A study on the reaction of 3-Alkyl(aryl)imidazo[1,5-A]pyridines with ninhydrin

Article abstract of DOI:10.1515/znb-2018-0039

The reaction of 3-Alkyl(aryl)imidazo[1,5-A]pyridines (1) with ninhydrin in dichloromethane at room temperature delivered good yields of the respective 2-hydroxy-2-(imidazo[1,5-A]pyridine-1-yl)indene-1,3-diones. In the presence of dimethyl acetylenedicarbo

Full text of DOI:10.1515/znb-2018-0039

Z. Naturforsch. 2018; aop
Mervat S. Sammor, Mustafa M. El-Abadelah*, Ahmad Q. Hussein, Firas F. Awwadi,
Salim S. Sabri and Wolfgang Voelter*
A study on the reaction of 3-alkyl(aryl)imidazo[1,5-
a]pyridines with ninhydrin
https://doi.org/10.1515/znb-2018-0039
Recently, we have reported on a one-pot synthe-
sis of condensed 1,3-oxazepine ring system (5) through
the cycloaddition of N-alkylisatins (3) and 1,4-dipoles
2 derived from imidazo[1,5-a]pyridines 1 and DMAD
(Scheme 1) [14]. In this reaction, the in situ-generated
dipole 2 undergoes a conventional cycloaddition at the
keto group of N-alkylisatin to form the respective spiro[1,3]
oxazine structure 4, which undergoes subsequent ring
expansion through multiple bond-breaking and bond-
making processes, eventually leading to the rearranged
tricyclic 1,3-oxazepino[7,6-b]indole (5) as the final product
[14]. Interestingly, acenaphthene-1,2-dione, a representa-
tive of arene-vic-diones (o-quinones), has also been found
to follow a similar path in its reaction with DMAD and 1
yielding the respective dihydroacenaphtho[1,2-f][1,3]oxaz-
Received February 16, 2018; accepted April 22, 2018
Abstract: The reaction of 3-alkyl(aryl)imidazo[1,5-a]pyri-
dines (1) with ninhydrin in dichloromethane at room
temperature delivered good yields of the respective
2-hydroxy-2-(imidazo[1,5-a]pyridine-1-yl)indene-1,3-diones.
In the presence of dimethyl acetylenedicarboxylate (DMAD),
this uncatalyzed electrophilic substitution reaction, involv-
ing C-1 (in 1) and the central C=O (in ninhydrin), takes prec-
edence over the three-component 1,4-dipolar cycloaddition
reaction. This selectivity is probably due to the higher elec-
trophilicity of the carbonyl carbon-2 in ninhydrin as com-
pared to that of the sp-carbon atoms in DMAD, augmented
with the high nucleophilicity of carbon-1 in 1.
Keywords: 2-hydroxy-2-(imidazo[1,5-a]pyridinyl)indenedi- epine dicarboxylates 6 (Scheme 2) [15].
ones; electrophilic substitution; imidazo[1,5-a]pyridines;
In extenso, we anticipated that cyclic 1,2,3-triones
ninhydrin; X-ray structure.
might be suitable dipolarophiles in cycloaddition reac-
tions with 1,4-dipoles of type 2 (see above, Scheme 1).
Recalling that ninhydrin, the hydrate of indane-1,2,3-tri-
one, has been used in many heterocyclic preparations,
and stands as an important building block in the synthesis
1 Introduction
1,4-Dipolar cycloaddition reactions are well-documented of organic compounds and drugs [16], we sought to inves-
in the literature and have often been used in the synthe- tigate the reaction of ninhydrin with 1 and DMAD. Previ-
sis of new heterocyclic systems. Among the most widely ous studies reported the formation of spiro[1,3]oxazine
studied 1,4-dipoles is that generated in situ from dime- N-heterocyclic adduct 7 via the three-component reaction
thyl acetylenedicarboxylate (DMAD) and a nucleophilic involving pyridine, DMAD, and ninhydrin (Scheme 3) [11].
nitrogen heteroarene [1–9]. Various N-heterocycles, such Corresponding adducts of spiro[1,3]oxazine N-heterocy-
as pyridine [10, 11], quinolone [12], and isoquinoline [13], cles were likewise formed in high yield from quinoline
readily add to DMAD giving a reactive 1,4-dipolar species, and isoquinoline in their reaction with DMAD in the pres-
which undergoes cycloaddition when trapped with a suit- ence of ninhydrin [17].
able dipolarophile. Several dipolarophiles with C=C, C=N,
and C=O bonds are used as reaction partners, leading to
interesting spiro-heterocyclic products.
