, 3H, C=C–CH3), 1.4–1.5 (m, 4H,
maleimide–CH2–CH2), 1.2–1.3 (m, 36H, CH2 (chain)), 0.87 (t, J = 6.5 Hz, 6H, CH3 terminal). 13C-NMR
(125 MHz, CDCl3): δ (ppm) 177.8, 172.4, 141.3, 137.0, 36.3, 32.3, 30.0, 29.9, 29.8, 29.7, 29.6, 29.5,
+
29.0, 28.6, 27.1, 24.0, 23.0, 14.5, 9.0. MS (DCI/NH3 ): m/z = 465 [M + NH4]+. Elemental Analysis: %C
77.58 %H 11.32 %N 3.13 %O 7.97 (found for C29H53NO2) vs. %C 77.79 %H 11.93 %N 3.13 %O 7.15
(calculated for C29H53NO2).
Tert-butyl 3-(4-iodophenoxy)propylcarbamate (9): To a solution of p-iodophenol (2 g, 9.1 mmol) and
tert-butyl-3-bromopropylcarbamate (2.38 g, 10 mmol) in dry acetonitrile (100 mL), were added Cs2CO3
(4.45 g, 13.65 mmol) and NaI (0.34 g, 2.28 mmol) and the mixture was let to react at 65 °C for 5 h. The
inorganic salts were filtered away and the solvent evaporated under reduced pressure. The product, a
light yellow solid, was purified by column chromatography on silica gel (pentane/diethyl ether 7:3,
Rf = 0.5) with a 83% yield. Melting point: 78–80 °C. 1H-NMR (300 MHz, CDCl3): δ (ppm) 7.53 (dt, 2H,
J1 = 9 Hz, J2 = 2.1 Hz, Ar–H (orto to O)), 49 (dt, 2H, J1 = 9 Hz, J2 = 2.1 Hz, Ar–H (ortho to I)), 4.72
(bs, 1H, –NH–), 3.97 (t, 2H, J = 6 Hz, –O–CH2–), 3.31 (q, 2H, J = 6 Hz, –NH–CH2–), 1.96 (q, 2H,
J = 6.3 Hz, CH2–CH2–CH2), 1.43 (s, 9H, –C(CH3)3).13C-NMR (75 MHz, CDCl3): δ (ppm) 158.9, 156.3,
+
138.5, 117.2, 83.1, 66.2, 38.2, 29.8, 28.7. MS (DCI/NH3 ): 338.9 [M − C(CH3)3 + H]+, 378.0 [M + H]+.
+
HR-MS (DCI CH4 /TOF): m/z 377.0488 for C14H20INO3 (calculated 377.0488) (13%); 278.0049 found
for C9H13INO+, (calculated 278.0036) (100%).

Molecules 2015, 20
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Tert-butyl 3,3',3''-(4,4',4''-(benzene-1,3,5-triyltris(ethyne-2,1-diyl))tris(benzene-4,1-diyl))tris(oxy)tris
(propane-3,1-diyl) tricarbamate (8): procedure a): 9 (1.57 g, 4.2 mmol) and 1,3,5-triethynylbenzene
(0.20 g, 1.3 mmol) were dissolved in distilled tetrahydrofuran (20 mL) and dry diethylamine (13 mL). Argon
was bubbled for 15 min then copper iodide (0.006 g, 0.03 mmol) and bis(triphenylphosphine)palladium(II)
dichloride (0.06 g, 0.08 mmol) were added and the mixture was let to react at 45 °C for 4 h. The mixture
was filtered on a silica pad (washing with ethyl acetate) and the solvent evaporated under reduced
pressure. The product (a slightly yellow solid) was obtained pure by column chromatography on silica
gel with cyclohexane/ethyl acetate 6:4 as eluent. (Rf = 0.4 in cyclohexane/ethyl acetate 6:4). The yield
was 48%. Melting point: 104–106 °C. 1H-NMR (300 MHz, CD2Cl2): δ (ppm) 7.59 (s, 3H, Ar–H), 7.49
(d, 6H, J = 8.7 Hz, Ar–H), 6.91 (d, 6H, J = 8.7 Hz, Ar–H), 4.82 (bs, 2.5H, –NHCO), 4.05 (t, 6H, J = 6.3 Hz,
CH2), 3.31 (q, 6H, J = 4 Hz, CH2), 1.98 (q, 6H, J = 4 Hz, CH2), 1.44 (s, 27H, –CO(CH3)3).13C-NMR (75
MHz, CD2Cl2): δ (ppm) 160.1 (–C=O), 154 (Ar–C), 134.1 (Ar–C), 134.0 (Ar–C), 125.1 (Ar–C), 115.6
(Ar–C), 115.4 (Ar–C), 91.2 (C–OR or C≡C), 87.3 (C≡C), 79.6 (C≡C), 65 (CH2), 38.6 (CH2),
30.4 (CH2), 28.9 (–C(CH3)3). HR-MS (ESI+/TOF): 920.4 [M + Na]+ (calculated 920.4), 933 [M + K]+
(calculated 933).
