Metal-free benzannulation of 1,7-diynes towards unexpected 1-aroyl-2-naphthaldehydes and their application in fused aza-heterocyclic synthesis

Article abstract of DOI:10.1039/c7cc00323d

A novel I₂-mediated benzannulation of 1,7-diyne-involved 1,4-oxo-migration was established, providing a range of unexpected 1-aroyl-2-naphthaldehydes with a 1,4-dicarbonyl unit. The resulting 1-aroyl-2-naphthaldehydes were successfully applied in the synthesis of benzo[e]isoindol-3-ones and benzo[e]benzo[4,5]imidazo[2,1-a]isoindoles using aromatic amines and benzene-1,2-diamines as nucleophiles, respectively. The mechanisms for the formation of these compounds were proposed.

Full text of DOI:10.1039/c7cc00323d

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Marilyn M. Olmstead, Alan L. Balch, Josep M. Poblet, Luis Echegoyenet al.
Reactivity differences of Sc
first methanofullerene derivatives of Sc
3
N@C2n (2n
=
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3
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Metal-free benzannulation of 1,7-diynes toward unexpected 1-
aroyl-2-naphthaldehydes and their application in fused aza-
heterocyclic synthesis
Received 00th January 20xx,
Accepted 00th January 20xx
a
a
a
,a
b
,a
DOI: 10.1039/x0xx00000x
Ai-Fang Wang, Peng Zhou, Yi-Long Zhu, Wen-Juan Hao,* Guigen Li, Shu-Jiang Tu,* and Bo
Jiang*
,
a
www.rsc.org/
A novel I
2
-mediated benzannulation of 1,7-diynes involved 1,4-
range of
oxo-migration has been established, providing
a
unexpected 1-aroyl-2-naphthaldehydes with a 1,4-dicarbonyl unit.
The resulting 1-aroyl-2-naphthaldehydes have been successfully
applied in the synthesis of benzo[e]isoindol-3-ones and
NTs
BzO R1
R1
BzO
R1
(a)
N
Ts
benzo[e]benzo[4,5]imidazo[2,1-a]isoindoles
using
aromatic
This work
R1
O
amines and benzene-1,2-diamines as nucleophiles, respectively.
The mechanisms for forming these compounds were proposed.
H
2
O, I
2
, O
2
(1.0 atm)
R2
(b)
(c)
CH
3
CN, 60 o
C
R2
O
1,4-Dicarbonyl compounds as key core components are
OMe
O
2
1
prevalent in a multitude of biological molecules of
R1
Ar
N
H N Ar
1
2
pharmaceutical and material interest. Specifically, 1,4-
dicarbonyls are types of competent reactants endowed with
two electrophilic sites, which could be served as versatile and
synthetically useful feedstocks for the preparation of various
3
R1
O
p-TsOH, EtOH
R2
o
1
20 C, MW
R3
O
R2
4
R3
TFA, HOAc
120 oC, MW
2
carbocyclic and heterocyclic compounds. To date, significant
2
R1
(
d)
efforts have been directed to develop efficient protocols
toward 1,4-dicarbonyl synthesis. Generally, the vast majority
of well-established synthetic strategies for the construction of
H N
R
3
N
2
N
R2
H
2
N
R3
5
6
1
,4-dicarbonyls include conjugate addition of acyl anions to
3
Scheme 1. Profile application of 1,7-diynes
Michael acceptors,
nucleophilic substitution of α-
4
5
haloketones, chain extension of 1,3-dicarbonyls, oxidative
Metal-catalyzed cycloisomerizations of 1,n-diynes have proven
to be exceptionally efficient methods to construct synthetically
significant poly-cyclic molecules in an atom-economical
6
coupling of enolates or alkenes, the addition of homoenolate
7
8
equivalents to acid derivatives, and enolate heterocoupling.
9
Despite these significant advances achieved in this field,
current 1,4-dicarbonyl synthesis has mainly relied on the use
of carbonyl precursor. To the best of our knowledge, the
utilization of 1,7-diynes without any carbonyl unit as starting
materials via domino benzannulation for the creation of
conjugate 1,4-dicarbonyls has not yet been documented.
10
manner. For instance, Chan and co-workers reported Au(I)-
catalyzed cycloisomerization reactions of 1,7-diyne benzoates
10g
to selectively generate indeno[1,2-c]azepines (Scheme 1a).
