The reaction of imidazo[1,5-a]pyridines with ninhydrin revisited

Article abstract of DOI:10.1515/znb-2020-0027

The synthesis of 2,2′-(Imidazo[1,5-a]pyridine-1,3-diyl)bis(2-hydroxy-1H-indene-1,3(2H)-dione) (11) is achieved by reaction of imidazo[1,5-a]pyridine (7) with two equivalents of ninhydrin (1) at room temperature. The structure of this new 1,3-bis-adduct 11 is evidenced from HRMS and NMR spectral data and confirmed by single-crystal X-ray crystallography. Employment of equimolar amounts of 1 and 7 gave a separable mixture of the respective 1- A nd 3-monomeric adducts (9, 10).

Full text of DOI:10.1515/znb-2020-0027

Z. Naturforsch. 2020; 75(6–7)b: 559–565
Mustafa M. El-Abadelah, Firas F. Awwadi*, Ahmad H. Abdullah and Wolfgang Voelter*
The reaction of imidazo[1,5-a]pyridines with
ninhydrin revisited
https://doi.org/10.1515/znb-2020-0027
Received January 30, 2020; accepted April 24, 2020; published online
June 29, 2020
3-(substituted)imidazo[1,5-a]pyridines (2) whereby nuclo-
philic addition of C-1 occurs at the central carbonyl carbon
(
(
C-2′) of ninhydrin to deliver the respected products 3
Scheme 1) [11].
Abstract: The synthesis of 2,2′-(Imidazo[1,5-a]pyridine-
In light of the preceding information, we sought it
1
,3-diyl)bis(2-hydroxy-1H-indene-1,3(2H)-dione) (11) is
would be worthwhile to investigate the reaction of ninhy-
drin with the parent imidazo[1,5-a]pyridine and its 1-
methyl derivative under neutral conditions. Herein we
report on our findings related to both reactions as illus-
trated in Schemes 2 and 3 (vide infra).
Further work regarding the electronic effect of sub-
stituents onto the nucleophilic character of carbon atoms 1
and 3 is in progress. The results will be communicated
achieved by reaction of imidazo[1,5-a]pyridine (7) with two
equivalents of ninhydrin (1) at room temperature. The
structure of this new 1,3-bis-adduct 11 is evidenced from
HRMS and NMR spectral data and confirmed by single-
crystal X-ray crystallography. Employment of equimolar
amounts of 1 and 7 gave a separable mixture of the
respective 1- and 3-monomeric adducts (9, 10).
Keywords: 1-methylimidazo[1,5-a]pyridine; imidazo[1,5-a] elsewhere.
pyridine; ninhydrin; nucleophilic addition at C-1/C-3;
X-ray structures.
2
Results and discussion
1
Introduction
2
.1 Chemistry
The parent imidazo[1,5-a]pyridine is an π-excessive aza-
aromatic system in which the bridgehead N-4 contributes Imidazo[1,5-a]pyridine (7) and its 1-methyl derivative (6),
to the aromaticity with its lone pair. Hence, this nitrogen is required in this study, were prepared by cyclization of the
not nuclophilic and the attack occurs at N-2 position. This respective N-[(1-pyridin-2-yl)alkylformamides (5, 4) [1] as
parent compound is known to undergo electrophilic sub- noted in the experimental section. Direct interaction of
stitution (S –Ar) with various electrophiles at C-1, but also ninhydrin (1) with the 1-methyl derivative (6) in dichloro-
E
at C-3 or both, depending, at least in part, on the reaction methane at room temperature delivered, as expected, the
conditions used [1–10]. Thus, imidazo[1,5-a]pyridine is respective adduct namely 2-hydroxy-2-(1-methylimidazo
acetylated at C-1 [1] or at C-3 [2], nitrosated (followed by [1,5-a]pyridin-3-yl)-1H-indene-1,3(2H)-dione (8) in high
rearrangement) at C-1 [3], mono-formylated at C-1 (70%) yield. Under similar conditions, the reaction of equimolar
and C-3 (30%) [4]. On the other hand, lithiation (and related amounts of (1) with the parent compound (7) produced a
means of generation of carbanion) takes place preferen- separable mixture of the mono adducts 2-hydroxy-2-(imi-
tially at C-3 [4, 5]. As expected, electrophilic substitution dazo[1,5-a]pyridin-1-yl)-1H-indene-1,3(2H)-dione (9) and 2-
occurs mainly at C-3 if C-1 is bloked [6–10]. Recently, hydroxy-2-(imidazo[1,5-a]pyridin-3-yl)-1H-indene-1,3(2H)-
we have reported on the reaction of ninhydrin (1) with dione (10) in an approximate ratio of 4:1 (Scheme 3). On the
other hand, employment of two equivalents of (1) and just
one equivalent of (7) gave the bis-1,3-adduct 2,2′-(imidazo
*
Corresponding authors: Firas F. Awwadi, Department of Chemistry,
[
1,5-a]pyridine-1,3-diyl)bis(2-hydroxy-1H-indene-1,3(2H)-
Faculty of Science, The University of Jordan, Amman, 11942, Jordan,
E-mail: f.Awwadi@ju.edu.jo; and Wolfgang Voelter, Interfakultäres
Institut für Biochemie, Universität Tübingen, Hoppe-Seyler Straße 4,
dione) (11) as the main product (Scheme 3).
The new compounds 8 (Scheme 2) and 9–11 (Scheme 3)
were characterized by IR, MS, and NMR spectral data.
These data, detailed in the experimental section, are
compatible with the suggested structures. Thus, the mass
spectra display the correct molecular ion peaks for which
the measured high resolution (HRMS) data are in good
7
2076 Tübingen, Germany, E-mail: wolfgang.voelter@uni-
tuebingen.de
Mustafa M. El-Abadelah and Ahmad H. Abdullah: Department of
Chemistry, Faculty of Science, The University of Jordan, Amman,
11942, Jordan, E-mail: mustelab@ju.edu.jo (M.M. El-Abadelah),
ahmad_zah1989@yahoo.com (A.H. Abdullah)