Procedure (b): 9 (1.92 g, 5.1 mmol) and 1,3,5-tri-ethynylbenzene (0.24 g, 1.6 mmol) were dissolved
in distilled tetrahydrofuran (25 mL) and triethylamine (7 mL). Argon was bubbled for 10 min then CuI
(0.024 g, 0.128 mmol) and Pd(PPh3)4 (0.074 g, 0.064 mmol) were added and the mixture was let to react
at room temperature (22 °C) for 18 h. The mixture was filtered on celite (washing with tetrahydrofuran)
and the solvent evaporated under reduced pressure. The product (a yellow solid) was obtained pure by two
column chromatographies on silica gel: (1) pentane/diethyl ether 6:4, then ethyl acetate; (2) pentane/ethyl
acetate 6:4. (Rf = 0.3 in pentane/ethyl acetate 7:3). The yields were ranging between 24% and 48%.
3,3',3''-(4,4',4''-(Benzene-1,3,5-triyltris(ethyne-2,1-diyl)) tris (benzene-4,1-diyl))tris(oxy)tripropan-1-amine
(7): deprotection by microwave irradiation: In a microwave reactor equipped with a magnetic stirrer, 8
(0.105 g, 0.12 mmol) was dissolved in 3 mL of dry dimethylformamide. The solution was warmed by
microwave irradiation setting the parameters as to keep the temperature at 180 °C for 10 min (PW
230 Watts). TLC analysis of the brown suspension revealed the disappearance of the reagent 8 and the
appearance of a new spot characteristic of the desired product at Rf = 0 (on SiO2, with hexane/ethyl
acetate 6:4 as eluent). After evaporation of the solvent under reduced pressure, a thick brown oil was
obtained. The oil was washed twice with petroleum ether and used without any purification for the next
step. The yield was quantitative.
Note: The product is only soluble in DMSO and does not elute on TLC stationary phases (SiO2, Al2O3
neutral), so it was directly used without any purification for the next step.
Deprotection by acidic treatment: 8 (0.180 g, 0.2 mmol) was dissolved in 10 mL of a solution 4 M of
HCl in THF at 0 °C. The mixture was stirred at 0 °C for 10 min, then at room temperature (25 °C) for
30 min. The solvent was evaporated under vacuum, and then 10 mL of water were added, causing the
precipitation of a white solid. The pH was basified to 14 by adding a solution of NaOH 0.01 M. The
water phase was extracted with ethyl acetate (3 × 30 mL). The combined organic phases were dried on
MgSO4 and evaporated. Since NMR analysis revealed that the reagent was not completely deprotected,
the reaction was restarted in the same conditions and let to stir at room temperature for 6 h. The product
was obtained with a 75% yield and used for the following reaction without further purification. (Rf = 0

Molecules 2015, 20
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both on SiO2 and Al2O3 neutral, with hexane/ethyl acetate 6:4 as eluent). 1H-NMR (300 MHz, CD2Cl2):
δ (ppm) 7.64 (s, 3H, Ar–H), 7.52 (d, 6H, J = 8.7 Hz, Ar–H), 7.01 (d, 6H, J = 8.7 Hz, Ar–H), 4.0–4.1 (m,
6H, CH2), 2.7–2.9 (m, 6H, CH2), 1.8–1.9 (m, 6H, CH2).
