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The title compound, C14H21NO4, was synthesized in 91% yield by condensation of 2,3,4-trimethoxy­benzaldehyde and N-tert-butyl­hydroxy­lamine acetate in the presence of triethyl­amine as the base and anhydrous magnesium sulfate as the dehydrating agent. The structure features a benzene ring and side chains. The C=N double bond leads to a planar C=N(-O)-C group; this group is not coplanar with the benzene ring. The N=C-Car-Car torsion angle is 10.2 (2)°.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536807031674/hj3042sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S1600536807031674/hj3042Isup2.hkl
Contains datablock I

CCDC reference: 659094

Key indicators

  • Single-crystal X-ray study
  • T = 293 K
  • Mean [sigma](C-C) = 0.002 Å
  • R factor = 0.042
  • wR factor = 0.124
  • Data-to-parameter ratio = 14.3

checkCIF/PLATON results

No syntax errors found



Alert level C ABSTM02_ALERT_3_C The ratio of expected to reported Tmax/Tmin(RR') is < 0.90 Tmin and Tmax reported: 0.857 0.965 Tmin(prime) and Tmax expected: 0.956 0.965 RR(prime) = 0.896 Please check that your absorption correction is appropriate.
Author Response: The transmission coefficients were calculated by the program SADABS, which not only estimated the absorption by the crystal, but also corrected othe factors such as the absorption of mounting glass fibre and crystal not being truely centered.
PLAT061_ALERT_3_C Tmax/Tmin Range Test RR' too Large .............       0.89
Author Response: see above
PLAT154_ALERT_1_C The su's on the Cell Angles are Equal  (x 10000)        300 Deg.
Author Response: It is correct.
PLAT242_ALERT_2_C Check Low       Ueq as Compared to Neighbors for         C8
Author Response: It is a false alert because C11 belongs to t-butyl moiety.

Alert level G 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 0 ALERT level B = Potentially serious problem 4 ALERT level C = Check and explain 2 ALERT level G = General alerts; check 3 ALERT type 1 CIF construction/syntax error, inconsistent or missing data 1 ALERT type 2 Indicator that the structure model may be wrong or deficient 2 ALERT type 3 Indicator that the structure quality may be low 0 ALERT type 4 Improvement, methodology, query or suggestion 0 ALERT type 5 Informative message, check

Comment top

Nitrones are versatile organic compounds widely used as 1,3-dipoles in cycloadditions,(Merino & Padwa, 2004; Torsell, 1988) spin trapping agents in free radical chemistry (Jasen, 1971; Usuki et al., 2006) and also in biological studies. (Zhang et al., 2000) Recently they have also been employed as therapeutics in age-related diseases. (Floyd, 2006) Nitrones undergo many reactions, such as the Behrend Rearrangement, nitrone-oxime O-ether rearrangement, and thermolytic alkene elimination. (Torsell, 1988) While the most conventional procedures for the preparation of nitrones have been the condensation of N-monosubstituted hydroxylamines with carbonyl compounds and the N-alkylation of oximes, (Torsell, 1988) a newly reported high yielding and chemoselective procedure for the conversion of imines to nitrones using catalytic amounts of methyltrioxorhenium represents a breakthrough in nitrone synthesis. (Soldaini et al., 2007) We have recently shown that nitrones derived from aromatic aldehydes can be used as convenient precursors to carbocyclic carbene ligands for the synthesis of novel and catalytically useful Pd compounds. (Yao et al., 2007) The formation of nitrone-based Pd complexes involves the selective C—H activation of the aromatic ring via orthopalladation directed by the oxygen atom on the nitrone moiety. It can be expected that the stereochemistry around the C=N of the nitrone group would have a pronounced effect in formation of the Ccarbene—Pd bond as we believe that the oxygen initially ligates the palladium species and directs the subsequent ortho-palladation. For this purpose, we have prepared the title compound and its structure analyzed by X-ray crystallography. The C7=N1 double bond leads to a plane containing C8, O1, N1, C7 and C6 which is not coplanar with the phenyl ring; the torsion angle N1 - C7 - C6 - C1 is -10.2 (3) °.