560
M.M. El-Abadelah et al.: The reaction of imidazo[1,5-a]pyridines
agreement with the calculated values. DEPT and 2D (COSY, atoms are 0.01 Å and 0.20 Å for the respective O20 and O21
HMQC, HMBC) experiments showed correlations that hel- in 10, 0.41 Å and 0.21 Å for the respective O15 and O17 in 11.
1
13
ped in the H and C signal assignments to the different O–H⋯N hydrogen bonding interactions link the molecular
carbons and their attached and/or neighbouring hydro- units of 10 to form a chain structure parallel to the crys-
gens. Eventually, the structures of 10 and 11 were tallographic c–axis (Figure 3). On the other hand, O–H⋯O
confirmed by single-crystal X-ray crystallography (Figures hydrogen bonding interactions link the molecular units of
1
and 2; vide infra).
11 to form a layer structure in the ab–crystallographic plane
Figure 4). The parameters of hydrogen bonding in-
teractions are listed in Table 4.
(
2
.2 Crystal structures
The X-ray crystal structures of compounds 10 and 11 were
determined at room temperature. A summary of data
collection and refinement parameters for 10 and 11 is given
in Table 1, whilst selected bond distances and angles are
listed in Tables 2 and 3. The molecular structures of the two
compounds are shown in Figures 1 and 2. The molecular
structure of 11 adheres to crystallographic two-fold symme-
try, the axis of rotation bisecting C5–C5A/C3–N3 and passing
3
Conclusion
The reaction of 1-methylimidazo[1,5-a]pyridine afforded
high yield of the respective 3-monomeric adduct, namely 2-
hydroxy-2-(1-methylimidazo[1,5-a]pyridin-3-yl)-1H-indene-
1,3(2H)-dione (8). On the other hand, interaction of the
parent imidazo[1,5-a]pyridine (7) can be utilized and
directed towards preparation of novel 1,3-bis-adduct (11) as
through N1. It results in a 50 : 50 split occupancy of C3 and well as the 1- and 3-monomeric adducts (9, 10). These ad-
_
N3. Only one of the components is shown in Figure 2.
ducts (8 11) are hybrids of bioactive imidazo[1,5-a]pyridine
As expected, imidazo[1,5-a]pyridine rings are planar in and indene-1,3(2H)-dione entities and might display inter-
the two compounds, the mean deviation of atoms from the esting bioactivity.
plane are 0.014 Å in 10, and 0.006 Å in 11. Similarly, the
carbon atoms of the ninhydrin rings are planar in 10, the
mean deviation of atoms from the plane is 0.024 Å. How- 4 Experimental
ever, the planarity of the carbon atoms in ninhydrin system
is less pronounced in 11, the mean deviations of carbon (2-Pyridyl)methylamine, ninhydrin, 2-acetylpyridine, formic
atoms from the plane is 0.04 Å, whilst C-7 is significantly acid, phosphorous oxychloride and dry dichloromethane
deviated from the aromatic plane of the ninhydrin system were purchased from Acros. Melting points (uncorrected)
by 0.12 Å. It is noteworthy that the oxygen atoms of the were determined on a Stuart scientific melting temperature
carbonyl groups of ninhydrin system are more significantly apparatus in open capillary tubes. IR spectra were measured
deviated from the aromatic planes in 11 than in 10; the with a Thermo Nicolet Nexus 670 FT-IR instrument. NMR
distances between the aromatic plane and the oxygen spectra were recorded on a 500 MHz spectrometer (Bruker
Scheme 1: Formation of 2-hydroxy-2-(imidazo
[1,5-a]pyridin-1-yl)indene-1,3(2H)-diones (3).
Scheme 2: Synthesis of 2-hydroxy-2-(1-
methylimidazo[1,5-a]pyridin-3-yl)indene-
1
,3(2H)-dione (8).

