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

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.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.004 Å
• R factor = 0.056
• wR factor = 0.165
• Data-to-parameter ratio = 15.5

checkCIF/PLATON results

No syntax errors found



Alert level B
PLAT417_ALERT_2_B Short Inter D-H..H-D       H1X    ..  H1X     ..       2.06 Ang.

Alert level C
DIFMX01_ALERT_2_C  The maximum difference density is > 0.1*ZMAX*0.75
            _refine_diff_density_max given =      0.613
            Test value =      0.600
DIFMX02_ALERT_1_C  The maximum difference density is > 0.1*ZMAX*0.75
            The relevant atom site should be identified.
PLAT097_ALERT_2_C Maximum (Positive) Residual Density ............       0.61 e/A   
PLAT230_ALERT_2_C Hirshfeld Test Diff for    C1     --  C2      ..       5.71 su
PLAT230_ALERT_2_C Hirshfeld Test Diff for    C2     --  C3      ..       6.25 su
PLAT241_ALERT_2_C Check High      Ueq as Compared to Neighbors for         O2
PLAT241_ALERT_2_C Check High      Ueq as Compared to Neighbors for         C2
PLAT066_ALERT_1_C Predicted and Reported Transmissions Identical .          ?
PLAT480_ALERT_4_C Long H...A H-Bond Reported H5     ..  N1      ..       2.76 Ang.
PLAT790_ALERT_4_C Centre of Gravity not Within Unit Cell: Resd.  #          1
              C14 H16 N2 O2

Alert level G
PLAT860_ALERT_3_G Note: Number of Least-Squares Restraints .......          2
PLAT199_ALERT_1_G Check the Reported _cell_measurement_temperature        293 K
PLAT200_ALERT_1_G Check the Reported _diffrn_ambient_temperature .        293 K

   0 ALERT level A = In general: serious problem
   1 ALERT level B = Potentially serious problem
  10 ALERT level C = Check and explain
   3 ALERT level G = General alerts; check

   4 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   7 ALERT type 2 Indicator that the structure model may be wrong or deficient
   1 ALERT type 3 Indicator that the structure quality may be low
   2 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

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S1. 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.

Related literature

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

S2. 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.

S3. Refinement

The H atoms bonded to N and O in the carbazolone oxime were located in a difference map and refined with distance restraints of O—H = 0.82 (2) and N—H = 0.89 (2) Å. The H atoms attached to O and all carbon-bound H atoms were placed in calculated positions and refined as riding; O—H=0.82 and C—H=0.93–0.98 Å;U_iso(H) = xU_eq(parent atom) where x=1.5 for O and 1.2 for C.

Computing details

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

Figures

	Fig. 1. The molecular structure of the title compound, showing ellipsoids at the 20% probability level.
	Fig. 2. A view of the crystal packing, showing the hydrogen-bonding network.

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

Crystal data

C14H16N2O2	F(000) = 520
Mr = 244.29	Dx = 1.318 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 777 reflections
a = 8.833 (5) Å	θ = 2.4–22.7°
b = 6.460 (4) Å	µ = 0.09 mm^−1
c = 22.247 (12) Å	T = 293 K
β = 104.14 (2)°	Prism, colorless
V = 1231.0 (12) Å^3	0.15 × 0.08 × 0.08 mm
Z = 4

Data collection

Bruker SMART APEX CCD area-detector diffractometer	2626 independent reflections
Radiation source: fine-focus sealed tube	1396 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.037
ϕ and ω scans	θmax = 27.0°, θmin = 1.9°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −11→11
Tmin = 0.987, Tmax = 0.993	k = −8→8
5647 measured reflections	l = −27→17

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.055	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.165	H atoms treated by a mixture of independent and constrained refinement
S = 0.89	w = 1/[σ^2(Fo^2) + (0.0985P)^2] where P = (Fo^2 + 2Fc^2)/3
2626 reflections	(Δ/σ)max < 0.001
169 parameters	Δρmax = 0.61 e Å^−3
2 restraints	Δρmin = −0.32 e Å^−3