2 Results and discussion
*Corresponding authors: Mustafa M. El-Abadelah, Department
2.1 Chemistry
of Chemistry, Faculty of Science, The University of Jordan,
Amman 11942, Jordan, e-mail: mustelab@ju.edu.jo; and
Wolfgang Voelter, Interfakultäres Institut für Biochemie, Universität
A three-component reaction was attempted by dissolv-
Tübingen, Hoppe-Seyler Straße 4, 72076 Tübingen, Germany,
ing equimolar amounts of 3-methylimidazo[1,5-a]imida-
e-mail: wolfgang.voelter@uni-tuebingen.de
zole (1a), DMAD, and ninhydrin in dichloromethane with
stirring at ambient temperature. To our delight, a yellow
solid product began to separate out of the reaction mixture
Mervat S. Sammor, Ahmad Q. Hussein, Firas F. Awwadi and
Salim S. Sabri: Department of Chemistry, Faculty of Science,
The University of Jordan, Amman 11942, Jordan
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ꢀꢀꢀꢁ
2ꢀ
ꢀM.S. Sammor et al.: Reaction of imidazo[1,5-a]pyridines with ninhydrin
CO2Me
CO2Me
CH2Cl2
CO2Me
CO2Me
N
N
N
+
N
N
N
r. t., 24 h
CO2Me
CO2Me
R1
R1
R1
2
1
DMAD
CO2Me
CO2Me
CO2Me
CO2Me
O
X
N
O
N
N
R1
X
2
R1
O
O
N
O
N
O
N
R2
R2
N
5
3
4
R2
(X = H, halogen)
(R1 = Me, 4-ClC6H4); (R2 = Me, Bn)
Scheme 1:ꢀFormation of oxazepino[7,6-b]indoles from the reaction of imidazo[1,5-a]pyridines, DMAD, and isatins.
CO2Me
O
CO2Me
R
N
O
O
CO2Me
C
N
CH2Cl2
+
+
N
O
C
N
24 h
R
CO2Me
1
6
acenaphthene-
1,2-dione
DMAD
(R = Me, Et, iPr, iBu, Bn, Ph, 4-ClC6H4)
Scheme 2:ꢀSynthesis of dihydroacenaphtho[1,2-f][1,3]oxazepines via 1,4-dipolar cycloaddition.
CO2Me
C
O
HO
HO
O
N
O
CH2Cl2 / r . t.
84%
C
MeO2C
N
O
CO2Me
DMAD
O
MeO2C
ninhydrin
7
Scheme 3:ꢀFormation of spiro adduct (7) from pyridine, DMAD and ninhydrin.
within 2–3 min; the reaction was monitored by thin layer Scheme 4, was obtained from spectral data and confirmed
chromatography (TLC) and completed within 25–30 min. by single-crystal X-ray structure determination (Fig. 1).
The MS and NMR spectral data revealed that the consti- Thus, it became clear that the presumed three-component
tution of the formed product lacks the DMAD unit, being reaction took a different path, whereby nucleophilic addi-
merely an 1:1 addition product of 1a and ninhydrin. This tion product 8a was fast formed in good yield (Scheme 4),
information was verified by reacting 1a with ninhydrin whereas none of the anticipated 1,4-dipolar cycloadducts
in absence of DMAD, whereby the resulting product was 9a/10a(involving DMAD as the third partner) were detected
identical with that formerly formed in presence of DMAD. (Scheme 5). Consequently, a selected set of nucleophilic
Eventually, the structure of the adduct 8a, as shown in adducts namely, 2-hydroxy-2-[3-alkyl(aryl)imidazo[1,5-a]
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ꢂ3
M.S. Sammor et al.: Reaction of imidazo[1,5-a]pyridines with ninhydrinꢂ
7
6
5
8
O
1
7'
8
O
1'
6'
7'a
OH
OH
(i)
8a
N
2'
N
5'
N
4
1
3'a
3
3
4'
5
3'
O
HO
N
R
O
R
1a−g
ninhydrin
8a−g
compounds 1a−g / 8a−g
(i) CH2Cl2 / r. t., 24 h
a
e
g
entry
R
c
b
d
f
Cl 4''
1''
1''
1''
4''
CH2
4''
Me
Et iPr
iBu
Scheme 4:ꢀSynthesis of 2-hydroxy-2-(imidazo[1,5-a]pyridinyl)indene-1,3(2H)-diones (8a–g).
pyridine-1-yl]indene-1,3-diones (8b–g), were likewise pre-
pared via interaction of the particular imidazo[1,5-a]pyri-
dines (1b–g) with ninhydrin (Scheme 4).
The formation of adducts 8a–g is not unexpected and
can be explained by following facts: (i) the imidazo[1,5-
a]pyridine, a π-excessive heteroaromatic system, under-
goes electrophilic substitution with various electrophiles
mainly at carbon-1, or at C-3 if C-1 is blocked [18–23]; (ii)
the central carbonyl carbon-2 of ninhydrin is highly elec-
trophilic and quite reactive toward various nucleophilic
species including carbon-based nucleophiles. Thus, in
the presence of concentrated sulfuric acid as a catalyst,
the reaction of ninhydrin with arenes/heterocylicarenes
was reported to afford the respective mono- and/or di-
substituted derivatives as exemplified by benzene and
N-methylpyrrole (Scheme 6) [24]. In many of the studied
Fig. 1:ꢀOrtep view of the molecular structure and atom numbering
scheme of 8a. (Displacement ellipsoids are drawn at the 30% prob-
ability level and H atoms are shown as spheres of arbitrary radii).
