Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270106001119/ln1192sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270106001119/ln1192Isup2.hkl | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270106001119/ln1192IIsup3.hkl |
CCDC references: 221590; 221591
For the preparation of (I) and (II), under an inert atmosphere, PhI═NTs (15 mmol, 5.598 g) was added in small portions over a period of 3 h to a solution of (-)-2-tert-butyl-5-methyl-4H-1,3-dioxin (10 mmol, 1.562 g, 92% ee) or (+)-2-tert-butyl-5-methyl-4H-1,3-dioxin (91% ee), respectively, and CuOTf benzene complex (0.503 g, 10 mol %) in dry tert-butylmethyl ether (25 ml). After complete conversion (monitored by gas chromatography), the solvent was evaporated under reduced pressure, and the oily residue was purified by column chromatography (silica, light petroleum/ diethyl ether, 5:1) to afford a diastereomeric mixture (70:30) of the oxazolidine carbaldehyde as a colourless solid. Recrystallization from tert-butylmethyl ether led to single crystals of the main diastereomer, (I) and (II), respectively (m.p. 398–399 K). 1H NMR (500 MHz, CDCl3): δ 0.84 [s, 9H, C(CH3)3], 1.63 (s, 3H, CH3), 2.44 (s, 3H, Ph—CH3), 4.04 (d, 1H, 2J = 10.0 Hz, O—CH2), 4.10 (d, 1H, 2J = 10.0 Hz, O—CH2), 5.44 (s, 1H, O—CHR—N), 7.32 (m, 2H, CH arom), 7.76 (m, 2H, CH arom), 9.87 (s, 1H, CHO). 13C NMR (125 MHz, CDCl3): δ 17.6 (1 C, CH3), 21.5 (1 C, Ph—CH3), 26.3 [3 C, C(CH3)3], 38.0 [1 C, C(CH3)3], 71.9 (1 C, N—C—CH3), 73.2 (1 C, OCH2), 100.5 (1 C, O—CHR—N), 127.5 (2 C, C2 + 6 arom), 129.9 (2 C, C3 + 5 arom), 138.0 (1 C, C1 arom), 144.0 (1 C, C4 arom), 198.4 (1 C, CHO). IR (ATR, cm−1): δ 2962, 2927, 2852, 1737, 1451, 1334, 1259, 1160, 1090, 1012, 812, 705, 665, 594, 547. Analysis calculated for C16H23NO4S (325.42): C 59.05, H 7.12, N 4.30%; found: C 59.03, H 7.07, N 4.28%. (I): [α]20D = −76.1 (c = 2.95, CHCl3). (II): [α]20D = +73.03 (c = 1.65, CHCl3).
The methyl H atoms were constrained to an ideal geometry with C—H distances of 0.96 Å and Uiso(H) values of 1.5Ueq(C), but were allowed to rotate freely about the C—C bonds. All other H atoms were positioned geometrically and refined using a riding model, with C—H distances in the range 0.93–0.98 Å and Uiso(H) values of 1.2Ueq(C).
For both compounds, data collection: X-AREA (Stoe & Cie, 2004); cell refinement: X-AREA; data reduction: X-RED (Stoe & Cie, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: SHELXL97.
C16H23NO4S | F(000) = 696 |
Mr = 325.41 | Dx = 1.317 Mg m−3 |
Orthorhombic, P212121 | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: P 2ac 2ab | Cell parameters from 16746 reflections |
a = 8.5175 (6) Å | θ = 2.2–27.0° |
b = 11.3011 (8) Å | µ = 0.21 mm−1 |
c = 17.0503 (13) Å | T = 100 K |
V = 1641.2 (2) Å3 | Plate, colourless |
Z = 4 | 0.30 × 0.20 × 0.10 mm |
STOE IPDS-II diffractometer | 3518 independent reflections |
Radiation source: fine-focus sealed tube | 3192 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.029 |
Detector resolution: 6.67 pixels mm-1 | θmax = 27.0°, θmin = 2.2° |
ϕ or ω scans? | h = −10→10 |
Absorption correction: integration (X-RED; Stoe & Cie, 2004) | k = −14→14 |
Tmin = 0.923, Tmax = 0.980 | l = −21→21 |
9743 measured reflections |
Refinement on F2 | Hydrogen site location: inferred from neighbouring sites |
Least-squares matrix: full | H-atom parameters constrained |
R[F2 > 2σ(F2)] = 0.025 | w = 1/[σ2(Fo2) + (0.0374P)2] where P = (Fo2 + 2Fc2)/3 |
wR(F2) = 0.059 | (Δ/σ)max = 0.001 |
S = 0.95 | Δρmax = 0.22 e Å−3 |
3518 reflections | Δρmin = −0.27 e Å−3 |
205 parameters | Extinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
0 restraints | Extinction coefficient: 0.0103 (10) |
