Cyclodehydrogenation of hetero-oligophenylenes

Article abstract of DOI:10.1016/j.tet.2009.02.029

Pyrimidyl-penta-phenylbenzenes have been synthesized by Diels-Alder addition of phenylethynylpyrimidines and tetraphenylcyclopentadienones under microwave irradiation. Scholl reactions of these compounds led to two types of hetero polyaromatic hydrocarbon

Full text of DOI:10.1016/j.tet.2009.02.029

Tetrahedron 65 (2009) 3767–3772
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Cyclodehydrogenation of hetero-oligophenylenes
y
*
´
´
Samuthirapandian Nagarajan , Cecile Barthes, Andre Gourdon
NanoSciences Group, CNRS, Universite´ de Toulouse, CEMES (Centre d’Elaboration des Mate´riaux et d’Etudes Structurales), BP 94347, 29 rue J. Marvig, F-31055 Toulouse, France
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 8 January 2009
Received in revised form 11 February 2009
Accepted 13 February 2009
Available online 21 February 2009
Pyrimidyl-penta-phenylbenzenes have been synthesized by Diels–Alder addition of phenyl-
ethynylpyrimidines and tetraphenylcyclopentadienones under microwave irradiation. Scholl reactions of
these compounds led to two types of hetero polyaromatic hydrocarbons: (a) partial cyclization by cre-
ation of two C–C bonds ortho to the pyrimidine nitrogen atoms gave substituted tribenzo[e,gh,j]per-
imidine (N-1/3HSB) in high yields; (b) when the position 2 of the pyrimidine ring was substituted by
a tert-butyl group, the Scholl reaction was complete and provided the first example of a diaza-hexa-peri-
benzocoronene.
Keywords:
Arenes
Nitrogen heterocycles
Cycloaddition
Cross-coupling
Scholl reaction
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
by microwave (mw) heating, which revealed as a very efficient tool
for cross-couplings and Diels–Alder reactions in terms of reaction
Polyaryl and polycyclic hydrocarbons are currently attracting
a lot of interest for their potential applications as molecular mate-
rials for electronic and optoelectronic applications. In the course of
a study of the mechanical and chemical properties of molecular
devices,1 we were interested in planar heterosuperbenzene as can-
didates for molecular moulding,2 metal atom manipulation,3 elec-
trode–molecule contact4 or controlled rotation5 experiments at the
single molecule level. In the present contribution, the investigation
of the synthesis of some pyrimidyl-penta-phenylbenzenes and the
influence of the substituents on the cyclodehydrogenation reaction
to access heterosuperbenzene is explored.
times and yields.6 Typically, the cross-coupling reactions were
completed in less than 0.5 h in good yields (61–93%).7–9 As pointed
10
´
out by Erdelyi and Gogoll, the reaction temperature was main-
tained just below 120 ꢀC to avoid decomposition of the palladium
catalyst. The Diels–Alder reactions, and the subsequent in-situ
oxidations, were done in diphenylether at 260 ꢀC for 45 min giving
the hexaaryl compounds in 40–50% yields.
The unsubstituted (5-pyrimidyl)pentaphenylbenzene 7 was
obtained in 44% yield by reaction of commercial 2,3,4,5-tetraphe-
nylcyclopenta-2,4-dienone with 5-(phenylethynyl)pyrimidine
(Scheme 2).
5
This latter compound 5 was prepared by coupling phenyl-
acetylene and 5-bromopyrimidine in good yield (93%), significantly
higher than by conventional heating.11–13 Similarly, the tri-
substituted (5-pyrimidyl)pentaphenylbenzene 11 was obtained by
[2þ4] cycloaddition of 5-((4-tert-butylphenyl)ethynyl)pyrimidine 9
and 3,4-bis(4-tert-butylphenyl)-2,5-diphenylcyclopenta-2,4-dien-
one 1014–16 (Scheme 3).
