(4S,5S)-(+)-4-Hydro­xy­methyl-2,5-di­phenyl­oxazoline

The absolute configuration of the title compound, alter­natively called (+)-(4,5-di­hydro-2,5-di­phenyl­oxazol-4-yl)­methanol, C₁₆H₁₅NO₂, has been confirmed as 4S,5S. The hydroxy­methyl group and phenyl ring at the asymmetric C atoms exhibit β and α orientations, respectively. The exocyclic C—C bonds at the asymmetric C atoms are mutually anticlinal (−ac). The hydroxyl group and the N atom of the oxazoline ring are involved in an intermolecular hydrogen bond leading to chains of mol­ecules.

S1. Comment

The synthesis of the title compound, (II), from (1S,2S)-(+)-2-amino-1-phenyl-1,3-propanediol, (I), and ethyl benzimidate hydrochloride or benzonitrile has recently been reported independently by three research groups (Allen & Williams, 1994; Hoarau et al., 1997; Rozwadowska, 1998). Although the stereochemistry of (II) has been accepted as (4S,5S), the samples of oxazoline (II) prepared in these laboratories differed significantly in their physical data, i.e. in specific rotations, both in the sign and dimension, melting points and solubility, whereas the spectral data were much the same, within experimental error, for all the samples (see Experimental). \sch

Oxazoline (II), prepared in our laboratory from (I) and ethyl benzimidate hydrochloride or benzonitrile, showed positive rotation, as did the sample described by Hoarau et al. (1997), whereas Allen & Williams (1994) reported negative rotation. There were also differences in melting points for all the samples: our sample melted much higher (459–460 K) than the samples prepared by Allen & Williams (400–402 K) and Hoarau et al. (408 K) Moreover, we reported poor solubility of the compound in chloroform at room temperature. Since oxazolines are intermediates in the O → N acyl group migration in acylated 1,2-aminoalcohols, involving in some cases inversion of configuration, we decided to confirm unambiguously the structure of oxazoline (II) of m.p. 459–460 K and [α]_D²⁰ = +51.0 (c = 0.54, CHCl₃) by X-ray analysis.

For the (+)-enantiomer shown in Fig. 1, the tetrahedral C4 and C5 atoms are chiral centres. The absolute configuration of those atoms was established as 4S and 5S by the structure refinement using Bijvoet-pair reflections. The hydroxymethyl group at the asymmetric C4 atom exhibits a β-orientation, whereas the phenyl group at the asymmetric C5 atom is α-oriented. The torsion angle C12—C4—C5—C14 [−111.39 (13)°] indicates anti-clinal conformation of the C12 atom in the hydroxymethyl group with respect to the C14 atom of the phenyl group.

The oxazoline ring is nearly planar with the r.m.s. deviation of 0.0306 Å. The C2 and C5 phenyl groups subtend very different interplanar angles oxazoline ring of 8.82 (10) and 82.47 (4)° to this ring. The C2—C6 distance of 1.4723 (17) Å is shorter than the C5—C14 single bond 1.4999 (16) Å by about 12σ. This fact indicates a weak conjugation effect between the C2 phenyl group and the oxazoline ring.

The bond distances and angles in the title molecule are consistent with those found in (4S,5S,S_S)-4-hydroxymethyl-2-[2-(4-methylphenylsulfinyl)phenyl]- 4,5-dihydro-5-phenyl-1,3-oxazole (Bower et al., 1996). Other hydroxymethyl-phenyloxazoline derivatives are not described in the Cambridge Structural Database, Version 518 (Allen & Kennard, 1993).

The O13 atom of the hydroxyl group is syn-clinal with respect to the N3—C4 bond of the oxazoline ring [torsion angle O13—C12—C4—N3 68.15 (14)°]. We assume that this arrangement of the O13 atom is stabilized by the intermolecular hydrogen bond O13—H13A···N3ⁱ (Table 2), which leads to chains of molecules parallel to the x axis. An intermolecular C16—H16A···O13ⁱⁱ contact (Table 2) links neighbouring chains into a two-dimensional hydrogen network parallel to the xy plane (Fig. 2).