MeO2C
CO2Me
O
N
O
N
Me
O
O
O
N
1
O
DMAD
O
O
N
MeO2C
MeO2C
O
10
9
Scheme 5:ꢀFruitless pathway leading to the anticipated compounds 9 and 10.
Me
N
O
O
O
O
O
O
Ph
Ph
Ph
OH
OH
benzene
(i)
N-Me-pyrrole
(i)
OH
OH
O
(55%)
O
(65%)
1
(23%)
(i) conc. H2SO4 (2 equiv.), r. t., 1 h
Scheme 6:ꢀFormation of 2-mono- and 2,2-di-substituted ninhydrins.
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4ꢀ ꢀM.S. Sammor et al.: Reaction of imidazo[1,5-a]pyridines with ninhydrin
cases, only monosubstituted products were reported as 53], whereas in situ-generated imidazo[1,5-a]pyridinium
exemplified by dimethoxyanilines [25] and indoles [26]. carbenes have been used in the synthesis of spiro- and
Several other relevant examples have been cited in a fused heterocycles via multicomponent reactions [54–58].
recent review dealing with the chemistry and reactions of
ninhydrin [16].
The new compounds 8a–g were characterized by IR, 2.2 X-ray structure determination
MS, and NMR spectral data. These data, given in the Experi-
mental section, are in compliance with the assigned struc- An X-ray crystal structure determination was performed to
tures. Thus, the mass spectra display the correct molecular confirm the structure of 8a (Scheme 4). A summary of data
ion peaks for which the measured high-resolution mass collection and refinement parameters is given in Table 1,
spectra (HRMS) data are in good agreement with the cal- whereas selected bond lengths and angles are provided in
culated values. Distortionless enhancement of polarization Table 2. The molecular structure of 8a, based on crystallo-
transfer and 2D (correlation spectroscopy, heteronuclear graphic data, is shown in Fig. 1. The two aromatic systems
multiple-quantum coherence, heteronuclear multiple- are nearly perpendicular to each other; the angle between
bond correlation) experiments showed correlations that the two planes is 81°. This perpendicular arrangement is
helped in the 1H and 13C signal assignments to the different stabilized by N2ꢀ·ꢀ·ꢀ·ꢀC11(carbonyl) attractive forces (Fig. 3);
carbons and their attached and/or neighboring hydrogens. the distance between the two atoms is 2.744 Å, which
In this context, it is worth noting that imidazo[1,5-a] is ≅ꢀ0.5 Å less than the sum of van der Waals radii. The
pyridine motif is encountered in the skeleton of a number interaction between the electron-deficient carbon atom of
of naturally occurring compounds. Examples, shown in carbonyl groups and electronegative atoms is frequently
Fig. 2, include cribrostatin-6, a growth inhibitor of cancer reported in the literature [59]. The molecular units are
cells and a number of pathogenic bacteria and fungi, connected through hydrogen bonding interactions. The
isolated from the blue marine sponge Cribrochalina sp. hydrogen bonding parameters are 2.865(3) and 1.93(3) Å
[27–30]; the aaptamine-related alkaloids, isolated from a for the O18ꢀ·ꢀ·ꢀ·ꢀO19 and H18ꢀ·ꢀ·ꢀO19 distances, respectively,
species of Indonesian marine sponge Xestospongia sp. [31]; and 174(3)o for the O18–H18ꢀ·ꢀ·ꢀ·ꢀO19 bond angle.
and isogranulatimide, a G2 checkpoint inhibitor isolated
from the Brazilian ascidian Didemnum granulatum [32].
Various synthetic imidazo[1,5-a]pyridine derivatives
were reported to exihibit the following biological activi- 3 Conclusion
ties: Antibacterial [33], antitumorial agents [34–38], HIV
protease inhibitors [39, 40], selective inhibitors of aro- A facile synthesis of 2-hydroxy-2-(imidazo[1,5-a]pyridine-
matase estrogen production suppressors [41, 42], poten- 1-yl)indene-1,3-diones (8a–g) is achieved in good yields via
tial positive inotropic (cardiotonic) agents [43], platelet uncatalyzed reaction between ninhydrin and the appro-
aggregation and thromboxane A2 synthetase inhibitors priate 3-(substituted)imidazo[1,5-a]pyridines at room
[44–46], 5-HT4 receptor partial agonists for the treatment temperature. These hybrid adducts might exhibit poten-
of cognitive disorders associated with Alzheimer’s disease tial bioactivity arising from the combination of bioactive
[47], Mek Kinase inhibitor [48] for the treatment of inflam- entities of which the imidazo[1,5-a]pyridine constitutes an
mation [49] and fertility disorders [50], and CCR1 recep- integral part.
tor antagonists [51]. In addition, imidazo[1,5-a]pyridines
We are currently investigating the reaction of ninhy-
have potential applications in materials chemistry [52, drine with imidazo[1,5-a]quinoline, imidazo[5,1-a]- and
H
O
N
O
O
N
Et
MeO
A
N
A
A
EtO
B
B
Me
N
N
B
N
N
N
O
N
R
H
Cribrostatin-6
Aaptamine related
alkaloids (R = H, iPr)
Isogranulatimide
Fig. 2:ꢀExamples of natural products incorporating an imidazo[1,5-a]pyridine unit (rings A, B).