Related literature top

For related literature, see: Floyd (2006); Jasen (1971); Merino & Padwa (2004); Soldaini et al. (2007); Torsell (1988); Usuki et al. (2006); Yao et al. (2007); Zhang et al. (2000).

Experimental top

An oven-dried Schlenk flask was charged with 2,3,4-Trimethoxybenzaldehyde (196 mg, 1.0 mmol), N-tert-butyl hydroxylamine acetate (298 mg, 2.0 mmol) and anhydrous magnesium sulfate (362 mg, 3.0 mmol) under argon. Triethylamine (350 µL, 253 mg, 2.5 mmol) was then added via syringe followed by anhydrous benzene (6 ml, distilled from sodium/benzophenone). After stirring at 90°C in a Schlenk flask for 8 days, the reaction mixture was filtered to remove the magnesium sulfate and the filtrate concentrated to dryness with a rotary evaporator. The crude mixture was purified by flash column chromatography on silica gel (60 230–400 mesh) using neat ethyl acetate as the eluent to give the title compound (244 mg, 91%) as white solid, m.p. 122–123°C. 1H-NMR (500 MHz, in CDCl3 at 25°C): δ 9.09 (1 H, d, J = 9.1 Hz), 7.82 (1 H, s), 6.66 (1 H, d, J = 9.1 Hz), 3.87 (3 H, s), 3.84 (3 H, s), 3.80 (3 H, s), 1.55 (9 H, s). 13C-NMR (125 MHz, CDCl3): δ155.2, 152.2, 141.4, 124.2, 124.0, 118.1, 106.8, 70.4, 61.5, 60.8, 55.9, 28.3. Anal. Calcd for C14H21NO4: C, 62.90; H, 7.92; N, 5.24. Found: C, 63.04; H, 7.90; N 5.15. Crystals suitable for X-ray analysis were grown by slow solvent diffusion by layering hexane over a solution of the nitrone in dichloromethane.

Refinement top

H atoms atoms are treated by constrained refinement. The bond lengths of the hydrogen atoms to their parent atoms in six methyl groups are all equal to 0.96 Å while the others are equal to 0.93 Å.

Structure description top

Nitrones are versatile organic compounds widely used as 1,3-dipoles in cycloadditions,(Merino & Padwa, 2004; Torsell, 1988) spin trapping agents in free radical chemistry (Jasen, 1971; Usuki et al., 2006) and also in biological studies. (Zhang et al., 2000) Recently they have also been employed as therapeutics in age-related diseases. (Floyd, 2006) Nitrones undergo many reactions, such as the Behrend Rearrangement, nitrone-oxime O-ether rearrangement, and thermolytic alkene elimination. (Torsell, 1988) While the most conventional procedures for the preparation of nitrones have been the condensation of N-monosubstituted hydroxylamines with carbonyl compounds and the N-alkylation of oximes, (Torsell, 1988) a newly reported high yielding and chemoselective procedure for the conversion of imines to nitrones using catalytic amounts of methyltrioxorhenium represents a breakthrough in nitrone synthesis. (Soldaini et al., 2007) We have recently shown that nitrones derived from aromatic aldehydes can be used as convenient precursors to carbocyclic carbene ligands for the synthesis of novel and catalytically useful Pd compounds. (Yao et al., 2007) The formation of nitrone-based Pd complexes involves the selective C—H activation of the aromatic ring via orthopalladation directed by the oxygen atom on the nitrone moiety. It can be expected that the stereochemistry around the C=N of the nitrone group would have a pronounced effect in formation of the Ccarbene—Pd bond as we believe that the oxygen initially ligates the palladium species and directs the subsequent ortho-palladation. For this purpose, we have prepared the title compound and its structure analyzed by X-ray crystallography. The C7=N1 double bond leads to a plane containing C8, O1, N1, C7 and C6 which is not coplanar with the phenyl ring; the torsion angle N1 - C7 - C6 - C1 is -10.2 (3) °.

For related literature, see: Floyd (2006); Jasen (1971); Merino & Padwa (2004); Soldaini et al. (2007); Torsell (1988); Usuki et al. (2006); Yao et al. (2007); Zhang et al. (2000).

