2,2-Dimethyl-2,3-dihydro­pyrano[2,3-a]carbazol-4(11H)-one

Makuteswaran Sridharan; Karnam J Rajendra Prasad; Aimable Ngendahimana; Matthias Zeller

doi:10.1107/S1600536808033849

. 2008 Oct 22;64(Pt 11):o2155. doi: 10.1107/S1600536808033849

2,2-Dimethyl-2,3-dihydropyrano[2,3-a]carbazol-4(11H)-one

Makuteswaran Sridharan ^a, Karnam J Rajendra Prasad ^a, Aimable Ngendahimana ^b, Matthias Zeller ^b,^*

PMCID: PMC2959512 PMID: 21581015

Abstract

The title compound, C₁₇H₁₅NO₂, was prepared from 1-hydroxycarbazole and 3,3-dimethylacrylic acid with a mixture of AlCl₃ and POCl₃ as the cyclization catalyst. Owing to the presence of the –CMe₂– group, the molecule is not quite planar. In the crystal structre, strong N—H⋯O hydrogen bonds and weaker C—H⋯π interactions occur, and a slipped π–π stacking interaction [centroid–centroid separation = 3.8425 (8) Å] is also observed.

Related literature

Knölker & Reddy (2002 ▶) report on the isolation of pyranocarbazoles from various plant species, and Shanazarov et al. (1989 ▶) on their potential beneficial properties. Kavitha & Prasad (2003 ▶) describe the synthesis of compounds related to the title compound. Sridharan, Rajendra Prasad & Zeller (2008 ▶) report the structure of the 9-methyl derivative of the title compound. Sridharan, Rajendra Prasad, Ngendahimana & Zeller (2008 ▶) report the structure of the 10-methyl derivative of the title compound.

Experimental

Crystal data

C₁₇H₁₅NO₂
M _r = 265.30
Monoclinic,
a = 5.9926 (5) Å
b = 14.3368 (12) Å
c = 15.6839 (13) Å
β = 95.270 (1)°
V = 1341.78 (19) Å³
Z = 4
Mo Kα radiation
μ = 0.09 mm⁻¹
T = 100 (2) K
0.37 × 0.19 × 0.16 mm

Data collection

Bruker SMART APEX CCD diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2007 ▶) T _min = 0.887, T _max = 0.986
12548 measured reflections
3083 independent reflections
2630 reflections with I > 2σ(I)
R _int = 0.026

Refinement

R[F ² > 2σ(F ²)] = 0.041
wR(F ²) = 0.094
S = 1.06
3083 reflections
186 parameters
1 restraint
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.20 e Å⁻³
Δρ_min = −0.19 e Å⁻³

Data collection: APEX2 (Bruker, 2007 ▶); cell refinement: SAINT (Bruker, 2007 ▶); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXTL; molecular graphics: Mercury (Macrae et al., 2006 ▶); software used to prepare material for publication: SHELXTL.

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536808033849/hb2803sup1.cif

e-64-o2155-sup1.cif^{(18.9KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536808033849/hb2803Isup2.hkl

e-64-o2155-Isup2.hkl^{(151.3KB, 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
N1—H1⋯O1ⁱ	0.878 (12)	1.973 (13)	2.7876 (14)	153.9 (13)
C14—H14B⋯Cg1ⁱⁱ	0.99	2.58	3.4754 (15)	151

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Symmetry codes: (i) Inline graphic ; (ii) . Cg1 is the centroid of the C1/C6/C7/C12/N1 ring.

Acknowledgments

We acknowledge UGC, New Delhi, India, for the award of Major Research Project grant No. F. 31-122/2005. MS thanks UGC, New Delhi, for the award of a research fellowship. The diffractometer was funded by NSF grant No. 0087210, by Ohio Board of Regents grant CAP-491 and by YSU.