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M.S. Sammor et al.: Reaction of imidazo[1,5-a]pyridines with ninhydrinꢂ
Table 1:ꢀCrystal data and structure refinement for compound 8a.
Empirical formula
Formula weight, g mol−1
Temperature, K
Wavelength λ, Å
Crystal system
Space group
Unit cell dimensions a, Å
b, Å
C17H12N2O3
292.29
293(2)
0.71073
Monoclinic
P21/n
8.0795(6)
16.6893(13)
10.5510(10)
104.519(8)
1377.3(2)
4
c, Å
β, deg
Volume, Å3
Z
Density (calcd.), g cm−3
1.410
Absorption coefficient μ, mm−1 0.099
F(000), e
608
0.4ꢁ×ꢁ0.2ꢁ×ꢁ0.15
Crystal size, mm3
θ range for data collection, deg 3.15–26.30
Index ranges hkl
Reflections collected
Independent reflections
Rint
−10ꢁ≤ꢁhꢁ≤ꢁ7, −16ꢁ≤ꢁkꢁ≤ꢁ20, −8ꢁ≤ꢁlꢁ≤ꢁ13
6436
Fig. 3:ꢀDimer formation through intermolecular hydrogen bonding
interactions in crystals of compound 8a. Symmetry transformations
used to generate equivalent atoms: 2–x, –y, 1–z.
2787
0.0429
Completeness to θꢁ=ꢁ26.30°, % 99.8
Absorption correction
Max./min. transmission
Refinement method
Semi-empirical from equivalents
1.00000/0.54673
Full-matrix least-squares on F2
2787/0/204
4 Experimental section
Data/restraints/parameters
R1a/wR2b [Iꢁ>ꢁ2 σ(I)]
0.0578/0.1150
0.1178/0.1502
1.027
2-Pyridylmethylamine, DMAD, ninhydrin, 2-acetylpyridine,
formic acid, and dry dichloromethane were purchased from
Acros. Melting points (uncorrected) were determined using
a Stuart scientific melting temperature apparatus in open
capillary tubes. IR spectra were measured with a Thermo
Nicolet Nexus 670 FT-IR instrument. NMR spectra were
recorded on a 500-MHz spectrometer (Bruker Avance-III)
with tetramethylsilane as internal standard. HRMS were
measured on a Bruker APEX-IV mass spectrometer using
electrospray ion trap (ESI) technique.
R1a/wR2b (all data)
Goodness-of-fitc on F2
Largest diff. peak/ hole, e Å−3
0.177/−0.184
aR1ꢁ=ꢁΣꢁ|ꢁ|ꢁFoꢁ|ꢁ–ꢁ|ꢁFcꢁ|ꢁ|ꢁ/Σꢁ|ꢁFoꢁ|; bwR2ꢁ=ꢁ[Σw(Fo –Fc2)2/Σw(Fo )2]1/2
,
2
2
2
2
wꢁ=ꢁ[σ2(Fo )ꢁ+(AP)2ꢁ+ꢁBP]−1, where Pꢁ=ꢁ(Max(Fo , 0)ꢁ+ꢁ2Fc2)/3;
2
cGoFꢁ=ꢁSꢁ=ꢁ[Σw(Fo –Fc2)2/(nobs–nparam)]1/2
.
Table 2:ꢀBond lengths (Å) and angles (deg) for compound 8a.
C(10)–C(1)
O(18)–C(10)
C(10)–C(9)
C(11)–C(10)
O(17)–C(9)
O(19)–C(11)
C(11A)–C(11)
C(11A)–C(15A)
C(15A)–C(9)
N(4)–C(3)
1.498(4)
1.410(3)
1.548(4)
1.535(4)
1.205(3)
1.217(3)
1.476(4)
1.379(4)
1.472(4)
1.373(3)
1.316(3)
1.377(3)
1.380(3)
1.484(4)
N(2)–C(1)–C(10)
C(8A)–C(1)–C(10)
C(1)–C(10)–C(11)
O(18)–C(10)–C(1)
C(11)–C(10)–C(9)
C(11A)–C(11)–C(10)
C(15A)–C(11A)–C(11)
C(15)–C(15A)–C(9)
O(19)–C(11)–C(10)
C(12)–C(11A)–C(11)
O(17)–C(9)–C(10)
N(2)–C(3)–C(16)
N(2)–C(3)–N(4)
121.2(2)
128.2(2)
109.7(2)
114.1(2)
102.2(2)
108.2(2)
109.6(2)
128.7(3)
125.1(2)
129.0(3)
125.5(3)
126.4(2)
111.0(2)
106.7(2)
4.1 3-Alkyl(aryl)imidazo[1,5-a]pyridines
(1a–g)
3-Methylimidazo[1,5-a]pyridine (1a) is prepared from
2-pyridymethylamine via acetylation of the amino
group, followed by cyclization of the resulting N-acetyl
product using phosphorus oxychloride [60] or p-tol-
uenesulfonic acid monohydrate [61] according to
reported procedures. The latter procedure [61] is also
adopted for the preparation of 3-ethylimidazo[1,5-a]pyri-
dine (1b), 3-isopropylimidazo[1,5-a]pyridine (1c), and
3-isobutylimidazo[1,5-a]pyridine (1d). Compound 1f is pre-
N(2)–C(3)
N(2)–C(1)
C(8A)–C(1)
C(3)–C(16)
C(3)–N(2)–C(1)
[1,5-b]isoquinoline, and other related imidazo[N-bridged] pared using pyridine-2-carboxaldehyde and ( )-phenyl-
heterocycles, and the results will be communicated in due glycine according to a typical reported procedure [62]. This
course.
