Aromatization-driven Grob-fragmentation approach toward polyazaacenes. Synthesis and amination of multi-functionalized diazapentacenes

Article abstract of DOI:10.1016/j.tet.2019.130689

A general approach toward the synthesis of multi-functionalized diazapentacene derivatives 1, using 1,2,3,4-tetrachloro-5,5-dimethoxycyclopentadiene (TDCp, 2), a substituted benzene-1,2-diamine (ADA, 6), and a naphthalene-1,4-dione (BQ, 3) as the building units, is described. The synthesis basically entails three operations: (i) oxidation of the dichloroetheno-bridge in the Diels-Alder cycloadduct 4 of TDCp and 3, (ii) condensation of the 1,2-diketone 5 thus generated with an ADA to give quinoxaline-fused polycyclic compounds 7, followed by (iii) an one-pot, three-reaction process keyed upon the base- or acid-catalyzed aromatization-driven Grob-type fragmentation to produce quinoxaline ring-embedded diazapentaceneesters 1. The diazapentacene derivative 1a underwent the nucleophilic aromatic ipso-amination with primary and secondary amines to afford the amino-substituted derivatives 12, which tend to self-assemble in solid state driven by the cofacial π-stacking interactions, demonstrated by the crystal packing structures of 12a and 12f.

Full text of DOI:10.1016/j.tet.2019.130689

Tetrahedron xxx (xxxx) xxx
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Aromatization-driven Grob-fragmentation approach toward
polyazaacenes. Synthesis and amination of multi-functionalized
diazapentacenes
, b,
Teh-Chang Chou a *, Ju-Fang Cheng b, Atul R. Gholap b, Jim Jing-Kai Huang b,
Jyun-Chang Chen b, Jing-Kai Huang a, Jui-Chang Tseng b
a Department of Chemistry and Biochemistry, National Chung Cheng University, Minsyong, Chiayi, 62102, Taiwan
b Department of Applied Chemistry, Chaoyang University of Technology, Wufong, Taichung, 41369, Taiwan
a r t i c l e i n f o
a b s t r a c t
Article history:
A general approach toward the synthesis of multi-functionalized diazapentacene derivatives 1, using
1,2,3,4-tetrachloro-5,5-dimethoxycyclopentadiene (TDCp, 2), a substituted benzene-1,2-diamine (ADA,
6), and a naphthalene-1,4-dione (BQ, 3) as the building units, is described. The synthesis basically entails
three operations: (i) oxidation of the dichloroetheno-bridge in the Diels-Alder cycloadduct 4 of TDCp and
3, (ii) condensation of the 1,2-diketone 5 thus generated with an ADA to give quinoxaline-fused poly-
cyclic compounds 7, followed by (iii) an one-pot, three-reaction process keyed upon the base- or acid-
catalyzed aromatization-driven Grob-type fragmentation to produce quinoxaline ring-embedded dia-
zapentaceneesters 1. The diazapentacene derivative 1a underwent the nucleophilic aromatic ipso-ami-
nation with primary and secondary amines to afford the amino-substituted derivatives 12, which tend to
Received 17 August 2019
Received in revised form
8 October 2019
Accepted 12 October 2019
Available online xxx
Keywords:
Polyazaacenes
Diazapentacenes
Acenes
self-assemble in solid state driven by the cofacial
p-stacking interactions, demonstrated by the crystal
packing structures of 12a and 12f.
Heteroacenes
Quinoxalines
ipso-Amination
Grob-fragmentation
© 2019 Elsevier Ltd. All rights reserved.
1. Introduction
and theoretically at a variety of levels [4]. Compared to carbo-acene
analogues, which are p-type semiconductors in the solid state, N-
heteroacenes are expected to be good candidates for n-type (elec-
tron-transporter) semiconducting material, since they generally
have substantial less electron deficiency and higher electron af-
finity [4,5]. They also display other properties of significant interest.
Acenes (“carbo-acenes”) are a class of polycyclic aromatic hy-
drocarbons (PAHs) composed of linearly fused benzene rings. The
noteworthy features of extended planar structure, high rigidity, and
the narrow gap between the HOMO and LUMO energy levels have
promoted acenes to be attractive organic materials for use in mo-
lecular electronic devices [1]. Among them, pentacene proves to
exhibit most outstanding properties in the fabrication of semi-
conductor devices and is most widely utilized to date. In conjunc-
tion with the promising properties and application, synthetic
endeavors in quest of the applicable precursors and derivatives
related to pentacene and higher acenes continues [2].
For example, they are more likely to form a cofacial
p-stacking
structure in favor of efficient orbital overlap and charge carrier
transport than their non-aza-substituted analogues [6].
Even though the polyazaacenes show promise in various ap-
plications, there are only a few reports regarding their synthesis [3].
In particular, there is no general approach for the synthesis multi-
functionalized derivatives, which could not only serve as proper
precursors toward polyazaacenes but also allow appropriate elab-
oration of molecular structures at the periphery to provide accesses
to a diversity of targeted molecules of interest and applications. In
this context, we have developed a general synthetic approach to-
ward the multi-functionalized polyazaacene derivatives having the
generic structure A and preliminarily reported the representing
synthesis and electronic properties of diazapentacenes (1:
n ¼ m ¼ 1, Fig. 1) [7]. Molecules of A are composed of three basic
Concurrently, study on N-embedded heteroacenes (poly-
azaacenes) for the development of high-performance electronic
materials has also been actively undertaken, both synthetically [3]
* Corresponding author. Department of Chemistry and Biochemistry, National
Chung Cheng University, Minsyong, Chiayi, 62102, Taiwan.
E-mail address: chetcc@ccu.edu.tw (T.-C. Chou).
https://doi.org/10.1016/j.tet.2019.130689
0040-4020/© 2019 Elsevier Ltd. All rights reserved.
Please cite this article as: T.-C. Chou et al., Aromatization-driven Grob-fragmentation approach toward polyazaacenes. Synthesis and amination
of multi-functionalized diazapentacenes, Tetrahedron, https://doi.org/10.1016/j.tet.2019.130689

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T.-C. Chou et al. / Tetrahedron xxx (xxxx) xxx
Scheme 1. Retro-synthetic analysis of the polyazaacene derivatives A.
Fig. 1. The polyazaacene derivatives having the generic structure A that can be syn-
thesized by the methodology of this study.
remains the most commonly and effective approach to the con-
struction of quinoxaline derivatives [9]. Although 1,2-diketones are
commonly obtainable by the oxidation of the corresponding 1,2-
diols or a-hydroxyketones [10], the preparation of unsymmetrical
aromatic ring systems of electron-accepting nature, namely pyr-
azine, 1,4-benzoquinone, and benzene with electron-withdrawing
methoxycarbonyl and chloro substituents. The synthetic approach
could potentially allow both pyrazine and 1,4-quinone ring systems
to be polycyclically fused and peripherally incorporated with sub-
stituents. The inherent peripheral functional groups (eCO2Me, eCl,
and ¼ O) in A could be removed en route to the corresponding
polyazaacenes B or be changed to modify the periphery of mole-
cules. Because of the electron-withdrawing nature of functional
groups, they are expected to have an electronic structure exhibiting
high electron affinity.
1,2-diketones, acyclic or cyclic, still is not a simple task, largely
owing to the difficult accessibility of suitable precursors. Especially
is the preparation of corresponding multi-functionalized catechols
for making quinone-annulated ortho-quinone derivatives like G
[11]. Obviously a source for an appropriate precursor must be
sought.
A precursor-in-thought for the diketonic compound G was
transpired by the observed one-pot conversion shown in Scheme 2
[12,13]. The DielseAlder cycloadducts H obtained from reactions of
various
BQ
(E)
and
1,2,3,4-tetrachloro-5,5-
dimethoxycyclopentadiene (TDCp, 2) [14] were promoted by trie-
thylamine to yield the corresponding trichlorinated acenoquinone
esters I. The facile Grob-type fragmentation of unstable in-
termediates J, formed via the triethylamine induced enolization-
oxidation of H, is evidently driven by the collective effect of ring-
strain relief, aromatization, and the proper push-pull setup for
electrons to flow from the electron-releasing methoxy to the
electron-withdrawing C]O group relayed by the C]C double bond
[12,15]. The driving forces for the Grob-type fragmentation of J
imply that the process could be also promoted under an acidic
condition and be facilitated by replacing C(sp2)ꢀCl on dichlor-
oethene bridge of H with electron-withdrawing groups, such as
carbonyl (C]O) or imino (C]N) [16].
It is well known that aromatic rings equipped with electron-
withdrawing substituents could undergo nucleophilic aromatic
substitution (SNAr) in the presence of a variety of nucleophiles at
the electrophilic carbon on which a good leaving group is atta-
cheddipso-substitution [8]. Owing to the electron-withdrawing
nature of the peripheral functional groups (eCO2Me, eCl, and
¼ O), besides the imine (C]N) groups of pyrazine ring, poly-
azaacene derivatives A are expected to have an electronic structure
exhibiting high electrophilicity and be able to undergo metal-free
aromatic nucleophilic ipso-substitution reaction (SNAr) at aryl car-
bon bearing chlorine atom. We thus carried out the ipso-amination
of A with primary and secondary amines as nucleophiles. In this
paper, we describe in detail the synthesis of multi-functionalized
diazapentacenes (1: n ¼ m ¼ 1, Fig. 1) [7] and the results of the
ipso-amination of A (1) to form the amino-substituted dia-
zapentacenes C.
As shown in Scheme 3, we envisioned that the cyclic diketonic
2. Results and discussion
2.1. Synthetic consideration
The approach toward the ring scaffold of polyazaacene A was
realized conceptually by assembling three fundamental building
units via annulation methods as illustrated in Scheme 1. The
building units are an arene-1,2-diamine (ADA, D),
a 1,4-
benzoquinone (BQ, E), and a four-carbon 1,2-diketonic synthon F.