Primary atom site location: structure-invariant direct methods | Absolute structure: Flack (1983), 1486 Friedel pairs |
Secondary atom site location: difference Fourier map | Absolute structure parameter: −0.04 (5) |
C16H23NO4S | V = 1641.2 (2) Å3 |
Mr = 325.41 | Z = 4 |
Orthorhombic, P212121 | Mo Kα radiation |
a = 8.5175 (6) Å | µ = 0.21 mm−1 |
b = 11.3011 (8) Å | T = 100 K |
c = 17.0503 (13) Å | 0.30 × 0.20 × 0.10 mm |
STOE IPDS-II diffractometer | 3518 independent reflections |
Absorption correction: integration (X-RED; Stoe & Cie, 2004) | 3192 reflections with I > 2σ(I) |
Tmin = 0.923, Tmax = 0.980 | Rint = 0.029 |
9743 measured reflections |
R[F2 > 2σ(F2)] = 0.025 | H-atom parameters constrained |
wR(F2) = 0.059 | Δρmax = 0.22 e Å−3 |
S = 0.95 | Δρmin = −0.27 e Å−3 |
3518 reflections | Absolute structure: Flack (1983), 1486 Friedel pairs |
205 parameters | Absolute structure parameter: −0.04 (5) |
0 restraints |
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. |
x | y | z | Uiso*/Ueq | ||
C4 | −0.02226 (18) | 0.15792 (11) | 0.62997 (8) | 0.0198 (3) | |
H4 | −0.0750 | 0.1761 | 0.6762 | 0.024* | |
C5 | 0.17191 (19) | 0.22723 (12) | 0.52784 (9) | 0.0226 (3) | |
H5A | 0.0918 | 0.2747 | 0.5038 | 0.034* | |
H5B | 0.1730 | 0.1502 | 0.5041 | 0.034* | |
H5C | 0.2722 | 0.2644 | 0.5206 | 0.034* | |
C6 | 0.41058 (17) | 0.37324 (12) | 0.73830 (9) | 0.0205 (3) | |
C9 | 0.49627 (19) | 0.32697 (12) | 0.81125 (9) | 0.0267 (3) | |
H9A | 0.5161 | 0.2438 | 0.8054 | 0.040* | |
H9B | 0.4322 | 0.3400 | 0.8568 | 0.040* | |
H9C | 0.5941 | 0.3682 | 0.8172 | 0.040* | |
C8 | 0.37661 (19) | 0.50512 (13) | 0.75071 (10) | 0.0287 (4) | |
H8A | 0.4736 | 0.5468 | 0.7584 | 0.043* | |
H8B | 0.3111 | 0.5150 | 0.7961 | 0.043* | |
H8C | 0.3238 | 0.5362 | 0.7054 | 0.043* | |
C7 | 0.51252 (19) | 0.35622 (15) | 0.66597 (10) | 0.0321 (3) | |
H7A | 0.4542 | 0.3783 | 0.6200 | 0.048* | |
H7B | 0.5432 | 0.2747 | 0.6621 | 0.048* | |
H7C | 0.6045 | 0.4049 | 0.6701 | 0.048* | |
C1 | 0.25244 (17) | 0.30696 (11) | 0.73339 (9) | 0.0174 (3) | |
H1 | 0.1881 | 0.3304 | 0.7784 | 0.021* | |
O1 | 0.27002 (12) | 0.18134 (8) | 0.73484 (6) | 0.0198 (2) | |
C2 | 0.26050 (17) | 0.13754 (11) | 0.65689 (9) | 0.0207 (3) | |
H2A | 0.2278 | 0.0553 | 0.6568 | 0.025* | |
H2B | 0.3616 | 0.1435 | 0.6310 | 0.025* | |
C3 | 0.13820 (17) | 0.21514 (11) | 0.61506 (9) | 0.0180 (3) | |
O2 | −0.08277 (13) | 0.09072 (9) | 0.58466 (7) | 0.0284 (3) | |
N1 | 0.15862 (13) | 0.32747 (9) | 0.65998 (7) | 0.0168 (2) | |
S1 | 0.01560 (4) | 0.42522 (3) | 0.65859 (2) | 0.01677 (8) | |
O3 | −0.02654 (12) | 0.45591 (8) | 0.73767 (6) | 0.0222 (2) | |
O4 | −0.10141 (12) | 0.37777 (8) | 0.60675 (6) | 0.0222 (2) | |
C10 | 0.09087 (16) | 0.55395 (11) | 0.61323 (8) | 0.0175 (3) | |
C11 | 0.04177 (16) | 0.66292 (12) | 0.64254 (8) | 0.0187 (3) | |
H11 | −0.0207 | 0.6668 | 0.6872 | 0.022* | |
C12 | 0.08755 (18) | 0.76584 (12) | 0.60399 (9) | 0.0219 (3) | |
H12 | 0.0559 | 0.8389 | 0.6236 | 0.026* | |
C13 | 0.17950 (18) | 0.76151 (13) | 0.53693 (9) | 0.0228 (3) | |
C14 | 0.22948 (19) | 0.65080 (12) | 0.50938 (9) | 0.0238 (3) | |
H14 | 0.2935 | 0.6468 | 0.4653 | 0.029* | |
C15 | 0.18482 (18) | 0.54717 (13) | 0.54699 (9) | 0.0215 (3) | |
H15 | 0.2175 | 0.4741 | 0.5280 | 0.026* | |
C16 | 0.2250 (2) | 0.87375 (14) | 0.49491 (11) | 0.0327 (4) | |
H16A | 0.1522 | 0.9354 | 0.5082 | 0.049* | |
H16B | 0.2228 | 0.8605 | 0.4393 | 0.049* | |
H16C | 0.3289 | 0.8968 | 0.5105 | 0.049* |
U11 | U22 | U33 | U12 | U13 | U23 | |
C4 | 0.0227 (7) | 0.0166 (6) | 0.0199 (7) | 0.0003 (6) | −0.0035 (6) | 0.0019 (5) |
C5 | 0.0298 (8) | 0.0192 (7) | 0.0188 (7) | −0.0011 (6) | 0.0025 (7) | −0.0010 (6) |