same procedure is also applied for the preparation of 1e
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6ꢀ ꢀM.S. Sammor et al.: Reaction of imidazo[1,5-a]pyridines with ninhydrin
using ( )-phenylalanine. 3-(4-Chlorophenyl)imidazo[1,5- 4.2.2 2-(3-Ethylimidazo[1,5-a]pyridin-1-yl)-2-hydroxy-
a]pyridine was prepared from 2-pyridylmethylamine
1H-indene-1,3(2H)-dione (8b)
via aroylation [63], followed by cyclization of the result-
ing carboxamide with phosphorus oxychloride [60]. The Yellow solid; yield 0.18 g (58%); m.p. 152–153°C. – IR:
NMR data of 1a–g are identical to those reported in the
literature [64].
v
maxꢀ=ꢀ3364, 3096, 2982, 2939, 2843, 1749, 1707, 1631, 1589,
1519, 1452, 1354, 1247, 1170, 1143, 1044 cm−1. – H NMR
(500 MHz, CDCl3): δꢀ=ꢀ1.21 (t, Jꢀ=ꢀ7.6 Hz, 3H, CH3CH2-), 2.89
(q, Jꢀ=ꢀ7.6 Hz, 2H, -CH2Me), 3.82 (br s, 1H, 2′-OH, exchange-
able with D2O), 6.59 (pseudo t, 1H, 6-H), 6.75 (pseudo t,
1H, 7-H), 7.67 (d, Jꢀ=ꢀ6.8 Hz, 1H, 5-H), 7.69 (d, Jꢀ=ꢀ9.3 Hz, 1H,
8-H), 7.90, 7.91 (2d, Jꢀ=ꢀ5.6 Hz, 2H, 5′-H/6′-H), 8.09, 8.10 (2d,
Jꢀ=ꢀ5.6 Hz, 2H, 4′-H/7′-H) ppm. – 13C NMR (125 MHz, CDCl3):
δꢀ=ꢀ11.0 (CH3CH2-), 19.9 (-CH2Me), 78.3 (C-2′), 112.9 (C-6), 119.1
(C-8), 119.5 (C-7), 120.8 (C-5), 124.2 (C-4′/C-7′), 124.7 (C-1),
128.7 (C-8a), 136.2 (C-5′/C-6′), 139.5 (C-3), 141.0 (C-3′a/C-7′a),
196.9 (C-1′/C-3′) ppm. – HRMS ((+)-ESI): m/zꢀ=ꢀ329.08904
1
4.2 General experimental procedure for the
synthesis of compounds 8a–g
A solution of the appropriate 3-(substituted)imidazo[1,5-
a]pyridine (1.0 mmol) in anhydrous dichloromethane
(5 mL) was dropwise added, under argon, to a stirred solu-
tion of ninhydrin (0.18 g, 1.0 mmol) in anhydrous dichlo-
romethane (15 mL) at room temperature. The progress of
the reaction was monitored by TLC and was completed
within 2–3 h. The solvent was removed under reduced
pressure, and the residual product was purified by pre-
parative silica gel TLC plates, eluting with n-hexane-ethyl
acetate (4:1, v/v).
For compounds 8a, 8b, and 8e, the products started
to separate as bright yellow solids within a few minutes
after the addition, and the reactions reached comple-
tion in 30–40 min. The products were collected by fil-
tration, washed with n-hexane, and recrystallized from
acetonitrile.
+
(calcd. 329.08966 for C18H14N2O3Na, [Mꢀ+ꢀNa] ), 635.19072
(calcd. 635.19011 for C36H28N4O6Na, [2Mꢀ+ꢀNa] ).
