Imino Diels-Alder adducts. XII. Two pyrano[3,2-c]quinolines

Article abstract of DOI:10.1107/S0108270106029465

The crystal structures of pyranoquinolines 9-fluoro-5-phenyl3,4,4a,5,6,10b- hexahydro-2H-pyrano[3,2-c]quinoline, C₁₈H₁₈FNO, and 9-methyl-5-phenyl-3,4,4a,5,6,10b-hexahydro-2H-pyrano[3,2-c]quinoline, C ₁₉H₂₁NO, ar

Full text of DOI:10.1107/S0108270106029465

organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
tion of the diene and the dienophile. In the course of these
studies, the crystal structures of the title compounds, (Ia) and
(Ib), have been determined.
ISSN 0108-2701
Imino Diels±Alder adducts. XII. Two
pyrano[3,2-c]quinolines
K. Ravikumar,a* B. Sridhar,a M. Maheshb and
V. V. Narayana Reddyb
aLaboratory of X-ray Crystallography, Indian Institute of Chemical Technology,
Hyderabad 500 007, India, and bOrganic Chemistry Division II, Indian Institute of
Chemical Technology, Hyderabad 500 007, India
Compounds (Ia) and (Ib) have isomorphous crystal struc-
tures (Figs. 1 and 2), despite one having F (electron with-
drawing) and the other having CH3 (electron donating)
Correspondence e-mail: ravikumar_iict@yahoo.co.in
Received 20 July 2006
Accepted 28 July 2006
Online 23 August 2006
3
Ê
substituents; the difference in volume is also signi®cant (9.6 A
3
for F and 23.5 A for CH3; Kitaigorodsky, 1973; Bertault et al.,
Ê
1998). The geometries of the molecules are very similar;
differences ranging from 1.7 to 4.9ꢀ in bond angles involving
atom C9 (Tables 1 and 2) may be attributed to the nature of
the substituent (F or CH3). The CÐF bond distance in (Ia)
The crystal structures of pyranoquinolines 9-¯uoro-5-phenyl-
3,4,4a,5,6,10b-hexahydro-2H-pyrano[3,2-c]quinoline, C18H18-
FNO, and 9-methyl-5-phenyl-3,4,4a,5,6,10b-hexahydro-2H-
pyrano[3,2-c]quinoline, C19H21NO, are isomorphous. In both
structures, the pyran ring is exo to the six-membered N-
heterocyclic ring formed in the cycloaddition step. The torsion
angles across the phenyl linkage for the two structures are
91.2 (1) and 88.3 (2)ꢀ. The striking feature in both crystal
packings is that they do not contain the expected conventional
hydrogen bonds, in spite of the presence of good hydrogen-
bonding functionalities. Possible CÐHÁ Á Áꢀ interactions are,
however, observed.
Ê
[1.3691 (15) A] agrees well with the mean value for CÐF
distances for mono¯uoroarenes tabulated by Allen et al.
Ê
(1987) [1.363 (8) A].
The structures reveal that the dihydropyran ring is attached
to the central N-heterocyclic ring in an exo (trans) fashion
[C5ÐC4ÐC12ÐO1 = 178.2 (1)ꢀ for (Ia) and 179.6 (1)ꢀ for
(Ib)]. The H4ÐC4ÐC12ÐH12 torsion angle of 51.3ꢀ in (Ia)
and 52.6ꢀ in (Ib) indicates that the junction between the pyran
and quinoline rings is cis. Similarly, the orientation of atoms
H5 and H4, de®ned by the H5ÐC5ÐC4ÐH4 torsion angle
Comment
Pyranoquinoline systems are of interest because they consti-
tute the parent ring structure of pyranoquinoline alkaloids,
such as khaplofoline, simulenoline and zanthodiaoline. A
range of biological activities have been reported for pyrano-
quinolines and their derivatives (Yamada et al., 1992;
Nesterova et al., 1995), and these compounds are used as
building blocks for the synthesis of various bridgehead N-
heterocycles (Faber et al., 1984). Pyranoquinolines possess a
diverse array of structural patterns in linear or angular forms,
which provide to the organic chemist a challenging ®eld for
investigations of their structures and accomplishment of their
syntheses. Imino Diels±Alder reactions catalyzed by Lewis
acids are a powerful and ef®cient methodology for the
construction of nitrogen-containing heterocyclic compounds.
Recently, the synthesis of disubstituted pyrano- and furo-
quinolines by the application of imino Diels±Alder reactions
between N-benzylideneanilines as dienes and 3,4-dihydro-
pyran or 2,3-dihydrofuran as dienophiles, using ZrCl4 as a
catalyst, have been reported (Mahesh et al., 2004). We have
been investigating how the formation of endo/exo isomers via
Diels±Alder cycloadditions depends on the relative orienta-
Figure 1
A perspective view of the molecule of (Ia). Displacement ellipsoids are
drawn at the 30% probability level and H atoms are drawn as small circles
of arbitrary radii.
o574 # 2006 International Union of Crystallography
DOI: 10.1107/S0108270106029465
Acta Cryst. (2006). C62, o574±o576