supplementary crystallographic information

Comment

Pyranocarbazoles such as grinimbine, mupamine, mahanimbine, murrayanol and mahanine have been isolated from plant species of the Rutaceae family (Knölker & Reddy, 2002, and references therein) and these alkaloids possess mosquitocidal, antimicrobial, anti-inflammatory and antioxidant activities (Shanazarov et al., 1989). In general pyranocarbazole alkaloids have a C-13, C-18 or C-23 framework with a C-12 carbazole nucleus as the basic unit in which one carbon is attached as a methyl, formyl, carboxylic or ester group. Another observation is that in many of the pyranocarbazole derivatives isolated so far, the oxygen atom of the pyran ring is attached to carbon atom 2 of the carbazole nucleus to form pyrano[3,2-a]carbazoles as in grinimbine. Of the 10 simple carbazole alkaloids isolated so far, five have the oxygen function on carbon 1 (or its equivalent position C 8). The C-18 pyrano[3,2-a] alkaloid mupamine posseses a methoxy group at position 8, hence there exists a substrate on which a pyrano[2,3-a]carbazole could be built upon in the plant body; however, none of the pyranocarbazoles isolated so far has a pyran ring with oxygen on carbon 1 or its equivalent position C 8.

In this context we aimed to prepare pyrano[2,3-a]carbazoles using 1-hydroxycarbazoles as starting synthons under various reaction conditions (Kavitha & Prasad, 2003, and references therein). Using the catalyst mixture AlCl₃/POCl₃ along with 1-hydroxycarbazole and 3,3-dimethyacrylic acid as the reactants we were able to generate a mixture of two products i.e., 2-(3,3-dimethylacryloyl)-1-hydroxycarbazole (2) and the title compound 2,2-dimethyl-2,3-dihydropyrano-[2,3-a]carbazol-4(11H)-one (3) (Figure 1).

The single-crystal structure confirmed the formation of the dihydropyrano-[2,3-a]carbazol-4(11H)-one framework as shown in Figure 2. Data collection and structure refinement were unproblematic and all structural parameters (bond lengths, angles, etc) are in the expected ranges. The molecules crystallize in a monoclinic setting in P2₁/n with four largely planar molecules per unit cell. The plane defined by the sp² hybridized carbon atoms, the CH₂ group and the N and O atoms has an r.m.s. deviation from planarity of only 0.036 Å. Of all the ring C atoms only C15 of the pyran C(Me)₂ unit is significately out of plane with the atoms of the four fused rings, its deviation being 0.611 (1) Å. The pyran ring thus exhibits a half chair conformation.

One of the methyl groups of the C(Me)₂ unit is also located close to the average plane of the molecule (C17 with a deviation of 0.264 (1) Å). The other, C16, is however located 2.121 (1) Å away from this plane and thus makes the molecule as a whole not planar and prevents it form forming extensive π-π stacked entities in the solid state. The packing is thus indeed dominated by strong N—H···O hydrogen bonds (Table 1) and a weaker C—H···C (Table 1) interaction. The unusual C—H···C bond could also be described as a C—H···π interaction [C14—H14b···Cg1ⁱⁱⁱ = 2.58 Å with Cg1 being the centroid of the C1/C6/C7/C12/N1 pyrrole ring and iii = 1 + x, y, z)]. The only noticeable π···π stacking interaction observed is a slipped one between Cg3 and Cg4^iv with a centroid to centroid distance of 3.8425 (8) Å (Cg3 and Cg4 are C1 to C6 and C7 to C12, respectively, iv = -1 + x, y, z).

The N—H···O hydrogen bonds that dominate the packing of the title compound tie molecules together to infinite chains that extend along the crystallographic b axis as shown in Figure 3.

The structures of the 9- and 10-methyl derivatives of (I) are described in Sridharan, Rajendra Prasad & Zeller (2008) and Sridharan, Rajendra Prasad, Ngendahimana et al. (2008). For a more detailed comparison of structures and packing of these three compounds, see Sridharan, Rajendra Prasad & Zeller (2008).

Experimental

1-Hydroxycarbazole (1, 0.001 mol) and 3,3-dimethylacrylicacid (0.001 mol) was dissolved in an ice-cold mixture of AlCl₃/POCl₃ (400 mg/ 6 ml) and were kept at room temperature for 24 h. Reaction monitoring by TLC indicated the formation of two compounds. After the completion of reaction (disappearance of starting material), the residue was poured onto ice water. The solid that separated out was filtered, dried and then separated by column chromatography on silica gel using petroleum ether/ ethyl acetate (98:2) as eluants to yield 2-(3,3-dimethylacryloyl)-1-hydroxycarbazole (2) and 2,2-dimethyl-2,3-dihydropyrano-[2,3-a] carbazol-4(11H)-one (3), respectively as yellow prisms. The product 3 thus separated was recrystallized from ethanol (0.106 g, 40%), m.p. 472–474 K.