Combination of the synthon F with a dienophile E, via a [4 þ 2]
cycloaddition with bond-multiplicity correction, would lead to the
para-quinone-fused ortho-quinone G. The ortho-quinone G thus
formed could deliver the corresponding polyazaacene A via the
condensation reaction with D (ADA) by its two more electrophilic
adjacent C]O groups; a classic, straightforward reaction that
Scheme 2. Aromatization-driven Grob-fragmentation of the DielseAlder cycloadducts
H.
Please cite this article as: T.-C. Chou et al., Aromatization-driven Grob-fragmentation approach toward polyazaacenes. Synthesis and amination
of multi-functionalized diazapentacenes, Tetrahedron, https://doi.org/10.1016/j.tet.2019.130689

T.-C. Chou et al. / Tetrahedron xxx (xxxx) xxx
3
which displayed a rather complex 1H NMR spectrum and an IR
spectrum containing absorption bands attributable to hydroxyl and
carbonyl groups. Apparently, the product was obtained in the
monohydrate form 5′ resulting from transannular hemiacetal for-
mation; a commonly phenomenon observed in the RuO4 oxidation
of structurally similar DielseAlder adducts [17a,c], as shown in
Scheme 4. Dehydration by benzene under azeotropic reflux yielded
hygroscopic 1,2- diketone 5 (K: m ¼ 1), indicated by the expected
simple and symmetry-reflect 1H NMR spectrum [7].
In practice, monohydrated 1,2-diketone 5′ was used directly in
the condensation reactions with various ADA [D: substituted ben-
zene-1,2-diamines (6aee) or naphthalene-2,3-diamine (6f)] in
AcOH at 45 ꢁC under N2 atmosphere for a period of time to afford
colorless crystals of the corresponding quinoxaline ring-fused de-
rivatives 7aef isolated in moderate yields of 55e75% by direct
filtration. As expected, the successive enolization-oxidation-
fragmentation reactions of 7aef performed under previously
employed protocol (Scheme 2) furnished respectively the bright
yellow-colored solids of diazapentacene esters 1aef, albeit the
isolated yields were only moderate in the range of 45e75%. The
results are summarized in Table 1. It was found necessary to
conduct the condensation reactions at 45 ꢁC to minimize AcOH-
promoted decomposition of 1,2-diketone 5/5′, which occurred at
higher temperature and particularly in the absence of ADA [16,20].
All compounds 7aef were properly characterized and the general
structures of 7 was supported by the single-crystal X-ray analysis of
7f (Insert, Table 1). Compound 1f (reddish solids) derived from 7f is
a diazahexacene derivative, considered here for descriptive con-
Scheme 3. The synthetic approach of the multi-functionalized diazapentacenes A
keyed upon the aromatization-driven Grob fragmentation of the quinoxaline-fused
polycyclic compounds L.
compounds K, which were made available from the DielseAlder
adducts H by Khan's oxidation protocol [RuCl3(cat.)/NaIO4] [17],
might be the source for quinone-annulated ortho-quinones G via
the Grob-type fragmentation promoted by triethylamine or an acid.
Once the ortho-quinones G were in hand, condensation reactions
with ADA (D) would afford the corresponding polyazaacenes A (1).
However, decision was soon made to take an alternative route,
since working with ortho-quinones G having five conjugated
carbonyl groups appears to be disturbing. Thus, we chose to carry
out the condensation reactions [18] of 1,2-diketones K with ADA
(D) to obtain the curve-structured, quinoxaline-fused polycyclic
compounds L, which were then subjected to the base or acid-
promoted Grob-type fragmentation. As expected, the three-step
transformation (H / K / L / A, Scheme 3), keyed upon the
aromatization-driven Grob fragmentation, have realized our
rational thinking to bestow the quinoxaline ring-embedded poly-
azaacenes A, as demonstrated by the synthesis of diazapentacenes
1.
venience to be
a benzodiazapentacene derivative. All dia-
zapentacene esters 1aef were properly characterized by spectral
analyses, and among them 1a, 1b-a, and 1f had been reported
earlier (Table 1, entries 1, 2, and 6) [7]. A case merits attention
(entry 2). Quinoxaline ring-fused compound 7b, unlike others, is
asymmetrical and was expected to render two isomeric fragmen-
tation products, in which the methoxy group is anti (1b-a) or syn
(1b-s) to the methoxycarbonyl group. However, only one
regioisomer was found, which was identified by X-ray crystallog-
raphy to be the anti-isomer 1b-a [7].
The two-step synthesis of diazapentacene derivatives 1 form
1,2-diketone 5/5′ resulted in low overall yields (<40%) of desired
products (Table 1) [21]. With the expectation that the successive
enolization-oxidation-fragmentation transformation of quinoxa-
line ring-fused compound 7 to diazapentacenes 1 could be pro-
moted under acidic conditions, we decided to amend the synthetic
method by a one-pot operation without isolation of the conden-
sation products 7 as shown in Table 2. Thus, a solution of equal
molar of 1,2-diketone 5/5′ and an ADA (6aec, 6f, 6g, and 6h) in
AcOH was heated at 45 ꢁC under N2 atmosphere for 3 h; the same
procedure (Table 1) used previously to ensure the complete con-
version of 5/5′ to the condensation product 7. The reaction mixture
was then heated at refluxing temperature for 24e48 h under air
atmosphere, followed by removal of solvent AcOH under reduced
pressure to give a dark-colored solid residue, which was water-
rinsed and subsequently subjected to stirring at room tempera-
ture with 5% aq. NaOH in CH2Cl2 under air atmosphere for 2 h [22].
The corresponding bright yellow-colored diazapentacene de-
rivatives 1aec and 1feh were obtained in much improved overall
yields ranging from about 70% to 90%. It is interesting to note that
both anti- and syn-regioisomers were observed in diazapentacene
derivatives 1 derived from unsymmetrical ADA (6b, 6g, and 6h).
The ratios of anti-to syn-isomer for 1b-a:1b-s, 1g-a:1g-s, and 1h-
a:1h-s were 2.3:1, 1.3:1, and 1:1.9, respectively, determined by 1H
NMR spectral analysis. It is also interesting to recall that only one
regioisomer (1b-a) was observed previously (Table 1, entry 2) [7].
The observations suggest that the Grob-type fragmentation
2.2. Synthesis of diazapentacenes
The known DielseAlder cycloadduct 4 (H: m ¼ 1) between TDCp
(2) and naphthalene-1,4-dione (3, E: m ¼ 1) was utilized as the
starting material [12,14,19]. As shown in Scheme 4, when com-
pound 4 was subjected to the modified Khan's oxidation procedure
[17] employing RuCl3$3H2O/NaIO4 in a solvent system of CHCl3/
CH3CN/H2O (3:3:1) at 0 ꢁC for 12 h, a product was isolated in 96%,
Scheme 4. The synthesis of 1,2-diketone 5 and its monohydrated derivative 5′.
Please cite this article as: T.-C. Chou et al., Aromatization-driven Grob-fragmentation approach toward polyazaacenes. Synthesis and amination
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Table 1
Two-step synthesis of diazapentacene derivatives 1aef from 1,2-diketone 5/5’ via the condensation products 7aef followed by the consecutive enolization-oxidation-
fragmentation reactions of 7aef promoted by triethylamine.
entry
1
6
7
1
R1
R2
H
R3
H
R4
H
(time1, yield) a,b
(time2, yield) a,b
6a
6b
6c
H
7a
7b
7c
1a
(2 h, 71%)
(4 h, 76%)
(24 h, 52%)
(18 h, 49%)
2
3
H
H
H
OMe
OMe
H
H
1b-a
1c
OMe
(3 h, 54%)
(30 h, 76%)
(30 h, 65%)
4
5
6d
6e
H
H
H
H
7d
7e
1d
1e
(0.5 h, 59%)
(0.5 h, 56%)
(30 h, 68%)
6
6f
H
H
7f
1f
c
(3 h, 76%)
(24 h, 48%)
a
The progress of reaction (the reaction time) was monitored by TLC or 1H NMR spectroscopy.
The yields are for the isolated products after purification via flash chromatography or recrystallization.
The structure of compound 7f is supported and shown in the Table by its X-ray crystal structure.
b
c
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5
Table 2
The synthesis of diazapentacenes 1 from 1,2-diketone 5/5′ and arene-1,2-diamine (ADA) by a one-pot operation without isolation of the intermediate quinoxaline ring-fused
compounds 7.
entry
1
ADA
R1
H
R2
H
R3
H
R4
H
Product (1)
Yield (%)a
92
6a
2
6b
H
H
OMe
OMe
H
74
3
4
6c
6f
H
H
OMe
H
H
79
89
benzo
5
6
6g
6h
NO2
H
H
H
H
H
83
82
H
NO2
a
Isolated yields of one-pot operation.
pathways for 7 leading to the regioisomeric diazapentacenes 1
could be directed by the electronic nature and the location of
substituent at quinoxaline ring. We discuss this point in the next
section.
mesomeric. In contrast, the bridge-opening of hydroquinone 8
(pathway ii), lacking the electron-withdrawing enone moiety, in-
volves only electron-flow from eOMe directly to C]N group,
forming a zwitterion with mesomeric structures M1 and M2. Both
fragmentation pathways are expected to be accelerated by the acid
catalyst, which forms complex with carbonyl oxygen or imine ni-
trogen and hence increases electron pull ability of aromatic rings in
hydroquinone 8 and benzoquinone 9. The intermediate zwitterions
M and N thus generated expel chloride ion to achieve aromatization
followed by elimination of methyl group in form of CH3Cl to yield
diazapentacene derivatives 1 and the antecedent non-oxidized
hydroquinone esters 10, respectively.