M.M. El-Abadelah et al.: The reaction of imidazo[1,5-a]pyridines
561
Scheme 3: Formation of compounds 9–11.
Avance-III) with TMS as internal standard. High resolution 1H, –CHMe), 7.23 (pseudo t, 1H, 5-H), 7.26 (d, J = 7.8 Hz, 1H,
mass spectra (HRMS) were measured on a Bruker APEX-IV 3-H), 7.39 (br s, 1H, CONH, exchangeable with D O), 7.67
2
mass spectrometer using ESI technique.
(pseudo t, 1H, 4-H), 8.20 (s, 1H, –CHO), 8.51 (d, J = 4.4 Hz,
13
The NMR spectral data for the intermediate com- 1H, 6-H) ppm. – C NMR (125 MHz, DMSO-d ): δ = 25.1 (CH ),
6
3
pounds 4–7 are hitherto unreported, and are thus pro- 52.5 (–CHMe), 120.4 (C-5), 122.3 (C-3), 137.0 (C-4), 148.9 (C-
duced herewith.
6), 157.4 (C-2), 166.9 (COCH) ppm.
4.1 N-[(1-Pyridin-2-yl)ethyl)]formamide (4)
4.2 N-((Pyridin-2-yl)methyl)formamide (5)
This compound was obtained by interaction of 1-(pyridin-2- This compound was obtained by formylation of the amino
yl)ethanamine with formic acid following a literature pro- group of (2-pyridy)methylamine according to a literature
1
cedure [1]. The required 1-(pyridin-2-yl)ethanamine, in procedure [1]. Yellow oil; yield 70%. – H NMR (500 MHz,
turn, is prepared by reduction of 1-(pyridin-2-yl)ethanone CDCl ): δ = 4.40 (d, J = 5.7 Hz, 2H, CH ), 7.03 (pseudo t, 1H,
3
2
oxime [1] with zinc powder and acetic acid, following a 5-H), 7.13 (d, J = 7.8 Hz, 1H, 3-H), 7.71 (br s, 1H, CONH,
1
reported method [1]. Yellow oil; yield 68%. – H NMR exchangeable with D O), 7.50 (pseudo t, 1H, 4-H), 8.10 (s,
2
13
(
500 MHz, CDCl ): δ = 1.48 (d, J = 6.8 Hz, 3H, CH ), 5.22 (m, 1H, –CHO), 8.32 (d, J = 4.5 Hz,1H, 6-H) ppm. – C NMR
3
3
(
125 MHz, CDCl ): δ = 43.0 (CH ), 122.2 (C-5), 122.5 (C-3),
3
2
137.0 (C-4), 148.8 (C-6), 156.4 (C-2), 161.8 (HC=O) ppm.
4
.3 1-Methylimidazo[1,5-a]pyridine (6)
This compound was obtained as sticky greenish solid via
cyclization of N-[(1-pyridin-2-yl)ethyl]formamide (4) using
phosphours oxychloride according to a previously reported
procedure [1]. The title compound is purified by recrystalli-
zation in chloroform + hexane. Yellow solid; yield 55%; m.p.
1
6
3–64 °C, (Lit. [1] m.p. 64–65 °C). – H NMR (500 MHz, DMSO-
d ): δ = 2.57 (s, 3H, CH ), 7.02 (2overlapped pseudo t, 2H, 6-H,
6
3
7
-H), 9.38 (s, 1H, 3-H), 7.80 (d, J = 9.1 Hz, 1H, 8-H), 8.47 (d,
Figure 1: ORTEP view of the molecular structure and atom numbering
scheme of 10. (displacement ellipsoids are drawn at the 30%
probability level, and H atoms are shown as small spheres of
arbitrary radii).
13
J = 6.9 Hz, 1H, 5-H) ppm. – C NMR (125 MHz, DMSO-d ):
δ = 9.9 (CH ), 116.7 (C-6), 118.5 (C-7), 121.9 (C- 8), 121.8 (C-1),
124.4 (C-5), 124.7 (C-3), 126.4 (C-8a) ppm.
6
3

