The absolute configuration of (2S,4S)- and (2R,4R)-2-tert-butyl-4-methyl-3-(4-tolyl­sulfon­yl)-1,3-oxazolidine-4-carbaldehyde

The title enanti­omorphic compounds, C₁₆H₂₃NO₄S, have been obtained in an enanti­omerically pure form by crystallization from a diastereomeric mixture either of (2S,4S)- and (2R,4S)- or of (2R,4R)- and (2S,4R)-2-tert-butyl-4-methyl-3-(4-tolyl­sulfon­yl)-1,3-oxazolidine-4-carbaldehyde. These mixtures were prepared by an aziridination rearrangement process starting with (S)- or (R)-2-tert-butyl-5-methyl-4H-1,3-dioxine. The crystal structures indicate an envelope conformation of the oxazolidine moiety for both compounds.

S1. Comment

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.

S2. Experimental

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]²⁰_D = −76.1 (c = 2.95, CHCl₃). (II): [α]²⁰_D = +73.03 (c = 1.65, CHCl₃).

S3. Refinement

The methyl H atoms were constrained to an ideal geometry with C—H distances of 0.96 Å and U_iso(H) values of 1.5U_eq(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 U_iso(H) values of 1.2U_eq(C).

Computing details

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.

Figures

	Fig. 1. The molecular structure of (I), showing the atom-labelling scheme. Displacement ellipsoids for non-H atoms are drawn at the 30% probability level and H atoms are drawn as circles of arbitrary radii.
	Fig. 2. The asymmetric unit of (II), showing the atom-labelling scheme. Displacement ellipsoids for non-H atoms are drawn at the 30% probability level and H atoms are drawn as circles of arbitrary radii.

(I) (2S,4S)-2-tert-butyl-4-methyl-3-(4-tolylsulfonyl)-1,3-oxazolidine- 4-carbaldehyde

Crystal data

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) Å^3	Plate, colourless
Z = 4	0.30 × 0.20 × 0.10 mm

Data collection

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

Refinement on F^2	Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: full	H-atom parameters constrained
R[F^2 > 2σ(F^2)] = 0.025	w = 1/[σ^2(Fo^2) + (0.0374P)^2] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 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+0.001xFc^2λ^3/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)

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
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*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
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)

Geometric parameters (Å, º)

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)

(II) (2R,4R)-2-tert-butyl-4-methyl-3-(4-tolylsulfonyl)-1,3-oxazolidine- 4-carbaldehyde

Crystal data

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) Å^3	Plate, colourless
Z = 4	0.35 × 0.30 × 0.20 mm

Data collection

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

Refinement on F^2	Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: full	H-atom parameters constrained
R[F^2 > 2σ(F^2)] = 0.028	w = 1/[σ^2(Fo^2) + (0.0579P)^2] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 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+0.001xFc^2λ^3/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)

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
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*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
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)

Geometric parameters (Å, º)

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)