Both fragmentation pathways proposed in Scheme 5 would be
additionally facilitated by the presence of electron-withdrawing
substituents at quinoxaline ring. Particularly, when such an
electron-withdrawing substituent is located ortho or para to the
imine group that accepts the electrons flowing from the adjacent
bridge CeC bond being ruptured, because the zwitterions thus
formed would gain more stabilization. The preference of one
2.3. Mechanistic consideration
The synthesis of the flat diazapentacene carboxylates 1 (A) is
keyed upon the aromatization-driven Grob fragmentation of
quinoxaline-fused, bridged polycyclic compounds 7 (L) (Scheme 3).
Scheme 5 illustrates two plausible pathways for the fragmentation
of 7 which involve the unstable hydroquinone 8 and benzoquinone
9 as key intermediates. As shown for the bridge-opening of ben-
zoquinone 9 (pathway i), the fragmentation is driven by, besides
the relief of ring strain and aromatization, the pushepull setup for
electrons to flow from eOMe to C]O group (a) relayed by the
enone C]C bond [12,15] or (b) directly to the nitrogen atom of
properly situated C]N group [16] to form a zwitterion having a
structure of N1 or N2, respectively. Structures N1 and N2 are in fact
Please cite this article as: T.-C. Chou et al., Aromatization-driven Grob-fragmentation approach toward polyazaacenes. Synthesis and amination
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T.-C. Chou et al. / Tetrahedron xxx (xxxx) xxx
mixture of 1b-a and 1b-s in a ratio of 2.2:1, the opposite regiose-
lectivity displayed by 7h (R3 ¼ NO2). Incidentally, the regiose-
lectivity was much enhanced in the Et3N-promoted fragmentation
of 7b in CH2Cl2 at lower temperature (rt), which gave only the anti-
isomeric 1b-a (Table 1) [7].
2.4. Amination of Diazapentacene 1a
In all the cases, the aromatic nucleophilic ipso-substitution [8] of
1a at the aryl carbon bearing chlorine atom to produce the amino-
substituted diazapentacene derivatives 12 were performed in
dichloromethane using triethylamine as HCl-scavenger. The results
of the ipso-amination reactions of 1a are outlined in Scheme 6.
Thus, a primary amine [butan-1-amine (11a), phenylmethanamine
(11b), cyclohexanamine (11c), aniline (11d)] or a secondary amine
[piperidine (11e)] was dissolved in CH2Cl2 and added in dropwise
manner to an ice-water cooled CH2Cl2 solution containing 1a and
molar equivalent of Et3N. A change of solution color from pale
yellow to pink or dark purple was instantly noticed [23]. After the
addition of amine was complete (<30 min), the reaction mixture
was allowed to warm to room temperature and stirred for a period
of time, thereby affording the dark colored solids of amino-
substituted diazapentacenes 12a-e in yields ranging from 80% to
90%. Under similar condition, ipso-amination of 1a to render
amino-substituted diazapentacenes 12f and 12g was realized in
yields of 99% and 65%, respectively, via reactions with the corre-
sponding hydrochloride salts of N1-(arylmethyl)propane-1,3-
diamines 11f [24] and 11g. When a CH2Cl2 solution containing 1a
and Et3N was treated under similar condition with 0.5 molar
equivalent of propane-1,3-diamine (11h) as an aminating agent, a
binary amination occurred to furnish the corresponding 1,5-
diazapentandiyl-tethered diazapentacene 12h in 76% yield.
In the 1H and 13C NMR spectra of diazapentacene derivatives
12a-h, besides the signals and pattern inherited from 1a, signals
assignable to the corresponding hydrogen and carbon atoms of the
appending alkylamino-substituent were observed (see Supple-
mentary data). Particularly worthy of attention is the observed
diagnostic NeH proton signal at extra lower field (d ~ 13 ppm,
Scheme 6) in the 1H NMR spectra of compounds 12a-d/f-h derived
from the ipso-amination with primary amines (11a-d/f-h). The low-
field signal is attributable to the intramolecular hydrogen bonding
between the NeH and nearby oxygen atom of naphthoquinone C]
O group, which is also revealed in the X-ray crystal structures of 12a
and 12f.
Single crystals of 12a and 12f were grown by slow evaporation
of CHCl2 or CHCl3/n-Hex solution. The ORTEP plots of their X-ray
crystal structures are depicted in Fig. 2. The tables for crystal data/
structure refinement are provided in the Supplementary Data. The
n-butylamino-appended diazapentacene 12a displayed two mo-
lecular structures in the crystal, different in the conformation of n-
butyl chain. Two conformational isomers exhibited the NeHꢂꢂꢂO
hydrogen bonding of different distance and angle (Fig. 2A). Com-
pound 12f (Fig. 2B) consists of electron-accepting diazapentacene
and electron-releasing naphthalene rings, connected by a 1,5-
diazahexandiyl linker. An intramolecular hydrogen bonding be-
tween NeH and C]O groups was also observed. Resembling the
previous reported crystal structure of 1b-a [7], the plane of dia-
zapentacene ring of 12a and 12f is slightly twisted (ca. 6ꢁ/10ꢁ) and
aligns in a nearly perpendicular manner (ca. 101ꢁ/93ꢁ) with the
plane of the appending methoxycarbonyl (eCOOMe) group.
The electron-deficient aromatic rings tend to self-assemble in
Scheme 5. Two plausible pathways for the Grob-fragmentation of the quinoxaline
ring-fused compounds 7.
bridge-opening mode over the other is consequently expected to be
dictated by the electronic nature and location of substituent at
quinoxaline ring. For example, if R1 (or R3) is an electron-
withdrawing substituent, such as eNO2, the bridge-opening
mode illustrated in Scheme 5 would be favored, leading to the
formation of more anti-regioisomer (or syn-regioisomer) in the
final product mixture of 1. The mechanistic rationale is supported
by the experimental results. As shown in Table 2, the fragmentation
of 7g (R1 ¼ NO2) in AcOH resulted in the formation of a mixture of
regioisomeric 1g in favor of anti-regioisomer 1g-a by a ratio of
1.3:1, whereas the fragmentation of 7h (R3 ¼ NO2) gave a mixture of
1h-a and 1h-s in a ratio of 1:1.9. Exchanging NO2 group by an
electron-releasing substituent, the AcOH-catalyzed fragmentation
of 7b (R3 ¼ OMe) at refluxing temperature led to the formation of a
the solid state by the cofacial packing arrangement driven by
stacking interactions [25]. As illustrated in Fig. 3, single crystals of
12a and 12f (cf. 1a and 1b-a) [7] evidently implement -stacking
motifs in mode of either direct face-to-face or parallel-displaced
p-
p
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T.-C. Chou et al. / Tetrahedron xxx (xxxx) xxx
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Scheme 6. Amination of Diazapentacene 1a.
Fig. 3. The crystal packing diagrams showing cofacial
p
ꢀ
p
stacking structures: (A) 12a
and (B) 12f. Hydrogen atoms in the crystal packing diagrams are hidden for clarity.
Two conformers of 12a show different stacking modes independently. Compound
12f displays stacking arrangement of the electron-rich naphthalene ring against
p p
ꢀ
pꢀp
the electron-deficient diazapentacene ring and the solvate (CHCl3) molecules in the
crystal are hidden.
Fig. 2. ORTEP plots of amino-substituted diazapentacenes: (A) Two observed. con-
formers of 12a and (B) 12f.
Please cite this article as: T.-C. Chou et al., Aromatization-driven Grob-fragmentation approach toward polyazaacenes. Synthesis and amination
of multi-functionalized diazapentacenes, Tetrahedron, https://doi.org/10.1016/j.tet.2019.130689

8
T.-C. Chou et al. / Tetrahedron xxx (xxxx) xxx
geometry [26] between aromatic rings as pivotal crystal packing
motifs. The -stacked column has regular alternating intermolec-
ular distances forming cofacial -stacks of -dimers. As shown in
Fig. 3A, each of conformational isomeric molecules of 12a inde-
pendently stacks against identical molecules on both sides in a
obtained at an electron beam energy of 70 eV, unless otherwise
specified. Fast atom bombardment (FAB) mass spectra were ob-
tained with a resolution of 8000 and 3000 for HR and LR FAB-mass
spectra, respectively. The source accelerating voltage was operated
at 10 kV with Xe gun for FAB-mass spectra, using 3-nitrobenzyl
alcohol as matrix. Low resolution MS spectral data were reported
at m/z, and the relative intensities (%) were expressed in paren-
thesis, where the base peak was calibrated to be 100. The X-ray
crystallographic data were recorded with a Bruker AXS SMART
p
p
p
head-to-tail style via cofacial p-stacking interactions, alternatively
in mode of face-to-face and parallel-displaced geometry, leading to
the formation of ribbon-like packing structures along crystallo-
graphic ac-plane. The most prominent feature displayed in the
crystal packing structure of 12f is the head-to-tail, face-to-face
stacking arrangement of the electron-rich naphthalene and the
electron-deficient diazapentacene rings (Fig. 3B), which well
p
ꢀ
p
APEX CCD X-ray diffractometer. Graphite monochromatized Mo K
a
radiation [
l
¼ 0.71073 Å] and temperature of 298 (2) K were used.
The CCD data were processed with SAINT and the structures were
solved by direct method (SHELXS-97) and refined on F2 by full-
matrix least-squares techniques (SHELXL-97). Thin-layer chroma-
tography (TLC) was performed on E. Merck silica gel 60 F254 plate
(0.20 mm). The developed TLC sheets were examined under UV
light. 1,4-Naphthoquinone (3) was commercially available and was
purified by recrystallization. Unless otherwise stated, all other re-
agents, such as 1,2-diaminoarenes (6) and amines (11) were pur-
chased from Merck or Aldrich, and used without further
purification; solvents were used without further distillation.
demonstrates an electron donoreacceptor driven
[27], forming deck-like packing structures along crystallographic
p p stacking
ꢀ
ab-plane.