The tolane 9 was synthesized from 1-tert-butyl-4-ethynyl-
benzene 8. This latter compound17,18 was prepared in 88% yield by
cross-coupling under microwave irradiation of 1-bromo-4-tert-
butylbenzene and trimethylsilylacetylene, and deprotection by
aqueous NaOH in methanol.
2. Results and discussion
2.1. Synthesis of the pyrimidyl-penta-phenylbenzenes
The general synthetic route towards (partially or fully) cyclo-
dehydrogenated hetero-oligophenylenes is shown on Scheme 1.
The propeller-like pyrimidyl-penta-phenylbenzenes were obtained
by [2þ4] Diels–Alder cycloaddition of tetraphenylcyclopentadie-
nones to phenylethynylpyrimidines.
These latter were prepared by Sonogashira coupling of bromo-
pyrimidines with ethynylbenzenes. All these syntheses were done
The penta-tert-butyl propeller 13 (Scheme 4) was correspond-
ingly synthesized by cycloaddition of 9 with the known cyclo-
pentadienone 12,14,15 obtained by double Knoevenagel
condensation of 4,40-di-tert-butylbenzil and 1,3-bis(3,5-di-tert-
butylphenyl)-2-propanone.
* Corresponding author. Tel.: þ33 (0)5 62 25 78 59; fax: þ33 (0)5 62 25 79 99.
E-mail address: gourdon@cemes.fr (A. Gourdon).
Present address: Department of Chemistry, Annamalai University, Annamalai-
y
nagar 608002, India.
0040-4020/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2009.02.029

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S. Nagarajan et al. / Tetrahedron 65 (2009) 3767–3772
Scheme 1. General route towards pyrimidyl-penta-phenylbenzenes and their cyclodehydrogenation products. (a) Sonogashira coupling,
cyclodehydrogenation, FeCl3, DCM, CH3NO2.
mw; (b) [2þ4] cycloaddition, Ph2O,
mw; (c)
Finally, the fully substituted propeller 16 was obtained by con-
densation of 15 and 12.
genation of 1,2-dipyrimidyl-3,4,5,6-tetra(4-tert-butylphenyl)benzene
(Scheme 6).25,26
The preparation of 15 requires the synthesis of 5-bromo-2-tert-
butylpyrimidine 14, which was made by condensation of malon-
dialdehyde bis(dimethylacetal) and 2,2-dimethylpropanamidine19
to give the 2-tert-butylpyrimidine, subsequently brominated in
position 5 by bromine in acetic acid20 (Scheme 5).
Remarkably, whereas Scholl cyclodehydrogenation by AlCl3/
CuCl2 in CS2 gave solely the fully cyclized heterosuperbenzene N-
HSB, the reaction employing a milder catalyst (FeCl3/nitromethane/
DCM) gave a mixture of N-HSB (35%) and of ‘half-cyclized’ N-1/
2HSB (32%). Surprisingly, treatment of N-1/2HSB by FeCl3, or under
forcing conditions by AlCl3/CuCl2, did not give N-HSB, which
indicates that the partially cyclodehydrogenated compound is not
a parent intermediate of the heterosuperbenzene in this reaction. It
is worth noting that some partially cyclodehydrogenated oligo-
phenylenes can be fully cyclodehydrogenated to give HBC in
quantitative yield and without chlorination.27
2.2. Cyclodehydrogenations
With the objective to prepare series of heterosuperbenzene, we
have investigated the intramolecular Scholl reaction on these
contiguous hexaarylbenzenes 7, 11, 13 and 16. The Scholl reaction,
i.e., the condensation of aromatics by reaction with Lewis acids, is
known to be very efficient for the cyclodehydrogenation of oligo-
phenylene compounds. Mu¨llen and co-workers have extensively
used this reaction to convert 3D-polyphenylene structures to all
benzenoid 2D-hydrocarbons,21 and in particular for the preparation
of hexabenzocoronenes from hexaphenylbenzenes.22 In this Scholl
reaction, the oxidative aryl–aryl coupling is effected in general by
transition metal halides such as AlCl3/Cu(II), FeCl3, MoCl5 but
also by PhI(O2CCF3)2/BF3$OEt2,23,24 which act in the same time as
oxidants and Lewis acids. This synthetic route has been
recently extended by Draper and co-workers to the cyclodehydro-
2.3. Scholl reaction on the hexaarylbenzenes 7, 11, 13 and 16
Attempts to cyclodehydrogenate these four compounds by
AlCl3/CuCl2 in CS2 or MoCl5 in dichloromethane in various condi-
tions gave invariably fully insoluble products, containing poly-
chlorinated products as shown by mass spectroscopy. For 7 and 11,
it is possible that the presence of unsubstituted phenyl groups in
para-position to the central benzene favours oligomerization. Fur-
thermore the pyrimidine could maintain some solubility to the
reaction intermediates by complexation with the aluminium,
which would favour the polymerization and the chlorination. And
Scheme 2. Reagents and conditions: (a) DIPA, PPh3, PdCl2(PPh3)2, CuI, DMF, m
w, 115 ꢀC, 93%; (b) Ph2O, 260 ꢀC, 44%; (c) FeCl3/CH3NO2, DCM, 94%.