+
4.2.3 2-Hydroxy-2-(3-isopropylimidazo[1,5-a]pyridin-1-
yl)-1H-indene-1,3(2H)-dione (8c)
Yellow solid; yield 0.20 g (62%); m.p. 150–151°C. – IR:
v
maxꢀ=ꢀ3359, 2987, 2946, 1742, 1707, 1635, 1585, 1460, 1369,
1
1332, 1254, 1138, 1003 cm−1. – H NMR (500 MHz, CDCl3):
δꢀ=ꢀ1.33 (d, Jꢀ=ꢀ6.9 Hz, 6H, CH(CH3)2), 3.21 (septet, Jꢀ=ꢀ6.9 Hz,
1H, CHMe2), 3.75 (br s, 1H, 2′-OH, exchangeable with D2O),
6.59 (pseudo t, 1H, 6-H), 6.75 (pseudo t, 1H, 7-H), 7.67 (d,
Jꢀ=ꢀ7.0 Hz, 1H, 5-H), 7.69 (d, Jꢀ=ꢀ9.3 Hz, 1H, 8-H), 7.90, 7.91
(2d, Jꢀ=ꢀ5.6 Hz, 2H, 5′-H/6′-H), 8.08, 8.09 (2d, Jꢀ=ꢀ5.6 Hz,
The same products were also obtained when DMAD
(1.0 mmol) was included in the ninhydrin solution, to
which imidazopyridine solution was dropwise added.
13
2H, 4′-H/7′-H) ppm. – C NMR (125 MHz, CDCl3): δꢀ=ꢀ20.1
(-CH(CH3)2), 26.1 (-CHMe2), 78.2 (C-2′), 112.7 (C-6), 118.8
(C-8), 119.4 (C-7), 120.8 (C-5), 124.2 (C-4′/C-7′), 125.3 (C-1),
128.1 (C-8a), 136.2 (C-5′/C-6′), 141.1 (C-3′a/C-7′a), 142.9 (C-3),
4.2.1 2-Hydroxy-2-(3-methylimidazo[1,5-a]pyridin-1-yl)-
1H-indene-1,3(2H)-dione (8a)
197.0 (C-1′/C-3′) ppm. – HRMS ((+)-ESI): m/zꢀ=ꢀ343.10500
+
Yellow solid; yield 0.25 g (86%); m.p. 205–207°C. – IR: (calcd. 343.10531 for C19H16N2O3Na, [Mꢀ+ꢀNa] ).
v
maxꢀ=ꢀ3427, 3163, 3060, 3003, 1742, 1705, 1634, 1590, 1518,
1360, 1262, 1177, 1147, 1114, 1031 cm−1. – 1H NMR (500 MHz,
CDCl3): δꢀ=ꢀ2.66 (s, 3H, 3-CH3), 3.90 (br s, 1H, 2′-OH, 4.2.4 2-Hydroxy-2-(3-isobutylimidazo[1,5-a]pyridin-1-
exchangeable with D2O), 6.62 (pseudo t, 1H, 6-H), 6.79
(dd, Jꢀ=ꢀ6.5, 9.2 Hz, 1H, 7-H), 7.70 (d, Jꢀ=ꢀ7.1 Hz, 1H, 5-H),
yl)-1H-indene-1,3(2H)-dione (8d)
7.79 (d, Jꢀ=ꢀ9.2 Hz, 1H, 8-H), 7.88, 7.89 (2d, Jꢀ=ꢀ5.6 Hz, 2H, Yellow solid; yield 0.38 g (40%); m.p. 74–75°C. – IR:
5′-H/6′-H), 8.08, 8.09 (2d, Jꢀ=ꢀ5.6 Hz, 2H, 4′-H/7′-H) ppm.
vmaxꢀ=ꢀ3405, 2953, 2914, 2864, 1741, 1707, 1588, 1515, 1462,
– C NMR (125 MHz, CDCl3): δꢀ=ꢀ12.4 (3-CH3), 78.3 (C-2′), 1370, 1332, 1254, 1138, 1087, 1048 cm−1. – 1H NMR (500 MHz,
113.1 (C-6), 119.1 (C-7), 119.7 (C-8), 120.8 (C-5), 124.3 (C-4′/C- CDCl3): δꢀ=ꢀ0.88 (d, Jꢀ=ꢀ6.6 Hz, 6H, CH(CH3)2), 2.10 (m,
7′), 124.6 (C-1), 129.0 (C-8a), 134.8 (C-3), 136.2 (C-5′/C-6′), 1H, CH(Me)2), 2.73 (d, Jꢀ=ꢀ7.2 Hz, 2H, CH2), 3.67 (br s, 1H,
140.9 (C-3′a/C-7′a), 196.9 (C-1′/C-3′) ppm. – HRMS ((+)- HO-2′, exchangeable with D2O), 6.56 (pseudo t, 1H, 6-H),
ESI): m/zꢀ=ꢀ293.09174 (calcd. 293.09207 for C17H13N2O3, 6.67 (d, Jꢀ=ꢀ6.9 Hz, 1H, 5-H), 6.72 (dd, Jꢀ=ꢀ6.9 Hz, 9.2 Hz,
13
+
[Mꢀ+ꢀH] ), 315.07349 (calcd. 315.07401 for C17H12N2O3Na, 1H, 7-H), 7.88, 7.89 (2d, Jꢀ=ꢀ5.5 Hz, 2H, 5′-H/6′-H), 7.67 (d,
+
[Mꢀ+ꢀNa] ).