3. Conclusion
We have developed a general synthetic approach (Schemes 1
and 3) toward the multi-functionalized polyazaacene derivatives
having the generic structure A by demonstrating the synthesis of
quinoxaline ring-embedded diazapentacene esters 1 (Tables 1 and
2). The synthetic strategy utilizes three fundamental building units:
4.2. Synthesis
1,2,3,4-tetrachloro-5,5-dimethoxycyclopentadiene (TDCp, 2),
a
naphthalene-1,4-dione (BQ, 3), and an arene-1,2-diamines (ADA, 6).
The synthetic approach basically consists of three operations: (i)
oxidation of the dichloroetheno-bridge in the Diels-Alder cyclo-
adduct 4 derived from BQ and TDCp, (ii) condensation of the 1,2-
4.2.1. Ruthenium-promoted NaIO4-oxidation of Diels-Alder
cycloadduct 4. preparation of 1,2-diketone 5
A solution of RuCl3$3H2O (49 mg, 0.24 mmol) in water (16 mL)
was added in portions to a suspension of 4 (1000 mg, 2.37 mmol)
and NaIO4 (760 mg, 3.55 mmol) in a mixture of CHCl3 (48 mL) and
CH3CN (48 mL), cooled with an ice-water bath at 0 ꢁC. The progress
of reaction was monitored by TLC or 1H NMR spectroscopy. After
the reaction was completed (~12 h), the lower organic layer (pale
yellow colored) of the resulting reaction mixture was separated
from the top aqueous layer (red brownish colored) and filtered
through a pad of Celite to give 1,2-diketone 5 in monohydrate form
5' (910 mg, 96%) after removal of solvent. 1,2-Diketonic mono-
hydrate 5′ could be dehydrated to hygroscopic 1,2-diketone 5 by
benzene under azeotropic reflux with a Dean-Stark apparatus.
diketone
5 thus generated with an ADA to give curved
quinoxaline-fused polycyclic compounds 7, followed by (iii) an one-
pot, three-reaction process keyed upon the base- or acid-catalyzed
aromatization-driven Grob-type fragmentation to produce planar
quinoxaline ring-embedded diazapentacene esters 1. We have also
taken advantage of the electron affinity nature of diazapentacene
ring bestowed by the electron-withdrawing functional groups to
examine the ipso-amination of 1a with electron-donating primary
and secondary amines as nucleophiles (Scheme 6), paving the way
for exploring prospective application of synthesizing the DepeA
molecules (pushepull systems) [28]. The present synthetic strategy
appears flexible and feasible as manifested by the occurrence of
two changeable building units: BQ (3) and ADA (6), and the
amendable functional groups. We envisage the synthetic approach
could be further exploited to make analogous polyazaacene sys-
tems of interest and applications.
5': colorless solids; mp 142e148 ꢁC (dehydrated); IR (cmꢀ1
3545, 3320 (br), 1788, 1677, 1597, 1278, 1225; 1H NMR (200 MHz,
CDCl3) 3.68 (s, 3 H), 3.70 (s, 2 H), 3.76 (s, 3 H), 7.48e7.56 (m, 1 H),
)
d
7.66e7.73 (m, 1 H), 7.92e8.00 (m, 2 H); MS (FAB) m/z (%) 403
(Mþ þ 2, 11.5), 401 (Mþ, 15.5), 383 (Mþ ꢀ H2O, 8.2), 333 (28.0), 307
(68.2), 301 (32.5), 289 (49.7). HRMS (FAB) Calcd for C17H15Cl2O7
(Mþ þ H): 401.0189; Found: 401.0209.
4. Experimental section
5: colorless solids; mp 267 ꢁC (decomp.); IR (cmꢀ1) 1798, 1770,
1690, 1590, 1289, 1220; 1H NMR (200 MHz, CDCl3)
d 3.61 (s, 3 H),
4.1. General
3.83 (s, 3 H), 4.03 (s, 2 H), 7.77 (dd, J ¼ 3.2, 6.0 Hz, 2H), 7.92 (dd,
J ¼ 3.3, 5.9 Hz, 2H). HRMS (FAB) Calcd for C17H13Cl2O6 (Mþ þ H):
383.0084; Found: 383.0090.
Melting points were determined in capillaries and are uncor-
rected. 1H and 13C NMR spectra were recorded at ambient tem-
perature. Chemical shift
expressed in unit of ppm and Hz, respectively. The chemical shift of
CHCl3 was calibrated at
7.26 ppm in 1H NMR spectra and
77.0 ppm in 13C NMR spectra. Multiplicities of splitting pattern in
(
d
)
and coupling constant (J) were
4.2.2. General procedure for the preparation of quinoxaline-fused
polycyclic compounds 7
Into a solution of 1,2-diketone monohydrate 5′ or 5 (1.00 mmol)
in acetic acid (8 mL) was added arene-1,2-diamine (1.10 mmol) [ο-
phenylenediamine (6a), 4-methoxybenzene-1,2-diamine (6b), 4,5-
d
d
1H NMR spectra were abbreviated: s (singlet), d (doublet), t
(triplet), q (quartet), m (multiplet) and br (broad). All 13C NMR
spectra were recorded with the protons completely decoupled. The
number of attached hydrogen on the carbon atom was determined
by the Distortionless Enhancement by Polarization Transfer (DEPT)
analysis. Infrared (IR) spectra were obtained using samples sus-
pended in a KBr disk. The spectral data were recorded in unit of
wavenumber (cmꢀ1). Mass spectral (MS) analysis, both low and
high resolution (HRMS), was performed with a double focusing
mass spectrometer. Electron-Impact (EI) mass spectra were
dimethoxybenzene-1,2-diamine
(6c),
3,4-diaminobenzo-15-
crown-5-ether (6d), 3,4-diaminobenzo-18-crown-6-ether (6e), or
naphthalene-2,3-diamine (6f)]. The reaction mixture was stirred at
45 ꢁC under N2 atmosphere for a period of time (~3 h), and the
progress of reaction was monitored by TLC or 1H NMR spectroscopy.
After the reaction was complete, the reaction mixture was cooled to
room temperature. The resulting solid residue of quinoxaline
product was collected by filtration, washed with acetic acid (~2 mL)
and then with water (~10 mL). The filtrate was added water to
Please cite this article as: T.-C. Chou et al., Aromatization-driven Grob-fragmentation approach toward polyazaacenes. Synthesis and amination
of multi-functionalized diazapentacenes, Tetrahedron, https://doi.org/10.1016/j.tet.2019.130689

T.-C. Chou et al. / Tetrahedron xxx (xxxx) xxx
9
precipitate the second crop of crude product, collected by filtration.
The combined crude product was purified via recrystallization from
EtOH/CHCl3 (3/2 by vol.) to afford the corresponding pure
quinoxaline-fused polycyclic compounds 7aef.
70 eV) m/z (%) 690 (Mþ þ 2, 63), 688 (Mþ, 90), 652 (Mþ ꢀ HCl, 52),
617 (Mþ ꢀ 2Cl ꢀ H, 100); HRMS (EI, 70 eV) Calcd for C33H34Cl2N2O10
(Mþ): 688.1591; Found: 688.1599.
7f. Reaction time 3 h, yield 76%, dark green solids; mp 224 ꢁC
7a. Reaction time 2 h, yield 71%, colorless crystals; mp 239 ꢁC
(decomp.); IR (cmꢀ1) 1687, 1590, 1295, 1182, 999; 1H NMR
(400 MHz, CDCl3) d 3.55 (s, 3 H), 3.92 (s, 3 H), 4.20 (s, 2 H), 6.95 (dd,
(decomp.); IR (cmꢀ1) 1686, 1590, 1290, 1248, 1178, 999; 1H NMR
(400 MHz, CDCl3)
d
3.52 (s, 3H), 3.89 (s, 3H), 4.16 (s, 2H), 7.06 (dd,
J ¼ 5.8, 3.3 Hz, 2H), 7.47 (dd, J ¼ 5.8, 3.3 Hz, 2H), 7.58 (dd, J ¼ 6.5,
J ¼ 5.8, 3.3 Hz, 2H), 7.41 (dd, J ¼ 5.8, 3.3 Hz, 2H), 7.62 (dd, J ¼ 6.2,
3.2 Hz, 2H), 8.02 (dd, J ¼ 6.5, 3.2 Hz, 2H), 8.50 (s, 2 H); 13C NMR
3.2 Hz, 2H), 7.91 (dd, J ¼ 6.2, 3.2 Hz, 2H); 13C NMR (100 MHz, CDCl3)
(100 MHz, CDCl3) d 190.6 (C), 151.3 (C), 138.2 (C), 134.7 (C), 133.6 (C),
d
190.6 (C), 150.5 (C), 142.1 (C), 134.7 (C), 133.4 (CH), 130.2 (CH),
133.5 (CH), 128.4 (CH), 127.8 (CH), 127.3 (CH), 126.2 (CH), 110.0 (C),
74.0 (C), 53.9 (CH), 52.8 (CH3), 52.6 (CH3); MS (FAB) m/z (%) 507
(Mþ þ H þ 2, 54.8), 506 (Mþ þ 2, 41.9), 505 (Mþ þ H, 65.3), 504 (Mþ,
26.1), 433 (22.4), 337 (23.7), 289 (29.9). HRMS (FAB) Calcd for
129.0 (CH), 126.1 (CH), 110.9 (C), 73.9 (C), 54.1 (CH), 52.8 (CH3), 52.6
(CH3); MS (FAB) m/z (%) 457 (Mþ þ H þ 2, 80.6), 456 (Mþ þ H þ 1,
54.9), 455 (Mþ þ H, 93.5), 454 (Mþ, 21.3), 307 (59.7), 289 (51.7).