S. Nagarajan et al. / Tetrahedron 65 (2009) 3767–3772
3769
Scheme 3. Reagents and conditions: (a) DIPA, PPh3, PdCl2(PPh3)2, CuI, DMF, m
w, 115 ꢀC, 61%; (b) Ph2O, 260 ꢀC, 52%; (c) FeCl3/CH3NO2, DCM, 90%.
the presence of a dipole in the reaction products due to the
pyrimidine ring decreases further the solubility of the final oligo-
mers. The impossibility to fully cyclodehydrogenate 13 in the
conditions used to prepare N-HSB from the very similar 1,2-
dipyrimidyl-3,4,5,6-tetra(4-tert-butylphenyl)benzene (Scheme 6)
is very puzzling. In contrast, reaction of 7, 11 and 13 in dichloro-
methane with FeCl3/nitromethane gave very good yields of par-
solubility of reagents, intermediates and products, and (d) prevents
complexation by the nitrogen atoms by steric crowding. At this
stage, further work is required to unveil the cyclodehydrogenation
mechanisms leading to these very different chemical behaviours.
In conclusion, pyrimidyl-penta-phenylbenzenes have been
synthesized by Diels–Alder addition of phenylethynylpyrimidines
and tetraphenylcyclopentadienones under microwave irradiation.
Scholl reactions of these compounds (ferric chloride/nitromethane/
dichloromethane) led to two types of hetero polyaromatic hydro-
carbons: (a) partial cyclization by creation of two C–C bonds ortho
to the pyrimidine nitrogen atoms gave substituted tri-
benzo[e,gh,j]perimidine (N-1/3HSB) in high yields; (b) when the
position 2 of the pyrimidine ring was substituted by a tert-butyl
group, the Scholl reaction was complete and provided the first
example of a diaza-hexa-peri-benzocoronene.