Jꢀ=ꢀ5.9 Hz, 1H, 5-H), 7.69 (d, Jꢀ=ꢀ9.0 Hz, 1H, 8-H), 8.06, 8.07
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ꢁꢀꢀꢀ
ꢂ7
M.S. Sammor et al.: Reaction of imidazo[1,5-a]pyridines with ninhydrinꢂ
13
(2d, Jꢀ=ꢀ5.5 Hz, 2H, 4′-H/7′-H) ppm. – C NMR (125 MHz, 4.2.7 2-Hydroxy-2-[3-(4-chlorophenyl)imidazo[1,5-a]
CDCl3): δꢀ=ꢀ22.5 (CH(CH3)2), 27.4 (CHMe2), 35.2 (CH2), 78.4
(C-2′), 112.8 (C-6), 119.4 (C-7), 119.0 (C-8), 120.9 (C-5), 124.2
pyridin-1-yl]-1H-indene-1,3(2H)-dione (8g)
(C-4′/C-7′), 124.7 (C-1), 128.5 (C-8a), 136.2 (C-5′/C-6′), 138.1 Yellow solid; yield 0.36 g (42%); m.p. 186–187°C. – IR:
(C-3), 141.0 (C-3′a/C-7′a), 196.9 (C-1′/C-3′) ppm. – HRMS
v
maxꢀ=ꢀ3430, 3085, 3020, 2957, 2922, 2851, 1747, 1700, 1593,
((+)-ESI): m/zꢀ=ꢀ335.13898 (calcd. 335.13902 for C20H19N2O3, 1510, 1460, 1402, 1315, 1260, 1145, 1086, 1010 cm−1. – H
1
+
[Mꢀ+ꢀH] ).
NMR (500 MHz, CDCl3): δꢀ=ꢀ4.39 (s, 1H, HO-2′, exchange-
able with D2O), 6.59 (pseudo t, 1H, 6-H), 6.80 (pseudo
t, 1H, 7-H), 7.36 (d, Jꢀ=ꢀ8.3 Hz, 2H, 3″-H/5″-H), 7.53 (d, 2H,
Jꢀ=ꢀ8.3 Hz, 2″-H/6″-H), 7.83, 7.84 (2d, Jꢀ=ꢀ5.3 Hz, 5.4 Hz,
2H, 5′-H/6′-H), 7.91 (d, Jꢀ=ꢀ9.2 Hz, 1H, 8-H), 8.01, 8.02 (2d,
Jꢀ=ꢀ5.3 Hz, 5.4 Hz, 2H, 4′-H/7′-H), 8.07 (d, Jꢀ=ꢀ7.1 Hz, 1H,
4.2.5 2-(3-Benzylimidazo[1,5-a]pyridin-1-yl)-2-hydroxy-
1H-indene-1,3(2H)-dione (8e)
Yellow solid; yield 0.23 g (65%); m.p. 180–182°C. – IR: 5-H) ppm. – 13C NMR (125 MHz, CDCl3): δꢀ=ꢀ78.6 (C-2′), 114.1
v
maxꢀ=ꢀ3384, 2953, 2922, 2851, 1741, 1704, 1584, 1452, 1379, (C-6), 120.5 (C-7), 119.7 (C-8), 121.3 (C-5), 124.2 (C-4′/ C-7′),
1
1327, 1254, 1158, 1132, 1103 cm−1. – H NMR (500 MHz, 126.7 (C-1), 127.4 (C-1″), 128.0 (C-8a), 129.1 (C-3″/ C-5″), 129.4
CDCl3): δꢀ=ꢀ3.73 (br s, 1H, 2′-OH, exchangeable with D2O), (C-2″/ C-6″), 134.6 (C-4″), 136.3 (C-5′/ C-6′), 130.3 (C-3),
4.11 (s, 2H, CH2Ph), 6.47 (pseudo t, 1H, 6-H), 6.74 (dd, 141.0 (C-3′a/C-7′a), 197.0 (C-1′/ C-3′) ppm. – HRMS ((+)-
Jꢀ=ꢀ8.6, 9.3 Hz, 1H, 7-H), 7.04 (d, Jꢀ=ꢀ7.2 Hz, 2H, 2″-H/6″-H), ESI): m/zꢀ=ꢀ389.06926 (calcd. 389.06875 for C22H1435ClN2O3,
7.19 (t, Jꢀ=ꢀ7.0, 1H, 4″-H), 7.22 (pseudo t, 2H, 3″-H/5″-H), [Mꢀ+ꢀH] ), 391.06642 (calcd. 391.06669 for C22H1437ClN2O3,
+
7.50 (d, Jꢀ=ꢀ7.2 Hz, 1H, 5-H), 7.78 (d, Jꢀ=ꢀ9.3 Hz, 1H, 8-H), 7.90, [Mꢀ+ꢀ2ꢀ+ꢀH] ), 411.05070 (calcd. 411.05069 for C22H1335ClN2O3,
+
7.91 (2d, Jꢀ=ꢀ5.7 Hz, 2H, 5′-H/6′-H), 8.09, 8.10 (2d, Jꢀ=ꢀ5.7 Hz, [Mꢀ+ꢀNa] ), 413.04754 (calcd. 413.04864 for C22H1337ClN2O3Na,
+
13
+
2H, 4′-H/7′-H) ppm. – C NMR (125 MHz, CDCl3): δꢀ=ꢀ33.3 [Mꢀ+ꢀ2ꢀ+ꢀNa] ).