HRMS (FAB) Calcd for C23H17Cl2N2O4 (Mþ þ H): 455.0560; Found:
455.0553. Anal Calcd for C23H16Cl2N2O4: C, 60.67; H, 3.54; N, 6.15;
O, 14.06; found: C, 60.72; H, 3.55; N, 5.94; O, 14.18.
C
27H19Cl2N2O4 (Mþ þ H): 505.0716; Found: 505.0714. Anal Calcd
for C27H18Cl2N2O4: C, 64.17; H, 3.59; N, 5.54; O, 12.66; found: C,
64.05; H, 3.81; N, 5.36; O, 12.77.
7b. Reaction time 4 h, yield 76%, green solids; mp 250 ꢁC
(decomp.); IR (cmꢀ1) 1711, 1692, 1660, 1624, 1590, 1487; 1H NMR
4.2.3. General procedure for the synthesis of diazapentacene esters
1 from 7
(500 MHz, CD2Cl2)
d 3.53 (s, 3 H), 3.91 (s, 3 H), 3.93 (s, 3 H), 4.15 (s,
2 H), 7.16e7.18 (m, 2H), 7.26 (d, J ¼ 2.5 Hz,1H), 7.31 (dd, J ¼ 9, 2.5 Hz,
Triethylamine (2.12 mmol) was added into an uncapped reac-
tion bottle containing a stirring solution of quinoxaline-fused
polycyclic compounds 7 (1.00 mmol) in dichloromethane (30 mL)
at room temperature. The progress of reaction was monitored by
TLC or 1H NMR spectroscopy. After the compound 7 completely
disappeared, the reaction mixture was cooled with an ice-water
bath and quenched by the addition of saturated aqueous ammo-
nium chloride solution (25 mL). The organic layer was separated,
washed sequentially with water (50 mL ꢃ 3) and brine (50 mL ꢃ 3).
The organic layer was dried over anhydrous magnesium sulfate and
filtered, and the filtrate was concentrated in vacuo. The colored
solid residue thus obtained was purified via flash chromatography
and recrystallization (CHCl3/EtOH) to afford the corresponding
pure diazapentacene esters 1aef.
1H), 7.41e7.44 (m, 2 H), 7.78 (d, J ¼ 9 Hz, 1H); 13C NMR (125 MHz,
CD2Cl2) d 191.1 (C), 191.0 (C), 161.4 (C), 150.6 (C), 148.0 (C), 144.2 (C),
138.2 (C), 135.0 (2 ꢃ C), 133.8 (CH), 133.7 (CH) (CH), 130.0 (C) (CH),
126.2 (C) (CH), 123.1 (C) (CH), 111.3 (C), 107.4 (CH), 74.5 (C), 74.3 (C),
56.2 (CH) (CH3), 54.6 (2 ꢃ CH), 53.0 (CH3), 52.8 (CH3); MS (EI) m/z
(%) 484 (Mþ, 63), 449 (Mþ ꢀ Cl, 33), 413 (Mþ ꢀ 2Cl, 100), 317 (55).
HRMS (EI) Calcd for
C
24H18Cl2N2O5 (Mþ): 484.0593; Found:
484.0591. Anal Calcd for C24H18Cl2N2O5: C, 59.40; H, 3.74; N, 5.77;
O, 16.48; found: C, 59.28; H, 3.70; N, 5.68; O, 16.25.
7c. Reaction time 3 h, yield 54%, colorless crystals; mp
277e278 ꢁC; IR (cmꢀ1) 2952 (w), 2930 (w), 2857 (w), 1684 (s), 1591
(w), 1467 (m), 1294 (w), 1237 (s), 1192 (m), 734 (m); 1H NMR
(500 MHz, CDCl3, ppm)
7.15 (dd, J ¼ 5.8, 3.3 Hz, 2 H), 4.15 (s, 2 H), 3.95 (s, 6 H), 3.88 (s, 3 H),
3.51 (s, 3 H); 13C NMR (125 MHz, CDCl3)
190.9 (C), 152.7 (C), 147.7
d
7.48 (dd, J ¼ 5.8, 3.3 Hz, 2 H), 7.23 (s, 2 H),
1a. Reaction time 24 h, yield 52%, bright yellow crystallines; mp
d
319e321 ꢁC (decomp.); IR (cmꢀ1) 1736, 1680, 1590, 1560, 1505,
(C), 139.3 (C), 134.8 (C), 133.4 (CH), 126.2 (CH), 111.3 (C), 106.9 (CH),
74.1 (C), 56.4 (CH3), 54.4 (CH), 52.7 (CH3), 52.5 (CH3); MS (EI,
70 eV) m/z (%) 516 (Mþ þ 2, 15), 514 (Mþ, 22), 479 (Mþ ꢀ Cl, 21), 443
(Mþ ꢀ 2Cl ꢀ H, 100); HRMS (EI, 70 eV) Calcd for C25H20Cl2N2O6
(Mþ): 514.0698; Found: 514.0692; Anal. Calcd for C25H20Cl2N2O6: C,
58.27; H, 3.91; N, 5.44; O, 18.63; Found: C, 58.14; H, 3.80; N, 5.43; O,
18.55.
7d. Reaction time 0.5 h, yield 59%, colorless crystals; mp
246e250 ꢁC; IR (cmꢀ1) 2950 (w), 2873 (w), 1688 (s), 1592 (w), 1447
(m), 1292 (m), 1246 (s), 1190 (s), 1129 (s), 752 (m); 1H NMR
1405, 1244, 1009; 1H NMR (400 MHz, CDCl3)
d
4.29 (s, 3 H),
7.85e7.90 (m, 2 H), 8.01e8.03 (m, 2 H), 8.32e8.34 (m, 2 H),
8.39e8.42 (m, 2 H); 13C NMR (100 MHz, CDCl3)
181.6 (C), 181.3 (C),
d
168.0 (C) 145.2 (C), 145.1 (C), 141.9 (C), 141.4 (C), 139.5 (C), 136.1 (C),
135.6 (C), 135.5 (CH), 134.7 (CH), 133.8 (CH), 133.7 (CH), 133.1 (C),
130.6 (CH), 130.5 (CH), 129.7 (C), 128.8 (C), 128.3 (CH), 127.8 (CH),
53.6 (CH3); MS (EI) m/z (%) 404 (Mþ, 11.8), 402 (Mþ, 34.6), 373
(34.4), 372 (32.0), 371 (Mþ ꢀ OMe, 100), 252 (24.6). HRMS (EI)
Calcd for C22H11ClN2O4 (Mþ): 402.0407; Found: 402.0399. Anal
Calcd for C22H11ClN2O4: C, 65.60; H, 2.75; N, 6.95; O, 15.89; found:
C, 65.60; H, 2.92; N, 6.89; O, 15.53.
(500 MHz, CDCl3)
d
7.43 (dd, J ¼ 5.8, 3.3 Hz, 2 H), 7.15 (dd, J ¼ 5.8,
3.3 Hz, 2 H), 7.13 (s, 2 H), 4.15e4.11 (m, 6 H), 3.92e3.91 (m, 4 H), 3.86
1b. Reaction time 18 h, yield 49%. bright yellow crystallines; mp
250e251 ꢁC; sparsely soluble in CHCl3 and CH2Cl2, IR (cmꢀ1) 1734,
1678, 1622, 1471, 1409, 1297, 1239, 1202, 1004; 1H NMR (500 MHz,
(s, 3 H), 3.80e3.72 (m, 8 H), 3.49 (s, 3 H); 13C NMR (125 MHz, CDCl3,
ppm) d 190.8 (C), 152.3 (C), 147.4 (C), 139.2 (C), 134.6 (C), 133.5 (CH),
126.0 (CH), 111.2 (C), 107.3 (CH), 74.0 (C), 70.9 (CH2), 69.7 (CH2), 68.6
(CH2), 68.2 (CH2), 54.3 (CH), 52.6 (CH3), 52.4 (CH3); MS (EI,
70 eV) m/z (%) 646 (Mþ þ 2, 21), 644 (Mþ, 30), 608 (Mþ ꢀ HCl, 22),
573 (Mþ ꢀ 2Cl ꢀ H, 100); HRMS (EI, 70 eV) Calcd for C31H30Cl2N2O9
(Mþ): 644.1328; Found: 644.1335; Anal. Calcd for C31H30Cl2N2O9: C,
57.68; H, 4.68; N, 4.34; O, 22.31; Found: C, 57.80; H, 4.28; N, 4.19; O,
22.50.
7e. Reaction time 0.5 h, yield 58%, colorless crystals; mp
242e246 ꢁC; IR (cmꢀ1) 2949 (w), 2818 (w), 1687 (s), 1590 (w), 1444
(m), 1290 (m), 1240 (s), 1189 (s), 732 (w); 1H NMR (500 MHz, CDCl3,
CDCl3)
d
4.10 (s, 3 H), 4.28 (s, 3H), 7.59 (d, J ¼ 2.5 Hz, 1H), 7.66 (dd,
J ¼ 9.5, 2.5 Hz, 1 H), 7.84e7.91 (m, 2 H), 8.18 (d, J ¼ 9.5 Hz, 1 H), 8.33
(d, J ¼ 7.5 Hz,1H), 8.40 (d, J ¼ 7.5 Hz,1H); 13C NMR (125 MHz, CDCl3)
d
181.6, 181.1, 168.1, 164.0, 146.9, 142.7, 141.9, 139.5, 138.0, 135.9,
135.4, 135.2, 134.4, 132.8, 131.4, 129.9, 128.7, 128.2, 128.0, 127.5,
104.9, 56.6, 53.3; MS (FAB) m/z (%) 432 (Mþ, 49), 401 (Mþ ꢀ OMe,
100), HRMS (EI) Calcd for C23H13ClN2O5 (Mþ): 432.0513; Found:
432.0518. Anal Calcd for C23H13ClN2O5: C, 63.83; H, 3.03; N, 6.47; O,
18.48; found: C, 63.60; H, 2.98; N, 6.15; O, 18.45.