tially cyclodehydrogenated
1 (94%), 2 (90%) and 3 (85%),
respectively (Scheme 1). In this reaction, and very similarly to what
is observed for bipyrimidines (Scheme 6), the only C–C bonds that
have been created are those in ortho position with respect to the
pyrimidine nitrogen, leading to tribenzo[e,gh,j]perimidine cores
(N-1/3HSB according to Draper’s nomenclature).26 The cyclo-
dehydrogenation mechanisms are therefore probably similar and
could involve arenium intermediates and/or the coordination of the
iron.24 Very similarly to what was observed with N-1/2HSB,
attempts to complete the cyclodehydrogenation of these N-1/3HSB
by reaction with AlCl3 or FeCl3 were unsuccessful. In contrast,
reaction of the per-tert-butylated 16 with FeCl3, in the same con-
ditions as above for 7, 11, 13, provided the N-heterosuperbenzene 4
in 60% yield. The substitution of the hydrogen atom in position 2 in
the pyrimidine ring (in 13) by a tert-butyl group (in 16) has a pro-
found effect on the reactivity of these compounds. This substitution
by a bulky, electron donating group has several consequences: (a) it
increases the pyrimidine nucleophilicity, (b) blocks the position 2
and could hinder oligomerization at this position, (c) increases the
3. Experimental
3.1. General
1H and 13C NMR spectra were recorded with a Bruker WF-250/
300 MHz in CDCl3 or CD2Cl2 solutions at 20 ꢀC using solvent residue
as the internal standard (CDCl3 at dH: 7.25 ppm, dC: 77.0 ppm,
CD2Cl2 at dH: 5.30 ppm, dC: 53.8 ppm). Mass Spectroscopy was
performed with a Nermag R10-R10 (DCI). Elemental analyses were
done by the Service d’Analyse de l’ICSN (Paris) and by the Service
Scheme 4. Reagents and conditions: (a) Ph2O, 260 ꢀC, 46%; (b) FeCl3/CH3NO2, DCM, 85%.

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S. Nagarajan et al. / Tetrahedron 65 (2009) 3767–3772
Scheme 5. Reagents and conditions: (a) DIPA, PPh3, PdCl2(PPh3)2, CuI, DMF,
m
w, 115 ꢀC, 78%; (b) Ph2O, 260 ꢀC, 62%; (c) FeCl3/CH3NO2, DCM, 60%.
d’Analyse du LCC (Toulouse). Note that, as observed by others, the
carbon analysis of extended polyaromatic compounds 1–3 is
inaccurate, due to incomplete combustion. The cyclopentadienones
10 and 12 were prepared according to Refs. 14 and 15. THF was
distilled from Na/benzophenone. Dichloromethane was distilled
over calcium hydride. Nitromethane was dried on molecular sieves
prior use. Other solvents and reagents were used as obtained in the
best quality available. The microwave heating was carried out in
closed vials with a CEM-Discover monomode microwave apparatus
under the conditions (power, temperature, time) given here. After
completion of the reaction, the vessel was cooled down rapidly to
60 ꢀC.
DCM as eluent. Drying under vacuum in ice gave pale yellow
powder. Yield: 167 mg (93%).
1H NMR (250 MHz, CD2Cl2):
d
¼7.41 (m, 3H, Ar–H), 7.57 (m, 2H,
Ar–H), 8.86 (s, 2H, H4, H6), 9.11 (s, 1H, H2); 13C NMR (75 MHz,
CD2Cl2)
d
¼82.6, 95.9, 119.8, 121.9, 128.6, 129.4, 131.8, 156.8, 158.7;
MS (CI, NH3): m/z calcd for C12H8N2: 180.0; found: 181 [Mþþ1].
Anal. Calcd for C12H8N2: C, 79.98; H, 4.47; N, 15.55. Found: C, 79.88;
H, 4.44; N, 14.55.
3.3. Synthesis of 1-tert-butyl-4-ethynylbenzene 8
To a degassed mixture of 3 g of 1-bromo-4-tert-butylbenzene
(14.08 mmol), 485 mg of Pd(P(C6H5)3)4 (3%), 160 mg of CuI (6%) in
10 mL DIPA and 30 mL dry THF was added 2 mL of TMSA (1.38 g,
14 mmol). The mixture was irradiated at 150 W, 33 min, 110 ꢀC.
After cooling the mixture was filtered over Celite; the Celite was
washed with diethylether until colourless and the solvent evapo-
rated under vacuum. The residue was then dissolved in ether,
washed with HCl 1%, brine then dried on MgSO4. Purification by
chromatography using hexane as eluent yielded 3.08 g of (4-tert-
butylphenylethynyl)-trimethylsilane, which was then dissolved in
150 mL of methanol. To this solution was added 14 mL of aqueous
2.5 M NaOH. After 15 min of stirring the mixture was acidified to
neutrality with 1 M HCl.