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
O1	0.3608 (3)	−0.1623 (4)	−0.01619 (11)	0.0908 (7)
H1X	0.392 (4)	−0.054 (4)	0.0026 (18)	0.127 (16)*
O2	1.0030 (2)	0.1510 (3)	−0.09437 (10)	0.0781 (6)
N1	0.4790 (2)	−0.1762 (4)	−0.04926 (10)	0.0618 (6)
C1	0.4333 (3)	−0.7039 (4)	−0.16677 (13)	0.0631 (7)
H1A	0.4711	−0.8230	−0.1409	0.076*
H1B	0.4036	−0.7496	−0.2096	0.076*
C2	0.2945 (4)	−0.6123 (6)	−0.14878 (16)	0.0868 (10)
H2A	0.2228	−0.7231	−0.1455	0.104*
H2B	0.2410	−0.5203	−0.1816	0.104*
C3	0.3335 (3)	−0.4929 (5)	−0.08831 (13)	0.0656 (7)
H3A	0.2402	−0.4226	−0.0834	0.079*
H3B	0.3647	−0.5901	−0.0543	0.079*
C4	0.4606 (2)	−0.3367 (4)	−0.08413 (11)	0.0485 (6)
C4'	0.5725 (2)	−0.3745 (3)	−0.12087 (9)	0.0422 (5)
C5'	0.7093 (2)	−0.2625 (3)	−0.12699 (9)	0.0407 (5)
C5	0.7843 (2)	−0.0819 (4)	−0.10084 (10)	0.0445 (5)
H5	0.7437	−0.0036	−0.0734	0.053*
C6	0.9189 (3)	−0.0218 (4)	−0.11637 (11)	0.0511 (6)
C7	0.9790 (3)	−0.1381 (4)	−0.15859 (12)	0.0587 (7)
H7	1.0704	−0.0947	−0.1685	0.070*
C8	0.9066 (3)	−0.3127 (4)	−0.18535 (11)	0.0536 (6)
H8	0.9468	−0.3879	−0.2136	0.064*
C8'	0.7708 (2)	−0.3758 (4)	−0.16943 (9)	0.0441 (5)
C9	0.7019 (3)	−0.6996 (4)	−0.23323 (12)	0.0674 (8)
H9A	0.6501	−0.8262	−0.2277	0.101*
H9B	0.8117	−0.7251	−0.2273	0.101*
H9C	0.6599	−0.6479	−0.2744	0.101*
N9	0.6779 (2)	−0.5471 (3)	−0.18818 (8)	0.0499 (5)
C9'	0.5588 (3)	−0.5450 (4)	−0.15895 (10)	0.0477 (6)
C10	0.9545 (3)	0.2735 (4)	−0.04983 (13)	0.0669 (7)
H10A	0.8514	0.3259	−0.0673	0.100*
H10B	1.0254	0.3872	−0.0379	0.100*
H10C	0.9536	0.1907	−0.0141	0.100*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0865 (15)	0.1012 (18)	0.1098 (17)	−0.0189 (14)	0.0724 (14)	−0.0310 (15)
O2	0.0703 (12)	0.0740 (13)	0.1042 (15)	−0.0285 (10)	0.0485 (11)	−0.0276 (11)
N1	0.0588 (13)	0.0686 (15)	0.0708 (14)	−0.0054 (11)	0.0408 (11)	−0.0104 (12)
C1	0.0635 (15)	0.0564 (16)	0.0647 (16)	−0.0101 (13)	0.0067 (13)	−0.0052 (13)
C2	0.0733 (18)	0.091 (2)	0.101 (2)	−0.0302 (17)	0.0300 (17)	−0.0095 (18)
C3	0.0569 (15)	0.0730 (19)	0.0708 (17)	−0.0128 (14)	0.0233 (13)	0.0026 (14)
C4	0.0447 (12)	0.0537 (15)	0.0499 (13)	0.0003 (11)	0.0167 (10)	0.0059 (12)
C4'	0.0406 (11)	0.0448 (13)	0.0413 (12)	0.0003 (10)	0.0104 (9)	0.0019 (10)
C5'	0.0384 (11)	0.0489 (13)	0.0354 (11)	0.0046 (10)	0.0100 (9)	0.0029 (10)
C5	0.0441 (12)	0.0484 (14)	0.0448 (12)	−0.0004 (10)	0.0185 (10)	−0.0026 (10)
C6	0.0472 (12)	0.0525 (15)	0.0574 (14)	−0.0061 (11)	0.0198 (11)	−0.0045 (12)
C7	0.0480 (13)	0.0679 (18)	0.0688 (16)	−0.0044 (13)	0.0311 (12)	−0.0021 (14)
C8	0.0530 (13)	0.0642 (17)	0.0496 (13)	0.0078 (12)	0.0243 (11)	−0.0033 (12)
C8'	0.0434 (12)	0.0499 (14)	0.0391 (11)	0.0055 (10)	0.0102 (9)	−0.0019 (10)
C9	0.0851 (19)	0.0615 (17)	0.0577 (15)	0.0048 (14)	0.0216 (14)	−0.0169 (13)
N9	0.0531 (11)	0.0521 (12)	0.0450 (11)	0.0026 (10)	0.0132 (9)	−0.0093 (9)
C9'	0.0473 (12)	0.0495 (14)	0.0444 (12)	0.0018 (11)	0.0074 (10)	0.0019 (11)
C10	0.0744 (17)	0.0602 (17)	0.0676 (17)	−0.0170 (14)	0.0204 (14)	−0.0140 (14)