1c. Reaction time 30 h, yield 76%, bright yellow crystallines;
mp > 325 ꢁC (decomp.); IR (cmꢀ1) 3022 (w), 2953 (w), 2923 (w),
2850 (w), 1738 (m), 1681 (m), 1553 (w), 1414 (m), 1295 (s), 1230 (s),
ppm)
7.16 (s, 2 H), 4.20e4.13 (m, 6 H), 3.99e3.90 (m, 4 H), 3.87 (s, 3 H),
3.77e3.68 (m,12 H), 3.50 (s, 3 H); 13C NMR (125 MHz, CDCl3)
190.9
d
7.45 (dd, J ¼ 5.3, 3.3 Hz, 2 H), 7.18 (dd, J ¼ 5.8, 3.3 Hz, 2 H),
d
1198 (m), 724 (w); 1H NMR (500 MHz, CDCl3)
d
8.39 (d, J ¼ 7.5 Hz,
(C), 152.3 (C), 147.5 (C), 139.2 (C), 134.7 (C), 133.7 (CH), 126.1 (CH),
111.3 (C), 107.4 (CH), 74.1 (C), 70.8 (CH2), 70.6 (CH2), 70.3 (CH2), 68.9
(CH2), 68.8 (CH2), 54.4 (CH), 52.7 (CH3), 52.5 (CH3); MS (EI,
1 H), 8.22 (d, J ¼ 7.0 Hz, 1 H), 7.88 (t, J ¼ 6.8 Hz, 1 H), 7.83 (t,
J ¼ 7.0 Hz, 1 H), 7.55 (s, 1 H), 7.44 (s, 1 H), 4.28 (s, 3 H), 4.16 (d,
J ¼ 5.5 Hz, 6 H); 13C NMR (125 MHz, CDCl3, ppm)
d 181.6 (C), 181.3
Please cite this article as: T.-C. Chou et al., Aromatization-driven Grob-fragmentation approach toward polyazaacenes. Synthesis and amination
of multi-functionalized diazapentacenes, Tetrahedron, https://doi.org/10.1016/j.tet.2019.130689

10
T.-C. Chou et al. / Tetrahedron xxx (xxxx) xxx
(C), 168.4 (C), 157.2 (C), 157.1 (C), 144.2 (C), 144.1 (C), 140.6 (C), 140.0
(C), 138.1 (C), 135.4 (C), 135.1 (CH), 135.1 (C), 134.2 (CH), 132.8 (C),
128.5 (C), 128.0 (CH), 127.6 (C), 127.4 (CH), 105.7 (CH), 105.6 (CH),
57.1 (CH3), 57.0 (CH3), 53.3 (CH3); MS (EI, 70 eV) m/z (%) 464
(Mþ þ 2, 20), 462 (Mþ, 57), 431 (Mþ ꢀ OMe, 100); HRMS (EI, 70 eV)
Calcd for C24H15ClN2O6 (Mþ): 462.0619; Found: 462.0617; Anal.
Calcd for C24H15ClN2O6: C, 62.28; H, 3.27; N, 6.05; O, 20.74; Found:
C, 61.96; H, 3.40; N, 5.79; O, 20.57.
under reflux for 24e48 h, the solvent (AcOH) was removed under
reduced pressure. The resulting dark-colored residue (containing
compounds 1 and 10, analyzed by 1H NMR spectroscopy) was
rinsed with water and dissolved in dichlomethane. An aqueous
solution of NaOH (5%) or KOH (15%) was then added and the re-
action mixture was stirred at room temperature for a period of
time. The progress of reaction was monitored by TLC or 1H NMR
spectroscopy or color changing from brown to yellow. After the
reaction was completed (<2 h), the lower organic layer of the
resulting reaction mixture was separated, washed with water,
filtered through a pad of Celite, and concentrated under reduced
pressure. The solid residue thus obtained was purified via flash
chromatography or recrystallization to afford the corresponding
pure colored diazapentacene esters 1a (92%), 1b (74%), 1c (79%), 1f
(89%), 1g (83%), and 1h (82%).
1d. Reaction time 30 h, yield 65%, bright yellow crystallines;
mp > 316e318 ꢁC (decomp.); IR (cmꢀ1) 2941 (w), 2875 (w), 1736
(m), 1678 (m), 1561 (w), 1449 (m), 1296 (s), 1227 (m), 1198 (m), 728
(w); 1H NMR (500 MHz, CDCl3)
d
8.39 (d, J ¼ 7.5 Hz, 1 H), 8.32 (d,
J ¼ 8.0 Hz, 1 H), 7.88 (t, J ¼ 7.0 Hz, 1 H), 7.83 (t, J ¼ 7.5 Hz, 1H), 7.42 (s,
1 H), 7.34 (s, 1 H), 4.37 (d, J ¼ 3.0 Hz, 4 H), 4.28 (s, 3 H), 4.00 (s, 4 H),
3.77 (dd, J1 ¼7.1 J2 ¼ 4.8 Hz, 8 H); 13C NMR (125 MHz, CDCl3)
d 181.5
(C), 181.3 (C), 168.4 (C), 156.7 (C), 156.5 (C), 144.1 (C), 144.0 (C), 140.4
(C), 140.0 (C), 138.0 (C), 135.4 (C), 135.0 (CH), 135.0 (C), 134.2 (CH),
132.9 (C), 128.3 (C), 127.9 (CH), 127.4 (CH), 127.3 (C), 105.8 (d, 2 C),
71.1 (CH2), 69.8 (CH2), 69.0 (CH2), 68.9 (CH2), 68.5 (CH2), 53.2 (CH3);
MS (EI, 70 eV) m/z (%) 594 (Mþ þ 2, 19), 592 (Mþ, 47), 563 (Mþ þ 2 e
OMe, 2), 561 (Mþ ꢀ OMe, 6), 559 (Mþ þ 2 e Cl, 3), 557 (Mþ ꢀ Cl, 3),
533 (Mþ ꢀ CO2Me, 17), 429 (Mþ ꢀ C6H12O3 e OMe, 100); HRMS (EI,
70 eV) Calcd for C30H25ClN2O9 (Mþ): 592.1249; Found: 592.1238;
Anal. Calcd for C30H25ClN2O9: C, 60.76; H, 4.25; N, 4.72; O, 24.28;
Found: C, 60.58; H, 4.37; N, 4.67; O, 24.20.
1g-a þ 1g-s. yellow crystals; mp 270e275 ꢁC (decomp.); 1H
NMR (500 MHz, CDCl3)
d
8.70 (d, J ¼ 9 Hz,1 H), 8.59 (d, J ¼ 9 Hz,1 H),
8.53 (d, J ¼ 7.5 Hz, 1 H), 8.45 (d, J ¼ 7.5 Hz, 1 H), 8.41 (d, J ¼ 7 Hz, 1 H),
8.35 (dd, J ¼ 6 Hz, 2 H), 8.10 (m, 2 H), 7.93 (dd, J ¼ 7.5 Hz, 2 H), 7.88
(dd, J ¼ 7 Hz, 2 H), 4.28 (s, 6 H).
1h-a þ 1h-s. yellow crystals; mp 256e260 ꢁC (decomp.); 1H
NMR (500 MHz, CDCl3)
d
9.39 (d, J ¼ 2 Hz,1 H), 9.28 (d, J ¼ 2 Hz,1 H),
8.64 (dt, J ¼ 9.5, 2 Hz, 2 H), 8.63 (d, J ¼ 9.5 Hz, 1 H), 8.53 (d,
J ¼ 9.5 Hz, 1 H), 8.42 (d, J ¼ 7.5 Hz, 2 H), 8.36 (d, J ¼ 7.5 Hz, 2 H), 7.94
(dd, J ¼ 7.5 Hz, 2 H), 7.89 (dd, J ¼ 7 Hz, 2 H), 4.31 (s, 3H), 4.29 (s, 3H).