3.2. Synthesis of 5-phenylethynylpyrimidine 5
A mixture of 102 mg of phenylacetylene (1 mmol) and 159 mg
(1 mmol) 5-bromopyrimidine in 0.5 mL of dry DMF was degassed
and 1.5 mL of dry DIPA, triphenylphosphine (23 mg, 0.087 mmol),
Pd(P(C6H5)3)Cl2 (15 mg, 0.021 mmol) and CuI (4 mg, 0.02 mmol)
were added and the mixture was irradiated at 150 W, 115 ꢀC,
25 min. After cooling the brown-orange coloured suspension was
extracted with 2ꢁ50 mL ether and washed with 2ꢁ25 mL saturated
NH4Cl, 2ꢁ25 mL water then dried with MgSO4. The crude product
was further purified by chromatographic column in silica gel using
Scheme 6. Reagents and conditions from Refs. 25 and 26. (a) AlCl3, CuCl2, CS2, rt, 49%; (b) FeCl3/CH3NO2, DCM, rt; N-HSB (35%)þN-1/2HSB (32%); (c) AlCl3/CuCl2 or FeCl3.

S. Nagarajan et al. / Tetrahedron 65 (2009) 3767–3772
3771
Then the product was extracted with hexane (3ꢁ150 mL) and
3.6.2. Compound 11
washed with water (100 mL), dried over MgSO4, giving 1.96 g of
pure 8 as orange oil (yield for the two steps: 88%). Analyses and
spectroscopic data were in agreement with the literature.17,18
Yield 52%; 1H NMR (300 MHz, CD2Cl2):
d
¼1.12 (br m, 27H,
3ꢁtert-Bu), 6.70–6.97 (m, 20H, Ar–H), 8.14 (s, 2H, H4, H6), 8.59 (s,
1H, H2); 13C NMR (75 MHz, CD2Cl2)
d¼31.2, 34.3, 123.6, 124.2, 124.2,
126.1, 126.8, 127.4, 131.1, 131.3, 131.5, 131.6, 135.4, 136.8, 137.4, 137.6,
140.2, 140.6, 140.8, 141.3, 142.4, 148.4, 149.1, 155.4, 158.0; MS (CI,
NH3): m/z calcd for C52H48N2: 700.4; found: 701.4 [Mþþ1]. Anal.
Calcd for C52H52N2: C, 88.59; H, 7.43; N, 3.57. Found: C, 88.42; H,
7.21; N, 3.27.
3.4. Synthesis of 9
To a degassed solution of 8 (158 mg, 1 mmol) and 5-bromo-
pyrimidine (156 mg, 1 mmol) in 0.5 mL DMF and 1.5 mL dry
DIPA were added triphenylphosphine (23 mg, 0.087 mmol),
Pd(P(C6H5)3)Cl2 (15 mg, 0.0213 mmol) and CuI (4 mg, 0.021 mmol).
The mixture was irradiated at 150 W, 115 ꢀC, 25 min. After cooling
the brown-orange suspension was extracted with 2ꢁ50 mL ether
and filtered. The solution was washed with saturated NH4Cl
(2ꢁ25 mL), water (2ꢁ25 mL) and finally dried over MgSO4. The
crude product was purified by chromatography (silica gel, eluent:
DCM/ethylacetate 5%). Yield: 145 mg of pale yellow powder (61%).
3.6.3. Compound 13
Yield: 46%; 1H NMR (300 MHz, CD2Cl2):
d
¼1.10 (s, 45H, 5ꢁtert-
Bu), 6.70–6.77 (m, 10H, Ar–H), 6.84–6.90 (m, 6H, Ar–H), 6.937 (br d,
3JH–H¼8.4 Hz, 4H, Ar–H), 8.16 (s, 2H, H4, H6), 8.59 (s, 1H, H2); 13C
NMR (75 MHz, CD2Cl2)
d¼31.6, 34.7, 124.1, 124.6, 131.5, 131.7, 137.5,
138.1, 141.3, 141.7, 148.8, 149.4, 155.8, 158.5; MS (CI, NH3): m/z calcd
for C60H68N2: 817.2; found: 817 [Mþ]. Anal. Calcd for C60H68N2: C,
88.18; H, 8.39; N, 3.43. Found C, 87.72; H, 8.33; N, 3.29.