Geometric parameters (Å, º)

O1—N1	1.419 (3)	C5'—C5	1.397 (3)
O1—H1X	0.827 (18)	C5'—C8'	1.405 (3)
O2—C6	1.364 (3)	C5—C6	1.373 (3)
O2—C10	1.414 (3)	C5—H5	0.9300
N1—C4	1.281 (3)	C6—C7	1.404 (3)
C1—C9'	1.489 (3)	C7—C8	1.360 (3)
C1—C2	1.502 (4)	C7—H7	0.9300
C1—H1A	0.9700	C8—C8'	1.392 (3)
C1—H1B	0.9700	C8—H8	0.9300
C2—C3	1.516 (4)	C8'—N9	1.380 (3)
C2—H2A	0.9700	C9—N9	1.457 (3)
C2—H2B	0.9700	C9—H9A	0.9599
C3—C4	1.495 (3)	C9—H9B	0.9599
C3—H3A	0.9700	C9—H9C	0.9599
C3—H3B	0.9700	N9—C9'	1.365 (3)
C4—C4'	1.449 (3)	C10—H10A	0.9599
C4'—C9'	1.377 (3)	C10—H10B	0.9599
C4'—C5'	1.443 (3)	C10—H10C	0.9599
N1—O1—H1X	97 (3)	C5'—C5—H5	120.6
C6—O2—C10	118.53 (19)	O2—C6—C5	124.8 (2)
C4—N1—O1	111.4 (2)	O2—C6—C7	114.6 (2)
C9'—C1—C2	109.3 (2)	C5—C6—C7	120.6 (2)
C9'—C1—H1A	109.8	C8—C7—C6	121.5 (2)
C2—C1—H1A	109.8	C8—C7—H7	119.3
C9'—C1—H1B	109.8	C6—C7—H7	119.3
C2—C1—H1B	109.8	C7—C8—C8'	118.3 (2)
H1A—C1—H1B	108.3	C7—C8—H8	120.9
C1—C2—C3	114.4 (3)	C8'—C8—H8	120.9
C1—C2—H2A	108.7	N9—C8'—C8	130.1 (2)
C3—C2—H2A	108.7	N9—C8'—C5'	108.78 (19)
C1—C2—H2B	108.7	C8—C8'—C5'	121.1 (2)
C3—C2—H2B	108.7	N9—C9—H9A	109.5
H2A—C2—H2B	107.6	N9—C9—H9B	109.5
C4—C3—C2	113.8 (2)	H9A—C9—H9B	109.5
C4—C3—H3A	108.8	N9—C9—H9C	109.5
C2—C3—H3A	108.8	H9A—C9—H9C	109.5
C4—C3—H3B	108.8	H9B—C9—H9C	109.5
C2—C3—H3B	108.8	C9'—N9—C8'	108.57 (17)
H3A—C3—H3B	107.7	C9'—N9—C9	126.4 (2)
N1—C4—C4'	118.3 (2)	C8'—N9—C9	125.0 (2)
N1—C4—C3	124.5 (2)	N9—C9'—C4'	109.8 (2)
C4'—C4—C3	117.2 (2)	N9—C9'—C1	125.1 (2)
C9'—C4'—C5'	107.03 (19)	C4'—C9'—C1	125.0 (2)