C6 | 0.0191 (7) | 0.0200 (6) | 0.0225 (8) | −0.0012 (5) | −0.0030 (6) | −0.0014 (6) |
C9 | 0.0256 (8) | 0.0232 (6) | 0.0313 (8) | −0.0010 (7) | −0.0103 (7) | −0.0011 (6) |
C8 | 0.0268 (8) | 0.0191 (7) | 0.0403 (10) | −0.0035 (6) | −0.0111 (8) | 0.0008 (7) |
C7 | 0.0223 (7) | 0.0410 (8) | 0.0331 (9) | −0.0091 (7) | 0.0029 (8) | −0.0009 (7) |
C1 | 0.0199 (7) | 0.0145 (6) | 0.0178 (7) | 0.0018 (5) | 0.0002 (6) | 0.0004 (5) |
O1 | 0.0249 (5) | 0.0142 (4) | 0.0203 (5) | 0.0002 (4) | −0.0039 (4) | 0.0013 (4) |
C2 | 0.0224 (7) | 0.0165 (6) | 0.0233 (7) | 0.0021 (5) | −0.0006 (7) | −0.0019 (6) |
C3 | 0.0217 (7) | 0.0139 (6) | 0.0183 (7) | −0.0005 (5) | −0.0001 (6) | −0.0007 (5) |
O2 | 0.0311 (6) | 0.0239 (5) | 0.0303 (6) | −0.0063 (5) | −0.0064 (5) | −0.0015 (5) |
N1 | 0.0188 (5) | 0.0144 (5) | 0.0172 (6) | 0.0012 (4) | −0.0012 (5) | −0.0018 (5) |
S1 | 0.01676 (15) | 0.01517 (14) | 0.01838 (16) | 0.00138 (12) | 0.00098 (14) | 0.00095 (12) |
O3 | 0.0257 (5) | 0.0199 (4) | 0.0209 (5) | 0.0038 (4) | 0.0052 (5) | 0.0019 (4) |
O4 | 0.0193 (5) | 0.0204 (5) | 0.0268 (6) | −0.0001 (4) | −0.0038 (5) | 0.0012 (4) |
C10 | 0.0186 (6) | 0.0162 (6) | 0.0177 (7) | 0.0007 (5) | −0.0024 (6) | 0.0009 (5) |
C11 | 0.0207 (7) | 0.0182 (6) | 0.0173 (7) | 0.0016 (5) | −0.0005 (6) | −0.0012 (5) |
C12 | 0.0250 (7) | 0.0166 (6) | 0.0239 (8) | 0.0024 (6) | −0.0005 (7) | −0.0019 (6) |
C13 | 0.0241 (7) | 0.0183 (7) | 0.0260 (9) | −0.0019 (6) | 0.0009 (7) | 0.0018 (6) |
C14 | 0.0282 (8) | 0.0213 (7) | 0.0220 (8) | 0.0006 (6) | 0.0064 (7) | −0.0005 (6) |
C15 | 0.0234 (7) | 0.0186 (6) | 0.0225 (8) | 0.0026 (5) | −0.0002 (6) | −0.0016 (5) |
C16 | 0.0418 (10) | 0.0193 (7) | 0.0372 (10) | −0.0009 (7) | 0.0103 (8) | 0.0033 (7) |
C4—O2 | 1.1997 (17) | O1—C2 | 1.4205 (18) |
C4—C3 | 1.533 (2) | C2—C3 | 1.5371 (19) |
C4—H4 | 0.9300 | C2—H2A | 0.9700 |
C5—C3 | 1.521 (2) | C2—H2B | 0.9700 |
C5—H5A | 0.9600 | C3—N1 | 1.4927 (17) |
C5—H5B | 0.9600 | N1—S1 | 1.6446 (11) |
C5—H5C | 0.9600 | S1—O4 | 1.4361 (11) |
C6—C7 | 1.521 (2) | S1—O3 | 1.4377 (10) |
C6—C8 | 1.533 (2) | S1—C10 | 1.7680 (14) |
C6—C9 | 1.534 (2) | C10—C15 | 1.386 (2) |
C6—C1 | 1.543 (2) | C10—C11 | 1.3933 (18) |
C9—H9A | 0.9600 | C11—C12 | 1.392 (2) |
C9—H9B | 0.9600 | C11—H11 | 0.9300 |
C9—H9C | 0.9600 | C12—C13 | 1.387 (2) |
C8—H8A | 0.9600 | C12—H12 | 0.9300 |
C8—H8B | 0.9600 | C13—C14 | 1.403 (2) |
C8—H8C | 0.9600 | C13—C16 | 1.507 (2) |
C7—H7A | 0.9600 | C14—C15 | 1.388 (2) |
C7—H7B | 0.9600 | C14—H14 | 0.9300 |
C7—H7C | 0.9600 | C15—H15 | 0.9300 |
C1—O1 | 1.4277 (15) | C16—H16A | 0.9600 |
C1—N1 | 1.5031 (18) | C16—H16B | 0.9600 |
C1—H1 | 0.9800 | C16—H16C | 0.9600 |
O2—C4—C3 | 122.90 (14) | O1—C2—H2B | 110.6 |
O2—C4—H4 | 118.6 | C3—C2—H2B | 110.6 |
C3—C4—H4 | 118.6 | H2A—C2—H2B | 108.7 |
C3—C5—H5A | 109.5 | N1—C3—C5 | 113.78 (11) |
C3—C5—H5B | 109.5 | N1—C3—C4 | 112.18 (11) |
H5A—C5—H5B | 109.5 | C5—C3—C4 | 111.61 (12) |
C3—C5—H5C | 109.5 | N1—C3—C2 | 99.69 (11) |
H5A—C5—H5C | 109.5 | C5—C3—C2 | 112.15 (12) |
H5B—C5—H5C | 109.5 | C4—C3—C2 | 106.65 (11) |
C7—C6—C8 | 110.04 (13) | C3—N1—C1 | 110.98 (10) |
C7—C6—C9 | 110.05 (13) | C3—N1—S1 | 118.53 (9) |
C8—C6—C9 | 108.02 (12) | C1—N1—S1 | 120.62 (9) |
C7—C6—C1 | 113.14 (12) | O4—S1—O3 | 119.61 (6) |
C8—C6—C1 | 108.34 (12) | O4—S1—N1 | 105.79 (6) |
C9—C6—C1 | 107.08 (12) | O3—S1—N1 | 109.48 (6) |
C6—C9—H9A | 109.5 | O4—S1—C10 | 106.84 (6) |
C6—C9—H9B | 109.5 | O3—S1—C10 | 107.60 (6) |
H9A—C9—H9B | 109.5 | N1—S1—C10 | 106.88 (6) |
C6—C9—H9C | 109.5 | C15—C10—C11 | 120.95 (12) |
H9A—C9—H9C | 109.5 | C15—C10—S1 | 121.35 (10) |
H9B—C9—H9C | 109.5 | C11—C10—S1 | 117.49 (11) |
C6—C8—H8A | 109.5 | C12—C11—C10 | 119.03 (13) |