1H NMR (300 MHz, CD2Cl2):
d
¼1.33 (s, 9H, tert-Bu), 7.29 (d, 3JH–H
¼
3
8.7 Hz, 2H, Ar–H), 7.51 (d, JH–H¼8.7 Hz, 2H, Ar–H), 8.84 (s, 2H, H4,
3.6.4. Compound 16
H6), 9.09 (s, 1H, H2); 13C NMR (75 MHz, CD2Cl2)
d¼31.0, 81.8, 96.1,
Yield: 62%; 1H NMR (300 MHz, CD2Cl2):
d
¼1.08–1.11 (m, 54H,
6ꢁtert-Bu), 6.72–6.75 (m, 10H, Ar–H), 6.83–6.93 (m, 10H, Ar–H),
8.04 (s, 2H, H4, H5); 13C NMR (75 MHz, CD2Cl2)
118.8, 120.6, 125.6, 131.4, 131.8, 152.9, 156.6, 158.5; MS (CI, NH3): m/z
calcd for C16H16N2: 236.1; found: 237 [Mþþ1]. Anal. Calcd for
C16H16N2: C, 81.32; H, 6.32; N,11.85. Found: C, 81.19; H, 6.99; N,11.87.
d
¼29.8, 31.3, 31.6,
124.0, 124.5, 131.5, 134.4, 137.7, 138.1, 141.5, 142.4, 148.8, 149.2, 157.8,
173.9; MS (CI, NH3): m/z calcd for C64H76N2: 872.6; found: 873.7
[Mþþ1]. Anal. Calcd for C64H76N2: C, 88.02; H, 8.77; N, 3.21. Found:
C, 88.03; H, 8.35; N, 3.15.
3.5. Synthesis of 15
To a degassed mixture of 158 mg (1 mmol) of 1-tert-butyl-4-
ethynylbenzene (8), 5-bromo-2-tert-butylpyrimidine (14) (215 mg,
1 mmol) in 0.5 mL of dry DMF and 1.5 mL of dry DIPA were added
triphenylphosphine (23 mg, 0.087 mmol), Pd(P(C6H5)3)Cl2 (15 mg,
0.021 mmol) and CuI (4 mg, 0.02 mmol), and the mixture was ir-
radiated at 150 W, 115 ꢀC, 25 min. After cooling the brown sus-
pension was extracted with 2ꢁ50 mL of diethylether, filtered and
washed with 2ꢁ25 mL saturated NH4Cl, 2ꢁ25 mL water then dried
with MgSO4. The crude product was further purified by chro-
matographic column in silica gel using a gradient of petroleum
ether/DCM as eluent (0–20% DCM). Yield: 205 mg (77%).
3.7. General procedure for cyclodehydrogenation
of 7, 11, 13 and 16
The hexaaryl compound was dissolved in anhydrous DCM. A
stream of argon saturated with DCM was bubbled into the solution
during the reaction to reduce chlorination. A solution of anhydrous
FeCl3 (1:30 mol ratio) in anhydrous nitromethane was quickly
added. After a reaction time of 90 min, the reaction was quenched
with methanol. Part of the dichloromethane was removed under
reduced pressure. The precipitate was filtered and washed with
aqueous HCl and methanol.
1H NMR (300 MHz, CD2Cl2):
d
¼1.30 (s, 9H, tert-Bu), 1.37 (s, 9H,
3
3
tert-Bu), 7.39 (d, JH–H¼8.7 Hz, 2H, Ar–H), 7.47 (d, JH–H¼8.7 Hz,
2H, Ar–H), 8.75 (s, 2H, H4, H6); 13C NMR (75 MHz, CD2Cl2)
d¼29.2,
3.7.1. Compound 1
30.8, 82.5, 94.9, 116.2, 119.1, 125.6, 131.4, 152.6, 158.2, 175.6; MS
(CI, NH3): m/z calcd for C20H24N2: 292.4; found: 293.3 [Mþþ1].