562
M.M. El-Abadelah et al.: The reaction of imidazo[1,5-a]pyridines
Table : Crystal data and structure refinement for compounds 
and .
4
.4 Imidazo[1,5-a]pyridine (7)
This compound is prepared from 2-pyridylmethylamine via
N-formylation, followed by cyclization with phosphorous
oxychloride following a reported procedure [1]. Yellow
Compound


Empirical formula
Formula weight, g mol
Temperature, K
Wavelength λ, Å
Crystal system
Space group
a, Å
C

H

N O
 
C

H

N
 
O
–

.
()
.
()
1
solid; yield 58%; m.p. 53–54 °C (Lit. [1] m.p. 54–55 °C). – H
NMR (500 MHz, DMSO-d ): δ = 6.57 (pseudo t, 1H, 6-H), 6.70
6
.
Monoclinic
P /c
.
Tetragonal
I /a
(dd, J = 6.6, 9.0 Hz,1H, 7-H), 7.31 (s, 1H, 1-H), 7.48 (d,


J = 9.0 Hz, 1H, 8-H), 8.27 (d, J = 7.0 Hz, 1H, 5-H), 8.33 (s, 1H,
.()
.()
.()
.()
.()

.()
.()
.()

13
3
-H) ppm. – C NMR (125 MHz, DMSO-d ): δ = 112.7 (C-6),
6
b, Å
c, Å
1
1
18.2 (C-7), 119.4 (C-1), 119.6 (C-8), 123.6 (C-5), 128.7 (C-3),
30.1 (C-8a) ppm.
γ, deg.

Volume, Å
Z
Density (calcd.), g cm
μ (MoKa), mm
F(), e
.()

–

.
.

.
.