C6—C8—H8B | 109.5 | C12—C11—H11 | 120.5 |
H8A—C8—H8B | 109.5 | C10—C11—H11 | 120.5 |
C6—C8—H8C | 109.5 | C13—C12—C11 | 121.21 (13) |
H8A—C8—H8C | 109.5 | C13—C12—H12 | 119.4 |
H8B—C8—H8C | 109.5 | C11—C12—H12 | 119.4 |
C6—C7—H7A | 109.5 | C12—C13—C14 | 118.62 (14) |
C6—C7—H7B | 109.5 | C12—C13—C16 | 120.49 (13) |
H7A—C7—H7B | 109.5 | C14—C13—C16 | 120.89 (14) |
C6—C7—H7C | 109.5 | C15—C14—C13 | 120.97 (15) |
H7A—C7—H7C | 109.5 | C15—C14—H14 | 119.5 |
H7B—C7—H7C | 109.5 | C13—C14—H14 | 119.5 |
O1—C1—N1 | 102.91 (10) | C10—C15—C14 | 119.20 (13) |
O1—C1—C6 | 112.96 (11) | C10—C15—H15 | 120.4 |
N1—C1—C6 | 115.74 (11) | C14—C15—H15 | 120.4 |
O1—C1—H1 | 108.3 | C13—C16—H16A | 109.5 |
N1—C1—H1 | 108.3 | C13—C16—H16B | 109.5 |
C6—C1—H1 | 108.3 | H16A—C16—H16B | 109.5 |
C2—O1—C1 | 108.93 (10) | C13—C16—H16C | 109.5 |
O1—C2—C3 | 105.90 (11) | H16A—C16—H16C | 109.5 |
O1—C2—H2A | 110.6 | H16B—C16—H16C | 109.5 |
C3—C2—H2A | 110.6 | ||
C7—C6—C1—O1 | 67.43 (16) | C6—C1—N1—S1 | −97.41 (13) |
C8—C6—C1—O1 | −170.28 (12) | C3—N1—S1—O4 | −3.19 (12) |
C9—C6—C1—O1 | −53.99 (16) | C1—N1—S1—O4 | −145.87 (10) |
C7—C6—C1—N1 | −50.85 (16) | C3—N1—S1—O3 | 126.95 (10) |
C8—C6—C1—N1 | 71.45 (16) | C1—N1—S1—O3 | −15.73 (12) |
C9—C6—C1—N1 | −172.27 (11) | C3—N1—S1—C10 | −116.79 (10) |
N1—C1—O1—C2 | 26.07 (14) | C1—N1—S1—C10 | 100.53 (11) |
C6—C1—O1—C2 | −99.46 (14) | O4—S1—C10—C15 | −70.55 (13) |
C1—O1—C2—C3 | −36.08 (14) | O3—S1—C10—C15 | 159.85 (12) |
O2—C4—C3—N1 | 156.63 (13) | N1—S1—C10—C15 | 42.34 (14) |
O2—C4—C3—C5 | 27.59 (18) | O4—S1—C10—C11 | 104.24 (12) |
O2—C4—C3—C2 | −95.22 (16) | O3—S1—C10—C11 | −25.37 (13) |
O1—C2—C3—N1 | 29.01 (13) | N1—S1—C10—C11 | −142.88 (11) |
O1—C2—C3—C5 | 149.76 (11) | C15—C10—C11—C12 | 0.4 (2) |
O1—C2—C3—C4 | −87.78 (12) | S1—C10—C11—C12 | −174.38 (11) |
C5—C3—N1—C1 | −133.07 (13) | C10—C11—C12—C13 | 0.6 (2) |
C4—C3—N1—C1 | 99.03 (13) | C11—C12—C13—C14 | −1.6 (2) |
C2—C3—N1—C1 | −13.52 (14) | C11—C12—C13—C16 | 178.63 (15) |
C5—C3—N1—S1 | 80.90 (14) | C12—C13—C14—C15 | 1.7 (2) |
C4—C3—N1—S1 | −47.00 (15) | C16—C13—C14—C15 | −178.55 (15) |
C2—C3—N1—S1 | −159.55 (10) | C11—C10—C15—C14 | −0.3 (2) |
O1—C1—N1—C3 | −6.33 (14) | S1—C10—C15—C14 | 174.26 (12) |
C6—C1—N1—C3 | 117.37 (12) | C13—C14—C15—C10 | −0.7 (2) |
O1—C1—N1—S1 | 138.89 (9) |
C16H23NO4S | F(000) = 696 |
Mr = 325.41 | Dx = 1.314 Mg m−3 |
Orthorhombic, P212121 | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: P 2ac 2ab | Cell parameters from 17010 reflections |
a = 8.5276 (6) Å | θ = 1.9–27.8° |
b = 11.3090 (11) Å | µ = 0.21 mm−1 |
c = 17.0624 (12) Å | T = 100 K |
V = 1645.5 (2) Å3 | Plate, colourless |
Z = 4 | 0.35 × 0.30 × 0.20 mm |
STOE IPDS-II diffractometer | 3772 independent reflections |
Radiation source: fine-focus sealed tube | 3554 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.043 |
Detector resolution: 6.67 pixels mm-1 | θmax = 27.6°, θmin = 2.2° |
ϕ or ω scans? | h = −10→11 |
Absorption correction: integration (X-RED; Stoe & Cie, 2004) | k = −14→14 |
Tmin = 0.941, Tmax = 0.971 | l = −21→21 |
13910 measured reflections |
Refinement on F2 | Hydrogen site location: inferred from neighbouring sites |
Least-squares matrix: full | H-atom parameters constrained |
R[F2 > 2σ(F2)] = 0.028 | w = 1/[σ2(Fo2) + (0.0579P)2] where P = (Fo2 + 2Fc2)/3 |
wR(F2) = 0.076 | (Δ/σ)max = 0.012 |
S = 1.02 | Δρmax = 0.19 e Å−3 |
3772 reflections | Δρmin = −0.31 e Å−3 |
205 parameters | Extinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
0 restraints | Extinction coefficient: 0.028 (2) |
Primary atom site location: structure-invariant direct methods | Absolute structure: Flack (1983), 1617 Friedel pairs |
