(E)-6-Meth­oxy-9-methyl-1,2,3,4-tetra­hydro-9H-carbazol-4-one oxime

Wei Sheng; Qi-Hong Zhang; Zhui-Bai Qiu

doi:10.1107/S1600536808020047

. 2008 Jul 5;64(Pt 8):o1418. doi: 10.1107/S1600536808020047

(E)-6-Methoxy-9-methyl-1,2,3,4-tetrahydro-9H-carbazol-4-one oxime

Wei Sheng ^a, Qi-Hong Zhang ^a, Zhui-Bai Qiu ^a,^*

PMCID: PMC2961900 PMID: 21203137

Abstract

The title compound, C₁₄H₁₆N₂O₂, is dimerized by inversion-related intermolecular O—H⋯O and O—H⋯N hydrogen bonding. There is also an intramolecular C—H⋯N bond, resulting in a six-membered ring.

Related literature

For general background, see: Hester (1967 ▶, 1970 ▶). For related literature, see: Sheng et al. (2008 ▶).

Experimental

Crystal data

C₁₄H₁₆N₂O₂
M _r = 244.29
Monoclinic,
a = 8.833 (5) Å
b = 6.460 (4) Å
c = 22.247 (12) Å
β = 104.14 (2)°
V = 1231.0 (12) Å³
Z = 4
Mo Kα radiation
μ = 0.09 mm⁻¹
T = 293 (2) K
0.15 × 0.08 × 0.08 mm

Data collection

Bruker SMART APEX CCD area-detector diffractometer
Absorption correction: multi-scan (SADABS; Sheldrick, 1996 ▶) T _min = 0.987, T _max = 0.993
5647 measured reflections
2626 independent reflections
1396 reflections with I > 2σ(I)
R _int = 0.037

Refinement

R[F ² > 2σ(F ²)] = 0.055
wR(F ²) = 0.165
S = 0.89
2626 reflections
169 parameters
2 restraints
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.61 e Å⁻³
Δρ_min = −0.32 e Å⁻³

Data collection: SMART (Bruker, 2000 ▶); cell refinement: SMART; data reduction: SAINT (Bruker, 2000 ▶); program(s) used to solve structure: SHELXTL (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL and ORTEP-3 (Farrugia, 1997 ▶); software used to prepare material for publication: SHELXTL.

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536808020047/om2245sup1.cif

e-64-o1418-sup1.cif^{(18.7KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536808020047/om2245Isup2.hkl

e-64-o1418-Isup2.hkl^{(129KB, 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
C5—H5⋯N1	0.93	2.76	3.236 (3)	113
O1—H1X⋯O1ⁱ	0.827 (18)	2.54 (3)	3.177 (5)	134 (3)
O1—H1X⋯N1ⁱ	0.827 (18)	2.00 (2)	2.810 (4)	166 (4)

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Symmetry code: (i) Inline graphic .

Acknowledgments

This work is funded in part by the National Natural Science Foundation of China (grant No. 30472088).

supplementary crystallographic information

Comment

The most famous of the rearrangements in which R migrates from carbon to nitrogen is undoubtedly the conversion of ketoximes to N-subsituted amides, the Beckmann rearrangement. The most interesting feature of the rearrangement is that, it is not the nature (e.g. relative electron-releasing ability)but the stereochemical arrangment of the R and R'groups that determines which of them migrates. Almost without exception it is found to be the R group anti to the OH group that migrates from C to N. Thus, the structure of the amide produced is quite often used to establish the configuration of the oxime from which it was derived.

Surprisingly, in our study we obtained two different amides from one oxime by applying two different Beckmann conditions. This particular oxime, 6-methoxy -9-methyl-1,2,3,9-tetrahydro-4H-carbazol-4-one oxime (I), is found to yield only 6-methyl-9-methoxy-2,3,4,5-tetrahydroazepino[4,3-b]indol- 1(6H)-one (II) while treated with polyphophoric acids. However, by converting the OH group of (I) into a better leaving tosyl group followed a catalysis using Al₂O₃, (I) undergoes the rearrangement to 6-methyl-9- methoxy-3,4,5,6-tetrahydroazepino[3,2-b]indol-2(1H)-one (III) exclusively. Here we report the crystal structure of (I) in order to get a better understanding of the mechanism of this peculiar process.

Fig.1. shows the molecular structure of the title compound (I), which is almost planar and has the (E)-configuration. As shown in Fig. 2, the title compound is dimerized by inversion of (E)-6-methoxy-9-methyl-1,2,3,9-tetrahydro-4H-carbazol-4-one oxime through intermolecular H-bond viz O1—H1X···O1ⁱ and O1—H1X···N1ⁱ[symmetry code i = -x + 1,-y,-z]. There is also an intramolecular hydrogen bond of C5—H5···N1 resulting in a six-membered ring.

Experimental

The title compound (I) was prepared in three steps as follows. Firstly, with use of a method described by Sheng et al. (2008), 6-Methoxy-1,2,3,9- tetrahydro-4H-carbazol-4-one (IV) was prepared as starting material. Then,(IV) was methylated using dimethyl sulfate in a mixed solution of acetone and NaOH aq. to give 6-methoxy-9-methyl-1,2,3,9-tetrahydro-4H-carbazol-4-one (V). A mixture of (V) and hydroxylamine hydrochloride was dissolved in methanol and the solution was refluxed with a catalytic amount of pyridine. The crude product of the title compound was recrystallized in acetone to afford colorless prismatic crystals suitable for X-ray analysis.