4.5 2-Hydroxy-2-(1-methylimidazo[1,5-a]
pyridin-3-yl)-1H-indene-1,3(2H)-
dione (8)
–

θ range data collection, deg
Index ranges hkl
.–.
– ≤ h ≤ 
.–.
– ≤ h ≤ 
– ≤ k ≤ 
– ≤ l ≤ 

–
–
 ≤ k ≤ 
 ≤ l ≤ 
A solution of 1-methylimidazo[1,5-a]pyridine 5 (5 mmol) in
anhydrous dichloromethane (30 mL) was added to a stirred
solution of ninhydrin 1 (5 mmol) in dichloromethane
Refl. collected


Refl. unique/Rint (F )
Absorption correction
Refinement method
/.
Semi-empirical from equivalents
Full-matrix least-squares on F
/.
(
25 mL) at room temperature. The resulting reaction

mixture was stirred further for 3–4 h at rt. Thereafter, the
Data/refined parameters
/
/
solvent was evaporated in vacuo and the residual crude
./. product was purified by preparative silica gel TLC plates
a
b
Final R /wR [I >  σ(I)]
./.
./.
.
a
b
Final R /wR (all data)
./.
.
./–.
eluting with n-hexane-ethyl acetate (3:1, v/v). Yellow solid;
c

Goodness-of-Fit on (F )
yield 84%; m.p. 208–210 °C. – IR: v
= 3418, 3360, 3028,
955, 2916, 1754, 1714, 1593, 1551, 1419, 1367, 1320, 1259,
–

max
Largest diff. peak/hole, e Å
./–.
2
a
R = Σ ||Fo| − |Fc||/Σ |Fo|.
–1
1
1
174, 1146, 1107 cm . – H NMR (500 MHz, DMSO-d ):
6
b





/



−
wR = [Σw(F
o
− F
c
) /Σw(F
o
) ] , w = [σ (F
o
) + (AP) + BP] , where
δ = 2.23 (s, 3H, CH ), 4.30 (s, 1H, 2′–OH, exchangeable with


3
P = (Max(F
GoF = S = [Σw(F
o
, ) + F
c
)/.
c



/
D O), 6.73 (pseudo t, 1H, 6-H), 6.77 (pseudo t, 1H, 7-H), 7.49
2
o
c
− F ) /(nobs − nparam)] .
(
5
d, J = 8.9 Hz, 1H, 8-H), 8.03 (overlapped 2d, 4H, 4′-H, 7′-H/
′-H, 6′-H), 8.80 (d, J = 7.1 Hz, 1H, 5-H) ppm. – C NMR
13
(
125 MHz, DMSO-d ):δ = 12.5 (CH ), 78.7 (C-2′), 112.9 (C-6),
6
3
Table : Selected bond lengths (Å) and angles (deg) for compound
.

Table : Selected bond lengths (Å) and angles (deg) for compound
.

C()–C()
O()–C()
C()–C()
C()–C()
O()–C()
O()–C()
C()–C()
C()–C()
C()–C()
C()–C()
.()
.()
.()
.()
.()
.|()
.()
.()
.()
.()
.()
.()
.()
.()
N()–C()–N()
.()
N()–C()–C()
O()–C()–C()
O()–C()–C()
C()–C()–C()
C()–C()–C()
C()–C()–C()
C()–C()–C()
O()–C()–C()
C()–C()–C()
O()–C()–C()
C()–N()–C()
.() N()–C()
.() N()–C()
.() N()–C()
.() C()–C()
.() C()–C()
.() C()–C(A)
.() C()–C()
.() C()–C()
.() C()–C()
.() C()–C()
.() C()–O()
.() O()–C()
.() C()–O()
.()
.()
.()
.()
.()
.()
.()
.()
.()
.()
.()
.()
.()
C()–N()–C(A)
N()–C()–C()
N()–C()–C()
C()–C()–C()
C()–C()–N()
N()–C()–C()
C()–C()–C()
C()–C()–C()
C()–C()–C()
O()–C()–C()
O()–C()–C()
O()–C()–C()
O()–C()–C()
.()
.()
.()
.()
.()
.()
.()
.()
.()
.()
.()
N()–C()
N()–C()
N()–C()
N()–C()
N()–C()–C()
C()–N()–C()
.()
.()