1e. Reaction time 30 h, yield 68%, bright yellow crystallines; mp
298e300 ꢁC (decomp.); IR (cmꢀ1) 2958 (w), 2919 (w), 2874 (w),
1731 (m), 1678 (m), 1556 (w), 1481 (m), 1295 (s), 1225 (s), 1196 (s),
4.2.5. tert-butyl 3-(pyren-1-ylmethylamino)propylcarbamate
(11gꢂBoc)
1117 (s), 725 (w); 1H NMR (500 MHz, CDCl3)
d
8.38 (d, J ¼ 7.5 Hz,
The procedure for the preparation of the Boc-protected N [1]-
(anthracen-9-ylmethyl)propane-1,3-diamine (11f) was generally
followed.29 A solution of pyrene-1-carbaldehyde (2.06 g, 8.9 mmol)
in MeOH/CH2Cl2 (20 mL, 1:3 by vol.) was added under N2 atmo-
sphere into a stirred solution of mono-Boc-protected 1,3-diamine
(1.95 g, 11 mmol) in MeOH/CH2Cl2 (20 mL, 1:3 by vol.). The
mixture was stirred at room temperature for 20 h and then cooled
to 0 ꢁC with an ice-water bath. NaBH4 (22 mmol) was added in
small portions to the solution and the mixture was stirred at room
temperature for 18 h. The solvent was removed in vacuo. The solid
residue thereby obtained was dissolved in CH2Cl2 (40 mL) and
washed with aqueous Na2CO3 solution (10%, 30 mL ꢃ 3). The
organic layer was dried over anhydrous Na2SO4 and filtered, and
the solvent was removed in vacuo to give an oily residue. The oil
was purified by flash column chromatography (3% MeOH/CHCl3) to
yield 11gꢂBoc as a thick oil (82%): IR (cmꢀ1) 3366 (m), 2913 (s),
2849 (s), 1698 (s), 1364 (s), 1249 (m), 1169 (s); 1H NMR (500 MHz,
1 H), 8.31 (d, J ¼ 7.0 Hz,1 H), 7.88 (t, J ¼ 7.5 Hz,1 H), 7.83 (t, J ¼ 7.3 Hz,
1H), 7.49 (s, 1 H), 7.38 (s, 1 H), 4.42 (d, J ¼ 0.5 Hz, 4 H), 4.27 (s, 3 H),
4.05 (s, 4 H), 3.81 (d, J ¼ 4.5 Hz, 4 H), 3.76e3.72 (m, 8 H); 13C NMR
(125 MHz, CDCl3) d 181.6 (C), 181.3 (C), 168.4 (C), 156.8 (C), 156.6 (C),
144.1 (C), 144.0 (C), 140.5 (C), 139.9 (C), 138.0 (C), 135.4 (C), 135.0
(CH), 135.0 (C), 134.2 (CH), 132.8 (C), 128.3 (C), 127.9 (CH), 127.4 (C),
127.4 (CH), 105.9 (CH), 105.8 (CH), 71.1 (CH2), 70.7 (CH2), 70.5 (CH2),
69.8 (CH2), 69.6 (CH2), 68.7 (CH2), 53.3 (CH3); MS (EI, 70 eV) m/z (%)
638 (Mþ þ 2, 34), 636 (Mþ, 86), 607 (Mþ þ 2 e OMe, 3), 605 (Mþ ꢀ
OMe, 9), 603 (Mþ þ 2 e Cl, 8), 601 (Mþ ꢀ Cl, 5), 577 (Mþ ꢀ CO2Me,
26), 429 (Mþ ꢀ C8H16O4 e OMe, 100); HRMS (EI, 70 eV) Calcd for
C
32H29ClN2O10 (Mþ): 636.1511; Found: 636.1516.
1f. Reaction time 24 h, yield 48%. Deep reddish solids; mp
324e329 ꢁC (decomp.); IR (cmꢀ1) 1731, 1678, 1589, 1395, 1280,
1252, 1011; 1H NMR (400 MHz, CDCl3)
d 4.34 (s, 3 H), 7.56e7.59 (m,
2 H), 7.86e7.92 (m, 2 H), 8.14e8.15 (m, 2 H), 8.35 (d, J ¼ 7.1 Hz, 1H),
8.42 (d, J ¼ 7.4 Hz,1H), 9.00 (s,1 H), 9.09 (s,1 H); 13C NMR (100 MHz,
CDCl3)
d
1.42 (s, 9 H), 1.6e1.8 (m, 2 H), 2.85 (t, J ¼ 6.6 Hz, 2 H), 3.25
CDCl3)
d
181.3 (C), 181.0 (C), 167.8 (C), 141.6 (C), 141.4 (C), 140.6 (C),
(m, 2 H), 4.46 (s, 2 H), 5.10e5.38 (br, 1 H), 8.00 (t, J ¼ 7.5 2 H), 8.04 (s,
140.4 (C), 139.7 (C), 136.5 (C), 136.4 (C), 136.3 (C), 135.5 (C), 135.3
(CH), 134.5 (CH), 132.9 (C), 129.1 (C), 129.0 (CH), 128.9 (CH), 128.8
(CH), 128.5 (CH), 128.5 (CH), 128.2 (C), 128.1 (CH), 127.6 (CH), 53.4
(CH3); MS (FAB) m/z (%) 454 (Mþ, 38.0), 452 (Mþ, 100), 423 (41.0),
422 (50.9), 421 (Mþ ꢀ OMe, 95.5), 394 (17.0), 302 (37.3), 142 (24.3).
2 H), 8.10e8.15 (m, 2 H), 8.15e8.21 (m, 2 H), 8.37 (d, J ¼ 9.5 Hz, 1 H);
13C NMR (125 MHz, CDCl3)
d 28.4 (CH3), 29.9 (CH2), 39.4 (CH2), 48.0
(CH2), 51.9 (CH2), 78.9 (CH), 123.1 (CH), 124.6 (CH), 124.9 (C), 125.0
(CH), 125.0 (C), 125.0 (CH), 125.8 (CH), 127.0 (CH), 127.0 (CH), 127.4
(CH), 127.6 (CH), 129.0 (C), 130.6 (C), 130.8 (C), 131.3 (C), 133.7 (C),
156.1 (C); MS (EI, 70 eV) 388 (Mþ, 2), 331 (15), 230 (44), 215 (100),
201 (6). HRMS (EI, 70 eV) m/z (%) Calcd for C25H28N2O2 (Mþ):
388.2151; Found: 388.2155; Anal. Calcd for C25H28N2O2: C, 77.29; H,
7.26; N, 7.21; O, 8.24; Found: C, 77.60; H, 7.42; N, 7.35; O, 8.29.
HRMS (EI) Calcd for
C
26H13ClN2O4 (Mþ): 452.0564; Found:
452.0569. Anal Calcd for C26H13ClN2O4: C, 68.96; H, 2.89; N, 6.19; O,
14.13; O; found: C, 68.95; H, 3.03; N, 5.95; O, 14.08.
4.2.4. General procedure for the one-pot synthesis of
diazapentacene esters 1 from 5
4.2.6. General procedure for amination of diazapentacene 1a.
Synthesis of compounds 12aeh
A solution of 1,2-diketone monohydrate 5′ or 5 (1.00 mmol) in
AcOH (8 mL) containing arene-1,2-diamine (1.10 mmol) [ο-phenyl-
enediamine (6a), 4-methoxybenzene-1,2-diamine (6b), 4,5-
dimethoxybenzene-1,2-diamine (6c), naphthalene-2,3-diamine
(6f), 3-nitrobenzene-1,2-diamine (6g), or 5-nitrobenzene-1,2-
diamine (6h)] was stirred at 45 ꢁC under N2 atmosphere for 3 h.
After the reaction mixture was subsequently heated in the open air
Into a stirring solution of compound 1a (1 mmol) and Et3N
(1.1 mmol) in DCM (20 mL) was added in dropwise manner at 0 ꢁC a
DCM (5 mL) solution of amine (1.1 mmol) [butan-1-amine (11a),
phenylmethanamine (11b), cyclohexanamine (11c), aniline (11d),
piperidine (11e), N1-(anthracen-9-ylmethyl)propane-1,3-diamine
(11f), N1-(pyren-1-ylmethyl)propane-1,3-diamine
(11g),
or
Please cite this article as: T.-C. Chou et al., Aromatization-driven Grob-fragmentation approach toward polyazaacenes. Synthesis and amination
of multi-functionalized diazapentacenes, Tetrahedron, https://doi.org/10.1016/j.tet.2019.130689

T.-C. Chou et al. / Tetrahedron xxx (xxxx) xxx
11
propane-1,3-diamine (11h, 0.5 mmol)]. The hydrochloride salts of
11f and 11g were used which were generated in situ from the
corresponding Boc-protected precursors (11fꢂBoc and 11gꢂBoc) by
treatment in absolute ethanol with a 4 N HCl solution. After addi-
tion of amine was completed, the reaction mixture was allowed to
warm to room temperature and stirred for a period of time
(1.5e48 h). The progress of reaction was monitored by TLC. After
the completion of reaction, water was added to reaction mixture
and stirred for a few min. The organic layer was separated,
concentrated, and purified by flash chromatography using DCM as
eluant.
7.92 (d, J ¼ 7.6 Hz, 1H), 8.12 (s, 1H), 8.16 (d, J ¼ 7.6 Hz, 1H), 8.17 (d,
J ¼ 7.6 Hz, 1H), 8.25 (d, J ¼ 7.3 Hz, 1H), 8.32 (d, J ¼ 8.1 Hz, 2H); 13C
NMR (125 MHz, CD2Cl2)
d 30.6 (CH2), 45.0 (CH2), 45.4 (CH2), 45.7
(CH2), 52.11 (CH3), 104.9 (C), 122.4 (C), 123.8 (CH), 124.1 (CH), 125.1
(CH), 126.3 (C), 126.3 (C), 126.4 (C), 128.3 (CH), 128.9 (CH), 129.4
(CH), 129.7 (C), 130.1 (C), 130.5 (C), 130.7 (C), 131.2 (C), 132.2 (CH),
132.4 (CH), 134.1 (CH), 135.4 (C), 138.6 (C), 140.1 (C), 143.2 (C), 143.3
(C); MS (ESIþ) 632 (Mþ þ 2, 41), 631 (Mþ þ H, 100), 437 (4), 191
(46); HRMS (ESIþ) m/z (%) Calcd for C40H31O4N4 (M þ H): 631.2340;
Found: 631.2343.