1,1',1''-(3,3',3''-(4,4',4''-(Benzene-1,3,5-triyltris(ethyne-2,1-diyl))tris(benzene-4,1-diyl))tris(oxy)tris
(propane-3,1-diyl))tris(3-dodecyl-4-methyl-1H-pyrrole-2,5-dione) (2): To a round bottom flask containing
the tri-amine 8 (0.110 g, 0.2 mmol), a solution of the alkylated maleic anhydride 4 (0.21 g, 0.7 mmol) in
8 mL of dry toluene was added. The mixture was let to react at 111 °C for 16 h, giving a brown solution.
Toluene was evaporated under reduced pressure. The obtained brown oil was redissolved in fresh dry
toluene (6 mL) and transferred in a three neck flask, equipped with a dropping funnel and argon entry.
Zinc bromide (0.13 g, 0.6 mmol) was added in one portion at room temperature, then the suspension was
warmed at 80 °C. A solution of hexamethyldisilazane (0.15 g, 0.19 mL, 0.9 mmol) in 2 mL of dry toluene
was added drop by drop. The mixture was let to react at 80 °C for 5 h then at room temperature (20–22 °C)
for 11 h. The reaction was quenched by adding 25 mL of water. Ethyl acetate was added (30 mL),
forming an emulsion. The emulsion was extracted with 2 × 30 mL of ethyl acetate, dried on anhydrous
MgSO4 and evaporated under reduced pressure. The product was obtained as a yellow oil by two column
chromatography purifications on silica gel: a first chromatography (eluent hexane/ethyl acetate 6:4)
allowed to recover 2 together with an impurity (fractions Rf = 0.8 to 0.9). This mixture was further
chromatographed (hexane/diethyl ether 95:5, then diethyl ether 100%) to obtain pure 2 in 20% yield.
1H-NMR (500 MHz, CDCl3): δ (ppm) 7.59 (s, 3H, Ar–H), 7.48 (d, 6H, J = 8.7 Hz, Ar–H ortho to CC),
6.87 (d, 6H, J = 8.7 Hz, Ar–H ortho to O), 4.00 (t, 6H, J = 6 Hz, N–CH2), 3.68 (t, 6H, J = 6.5 Hz,
O–CH2), 2.36 (t, 6H, 7 Hz, C=C–CH2), 2.07 (m, 6H, CH2CH2 CH2), 1.95 (s, 9H, C=C–CH3), 1.4–1.5 (m,
6H, CH2CH2), 1.2–1.3 (m, 54H, CH2, chain), 0.88 (t, 9H, J = 7 Hz, CH3 terminal). 13C-NMR (125 MHz,
CDCl3): δ (ppm) 173.0, 172.7, 160.0, 141.9, 137.7, 134.0, 133.9, 125.1, 115.6, 115.3, 91.2, 87.3, 64,
35.8, 32.7, 30.1–30.4, 29.0, 28.9, 24.3, 23.4, 14.7, 9.2. HR-MS (MALDI, DCTB/TOF): m/z 1383.8790
found for C90H117N3O9, 1383.8790 calculated for C90H117N3O9.
1
Copies of H- and 13C-NMR spectra of products 1, 2, 3, 8 and 9 can be found in the
supplementary materials.
Supplementary Materials
Supplementary data associated with this article are available at: http://www.mdpi.com/1420-3049/
20/10/18856/s1.
Acknowledgments
Support from the ANR-10-BLAN-1017 ChimiGraphN is gratefully acknowledged.
Author Contributions
C.M. and A.G. conceived and designed the experiments; C.M. performed the experiments; C.M. and
A.G. analyzed the data, contributed reagents/materials/analysis tools and wrote the paper.

Molecules 2015, 20
18868
Conflicts of Interest
The authors declare no conflict of interest.
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Sample Availability: Samples of the compounds are not available from the authors.
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