Secondary atom site location: difference Fourier map | Absolute structure parameter: −0.04 (5) |
C16H23NO4S | V = 1645.5 (2) Å3 |
Mr = 325.41 | Z = 4 |
Orthorhombic, P212121 | Mo Kα radiation |
a = 8.5276 (6) Å | µ = 0.21 mm−1 |
b = 11.3090 (11) Å | T = 100 K |
c = 17.0624 (12) Å | 0.35 × 0.30 × 0.20 mm |
STOE IPDS-II diffractometer | 3772 independent reflections |
Absorption correction: integration (X-RED; Stoe & Cie, 2004) | 3554 reflections with I > 2σ(I) |
Tmin = 0.941, Tmax = 0.971 | Rint = 0.043 |
13910 measured reflections |
R[F2 > 2σ(F2)] = 0.028 | H-atom parameters constrained |
wR(F2) = 0.076 | Δρmax = 0.19 e Å−3 |
S = 1.02 | Δρmin = −0.31 e Å−3 |
3772 reflections | Absolute structure: Flack (1983), 1617 Friedel pairs |
205 parameters | Absolute structure parameter: −0.04 (5) |
0 restraints |
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. |
x | y | z | Uiso*/Ueq | ||
S1 | 0.51561 (3) | 0.57476 (3) | 0.65858 (2) | 0.02166 (9) | |
O3 | 0.47337 (11) | 0.54408 (8) | 0.73763 (6) | 0.0270 (2) | |
O4 | 0.39856 (11) | 0.62247 (8) | 0.60672 (6) | 0.0271 (2) | |
N1 | 0.65852 (12) | 0.67247 (9) | 0.66014 (7) | 0.0218 (2) | |
O1 | 0.76996 (11) | 0.81849 (8) | 0.73488 (6) | 0.0245 (2) | |
O2 | 0.41727 (13) | 0.90936 (9) | 0.58459 (7) | 0.0332 (2) | |
C1 | 0.75211 (15) | 0.69330 (11) | 0.73329 (9) | 0.0224 (3) | |
H1 | 0.6865 | 0.6695 | 0.7792 | 0.027* | |
C2 | 0.76053 (15) | 0.86252 (11) | 0.65705 (9) | 0.0252 (3) | |
H2A | 0.8636 | 0.8566 | 0.6307 | 0.030* | |
H2B | 0.7271 | 0.9464 | 0.6571 | 0.030* | |
C3 | 0.63822 (15) | 0.78496 (11) | 0.61500 (8) | 0.0227 (3) | |
C4 | 0.47745 (15) | 0.84202 (11) | 0.63007 (8) | 0.0248 (3) | |
H4 | 0.4235 | 0.8233 | 0.6772 | 0.030* | |
C5 | 0.67219 (18) | 0.77260 (12) | 0.52791 (9) | 0.0281 (3) | |
H5A | 0.7747 | 0.7350 | 0.5207 | 0.042* | |
H5B | 0.6729 | 0.8510 | 0.5035 | 0.042* | |
H5C | 0.5909 | 0.7238 | 0.5034 | 0.042* | |
C6 | 0.91019 (15) | 0.62651 (12) | 0.73831 (9) | 0.0251 (3) | |
C7 | 1.01240 (17) | 0.64353 (15) | 0.66608 (10) | 0.0364 (3) | |
H7A | 1.1053 | 0.5928 | 0.6700 | 0.055* | |
H7B | 1.0452 | 0.7264 | 0.6626 | 0.055* | |
H7C | 0.9526 | 0.6223 | 0.6191 | 0.055* | |
C8 | 0.87645 (17) | 0.49493 (13) | 0.75057 (10) | 0.0339 (3) | |
H8A | 0.8264 | 0.4625 | 0.7035 | 0.051* | |
H8B | 0.8063 | 0.4850 | 0.7956 | 0.051* | |
H8C | 0.9750 | 0.4530 | 0.7604 | 0.051* | |
C9 | 0.99659 (18) | 0.67302 (12) | 0.81105 (9) | 0.0323 (3) | |
H9A | 1.0972 | 0.6319 | 0.8164 | 0.048* | |
H9B | 0.9325 | 0.6587 | 0.8578 | 0.048* | |
H9C | 1.0152 | 0.7581 | 0.8053 | 0.048* | |
C10 | 0.59033 (14) | 0.44626 (11) | 0.61332 (8) | 0.0229 (3) | |
C11 | 0.54186 (14) | 0.33703 (11) | 0.64256 (8) | 0.0238 (3) | |
H11 | 0.4788 | 0.3328 | 0.6884 | 0.029* | |
C12 | 0.58704 (17) | 0.23422 (12) | 0.60377 (9) | 0.0264 (3) | |
H12 | 0.5540 | 0.1597 | 0.6235 | 0.032* | |
C13 | 0.67928 (17) | 0.23852 (12) | 0.53689 (9) | 0.0275 (3) | |
C14 | 0.72945 (17) | 0.34922 (13) | 0.50939 (9) | 0.0288 (3) | |
H14 | 0.7952 | 0.3532 | 0.4645 | 0.035* | |
C15 | 0.68467 (16) | 0.45310 (12) | 0.54663 (9) | 0.0256 (3) | |
H15 | 0.7178 | 0.5277 | 0.5270 | 0.031* | |
C16 | 0.7249 (2) | 0.12631 (13) | 0.49486 (11) | 0.0380 (4) | |
H16A | 0.8294 | 0.1014 | 0.5122 | 0.057* | |
H16B | 0.7264 | 0.1406 | 0.4382 | 0.057* | |
H16C | 0.6487 | 0.0641 | 0.5069 | 0.057* |
U11 | U22 | U33 | U12 | U13 | U23 | |
S1 | 0.01631 (13) | 0.02281 (14) | 0.02588 (17) | −0.00114 (10) | 0.00100 (11) | −0.00086 (11) |
O3 | 0.0255 (5) | 0.0272 (4) | 0.0284 (5) | −0.0037 (4) | 0.0052 (4) | −0.0007 (4) |
O4 | 0.0173 (4) | 0.0290 (5) | 0.0349 (6) | −0.0005 (4) | −0.0041 (4) | −0.0012 (4) |