Anal. Calcd for C20H24N2: C, 82.15; H, 8.27; N, 9.58. Found: C,
82.38; H, 8.39; N, 9.21.
Yield 94%; product was precipitated with methanol; 1H NMR
(300 MHz, CD2Cl2,):
7.61 (m, 4H, Ar–H), 9.40 (d, JH–H¼9 Hz, 2H, Ar–H), 9.75 (s, 1H,
H2); 13C NMR (75 MHz, CD2Cl2)
d
¼6.90 (m, 5H, Ar–H), 7.17 (m, 12H, Ar–H),
3
d¼125.2, 125.4, 126.3, 126.6, 127.0,
127.1, 128.2, 128.9, 129.7, 130.5, 131.3, 131.8, 134.1, 139.8, 140.4,
142.7, 152.9, 155.6; MS (CI, CH4): m/z calcd for C40H24N2: 532.2;
found: 533.2 [Mþþ1]. Anal. Calcd for C40H24N2: C, 90.20; H, 4.54;
N, 5.26. Found: C, 89.75; H, 4.73; N, 4.93. Rf: 0.52 in dichloro-
methane, silica gel.
3.6. General procedure for the synthesis of 7, 11, 13 and 16
A mixture of phenylethynylpyrimidine (0.2 mmol) and cyclo-
pentadienone (0.2 mmol) in diphenylether (1.5 g) was irradiated at
300 W, 260 ꢀC, 45 min. After cooling, the dark-red mixture was
diluted with dichloromethane (1 mL), poured in methanol (50 mL)
and stirred; the off white precipitate was filtered, washed with
methanol and vacuum dried. The product was recrystallized by
partial evaporation (24 h) of a mixture of DCM (2.5 mL) and ethanol
(5 mL).
3.7.2. Compound 2
Yield 90%; product was precipitated with methanol; 1H NMR
(300 MHz, CD2Cl2):
d
¼1.15 (s, 9H, tert-Bu),1.26 (s, 9H, tert-Bu),1.45 (s,
9H, tert-Bu), 6.69 (d, 3JH–H¼8.4 Hz, 2H, Ar–H), 6.90 (d, 3JH–H¼8.4 Hz,
2H, Ar–H), 6.96 (d, 3JH–H¼8.4 Hz, 2H, Ar–H), 7.21–7.28 (m, 8H, Ar–H),
7.33 (dd, 3JH–H¼9.0 Hz, 4JH–H¼2.3 Hz,1H, Ar–H), 7.59 (d, 3JH–H¼6.9 Hz,
1H, Ar–H), 7.64 (d, 3JH–H¼9 Hz, 1H, Ar–H), 7.79 (d, 3JH–H¼8.4 Hz, 1H,
3
4
3.6.1. Compound 7
Ar–H), 9.41 (d, JH–H¼6.9 Hz, 1H, Ar–H), 9.48 (d, JH–H¼2.4 Hz, 1H,
Yield 44%; 1H NMR (300 MHz, CD2Cl2):
d
¼6.80–7.00 (m, 25H,
Ar–H), 8.2 (s, 2H, H4, H6), 8.60 (s, 1H, H2); 13C NMR (75 MHz,
CD2Cl2)
Ar–H), 9.76 (s, 1H, H2); 13C NMR (75 MHz, CD2Cl2)
d¼30.9, 30.0, 30.1,
123.0, 124.8, 125.1, 126.5, 126.9, 127.1, 128.1, 128.8, 129.5, 129.9, 130.7,
131.2, 131.3, 137.3, 139.8, 150.1, 155.3; MS (CI, CH4): m/z calcd for
C52H48N2: 700.4; found: 701.4 [Mþþ1]. Anal. Calcd for C52H48N2: C,
89.0; H, 6.90; N, 4.00. Found: C, 88.12; H, 7.01; N, 3.80. Rf: 0.45 in
dichloromethane, silica gel.