12g: Reaction time 28 h, yield 85%, reddish crystals; mp
12a: Reaction time 4 h, yield 89%, burgundy wine color crystals;
190e193 ꢁC; IR (cmꢀ1) 3362 (s), 2918 (s), 2849 (s), 1646 (s), 1541 (s),
mp 225e227 ꢁC; 1H NMR (500 MHz, CDCl3)
d
1.06 (t, J ¼ 7.5 Hz, 3H),
1374 (s), 1288 (m); 1H NMR (500 MHz, CDCl3)
d 2.093 (m, 2 H), 3.09
1.63e1.67 (m, 2H), 1.93 (quin, J ¼ 7.5 Hz, 3H), 4.21 (s, 3H), 4.58 (m,
2H), 7.69e7.72 (m, 1H), 7.79e7.85 (m, 2H), 7.88e7.91 (m, 1H), 8.16
(d, J ¼ 8 Hz,1H), 8.20 (d, J ¼ 8 Hz,1H), 8.26 (d, J ¼ 7.5 Hz,1H), 8.37 (d,
(t, J ¼ 6.5 Hz, 2H), 4.23 (s, 3H), 4.44e4.60 (m, 4H), 7.55 (dd,
J ¼ 7.5 Hz,1H), 7.66 (dd, J ¼ 7.5 Hz,1H), 7.69e7.78 (m, 4H), 7.79e7.97
(m, 8H), 8.03 (d, J ¼ 7.5 Hz, 1H), 8.07 (d, J ¼ 8.5 Hz, 1H), 8.15 (d,
J ¼ 7.5 Hz,1H), 8.20 (d, J ¼ 7.5 Hz,1H), 8.32 (d, J ¼ 9 Hz,1H); 13C NMR
J ¼ 7.5 Hz, 1H), 12.90 (br, 1H); 13CNMR (125 MHz, CDCl3)
d 13.9, 20.3,
32.7, 48.3, 52.9, 105.5, 123.1, 126.8, 127.1, 129.90, 129.95, 130.6, 131.1,
132.6, 132.71, 132.77, 134.6, 135.8, 139.3, 140.7, 143.7, 143.9, 153.7,
169.5, 182.2, 183.0; HRMS calcd for C26H21N3O4: 439.1532. Found
439.1541.
(125 MHz, CDCl3) d 30.9 (CH2), 46.0 (CH2), 46.3 (CH2), 52.1 (CH2),
52.9, (CH3),105.4(C),123.0 (C), 23.2 (CH),124.4 (CH),124.5 (C),124.8
(CH), 125.1 (CH), 125.8 (CH), 126.6 (CH), 127.0 (CH), 127.0 (CH), 127.2
(CH), 127.3 (CH), 127.3 (CH), 129.1 (C), 129.7 (CH), 129.7 (CH), 130.4
(C), 130.5 (C), 130.5 (C), 130.9 (CH), 130.9 (C), 132.4 (CH), 132.5 (CH),
132.6 (CH), 133.7 (C), 134.4 (CH), 135.6 (C), 139.0 (C), 140.4 (C), 143.5
(C), 143.7 (C), 153.2 (C), 169.4 (C), 181.9 (C), 182.9 (C); MS (EI, 70 eV)
654 (Mþ, 0.01), 352 (16), 231 (52), 215 (100), 201 (34); HRMS (EI,
70 eV) m/z (%) Calcd for C42H30N4O4 (Mþ): 654.2267; Found:
654.2261.
12b: Reaction time 6 h, yield 79%, reddish brown color crystals;
mp > 300 ꢁC; 1H NMR (500 MHz, CDCl3)
d 4.21 (s, 3H), 5.78 (s, 2H),
7.30e7.38 (m, 3H), 7.50e7.52 (m, 2H), 7.71e7.85 (m, 4H), 8.07 (d,
J ¼ 8.0 Hz,1H), 8.18 (d, J ¼ 8.0 Hz,1H), 8.27 (d, J ¼ 7.2 Hz,1H), 8.33 (d,
J ¼ 7.2 Hz, 1H), 13.08 (br 1H); 13CNMR (125 MHz, CDCl3)
d 52.2, 52.9,
106.1, 123.6, 126.9, 127.2, 127.4, 127.5, 128.9, 129.7, 129.9, 130.5,
131.3, 132.6, 132.7, 132.9, 134.6, 135.6, 138.8, 139.0, 140.7, 143.72,
143.79, 153.1, 169.4, 182.7, 182.9; HRMS calcd for C29H19N3O4:
473.1376. Found: 473.1371.
12h: Reaction time 24 h, yield 76%, reddish crystals; mp
266e268 ꢁC (decomp.); IR (cmꢀ1) 3358 (m), 2922 (s), 2852(m),1731
(w), 1633 (m), 1285 (m); 1H NMR (500 MHz, CDCl3)
d 2.63 (t,
12c: Reaction time 5 h, yield 62%, deep plum reddish color
J ¼ 6 Hz, 2 H), 4.19 (s, 6H), 4.70e5.20 (br, 4H), 7.62e7.69 (m, 6H) 7.79
crystals; mp 245e247 ꢁC; 1H NMR (500 MHz, CDCl3)
d 1.43e2.35
(dd, J ¼ 7.8 Hz, 2H), 8.03 (d, J ¼ 9.25 Hz, 2H), 8.09 (d, J ¼ 9.25 Hz, 6H),
(m, 10H), 4.21 (s, 3H), 5.50 (br, 1H), 7.70 (td, J ¼ 1.1, 7.5 Hz, 1H), 7.81
(td, J ¼ 1.1, 7.5 Hz, 1H), 7.83e7.87 (m, 1H), 7.89e7.92 (m, 1H), 8.13 (d,
J ¼ 8.5 Hz, 1H), 8.21 (d, J ¼ 8.5 Hz, 1H), 8.26 (d, J ¼ 8.0 Hz, 1H), 8.38
8.11 (d, J ¼ 8 Hz, 6H), 12.99 (s, 2H); 13C NMR (125 MHz, CDCl3)
d 32.1
(CH2), 46.3 (CH2), 52.8 (CH3), 106.0 (C), 123.5 (C), 126.8 (CH), 127.0
(CH), 129.6 (CH), 130.0 (CH), 130.3 (C), 131.2 (CH), 132.5 (C), 132.6
(CH), 132.8 (CH), 134.6 (CH), 135.4 (C), 139.0 (C), 140.5 (C), 143.7 (C),
153.4 (C), 169.2 (C), 182.5 (C); MS (ESIþ) 829 (M þ Na, 33), 808
(Mþ þ 2, 51), 807 (Mþ þ H, 100), 806 (Mþ, 15), 437 (14); HRMS
(ESIþ) m/z (%) Calcd for C47H31O8N6 (Mþ þ H): 807.2198; Found:
807.2161.
(d, J ¼ 8.0 Hz, 1H), 12.9 (br, 1H); 13CNMR (125 MHz, CDCl3)
d 25.1,
25.9, 34.4, 53.2, 55.8, 105.7, 123.3, 127.0, 127.4, 130.1, 130.2, 131.1,
131.5, 132.8, 132.9, 134.9, 136.1, 141.0, 144.0, 144.1, 153.1, 169.8, 182.5,
183.3; HRMS calcd for C28H23N3O4: 465.1689. Found: 465.1679.
12d: Reaction time 48 h, yield 83%, deep orange color crystals;
mp 253e255 ꢁC; 1H NMR (500 MHz, CDCl3)
d 4.26 (s, 3H), 7.20 (d,
J ¼ 7.8, 2H), 7.27e7.30 (m, 1H), 7.33e7.36 (m, 2H), 7.43 (d, J ¼ 8.0,
1H), 7.68 (td, J ¼ 1.2, 7.9 Hz, 1H), 7.76 (td, J ¼ 1.1, 7.4 Hz, 1H),
7.81e7.85 (m, 2H), 8.16 (d, J ¼ 8.3 Hz, 1H), 8.31 (d, J ¼ 7.8 Hz, 1H),
8.38 (d, J ¼ 7.8 Hz, 1H), 13.40 (br 1H); 13CNMR (125 MHz, CDCl3)
Acknowledgments
We are grateful to the Ministry of Science and Technology
(MOST) of Taiwan for financial support of this research.
d
53.0, 108.6, 124.4, 125.4, 125.5, 127.1, 127.4, 128.5, 129.7, 129.8,
130.0, 131.5, 132.7, 132.8, 133.4, 134.8, 135.3, 137.2, 140.3, 142.4,
143.1, 144.3, 150.5, 169.1, 182.5, 183.5; HRMS calcd for C28H17N3O4:
459.1219. Found 459.1213.
Appendix A. Supplementary data
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.tet.2019.130689.
12e: Reaction time 1.5 h, yield 80%, dark violet color crystals;
mp > 300 ꢁC; 1H NMR (500 MHz, CDCl3)
d 1.92e1.98 (m, 6H), 3.81
(br, 4H), 4.22 (s, 3H), 7.73 (td, J ¼ 7.3, 1.2 Hz, 1H), 7.81 (td, J ¼ 1.2,
7.5 Hz,1H), 7.86e7.90 (m, 2H), 8.16e8.18 (m,1H), 8.21e8.23 (m,1H),
8.26 (d, J ¼ 8.0 Hz, 1H), 8.31 (d, J ¼ 8.0 Hz, 1H); 13CNMR (125 MHz,
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d 24.5, 27.0, 53.0, 56.4, 115.8, 126.2, 127.1, 129.8, 131.5, 132.0,
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208e210 ꢁC (decomp.); IR (cmꢀ1) 3358 (m), 2918 (s), 2849 (s), 1717
(w), 1650 (m), 1541 (m), 1288 (m); 1H NMR (500 MHz, CD2Cl2)
d
2.05e2.08 (m, 2 H), 3.14 (t, J ¼ 6.2 Hz, 2 H), 4.17 (s, 3 H), 4.47 (q,
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Please cite this article as: T.-C. Chou et al., Aromatization-driven Grob-fragmentation approach toward polyazaacenes. Synthesis and amination
of multi-functionalized diazapentacenes, Tetrahedron, https://doi.org/10.1016/j.tet.2019.130689

12
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Please cite this article as: T.-C. Chou et al., Aromatization-driven Grob-fragmentation approach toward polyazaacenes. Synthesis and amination
of multi-functionalized diazapentacenes, Tetrahedron, https://doi.org/10.1016/j.tet.2019.130689