2-Bromo­methyl-N-isopropyl-7,8-dimeth­oxy-1,2-dihydro-1,3-oxazolo[3,2-a]quinoline-4-carboxamide

Svetlana V Shishkina; Oleg V Shishkin; Igor V Ukrainets; Nataliya L Bereznyakova; Alexandra A Davidenko

doi:10.1107/S1600536808013378

. 2008 May 10;64(Pt 6):o1031. doi: 10.1107/S1600536808013378

2-Bromomethyl-N-isopropyl-7,8-dimethoxy-1,2-dihydro-1,3-oxazolo[3,2-a]quinoline-4-carboxamide

Svetlana V Shishkina ^a,^*, Oleg V Shishkin ^a, Igor V Ukrainets ^b, Nataliya L Bereznyakova ^b, Alexandra A Davidenko ^b

PMCID: PMC2961529 PMID: 21202555

Abstract

In the title compound, C₁₈H₂₁BrN₂O₅, conjugation between the π-donating N—C—O fragment and the π-withdrawing carbonyl group results in considerable redistribution of the electron density within the dihydropyridinol ring. This effect is also promoted by the formation of an intramolecular N—H⋯O hydrogen bond. The five-membered heterocycle is disordered over two envelope conformations in a 0.35:0.65 ratio.

Related literature

For related literature, see: Ukrainets et al. (2007a ▶,b ▶); Bürgi & Dunitz (1994 ▶); Hutcheon & James (1977 ▶).

Experimental

Crystal data

C₁₈H₂₁BrN₂O₅
M _r = 425.28
Triclinic,
a = 8.736 (2) Å
b = 9.968 (2) Å
c = 10.588 (3) Å
α = 86.90 (2)°
β = 80.90 (2)°
γ = 80.04 (2)°
V = 896.4 (4) Å³
Z = 2
Mo Kα radiation
μ = 2.33 mm⁻¹
T = 100 (2) K
0.60 × 0.40 × 0.10 mm

Data collection

Oxford Diffraction Xcalibur3 diffractometer
Absorption correction: analytical (Alcock, 1970 ▶) T _min = 0.287, T _max = 0.793
6292 measured reflections
3105 independent reflections
2701 reflections with I > 2σ(I)
R _int = 0.089

Refinement

R[F ² > 2σ(F ²)] = 0.066
wR(F ²) = 0.171
S = 1.05
3105 reflections
258 parameters
6 restraints
H-atom parameters constrained
Δρ_max = 1.76 e Å⁻³
Δρ_min = −0.88 e Å⁻³

Data collection: CrysAlis CCD (Oxford Diffraction, 2005 ▶); cell refinement: CrysAlis RED (Oxford Diffraction, 2005 ▶); data reduction: CrysAlis RED; program(s) used to solve structure: SHELXTL (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXTL; molecular graphics: XP (Siemens, 1998 ▶); software used to prepare material for publication: SHELXTL.

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536808013378/kp2166sup1.cif

e-64-o1031-sup1.cif^{(23.4KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536808013378/kp2166Isup2.hkl

e-64-o1031-Isup2.hkl^{(152.3KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N2—H2A⋯O3	0.88	1.91	2.634 (5)	138
C10A—H10A⋯O3ⁱ	1.00	2.23	3.042	137
C12A—H12A⋯O2ⁱⁱ	0.99	2.33	3.289	164
C12A—H12B⋯O4ⁱⁱⁱ	0.99	2.41	3.173	134
C12B—H12D⋯O2ⁱⁱ	0.99	2.30	3.253	162
C17—H17A⋯O5^iv	0.98	2.41	3.380	172

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Symmetry codes: (i) Inline graphic ; (ii) ; (iii) ; (iv) .

supplementary crystallographic information

Comment

2-Bromomethyl-5-oxo-1,2-dihydro-5H-oxazolo[3,2-a]quinoline-4- carboxylic acids are labile compounds. Therefore, their amidation are not always successful (Ukrainets et al., 2007a; Ukrainets et al., 2007b). However the heterocyclization of the previously synthesized N—R-amides of 1-allyl-4-hydroxy-2-oxo-1,2-dihydroquinoline-3-carboxylic acids was straightforward into the N—R-amides of oxazolo-quinoline-4-carboxylic acids (I) (Scheme 1). In the present paper, we report the crystal structure of the title compound, (I). The benzpyridone fragment and the O1, C11, O5, O4, O3, C13, O2, N2 atoms are cooplanar whithin 0.02 Å. The C7—O3 (1.263 (5) Å) and C8—C9 (1.386 (6) Å) bonds are elongated comparing to the values in the literature (1.210 Å and 1.326 Å; Burgi & Dunitz, 1994) whereas the C9—O1 (1.336 (5) Å) and N1—C9 (1.333 (6) Å) bonds are shorter than their mean values retrieved from the quoted references (1.354 Å and 1.336 Å). Such redistribution of the electron density can be explained by the conjugation interactions between the N1—C9—O1 π-donating fragment and the C7—O3 π-acceptor carbonyl group. Similar effect was observed earlier in related structure (Hucheon & James, 1977). The formation of the N2—H2N···O3 intramolecular hydrogen bond (Table 1) also promotes the elongation of the carbonyl bond. The five-membered heterocycle ring is disodered over two envelope conformations (A and B) with population A:B 35:65%. The deviation of the C10 atom from the mean plane of the remaining atoms of the ring is -0.41 Å in the conformer A and 0.35 Å in B. The bromomethyl substituent in both conformers is in a pseudo-equatorial orientation (the C9—O1—C10—C12 torsion angle is 145.1 (7) %A in A and -138.1 (5) %A in B). The bromine atom is not disordered and it is located in ap-position relatively to the O1—C10 bond in both conformers [the O1—C10—C12—Br1 torsion angle is -179.9 (6) %A (A) and 178.5 (3) %A (B)]. The methoxy groups at the C3 and C4 atoms are almost coplanar to the plane of the aromatic ring (the C18—O5—C3—C2 and C17—O4—C4—C5 torsion angles are 4.2 (6) %A and -6.2 (6) %A, respectively). The isopropyl group has ap-conformation relatively to the C8—C13 bond and it is turned away from the C13—N2 bond (the C14—N2—C13—C8 and C13—N2—C14—H14a torsion angles are 174.7 (4) %A and -40%A, respectively). In the crystal the molecules of the title compound form the three-dimensional network via intermolecular hydrogen bonds (Table 1). The shortened intermolecular contacts H14a···Br1ⁱ (i = -x,-y,1 - z) 3.13 Å (van der Waals sum 3.23 Å), H18c···C7ⁱⁱ (ii = 1 - x,1 - y,1 - z) 2.70 Å (2.87 Å), Br1···Br1ⁱⁱⁱ(iii = 1 - x,-y,-z) 3.42 Å (3.94 Å) were observed in the crystal. Stacking interaction between parallel aromatic rings is observed [the shortest C3···C1ⁱⁱ (1 - x,1 - y,1 - z) distance is 3.45 Å].

Experimental

To a stirred solution of the 1-allyl-4-hydroxy-6,7-dimethoxy-2-oxo- 1,2-dihydroquinoline-3-carboxylic acid isopropylamide (3.46 g, 10.0 mmol) in acetic acid (70 ml) was added bromine (0.52 ml, 10.0 mmol) (the solution turned to be colourless). The mixture was diluted with water. The precipitate formed was filtered off, washed with cold water and dried. Yield 3.95 g (93%). m.p. 542–544 K.