Computing details top

Data collection: SMART (Bruker, 1999); cell refinement: SMART and SAINT (Bruker, 1999); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997a); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997a); molecular graphics: SHELXTL (Sheldrick, 1997b); software used to prepare material for publication: SHELXTL.

Figures top
[Figure 1] Fig. 1.  
(Z)-N-tert-Butyl-C-(2,3,4-trimethoxyphenyl)nitrone top
Crystal data top
C14H21NO4Z = 2
Mr = 267.32F(000) = 288
Triclinic, P1Dx = 1.214 Mg m3
Hall symbol: -P 1Melting point = 395–396 K
a = 8.7424 (15) ÅMo Kα radiation, λ = 0.71073 Å
b = 9.5039 (17) ÅCell parameters from 427 reflections
c = 9.8424 (17) Åθ = 14–14°
α = 74.055 (3)°µ = 0.09 mm1
β = 68.612 (3)°T = 293 K
γ = 82.108 (3)°Plate, colorless
V = 731.5 (2) Å30.50 × 0.40 × 0.40 mm
Data collection top
Siemens SMART CCD PLATFORM
diffractometer
2563 independent reflections
Radiation source: fine-focus sealed tube2189 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.017
Detector resolution: 0 pixels mm-1θmax = 25.0°, θmin = 2.2°
ω scansh = 1010
Absorption correction: multi-scan
(SADABS; Sheldrick, 2000)
k = 1111
Tmin = 0.857, Tmax = 0.965l = 1111
5580 measured reflections
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.042H-atom parameters constrained
wR(F2) = 0.124 w = 1/[σ2(Fo2) + (0.0678P)2 + 0.113P]
where P = (Fo2 + 2Fc2)/3
S = 1.07(Δ/σ)max < 0.001
2563 reflectionsΔρmax = 0.23 e Å3
179 parametersΔρmin = 0.17 e Å3
0 restraintsExtinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.024 (6)
Crystal data top
C14H21NO4γ = 82.108 (3)°
Mr = 267.32V = 731.5 (2) Å3
Triclinic, P1Z = 2
a = 8.7424 (15) ÅMo Kα radiation
b = 9.5039 (17) ŵ = 0.09 mm1
c = 9.8424 (17) ÅT = 293 K
α = 74.055 (3)°0.50 × 0.40 × 0.40 mm
β = 68.612 (3)°
Data collection top
Siemens SMART CCD PLATFORM
diffractometer
2563 independent reflections
Absorption correction: multi-scan
(SADABS; Sheldrick, 2000)
2189 reflections with I > 2σ(I)
Tmin = 0.857, Tmax = 0.965Rint = 0.017
5580 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0420 restraints
wR(F2) = 0.124H-atom parameters constrained
S = 1.07Δρmax = 0.23 e Å3
2563 reflectionsΔρmin = 0.17 e Å3
179 parameters
Special details top