M.M. El-Abadelah et al.: The reaction of imidazo[1,5-a]pyridines
563
Figure 3: Chain formation of compound 10 in the crystal through
hydrogen bonding.
(
9
2d, J = 5.6 Hz, 2H, 4′-H/7′-H), 8.52 (d, J = 7.0 Hz, 1H, 5-H),
13
.18 (s, 1H, 3-H) ppm. – C NMR (125 MHz, CDCl3) δ: 78.3 (C-
2
′), 113.2 (C6), 119.1 (C-8), 119.5 (C-7), 121.0 (C-5), 124.3 (C-4′/
C-7′), 124.8 (C-1), 126.1 (C-3), 129.1 (C-8a), 136.2 (C-5′/C-6′),
141.0 (C-3′a/C-7′a), 196.9 (C-1′/C-3′) ppm. – HRMS (ESI): m/
Figure 2: ORTEP view of the molecular structure and atom
numbering scheme of 11. (displacement ellipsoids are drawn at
the 30% probability level, and H atoms are shown as small
spheres of arbitrary radii). The molecular structure adheres to
crystallographic two-fold symmetry, the axis of rotation
bisecting C5–C5A/C3–N3 and passing through N1. Only one
alternative of C3 and N3 is shown.
+
z = 279.07614 (calcd. 279.07642 for C H N O , [M + H] ).
16 11 2 3
4
.7 2-Hydroxy-2-(imidazo[1,5-a]pyridin-3-
yl)-1H-indene-1,3(2H)-dione (10)
Thiscompound was obtained fromthe reaction of1 and 7 (as
noted above in the preparation of 9). Yellow solid; yield
1
1
7
18.0 (C-8), 119.1 (C-7), 124.3 (C-5′/C-6′), 124.6 (C-5), 127.8 (C-
), 128.5 (C-8a), 130.7 (C-3), 137.5 (C-4′/C-7′), 140.1 (C-3′a/C-
1
1
4%; m.p. 211–212 °C. – IR: vmax = 3426, 3061, 1740, 1718,
–1
603, 1594, 1558, 1487, 1450, 1362, 1277, 1211, 1150, 1014 cm .
′a), 196.5 (C-1′/C-3′) ppm. – HRMS (ESI): m/z = 293.09234
1
+
– H NMR (500 MHz, CDCl ) δ: 4.01 (br s, 1H, 2′–OH,
3
(calcd. 293.09207 for C H N O , [M + H] ).
17 13 2 3
exchangeable with D O), 6.74 (pseudo t, 1H, 6-H), 6.87
2
(
pseudo t, 1H, 7-H), 7.33 (s, 1H, 3-H), 7.43 (d, J = 9.1 Hz, 1H, 8-
4
.6 2-Hydroxy-2-(imidazo[1,5-a]pyridin-1-
H), 7.92 (d, J = 5.7 Hz, 2H, 5′-H/6′-H), 8.09 (d, J = 5.7 Hz, 2H,
13
4′-H/7′-H), 8.97 (d, J = 7.0 Hz, 1H, 5-H). – C NMR (125 MHz,
yl)-1H-indene-1,3(2H)-dione (9)
CDCl ): δ = 77.9 (C-2′), 113.3 (C-6), 118.0 (C-8), 120.4 (C-3),
3
1
8
20.6 (C-7), 124.4 (C-5), 124.6 (C-4′/C-7′), 131.4 (C-1), 132.4 (C-
a), 136.7 (C-5′/C-6′), 140.5 (C-3′a/C-7′a), 194.2 (C-1′/C-3′).
This compound was prepared from imidazo[1,5-a]pyridine
(5 mmol) and ninhydrin 1 (5 mmol) by following the same
7
procedure described above for compound 8. The crude
product was a composite mixture of the title compound 9
together with its 3-monomeric adduct 10. The two com-
ponents were separated by preparative silica gel plates, Table : O–H⋯A Hydrogen bonding interactions distances (Å) and
a
eluting with n-hexane-ethyl acetate (4:1, v/v). Yellow solid; angles (deg).
yield 55%; m.p. 201–203 °C. – IR: v
= 3412, 3048, 1750,
710, 1637, 1590, 1560, 1508, 1458, 1463, 1267, 1170, 1152,
max