Recently, our group has established a series of domino
11
cyclization reactions for multiple ring formations. For this
purpose, we planned the preparation of diyne-anchored
starting materials by taking advantage of a methodology in
which tandem cycloisomerization across its C
≡
C
π
system
results in functionalized polycyclic products. Surprisingly, we
found I -mediated reaction of the preformed 1,7-diynes
underwent unexpected oxygen migration and benzannulation
process in the presence of H O, providing functionalized 1-
aroyl-2-naphthaldehydes with conjugate 1,4-dicarbonyl unit
Scheme 1b). The resulting 1-aroyl-2-naphthaldehydes have
been subjected with the reactions of aryl amines , enabling
10
2
1
2
2
(
3
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microwave-assisted (MW) domino [4 + 1] cyclization to give similar inferior outcome was observed in the reaction of 1,7-
tricyclic benzo[e]isoindol-3-ones with good yields (Scheme diynes 1l (product 2l, 42% yield). These results revealed that
as replacement for aryl both electron-withdrawing and strong electron-donating
, the reaction afforded high yields of pentacyclic groups at the arylalkynyl moiety are not beneficial to the
via double [4 + reaction process. Alternatively, substrates 1i-1m without
] cyclization cascades (Scheme 1d). Herein, we would like to substituent on the internal arene ring were successfully
4
1c). Using benzene-1,2-diamines 5
amines
3
benzo[e]benzo [4,5]imidazo[2,1-a]isoindoles
6
1
report these interesting transformations.
converted to the corresponding products 2i-2m with yields
Our initial investigation was started with the treatment of ranging from 42% to 71%. Similarly, 1,7-diyne 1n bearing a
benzene-tethered 1,7-diyne 1a by water and 2.0 equivalents of methyl group resided at C5-position of the internal arene ring
1
2
o
under air conditions in acetonitrile at 50 C, and the still showed high reactivity, furnishing product 2n in 65% yield.
I
2
unexpected 2-naphthaldehyde 2a was generated in a low 27% Unfortunately, 1,7-diyne 1o carrying an n-butyl group was an
yield (Table 1, entry S1, See Supporting Information). After ineffective substrate.
careful screening of the reaction conditions, we found that the
reaction in the presence of I
o
2
(1.0 equiv) and H
2
O (2.0 equiv) in
acetonitrile at 60 C under O
in 72% yield (entry S15).
2
conditions afforded product 2a
Scheme 2 Substrate scope for forming products
2. Yields of
isolated products based on 1,7-diynes 1.
Under the above optimal conditions, we explored the reaction
scope by using a variety of the preformed benzene-tethered
1
,7-diynes
the internal arene rings of 1,7-diynes
hamper this benzannulation reaction. Both electron-donating
methyl 1a, ethyl 1b and t-butyl 1c) and electron-neutral (H 1d
1
(Scheme 2). Chloro substituent at C4-positions of
1
was proven not to
(
)
groups at para-positions of arylalkynyl motifs can all tolerate
the reaction conditions well, delivering the corresponding
substituted 1-aroyl-2-naphthaldehydes 2a
-d in good yields
(61%-72%). However, the presence of electron-withdrawing
chloro group (1e) at this position failed to provide the desired
product 2e, indicating electronic effect of substituents on the
arylalkynyl moiety showed a critical influence on the success of
Scheme 3 Synthesis of polycyclic products
4 and 6. Yields of
this
counterparts 1f
the arylalkynyl moiety were found to be adaptable to this
reaction, giving access to the corresponding products 2f in
4%-66% yields. Among them, a significant drop in the yields
transformation.
Afterward,
4-fluoro-substituted
isolated products based on compounds 2.
-
h
with various functional groups attached with
After our successful achievement with 1-aroyl-2-
naphthaldehydes having conjugate 1,4-dicarbonyl moiety,
we decided to employ them as starting materials to react with
aryl amines to investigate the feasibility of [4 + 1] cyclization
toward the expected tricyclic benzo[e]isoindol-3-ones , due
2
-h
4
3
was obtained (2g, 44%) as the p-methoxyphenyl (PMP)
counterpart (1g) was employed as a reaction partner. This
4
2
| J. Name., 2012, 00, 1-3
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to the isoindol-3-one framework extensively exists in natural protection of hydroxyl group is necessary for this
1
3
products and shows a broad spectrum of biological activities.
As expected, the reaction of with was conducted in EtOH at proceed, confirming that H
20 C under microwave heating using p-TsOH as a Brønsted this cyclization (Scheme 4b). The same reaction under Ar
acid promoter (1.0 equiv), leading to the corresponding conditions only gave 15% yield of 2a with the starting material
benzo[e]isoindol-3-ones (Scheme 3a). Next, the scope of this 1a remaining (Scheme 4c), suggesting that oxygen atom of
4 + 1] cyclization was evaluated by treating the preformed aroyl group may come from H O rather than molecular O and
substrates with a variety of aryl amines (Scheme 3). The molecular O may facilitate the regeneration of I from iodine
results from Scheme revealed that 1-aroyl-2- anion during the reaction process. The reaction in D
naphthaldehydes carrying electron-neutral and donating the desired product 2a without D-content (Scheme 4d).
transformation. Without H
2
O, the reaction of 1a did not
2
3
2
O plays a key role in the success of
o
1
4
[
2
2
2
3
2
2
1
4
3
2
O gave
2
groups at the para-position of aroyl ring all readily participated
in this transformation. The variety of substituents located on
naphthalene ring of 2, including fluoro, chloro and methyl,
would be compatible under the present reaction conditions.