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 (Å2) top
xyzUiso*/Ueq
O10.75304 (15)1.17217 (13)0.34565 (15)0.0717 (4)
O21.29356 (14)0.62646 (12)0.30972 (13)0.0647 (3)
O31.09014 (13)0.54726 (11)0.20004 (11)0.0584 (3)
O40.82513 (12)0.72922 (12)0.16273 (12)0.0610 (3)
N10.70119 (15)1.11834 (13)0.26398 (14)0.0523 (3)
C11.00430 (18)0.94615 (16)0.31636 (17)0.0518 (4)
H10.98381.03370.34620.062*
C21.13649 (18)0.85577 (16)0.33577 (17)0.0532 (4)
H21.20460.88370.37670.064*
C31.16811 (17)0.72379 (16)0.29453 (16)0.0496 (4)
C41.06241 (17)0.68092 (15)0.23628 (15)0.0481 (3)
C50.93260 (17)0.77314 (16)0.21437 (15)0.0481 (3)
C60.90073 (17)0.90925 (16)0.25308 (16)0.0484 (3)
C70.76466 (18)0.99913 (17)0.22132 (17)0.0526 (4)
H70.71750.96830.16420.063*
C80.55423 (19)1.20292 (18)0.22727 (18)0.0600 (4)
C90.5125 (3)1.1466 (3)0.1152 (3)0.0883 (6)
H930.47501.04860.16040.132*
H920.60871.14660.02750.132*
H910.42751.20890.08670.132*
C100.4129 (2)1.1846 (3)0.3765 (2)0.0886 (6)
H1030.31781.24030.36110.133*
H1020.44351.21900.44570.133*
H1010.38801.08300.41700.133*
C110.6005 (3)1.3618 (2)0.1600 (2)0.0835 (6)
H1130.50671.42080.14580.125*
H1120.68791.37010.06470.125*
H1110.63631.39490.22680.125*
C121.4108 (2)0.6695 (2)0.3579 (3)0.0795 (6)
H1231.46130.75670.28790.119*
H1221.49350.59240.36270.119*
H1211.35690.68830.45570.119*
C131.0042 (3)0.43237 (19)0.3183 (2)0.0809 (6)
H1331.04390.41560.40070.121*
H1321.02160.34470.28320.121*
H1310.88890.45880.35140.121*
C140.8909 (2)0.7105 (2)0.0131 (2)0.0747 (5)
H1430.90720.80470.05700.112*
H1420.81550.65810.00350.112*
H1410.99420.65610.00110.112*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.0737 (8)0.0711 (7)0.0942 (9)0.0155 (6)0.0461 (7)0.0434 (7)
O20.0582 (6)0.0675 (7)0.0777 (7)0.0129 (5)0.0316 (6)0.0285 (6)
O30.0680 (7)0.0514 (6)0.0548 (6)0.0026 (5)0.0134 (5)0.0216 (5)
O40.0507 (6)0.0757 (7)0.0690 (7)0.0063 (5)0.0217 (5)0.0342 (6)
N10.0497 (7)0.0544 (7)0.0547 (7)0.0009 (5)0.0195 (5)0.0147 (6)
C10.0526 (8)0.0492 (8)0.0589 (9)0.0023 (6)0.0211 (7)0.0187 (6)
C20.0500 (8)0.0579 (9)0.0590 (9)0.0043 (6)0.0231 (7)0.0189 (7)
C30.0447 (7)0.0540 (8)0.0479 (8)0.0008 (6)0.0134 (6)0.0130 (6)
C40.0487 (8)0.0488 (8)0.0439 (7)0.0049 (6)0.0092 (6)0.0148 (6)
C50.0438 (7)0.0551 (8)0.0465 (7)0.0091 (6)0.0117 (6)0.0161 (6)
C60.0454 (7)0.0512 (8)0.0488 (8)0.0042 (6)0.0147 (6)0.0138 (6)
C70.0502 (8)0.0571 (8)0.0563 (8)0.0015 (6)0.0213 (7)0.0189 (7)
C80.0497 (8)0.0659 (10)0.0597 (9)0.0058 (7)0.0200 (7)0.0102 (7)
C90.0826 (13)0.1032 (15)0.0964 (15)0.0171 (11)0.0562 (12)0.0270 (12)
C100.0535 (10)0.1182 (17)0.0748 (12)0.0084 (10)0.0133 (9)0.0105 (11)
C110.0779 (12)0.0673 (11)0.0897 (13)0.0123 (9)0.0241 (10)0.0081 (10)
C120.0618 (10)0.0927 (13)0.1025 (14)0.0184 (9)0.0449 (10)0.0404 (11)
C130.1072 (15)0.0552 (9)0.0737 (12)0.0161 (10)0.0179 (10)0.0171 (8)
C140.0801 (12)0.0939 (13)0.0658 (11)0.0018 (10)0.0364 (9)0.0298 (10)