N1 | 0.0182 (5) | 0.0218 (5) | 0.0255 (6) | −0.0007 (4) | −0.0007 (4) | 0.0011 (4) |
O1 | 0.0231 (4) | 0.0219 (4) | 0.0283 (5) | −0.0003 (3) | −0.0033 (4) | −0.0010 (3) |
O2 | 0.0301 (5) | 0.0311 (5) | 0.0383 (6) | 0.0064 (4) | −0.0073 (4) | 0.0023 (4) |
C1 | 0.0184 (5) | 0.0227 (6) | 0.0262 (7) | −0.0010 (5) | −0.0012 (5) | −0.0005 (5) |
C2 | 0.0222 (5) | 0.0241 (6) | 0.0294 (7) | −0.0012 (5) | −0.0026 (5) | 0.0025 (5) |
C3 | 0.0211 (6) | 0.0210 (6) | 0.0260 (7) | 0.0006 (5) | −0.0004 (5) | 0.0016 (5) |
C4 | 0.0213 (6) | 0.0239 (5) | 0.0291 (7) | 0.0001 (5) | −0.0027 (5) | −0.0020 (5) |
C5 | 0.0301 (7) | 0.0276 (7) | 0.0266 (8) | 0.0008 (5) | 0.0030 (6) | 0.0017 (5) |
C6 | 0.0173 (6) | 0.0282 (6) | 0.0298 (8) | 0.0008 (5) | −0.0024 (5) | 0.0011 (5) |
C7 | 0.0209 (6) | 0.0479 (8) | 0.0404 (9) | 0.0074 (6) | 0.0036 (6) | 0.0018 (6) |
C8 | 0.0264 (7) | 0.0269 (7) | 0.0484 (10) | 0.0040 (5) | −0.0110 (6) | −0.0002 (6) |
C9 | 0.0270 (7) | 0.0313 (6) | 0.0387 (8) | 0.0004 (6) | −0.0110 (6) | 0.0014 (6) |
C10 | 0.0184 (5) | 0.0242 (6) | 0.0261 (7) | −0.0019 (5) | −0.0011 (5) | −0.0013 (5) |
C11 | 0.0210 (6) | 0.0257 (6) | 0.0248 (7) | −0.0025 (4) | −0.0002 (5) | 0.0008 (5) |
C12 | 0.0240 (6) | 0.0239 (6) | 0.0315 (8) | −0.0007 (5) | 0.0005 (5) | 0.0017 (5) |
C13 | 0.0241 (6) | 0.0261 (6) | 0.0324 (8) | 0.0017 (5) | 0.0005 (6) | −0.0018 (6) |
C14 | 0.0269 (7) | 0.0295 (7) | 0.0299 (8) | −0.0004 (5) | 0.0069 (6) | 0.0008 (5) |
C15 | 0.0230 (6) | 0.0254 (6) | 0.0285 (7) | −0.0023 (5) | 0.0026 (5) | 0.0012 (5) |
C16 | 0.0435 (9) | 0.0267 (7) | 0.0439 (10) | 0.0009 (6) | 0.0111 (7) | −0.0034 (6) |
S1—O3 | 1.4385 (11) | C7—H7A | 0.9800 |
S1—O4 | 1.4390 (10) | C7—H7B | 0.9800 |
S1—N1 | 1.6452 (11) | C7—H7C | 0.9800 |
S1—C10 | 1.7648 (13) | C8—H8A | 0.9800 |
N1—C3 | 1.4971 (16) | C8—H8B | 0.9800 |
N1—C1 | 1.5001 (17) | C8—H8C | 0.9800 |
O1—C2 | 1.4205 (18) | C9—H9A | 0.9800 |
O1—C1 | 1.4242 (15) | C9—H9B | 0.9800 |
O2—C4 | 1.2024 (17) | C9—H9C | 0.9800 |
C1—C6 | 1.5476 (17) | C10—C11 | 1.3948 (17) |
C1—H1 | 1.0000 | C10—C15 | 1.3958 (19) |
C2—C3 | 1.5402 (18) | C11—C12 | 1.3922 (19) |
C2—H2A | 0.9900 | C11—H11 | 0.9500 |
C2—H2B | 0.9900 | C12—C13 | 1.387 (2) |
C3—C5 | 1.520 (2) | C12—H12 | 0.9500 |
C3—C4 | 1.5369 (17) | C13—C14 | 1.404 (2) |
C4—H4 | 0.9500 | C13—C16 | 1.5086 (19) |
C5—H5A | 0.9800 | C14—C15 | 1.3891 (19) |
C5—H5B | 0.9800 | C14—H14 | 0.9500 |
C5—H5C | 0.9800 | C15—H15 | 0.9500 |
C6—C7 | 1.522 (2) | C16—H16A | 0.9800 |
C6—C8 | 1.530 (2) | C16—H16B | 0.9800 |
C6—C9 | 1.536 (2) | C16—H16C | 0.9800 |
O3—S1—O4 | 119.56 (6) | C6—C7—H7A | 109.5 |
O3—S1—N1 | 109.41 (6) | C6—C7—H7B | 109.5 |
O4—S1—N1 | 105.78 (6) | H7A—C7—H7B | 109.5 |
O3—S1—C10 | 107.58 (6) | C6—C7—H7C | 109.5 |
O4—S1—C10 | 106.86 (6) | H7A—C7—H7C | 109.5 |
N1—S1—C10 | 107.02 (6) | H7B—C7—H7C | 109.5 |
C3—N1—C1 | 110.86 (10) | C6—C8—H8A | 109.5 |
C3—N1—S1 | 118.47 (8) | C6—C8—H8B | 109.5 |
C1—N1—S1 | 120.86 (9) | H8A—C8—H8B | 109.5 |
C2—O1—C1 | 108.94 (10) | C6—C8—H8C | 109.5 |
O1—C1—N1 | 103.23 (10) | H8A—C8—H8C | 109.5 |
O1—C1—C6 | 113.01 (10) | H8B—C8—H8C | 109.5 |
N1—C1—C6 | 115.64 (11) | C6—C9—H9A | 109.5 |
O1—C1—H1 | 108.2 | C6—C9—H9B | 109.5 |
N1—C1—H1 | 108.2 | H9A—C9—H9B | 109.5 |
C6—C1—H1 | 108.2 | C6—C9—H9C | 109.5 |
O1—C2—C3 | 105.91 (10) | H9A—C9—H9C | 109.5 |
O1—C2—H2A | 110.6 | H9B—C9—H9C | 109.5 |
C3—C2—H2A | 110.6 | C11—C10—C15 | 120.76 (12) |
O1—C2—H2B | 110.6 | C11—C10—S1 | 117.76 (10) |
C3—C2—H2B | 110.6 | C15—C10—S1 | 121.28 (10) |
H2A—C2—H2B | 108.7 | C12—C11—C10 | 119.18 (12) |
N1—C3—C5 | 113.75 (11) | C12—C11—H11 | 120.4 |
N1—C3—C4 | 111.95 (11) | C10—C11—H11 | 120.4 |
C5—C3—C4 | 111.84 (11) | C13—C12—C11 | 121.25 (13) |