Similarly, the reaction proceeded smoothly with various
functional groups (H 3a, chloro 3b, bromo 3c, and methyl 3d
on the phenyl ring of , delivering the collection of tricyclic
benzo[e]isoindol-3-ones 4a-4k with yields ranging from 69% to
3%. Heteroarylated amine 3e could also be accommodated,
thus confirming the reaction efficiency, as pyrazol-5-yl product
was obtained in 66% yield.
)
3
8
4l
To further expand the synthetic application of this
methodology, upon treatment of benzene-1,2-diamine 5a with
1-aroyl-2-naphthaldehydes 2
in the presence of trifluoroacetic Scheme 5. Plausible mechanism for forming 2
acid (TFA, 2.0 equiv) and HOAc allowed microwave-assisted
double [4 + 1] cyclization cascades to afford pentacyclic
benzo[e]benzo[4,5] imidazo[2,1-a]isoindoles 6a-c in 87%-92%
yields (Scheme 3b). Alternatively, 4,5-dimethylbenzene-1,2-
On the basis of the above analysis, a reasonable mechanism
for forming products
2
was proposed in Scheme 5. In the first
, intramolecular 5-endo-dig oxo-
stage, in the presence of I
2
cyclization occurs to give dihydrofuran cation, followed by ring
opening of dihydrofuran ring (1,4-oxo-migration) to yield diene
diamine 5b was proved to be a suitable diamine precursor (6d
,
72%). Notably, naphthalene-1,8-diamine 5c could be
intermediates
Information). Subsequent [2+2] cycloaddition of dienes
generates cyclobutene intermediates , which undergo allylic
nucleophilic substitution and ring opening of cyclobutenes to
B
detected by LC-MS (See Supporting
successfully engaged in the current bicyclization, providing the
1
5
B
corresponding hexacyclic benzo[4,5]isoindolo[2,1-a]perimidine
C
6
e
in 91% yield. The structures of products
been determined by NMR and HR-MS spectral analysis. In the
cases of products 2a 4h, and 4l, their structures have been
further confirmed by X-ray diffractional analysis.
2, 4 and 6 have
1
6
access products
reaction with iodine anion and molecular O
of products involved in situ formation of imines (
exo-trig cyclization ( to ), nucleophilic addition of H
), dehydration and tautomerization ( to ) sequence
(Scheme S1, see Supporting Information). Similar to the above,
the synthesis of products is expected to consist of
nucleophilic additions-dehydration ( to ), intramolecular
cyclization ( to ), second dehydration and tautomerization (
to ) sequence (Scheme S1).
2.
2
I is believed to be regenerated by
,
1
4
2
.
The formation
to ), 5-
O ( to
4
2
E
p-Tolyl
p-Tolyl
O
E
F
2
F
I2, H2O
(a)
G
G
4
O
CH3CN, 60 oC, O2
Cl
Cl
OH
6
7
2a (Not observed)
2
I
p-Tolyl
I
K
K
I2, dry CH3CN
0 oC, O2
6
No reaction
(b)
(c)
6
Cl
In conclusion, we have discovered a new I
2
-mediated synthesis of
OMe
a
unexpected 1-aroyl-2-naphthaldehydes through metal-free
benzannulation of 1,7-diynes involved 1,4-oxo-migration process.
The resulting 1-aroyl-2-naphthaldehydes as an alternative 1,4-
dielectrophilic reagent have been successfully applied in fused aza-
heterocyclic synthesis. The microwave-assisted [4 + 1] cyclization of
1
I2, H2O
1
a
2a (15%)
CH3CN, 60 oC, Ar
I2, D2O
1
a
2a (65%, No D-product) (d)
CH3CN, 60 oC, O2
1
-aroyl-2-naphthaldehydes with aromatic amines gave tricyclic
Scheme 4 Control experiments
benzo[e]isoindol-3-ones with good yields whereas pentacyclic
benzo[e]benzo[4,5]imidazo[2,1-a]isoindoles with high yields were
obtained through double [4 + 1] cyclization cascades using benzene-
To gain mechanistic insight into this reaction, several control
experiments were carried out. The reaction of O-unprotected
1
,7-diyne
no expected product 2a was observed with the starting
material remaining (Scheme 4a), indicating that the methyl
7 was performed under the standard conditions, but
1
,2-diamines as a reaction partner. A further investigation on
7
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reaction mechanism and assessing biological activity of these
resultant compounds is currently underway in our laboratory.
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We are grateful for financial support from the NSFC (No. 21232004,
21472071 and 21602087), PAPD of Jiangsu Higher Education
Institutions, the Outstanding Youth Fund of JSNU (YQ2015003), NSF
of Jiangsu Province (BK20151163 and BK20160212), the Qing Lan
Project and NSF of Jiangsu Education Committee (15KJB150006).
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