d¼125.8, 126.2, 126.9, 127.5, 129.3, 131.5, 133.3, 135.1, 139.8,
140.3,140.5, 142.0, 141.0, 155.6, 158.0, 206.8; MS (CI, NH3): m/z calcd
for C40H28N2: 536.6; found: 537 [Mþþ1]. Anal. Calcd for C40H28N2:
C, 89.52; H, 5.26; N, 5.22. Found: C, 88.09; H, 5.26; N, 5.04.

3772
S. Nagarajan et al. / Tetrahedron 65 (2009) 3767–3772
3.7.3. Compound 3
References and notes
Yield: 85%; product was precipitated with methanol; 1H NMR
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(300 MHz, CD2Cl2):
d
¼1.14 (s, 9H, tert-Bu), 1.27 (s, 18H, 2ꢁtert-Bu),
3
3
1.47 (s, 18H, 2ꢁtert-Bu), 6.58 (d, JH–H¼8.3 Hz, 2H), 6.87 (d, JH–H
¼
3
8.4 Hz, 2H, Ar–H), 6.93 (d, JH–H¼8.3 Hz, 4H, Ar–H), 7.19 (d,
3JH–H¼8.5 Hz, 4H, Ar–H), 7.49 (dd, JH–H¼9.1 Hz, JH–H¼2.1 Hz, 2H,
3
4
3
4
Ar–H), 7.83 (d, JH–H¼9.1 Hz, 2H, Ar–H), 9.43 (d, JH–H¼2.1 Hz, 2H,
Ar–H), 10.09 (s, 1H, H2); 13C NMR (75 MHz, CD2Cl2)
d
¼29.7, 34.4,
35.2, 123.1, 125.1, 129.9, 130.4, 130.5, 130.9, 138.1, 138.9, 139.0, 139.8,
141.5, 150.3, 158.8; MS (CI, CH4): m/z calcd for C60H64N2: 812.5;
found: 812.6 [Mþ]. Anal. Calcd for C60H64N2: C, 88.62; H, 7.93; N,
3.44. Found: C, 88.36; H, 7.72; N, 4.19. Rf: 0.70 in dichloromethane,
silica gel.
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3.7.4. Compound 4
´
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Yield: 60%; product was further purified using column chro-
matography, silica gel, petroleum ether–dichloromethane (4: 1); 1H
NMR (300 MHz, CD2Cl2):
d
¼1.75 (s, 9H, tert-Bu), 1.85 (s, 27H,
3ꢁtert-Bu), 1.93 (s, 18H, 2ꢁtert-Bu), 9.41 (br s, 6H, Ar–H), 9.56 (d,
4JH–H¼1.8 Hz, 2H, Ar–H), 10.11 (d, 4JH–H¼1.8 Hz, 2H, Ar–H); 13C NMR
(75 MHz, CD2Cl2)
d¼30.6, 31.7, 31.8, 125.9, 126.7, 128.5, 129.1, 130.3,
131.3, 132.3, 148.4, 150.0, 150.3, 166.2; MS (CI, CH4): m/z calcd for
C64H64N2: 860.5; found: 861.7 [Mþþ1]. Anal. Calcd for C64H64N2: C,
89.26; H, 7.49; N, 3.25. Found: C, 88.74; H, 7.04; N, 3.64. Rf: 0.83 in
petroleum ether–dichloromethane (4:1), silica gel.
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Acknowledgements
Partial support of this work by the European Commission within
the projects CHIC (Contract no. IST-2001-33578) and PicoInside
(Contract no. IST-015847) is gratefully acknowledged. One of the
authors (S.N.) thanks the Department of Science and Technology,
Government of India, for awarding a BOYSCAST fellowship.
27. Feng, X.; Wu, J.; Enkelmann, V.; Mu¨llen, K. Org. Lett. 2006, 8, 1145–1148.