N1—C3—C2 | 99.56 (10) | C13—C12—H12 | 119.4 |
C5—C3—C2 | 112.25 (11) | C11—C12—H12 | 119.4 |
C4—C3—C2 | 106.68 (10) | C12—C13—C14 | 118.63 (13) |
O2—C4—C3 | 122.60 (13) | C12—C13—C16 | 120.53 (13) |
O2—C4—H4 | 118.7 | C14—C13—C16 | 120.84 (14) |
C3—C4—H4 | 118.7 | C15—C14—C13 | 121.17 (14) |
C3—C5—H5A | 109.5 | C15—C14—H14 | 119.4 |
C3—C5—H5B | 109.5 | C13—C14—H14 | 119.4 |
H5A—C5—H5B | 109.5 | C14—C15—C10 | 118.98 (12) |
C3—C5—H5C | 109.5 | C14—C15—H15 | 120.5 |
H5A—C5—H5C | 109.5 | C10—C15—H15 | 120.5 |
H5B—C5—H5C | 109.5 | C13—C16—H16A | 109.5 |
C7—C6—C8 | 109.97 (13) | C13—C16—H16B | 109.5 |
C7—C6—C9 | 109.65 (12) | H16A—C16—H16B | 109.5 |
C8—C6—C9 | 108.23 (12) | C13—C16—H16C | 109.5 |
C7—C6—C1 | 113.10 (12) | H16A—C16—H16C | 109.5 |
C8—C6—C1 | 108.57 (11) | H16B—C16—H16C | 109.5 |
C9—C6—C1 | 107.18 (12) | ||
O3—S1—N1—C3 | −127.08 (10) | C2—C3—C4—O2 | 95.29 (16) |
O4—S1—N1—C3 | 2.95 (11) | O1—C1—C6—C7 | −67.43 (16) |
C10—S1—N1—C3 | 116.64 (10) | N1—C1—C6—C7 | 51.24 (16) |
O3—S1—N1—C1 | 15.67 (11) | O1—C1—C6—C8 | 170.24 (12) |
O4—S1—N1—C1 | 145.70 (10) | N1—C1—C6—C8 | −71.10 (15) |
C10—S1—N1—C1 | −100.62 (10) | O1—C1—C6—C9 | 53.54 (16) |
C2—O1—C1—N1 | −26.05 (12) | N1—C1—C6—C9 | 172.21 (11) |
C2—O1—C1—C6 | 99.60 (13) | O3—S1—C10—C11 | 25.11 (12) |
C3—N1—C1—O1 | 6.38 (13) | O4—S1—C10—C11 | −104.45 (11) |
S1—N1—C1—O1 | −138.91 (9) | N1—S1—C10—C11 | 142.60 (10) |
C3—N1—C1—C6 | −117.56 (12) | O3—S1—C10—C15 | −159.94 (11) |
S1—N1—C1—C6 | 97.15 (12) | O4—S1—C10—C15 | 70.50 (12) |
C1—O1—C2—C3 | 35.94 (13) | N1—S1—C10—C15 | −42.45 (13) |
C1—N1—C3—C5 | 132.96 (11) | C15—C10—C11—C12 | −0.8 (2) |
S1—N1—C3—C5 | −80.82 (13) | S1—C10—C11—C12 | 174.14 (11) |
C1—N1—C3—C4 | −99.05 (12) | C10—C11—C12—C13 | 0.1 (2) |
S1—N1—C3—C4 | 47.17 (14) | C11—C12—C13—C14 | 1.2 (2) |
C1—N1—C3—C2 | 13.39 (13) | C11—C12—C13—C16 | −179.00 (15) |
S1—N1—C3—C2 | 159.60 (9) | C12—C13—C14—C15 | −1.8 (2) |
O1—C2—C3—N1 | −28.83 (12) | C16—C13—C14—C15 | 178.37 (15) |
O1—C2—C3—C5 | −149.49 (11) | C13—C14—C15—C10 | 1.1 (2) |
O1—C2—C3—C4 | 87.67 (12) | C11—C10—C15—C14 | 0.2 (2) |
N1—C3—C4—O2 | −156.80 (13) | S1—C10—C15—C14 | −174.57 (11) |
C5—C3—C4—O2 | −27.80 (17) |
Experimental details
(I) | (II) | |
Crystal data | ||
Chemical formula | C16H23NO4S | C16H23NO4S |
Mr | 325.41 | 325.41 |
Crystal system, space group | Orthorhombic, P212121 | Orthorhombic, P212121 |
Temperature (K) | 100 | 100 |
a, b, c (Å) | 8.5175 (6), 11.3011 (8), 17.0503 (13) | 8.5276 (6), 11.3090 (11), 17.0624 (12) |
V (Å3) | 1641.2 (2) | 1645.5 (2) |
Z | 4 | 4 |
Radiation type | Mo Kα | Mo Kα |
µ (mm−1) | 0.21 | 0.21 |
Crystal size (mm) | 0.30 × 0.20 × 0.10 | 0.35 × 0.30 × 0.20 |
Data collection | ||
Diffractometer | STOE IPDS-II diffractometer | STOE IPDS-II diffractometer |
Absorption correction | Integration (X-RED; Stoe & Cie, 2004) | Integration (X-RED; Stoe & Cie, 2004) |
Tmin, Tmax | 0.923, 0.980 | 0.941, 0.971 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 9743, 3518, 3192 | 13910, 3772, 3554 |
Rint | 0.029 | 0.043 |
(sin θ/λ)max (Å−1) | 0.638 | 0.652 |
Refinement | ||
R[F2 > 2σ(F2)], wR(F2), S | 0.025, 0.059, 0.95 | 0.028, 0.076, 1.02 |
No. of reflections | 3518 | 3772 |
No. of parameters | 205 | 205 |
H-atom treatment | H-atom parameters constrained | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.22, −0.27 | 0.19, −0.31 |
Absolute structure | Flack (1983), 1486 Friedel pairs | Flack (1983), 1617 Friedel pairs |
Absolute structure parameter | −0.04 (5) | −0.04 (5) |
Computer programs: X-AREA (Stoe & Cie, 2004), X-AREA, X-RED (Stoe & Cie, 2004), SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), ORTEP-3 for Windows (Farrugia, 1997), SHELXL97.