organic compounds
[ 62.9ꢀ in (Ia) and 61.0ꢀ in (Ib)] is also cis. This orientation
facilitates the pyran and the phenyl rings being on the same
side of the quinoline ring [C3ÐC4ÐC5ÐC13 = 63.4 (1)ꢀ in
(Ia) and 61.0 (2)ꢀ in (Ib)]. This con®guration is in accor-
dance with the coupling constant J = 5.2 Hz observed between
atoms H4 and H5 for compounds (Ia) and (Ib).
In both structures, the fusion strain exerted during the
quinoline ring formation in the Diels±Alder process can be
seen from the twist about the C5Á Á ÁC11 vector [C5ÐC4Ð
C12ÐC11 = 51.3 (1)ꢀ in (Ia) and 52.4 (2)ꢀ in (Ib); C5ÐN1Ð
C6ÐC11 = 20.1 (2)ꢀ in (Ia) and 18.7 (2)ꢀ in (Ib)] The
coordination of the quinoline N atom is signi®cantly pyra-
midal, the sum of the angles at N being 347.6 (2)ꢀ in (Ia) and
349.2 (2)ꢀ in (Ib). The appropriate puckering description for
the N-heterocycle ring in the quinoline ring system is half-
chair in both structures, with asymmetry parameters (Nardelli,
1983) ÁC2(C5ÐC4) of 0.024 (1) in (Ia) and 0.039 (1) in (Ib).
The pyran rings in both structures are oriented almost
perpendicular to the quinoline ring systems. Atom O1 is
displaced above the N1/C6/C11/C12 least-squares plane by
Ê
Ê
0.686 (1) A in (Ia) and 0.651 (1) A in (Ib). The conformation
of the pyran ring in both structures is a chair, as expected, with
atoms C1, C3, C4 and O1 de®ning the plane, atom C2 being
Ê
Ê
displaced by 0.660 (2) A in (Ia) and 0.661 (2) A in (Ib), and
Ê
atom C12 being displaced by 0.614 (1) A in (Ia) and
Ê
0.623 (2) A in (Ib).
Figure 3
The crystal packing of (Ia), showing the formation of centrosymmetric
dimers through CÐHÁ Á Áꢀ hydrogen-bonding interactions (dashed lines).
H atoms not involved in hydrogen bonding have been omitted for clarity.
The phenyl ring substituted at atom C5 in both compounds
is planar and is rotated from the central N-heterocyclic ring
about the C5ÐC13 bond by 91.2 (1)ꢀ in (Ia) and 88.3 (2)ꢀ
in (Ib), so as to avoid short non-bonded interactions between
the atoms of this ring and the atoms of the N-heterocycle [e.g.
ciple hydrogen bonds could be formed. Recently, Bhatt &
Desiraju (2006) have reported a similar situation in the crystal
structure of desloratadine, where the NH group is not
hydrogen bonded in a conventional sense, although two
acceptors are available. A similar situation has also been
noted in the crystal structures of alloxan (Beyer et al., 2001;
Coombes et al., 1997), an oxalic acid±phthalocyanine complex
(Liu et al., 2002), and furo- and pyranoquinolines (Ravikumar
et al., 2004, 2005). The phenyl ring is the basis of a large
volume of experimental material on CÐHÁ Á Áꢀ hydrogen
bonds (Desiraju & Steiner, 1999). In both compounds,
geometry calculations show a signi®cant CÐHÁ Á Áꢀ interaction
involving C12ÐH12 and the centroid (Cg1) of the C6±C11
aromatic ring of an inversion-related molecule (Table 3). This
interaction for (Ia) is shown in Fig. 3; that for (Ib) is similar.
Ê
Ê
H1NÁ Á ÁH18 = 2.70 A in (Ia) and 2.62 A in (Ib)]
A striking feature is that the structures of (Ia) and (Ib) do
not contain conventional hydrogen bonds, although in prin-
Experimental
To a solution of the appropriate N-benzylideneaniline (5.5 mmol) in
dichloromethane (5 ml) at room temperature were added ZrCl4
(10 mol%) and 3,4-dihydropyran (5.5 mmol) and the mixture stirred
for 90 min. The completed reaction was quenched with water and the
crude product was puri®ed by column chromatography using 2%
ethyl acetate and hexane to yield the title compounds. Crystals
suitable for X-ray study were obtained by recrystallization from a
mixture of methanol and water (3:1) in both cases.
Figure 2
A perspective view of the molecule of (Ib). Displacement ellipsoids are
drawn at the 30% probability level and H atoms are drawn as small circles
of arbitrary radii.
ꢁ
Acta Cryst. (2006). C62, o574±o576
Ravikumar et al. C18H18FNO and C19H21NO o575