(CH2Ph), 78.4 (C-2′), 113.1 (C-6), 119.7 (C-8), 119.9 (C-7),
121.1 (C-5), 124.3 (C-4′/C-7′), 125.0 (C-1), 126.8 (C-4″), 128.1
(C-2″/C-6″), 128.7 (C-3″/C-5″), 129.4 (C-8a), 135.7 (C-1″), 136.2 4.3 X-ray structure analysis of 8a
(C-5′/C-6′), 136.5 (C-3), 141.0 (C-3′a/C-7′a), 196.9 (C-1′/C-3′)
ppm. – HRMS ((+)-ESI): m/zꢀ=ꢀ369.12325 (calcd. 369.12337 Crystals were grown by slow evaporation of a dilute solution
+
for C23H17N2O3, [Mꢀ+ꢀH] ), 391.10524 (calcd. 391.10531 for of 8a in dichloromethane whereby the compound crystal-
+
C23H16N2O3Na, [Mꢀ+ꢀNa] ).
lized out as rhombic pale yellow crystals. A suitable single
crystal with approximate dimensions of 0.4ꢀ×ꢀ0.3ꢀ×ꢀ0.2 mm3
was epoxy-mounted on a glass fiber. Data were collected at
room temperature (293 K) using an Oxford Xcalibur diffrac-
tometer. Data were acquired and processed to give Shelx-
format hkl files using CrysAlis Pro software (Agilent
4.2.6 2-Hydroxy-2-(3-phenylimidazo[1,5-a]pyridin-1-yl)-
1H-indene-1,3(2H)-dione (8f)
Yellow solid; yield 0.25 g (68%); m.p. 100–102°C. – IR: Technologies Ltd., Yarnton, Oxfordshire, UK) [65]. Cell
maxꢀ=ꢀ3412, 2954, 2925, 2851, 1747, 1708, 1632, 1593, 1514, parameters were determined and refined using CrysAlis
v
1460, 1356, 1257, 1178, 1138, 1085 cm−1. – 1H NMR (500 MHz, Pro [65]. A multiscan absorption collection was applied
CDCl3): δꢀ=ꢀ4.14 (s, 1H, 2′-OH, exchangeable with D2O), with maximum and minimum transmission factors of
6.60 (pseudo t, 1H, 6-H), 6.83 (dd, Jꢀ=ꢀ6.6, 8.4 Hz, 1H, 1.00000 and 0.54673, respectively. The structure was solved
7-H), 7.88 (d, Jꢀ=ꢀ8.4 Hz, 1H, 8-H), 7.39 (t, Jꢀ=ꢀ7.4 Hz, 1H, by Direct Methods and refined by full-matrix least-squares
4″-H), 7.45 (pseudo t, 2H, 3″-H/5″-H), 7.63 (d, Jꢀ=ꢀ7.2 Hz, on F2 using all unique data [66]. All nonhydrogen atoms
2H, 2″-H/6″-H), 7.89 (pseudo t, 2H, 5′-H/6′-H), 8.08, 8.09 were refined anisotropically with the hydrogen atoms
(2d, Jꢀ=ꢀ5.7 Hz, 2H, 4′-H/7′-H), 8.17 (d, Jꢀ=ꢀ7.2 Hz, 1H, 5-H) placed on the calculated positions using a riding model
ppm. – 13C NMR (125 MHz, CDCl3): δꢀ=ꢀ78.5 (C-2′), 113.8 except H18, which was located using Fourier difference
(C-6), 120.4 (C-7), 121.3 (C-8), 121.6 (C-5), 124.3 (C-4′/C-7′), maps and refined isotropically. The isotropic displacement
126.7 (C-1″), 128.6 (C-2″/C-6″), 128.7 (C-4″), 128.9 (C-3″/C- parameters of all other hydrogen atoms were set at 1.2ꢀ×ꢀ
5″), 129.6 (C-8a), 130.0 (C-1), 136.0 (C-5′/C-6′), 137.6 (C-3), that of the carbon atoms to which they are bonded.
141.1 (C-3′a/C-7′a), 196.9 (C-1′/C-3′) ppm. – HRMS ((+)-
CCDC 1563050 contains the supplementary crystallo-
ESI): m/zꢀ=ꢀ355.10810 (calcd. 355.10772 for C22H15N2O3, graphic data for this paper. These data can be obtained
+
[Mꢀ+ꢀH] ), 377.08940 (calcd. 377.08966 for C22H14N2O3Na, free of charge from The Cambridge Crystallographic Data
+
[Mꢀ+ꢀNa] ).
Centre (www.ccdc.cam.ac.uk/data_request/cif).
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8ꢀ ꢀM.S. Sammor et al.: Reaction of imidazo[1,5-a]pyridines with ninhydrin
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Acknowledgement: Authors thank the Deanship of Scien-
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