1
1
–
1
1
130, 1085, 1003 cm . – H NMR (500 MHz, CDCl ) δ: 3.95 (br O⋯A
.()
.()
()
.()
.()
()
3
H⋯A
O–H⋯A
s, 1H, 2′–OH, exchangeable with D O), 6.65 (pseudo t, 1H,
2
6
8
-H), 6.88 (dd, J = 9.1, 6.6 Hz 1H, 7-H), 7.84 (d, J = 9.1 Hz, 1H,
-H), 7.90, 7.92 (2d, J = 5.6 Hz, 2H, 5′-H/6′-H), 8.08, 8.09
a
A = N in , A = O in .

564
M.M. El-Abadelah et al.: The reaction of imidazo[1,5-a]pyridines
5
Collection of X-ray diffraction
data and structure analyses of
compounds 10 and 11
Suitable single crystals of 10 (approximate dimensions
3
of 0.4 × 0.1 × 0.1 mm ) and 11 with approximate di-
3
mensions of 0.4 × 0.2 × 0.1 mm were epoxy-mounted on
glass fibres. Data for 10 and 11 were then collected at
room temperature (T = 293 K) using an Oxford Calibur
Diffractometer. Data were acquired and processed to
give SHELX-format hkl files using CRYSALIS PRO software
[
12]. Cell parameters were determined and refined using
CRYSALIS PRO [12]. A multiscan absorption collection was
applied with maximum and minimum transmission
factors of 1.00000 and 0.79561, 1.00000 and 0.95256 for
1
0 and 11, respectively. The structures were solved by
Direct Methods and refined by full-matrix least-squares
2
on F using all unique data [13]. All nonhydrogen atoms
Figure 4: Layer formation in the crystal structure of compound 11
through hydrogen bonding.
were refined anisotropically with the hydrogen atoms
placed in calculated positions and refined using a riding
model.
The molecular structure of 11 adheres to crystallo-
graphic two-fold symmetry, the axis of rotation bisecting
C5–C5A/C3–N3 and passing through N1. It results in a
–
HRMS (ESI): m/z = 279.07605 (calcd. 279.07642 for
+
C H N O , [M + H] ).
1
6 11 2 3
5
0:50 split occupancy of C3 and N3.
Yellow needle crystals of 10, suitable for X-ray crystal-
lography, were obtained by recrystallization from acetonitrile.
CCDC 945167 and 1945168 for 10 and 11, respectively,
contain the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.
cam.ac.uk/data_request/cif.
4
.8 2,2′-(Imidazo[1,5-a]pyridine-1,3-diyl)
bis(2-hydroxy-1H-indene-1,3(2H)-
dione) (11)
Author contribution: All the authors have accepted
responsibility for the entire content of this submitted
This compound was prepared from imidazo[1,5-a]pyridine 7 manuscript and approved submission.
5 mmol) and ninhydrin 1 (10 mmol) by following the same Research funding: We thank the Deanship of Scientific
(
procedure described for 8 above. Orange solid; yield 63%; Research at The University of Jordan, Amman-Jordan, for
1
m.p. 217–219 °C (dec). – H NMR (500 MHz, MeOD): δ = 4.80 financial support.
(
s, 2H, 2″–OH/2′–OH, exchangeable with D O), 6.76 (pseudo Conflict of interest statement: The authors declare no
2
t, 1H, 6-H), 6.94 (dd, J = 9.3, 6.7 Hz, 1H, 7-H), 7.81 (m, 4H, 4′- conflicts of interest regarding this article.
H, 7′-H/4″-H, 7″-H), 7.83 (m, 4H, 5′-H, 6′-H/5″-H, 6″-H), 7.96
1
3
(
d, J = 9.3 Hz, 1H, 8-H), 8.86 (d, J = 7.3 Hz, 1H, 5-H) ppm. – C
NMR (125 MHz, MeOD): δ = 78.1 (C-2′/C-2″), 113.1 (C-6), 119.0
References
(
(
C-8), 121.0 (C-7), 123.1, 123.3 (C-4′, C-7′/C-4″, C-7″), 124.5
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