organic compounds
Re®nement
Compound (Ia)
Re®nement on F2
R[F2 > 2ꢅ(F2)] = 0.043
wR(F2) = 0.112
S = 1.05
2615 re¯ections
195 parameters
H atoms treated by a mixture of
independent and constrained
re®nement
w = 1/[ꢅ2(F2o) + (0.0509P)2
+ 0.2075P]
Crystal data
3
where P = (F2o + 2Fc2)/3
(Á/ꢅ)max < 0.001
Ê
V = 718.11 (14) A
C18H18FNO
Mr = 283.33
Triclinic, P1
a = 8.3005 (9) A
Ê
b = 9.6401 (11) A
Z = 2
Dx = 1.310 Mg m
Mo Kꢁ radiation
3
3
Ê
Áꢇmax = 0.20 e A
3
Ê
0.15 e A
Ê
Áꢇmin
=
1
ꢄ = 0.09 mm
T = 273 (2) K
Ê
c = 10.0400 (11) A
ꢁ = 66.154 (2)ꢀ
ꢂ = 79.666 (2)ꢀ
ꢃ = 79.880 (2)ꢀ
Block, colorless
0.20 Â 0.15 Â 0.10 mm
The H atom attached to the quinoline N atom was located in a
difference density map and re®ned isotropically. All other H atoms
were positioned geometrically and were treated as riding on their
Data collection
Bruker SMART APEX CCD area-
detector diffractometer
! scan
2504 independent re¯ections
2276 re¯ections with I > 2ꢅ(I)
Rint = 0.017
Ê
parent C atoms, with CÐH distances of 0.93±0.98 A, and with Uiso(H)
values of 1.5Ueq(C) for methyl H atoms and 1.2Ueq(C) for the other H
atoms.
6884 measured re¯ections
ꢆmax = 25.0ꢀ
Re®nement
For both compounds, data collection: SMART (Bruker, 2001); cell
re®nement: SAINT (Bruker, 2001); data reduction: SAINT;
program(s) used to solve structure: SHELXS97 (Sheldrick, 1997);
program(s) used to re®ne structure: SHELXL97 (Sheldrick, 1997);
molecular graphics: SHELXTL/PC (Sheldrick, 1990) and PLATON
(Spek, 2003); software used to prepare material for publication:
SHELXL97.
Re®nement on F2
R[F2 > 2ꢅ(F2)] = 0.039
wR(F2) = 0.113; S = 1.08
2504 re¯ections
194 parameters
H atoms: see below
w = 1/[ꢅ2(F2o) + (0.0612P)2
+ 0.1136P]
where P = (F2o + 2Fc2)/3
(Á/ꢅ)max < 0.001
3
Ê
Áꢇmax = 0.20 e A
3
Ê
0.23 e A
Áꢇmin
=
Table 1
Selected bond angles (ꢀ) for (Ia).
The authors thank Dr J. S. Yadav, Director of IICT, for his
kind encouragement and support.
C9ÐC8ÐC7
F1ÐC9ÐC8
F1ÐC9ÐC10
118.08 (13)
118.62 (13)
118.93 (13)
C8ÐC9ÐC10
C9ÐC10ÐC11
122.45 (13)
119.79 (12)
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: FG3027). Services for accessing these data are
described at the back of the journal.
Table 2
Hydrogen-bond geometry (A, ) for (Ia) and (Ib).
ꢀ
Ê
Cg1 is the centroid of the C6±C11 ring.
References
DÐHÁ Á ÁA
DÐH
HÁ Á ÁA
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0.98
0.98
2.68
2.73
3.647 (2)
3.682 (2)
170
165
C12ÐH12Á Á ÁCg1i
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3
Ê
V = 745.85 (11) A
C19H21NO
Mr = 279.37
Triclinic, P1
a = 8.2596 (7) A
b = 10.0084 (9) A
Z = 2
Dx = 1.244 Mg m
Mo Kꢁ radiation
3
Ê
1
Ê
Ê
ꢄ = 0.08 mm
T = 273 (2) K
c = 10.1134 (9) A
ꢁ = 66.435 (1)ꢀ
ꢂ = 81.927 (2)ꢀ
ꢃ = 77.141 (1)ꢀ
Needle, colorless
0.20 Â 0.11 Â 0.08 mm
Data collection
Bruker SMART APEX CCD area-
detector diffractometer
! scan
2615 independent re¯ections
2329 re¯ections with I > 2ꢅ(I)
Rint = 0.016
7067 measured re¯ections
ꢆmax = 25.0ꢀ
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Wisconsin, USA.
Sheldrick, G. M. (1997). SHELXS97 and SHELXL97. University of
Table 3
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È
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C7ÐC8ÐC9
C8ÐC9ÐC10
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121.15 (14)
117.52 (14)
120.34 (14)
C10ÐC9ÐC19
C9ÐC10ÐC11
122.14 (15)
122.59 (14)
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ꢁ
o576 Ravikumar et al.
C18H18FNO and C19H21NO
Acta Cryst. (2006). C62, o574±o576