Geometric parameters (Å, º) top
O1—N11.2918 (16)C8—C91.520 (3)
O2—C31.3586 (18)C8—C101.520 (2)
O2—C121.421 (2)C9—H930.9600
O3—C41.3788 (17)C9—H920.9600
O3—C131.414 (2)C9—H910.9600
O4—C51.3739 (16)C10—H1030.9600
O4—C141.425 (2)C10—H1020.9600
N1—C71.299 (2)C10—H1010.9600
N1—C81.5240 (19)C11—H1130.9600
C1—C21.381 (2)C11—H1120.9600
C1—C61.396 (2)C11—H1110.9600
C1—H10.9300C12—H1230.9600
C2—C31.385 (2)C12—H1220.9600
C2—H20.9300C12—H1210.9600
C3—C41.402 (2)C13—H1330.9600
C4—C51.380 (2)C13—H1320.9600
C5—C61.411 (2)C13—H1310.9600
C6—C71.445 (2)C14—H1430.9600
C7—H70.9300C14—H1420.9600
C8—C111.518 (3)C14—H1410.9600
C3—O2—C12117.46 (13)H93—C9—H92109.5
C4—O3—C13113.76 (12)C8—C9—H91109.5
C5—O4—C14116.22 (12)H93—C9—H91109.5
O1—N1—C7122.97 (12)H92—C9—H91109.5
O1—N1—C8114.34 (12)C8—C10—H103109.5
C7—N1—C8122.64 (13)C8—C10—H102109.5
C2—C1—C6121.58 (13)H103—C10—H102109.5
C2—C1—H1119.2C8—C10—H101109.5
C6—C1—H1119.2H103—C10—H101109.5
C1—C2—C3120.34 (13)H102—C10—H101109.5
C1—C2—H2119.8C8—C11—H113109.5
C3—C2—H2119.8C8—C11—H112109.5
O2—C3—C2125.16 (13)H113—C11—H112109.5
O2—C3—C4115.39 (13)C8—C11—H111109.5
C2—C3—C4119.42 (13)H113—C11—H111109.5
O3—C4—C5120.53 (13)H112—C11—H111109.5
O3—C4—C3119.60 (13)O2—C12—H123109.5
C5—C4—C3119.87 (13)O2—C12—H122109.5
O4—C5—C4120.03 (12)H123—C12—H122109.5
O4—C5—C6118.53 (13)O2—C12—H121109.5
C4—C5—C6121.32 (13)H123—C12—H121109.5
C1—C6—C5117.41 (13)H122—C12—H121109.5
C1—C6—C7125.82 (13)O3—C13—H133109.5
C5—C6—C7116.77 (13)O3—C13—H132109.5
N1—C7—C6126.98 (14)H133—C13—H132109.5
N1—C7—H7116.5O3—C13—H131109.5
C6—C7—H7116.5H133—C13—H131109.5
C11—C8—C9109.38 (16)H132—C13—H131109.5
C11—C8—C10111.50 (16)O4—C14—H143109.5
C9—C8—C10111.30 (17)O4—C14—H142109.5
C11—C8—N1106.89 (14)H143—C14—H142109.5
C9—C8—N1111.94 (14)O4—C14—H141109.5
C10—C8—N1105.73 (13)H143—C14—H141109.5
C8—C9—H93109.5H142—C14—H141109.5
C8—C9—H92109.5

Experimental details

Crystal data
Chemical formulaC14H21NO4
Mr267.32
Crystal system, space groupTriclinic, P1
Temperature (K)293
a, b, c (Å)8.7424 (15), 9.5039 (17), 9.8424 (17)
α, β, γ (°)74.055 (3), 68.612 (3), 82.108 (3)
V3)731.5 (2)
Z2
Radiation typeMo Kα
µ (mm1)0.09
Crystal size (mm)0.50 × 0.40 × 0.40
Data collection
DiffractometerSiemens SMART CCD PLATFORM
Absorption correctionMulti-scan
(SADABS; Sheldrick, 2000)
Tmin, Tmax0.857, 0.965
No. of measured, independent and
observed [I > 2σ(I)] reflections
5580, 2563, 2189
Rint0.017
(sin θ/λ)max1)0.595
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.042, 0.124, 1.07
No. of reflections2563
No. of parameters179
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.23, 0.17

Computer programs: SMART (Bruker, 1999), SMART and SAINT (Bruker, 1999), SAINT, SHELXS97 (Sheldrick, 1997a), SHELXL97 (Sheldrick, 1997a), SHELXTL (Sheldrick, 1997b), SHELXTL.

 

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