Aziridination of alkenes is an attractive process for the preparation of biologically active compounds (Tanner, 1994). Several aziridination methods are described in the literature, particularly for substituted alkenes (Evans et al., 1994). However, less is known about the aziridination of functionalized alkenes, for example enol ethers and related compounds. Recently, we have investigated the aziridination of cyclic vinyl acetals. We found that these compounds undergo an in situ aziridination-rearrangement process to give 1,3-oxazolidine-4-carbaldehydes (Flock & Frauenrath, 2001). For example, treatment of (S)-(-)-2-tert-butyl-5-methyl-4H-1,3-dioxin (92% ee), prepared by NiBr2[(-)-Diop]/LiBHEt3-catalyzed isomerization of 2-tert-butyl-5-methylene-1,3-dioxane (Diop is diisooctyl phthalate) (Frauenrath et al., 1998; Flock et al., 2005), with [N-(p-toluenesulfonyl)imino]phenyliodinane (PhI═NTs) in the presence of 10 mol% CuOTf benzene complex (OTf is trifluoromethanesulfonate) led in a one-step procedure to a 70:30 mixture of (2S,4S)- and (2R,4S)-2-tert-butyl-4-methyl-3-(toluene-4-sulfonyl) −1,3-oxazolidine-4-carbaldehyde (Flock, 2003). After purification of the crude reaction product and recrystallization from tert-butylmethyl ether, the major diastereomer, (2S,4S)-(I), was obtained in a crystalline form. For the determination of the optical purity by NMR spectroscopy, the crystalline solid was reacted with (2R,3R)-(-)-butanediol to give N-[(1-(4,5)-dimethyl-1,3-dioxolan-2-yl)-2-hydroxy-1-methylethyl]- 4-methylbenzenesulfonamide, (III). Surprisingly, only one diastereomer could be detected in the NMR spectra of the crude reaction mixture, indicating that the crystalline diastereomer, (I), was obtained in an enantiomerically pure form. The opposite enantiomer, (2R,4R)-(II), was prepared by the same procedure from (R)-(+)-2-tert-butyl-5-methyl-4H-1,3-dioxin (91% ee). The latter compound was readily obtained by asymmetric double-bond isomerization of 2-tert-butyl-5-methylene-1,3-dioxane using NiBr2[(+)-Diop]/LiBHEt3 as a catalyst (Flock et al., 2005). Compounds (I) and (II) are useful chiral building blocks, for example for the synthesis of unnatural amino acids bearing a quaternary chiral center, and a knowledge of the absolute configuration of these compounds is important for gaining more insight into the diastereoselective course of the intermediate aziridination process. For this reason, the structures and absolute configurations of compounds (I) and (II) have been established by X-ray crystallography.
The molecular structures and correct absolute configurations, as confirmed by refinement of the absolute structure parameter (Flack, 1983), of compounds (I) and (II) are shown in Figs. 1 and 2, respectively. In both structures, the bond distances and angles agree with the expected values and no unusual intermolecular interactions could be found. For (I), the closest intermolecular contacts to neighboring molecules are C4···C3i and C5···O4ii [3.2369 (16) and 3.2252 (19) Å; symmetry codes: (i) −x, y − 1/2, −z + 3/2; (ii) x + 1/2, −y + 1/2, −z + 1]. The C11···O1iii distance of 3.3863 (17) Å [symmetry code: (iii) −x, y + 1/2, −z + 3/2] may be regarded as an extremly weak C—H···O hydrogen bridge. The corresponding contact distances in compound (II) are almost identical. The oxazolidine moieties of both (I) and (II) adopt the same envelope conformation, with atom C2 lying 0.479 (2) Å (mean value) above the plane formed by atoms C1, C3, O1 and N1. The deviation of atoms C1, C3, O1 and N1 from the ring plane [the mean deviations are −0.035 (1), −0.022 (1), 0.022 (1) and 0.035 (1) Å, respectively] and the distance of atom C2 from this plane are identical within 3σ for the two structures. Oxazolidine rings preferably adopt envelope conformations in the crystalline state, but with different atoms lying out of the plane. In the archetypal unsubstituted p-tosyl-1,3-oxazolidine (Gálvez-Ruiz et al., 2004), the O atom lies out of the molecular plane, a conformation typically found for p-tosyl-1,3-oxazolidine derivatives with only Csp3 atoms and a CH2 group in the non acetalic α-position to the ring O atom. However, p-tosyl-1,3-oxazolidines with this CH2 group out of the molecular plane (as found for the present structures) are not unusual. Twisted five-membered rings or conformations with N or other C atoms out of the plane exist but are rarely found exceptions. Therefore, we assume that, in the present case, the envelope conformation is mostly influenced by the substitution pattern of the quarternary C atom in the α-position (C3) to the N atom. A closely related envelope conformation was found for 3-(tert-butyloxycarbonyl)-2,2-dimethyl-4-methyl-1,3-oxazolidine-4-carbaldehyde, which has a comparable substitution pattern in the C3 position (Avenoza et al., 2003). The absolute value of the N1—C3—C4—O2 torsion angle is 156.63 (13)° in (I) and 156.80 (13)° in (II), which are also identical within 3σ and indicate a gauche orientation of the carbonyl group [C4═O2] with respect to the methyl group at C5. Obviously, this orientation of the C4═O2 carbonyl group leads to a minimization of the interaction of the carbonyl atom O2 with atoms O1 and O4.