C9'—C4'—C4	120.8 (2)	O2—C10—H10A	109.5
C5'—C4'—C4	132.2 (2)	O2—C10—H10B	109.5
C5—C5'—C8'	119.57 (19)	H10A—C10—H10B	109.5
C5—C5'—C4'	134.6 (2)	O2—C10—H10C	109.5
C8'—C5'—C4'	105.8 (2)	H10A—C10—H10C	109.5
C6—C5—C5'	118.9 (2)	H10B—C10—H10C	109.5
C6—C5—H5	120.6
C9'—C1—C2—C3	−46.4 (3)	C6—C7—C8—C8'	−0.6 (4)
C1—C2—C3—C4	50.2 (4)	C7—C8—C8'—N9	−178.2 (2)
O1—N1—C4—C4'	−179.6 (2)	C7—C8—C8'—C5'	0.2 (3)
O1—N1—C4—C3	−1.5 (4)	C5—C5'—C8'—N9	179.49 (18)
C2—C3—C4—N1	155.9 (3)	C4'—C5'—C8'—N9	−0.1 (2)
C2—C3—C4—C4'	−26.0 (3)	C5—C5'—C8'—C8	0.8 (3)
N1—C4—C4'—C9'	179.7 (2)	C4'—C5'—C8'—C8	−178.8 (2)
C3—C4—C4'—C9'	1.5 (3)	C8—C8'—N9—C9'	178.7 (2)
N1—C4—C4'—C5'	0.0 (4)	C5'—C8'—N9—C9'	0.2 (2)
C3—C4—C4'—C5'	−178.2 (2)	C8—C8'—N9—C9	−3.0 (4)
C9'—C4'—C5'—C5	−179.6 (2)	C5'—C8'—N9—C9	178.4 (2)
C4—C4'—C5'—C5	0.2 (4)	C8'—N9—C9'—C4'	−0.3 (2)
C9'—C4'—C5'—C8'	0.0 (2)	C9—N9—C9'—C4'	−178.4 (2)
C4—C4'—C5'—C8'	179.7 (2)	C8'—N9—C9'—C1	−179.9 (2)
C8'—C5'—C5—C6	−1.4 (3)	C9—N9—C9'—C1	1.9 (4)
C4'—C5'—C5—C6	178.1 (2)	C5'—C4'—C9'—N9	0.2 (2)
C10—O2—C6—C5	3.4 (4)	C4—C4'—C9'—N9	−179.64 (19)
C10—O2—C6—C7	−177.7 (2)	C5'—C4'—C9'—C1	179.9 (2)
C5'—C5—C6—O2	179.8 (2)	C4—C4'—C9'—C1	0.0 (3)
C5'—C5—C6—C7	1.0 (3)	C2—C1—C9'—N9	−157.9 (2)
O2—C6—C7—C8	−178.9 (2)	C2—C1—C9'—C4'	22.4 (3)
C5—C6—C7—C8	0.0 (4)

Hydrogen-bond geometry (Å, º)

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···O1^i	0.83 (2)	2.54 (3)	3.177 (5)	134 (3)
O1—H1X···N1^i	0.83 (2)	2.00 (2)	2.810 (4)	166 (4)

Symmetry code: (i) −x+1, −y, −z.