S2. Experimental

The title compound, (II), was prepared according to the literature (Rozwadowska, 1998). Some of physical and spectral characteristics of our sample and of the othersare given below:

Our sample: m.p. 459–460 K; [α]_D²⁰ = +51,0 (c = 0,54, CHCl₃), [α]_D²⁰ = +70,0 (c = 0,5, CH₃OH),[α]_D²⁰ = +88,5 (c = 1,0, DMSO); IR (KBr) cm⁻¹: 1648 (C═N); ¹H NMR (CDCl₃): δ = 4,24 (d, J = 8,0 Hz, H4), 5,58 (d, J = 8,2 Hz, H5).

Allen & Williams (1994): m.p. 400–402 K; [α]_D²⁵ = −44,6 (c = 5,4, CHCl₃); IR (KBr) cm⁻¹: 1670 (C═N); ¹H NMR (CDCl₃): δ = 4,22 (H4), 5,56 (d, J = 8,0 Hz, H5).

Hoarau et al. (1997): m.p. 408 K; [α]_D²⁰ = +74,2 (c = 1,0, DMSO); ¹H NMR (CDCl₃): δ = 4,23 (d, J = 8,1 Hz, H4), 5,57 (d, J = 8,1 Hz, H5).

S3. Refinement

The crystals were grown from ethanol by slow evaporation of the solvent at room temperature. The positions of the H atoms were obtained from difference Fourier maps and refined freely. The absolute configuration of (II) was established on the basis of 930 Friedel opposite reflections using the Flack parameter (Flack 1983).

Computing details

Data collection: Kuma KM-4 Software (Kuma Diffraction, 1991); cell refinement: Kuma KM-4 Software; data reduction: Kuma KM-4 Software; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPII (Johnson, 1976) and ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. Molecular structure of (II); displacement ellipsoids are drawn at the 50% probability level; H atoms, treated as isotropic, are on an arbitrary scale.
	Fig. 2. Hydrogen bonding in the crystal lattice of (II). The hydrogen bonds are indicated with dashed lines; the symmetry codes are explained in Table 2.

(4S,5S)-(+)-4-Hydroxymethyl-2,5-diphenyloxazoline

Crystal data

C16H15NO2	Dx = 1.272 Mg m^−3
Mr = 253.29	Melting point: 459–460 K K
Orthorhombic, P212121	Cu Kα radiation, λ = 1.54178 Å
a = 4.8995 (10) Å	Cell parameters from 48 reflections
b = 11.3300 (13) Å	θ = 15.4–30.3°
c = 23.820 (3) Å	µ = 0.67 mm^−1
V = 1322.3 (4) Å^3	T = 293 K
Z = 4	Needle, colourless
F(000) = 536	0.50 × 0.25 × 0.11 mm

Data collection

Kuma Diffraction KM-4 diffractometer	Rint = 0.037
Radiation source: fine-focus sealed tube	θmax = 70.0°, θmin = 3.7°
Graphite monochromator	h = −5→5
ω–2θ scans	k = 0→13
2557 measured reflections	l = 0→29
2406 independent reflections	2 standard reflections every 100 reflections
2273 reflections with I > 2σ(I)	intensity decay: 0.7%

Refinement

Refinement on F^2	Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: full	All H-atom parameters refined
R[F^2 > 2σ(F^2)] = 0.029	w = 1/[σ^2(Fo^2) + (0.0536P)^2 + 0.0663P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.082	(Δ/σ)max < 0.001
S = 1.08	Δρmax = 0.13 e Å^−3
2406 reflections	Δρmin = −0.13 e Å^−3
233 parameters	Extinction correction: SHELXL97 (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.0047 (7)
Primary atom site location: structure-invariant direct methods	Absolute structure: Flack (1983)
Secondary atom site location: difference Fourier map	Absolute structure parameter: −0.09 (19)

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	0.6153 (2)	0.95123 (7)	0.12135 (4)	0.0560 (3)
C2	0.6976 (3)	0.83793 (10)	0.11417 (5)	0.0446 (3)
N3	0.8497 (2)	0.81512 (8)	0.07251 (4)	0.0454 (2)
C4	0.8914 (3)	0.92531 (9)	0.04140 (5)	0.0428 (3)
C5	0.7121 (3)	1.01667 (10)	0.07262 (5)	0.0428 (3)
C6	0.5973 (3)	0.75357 (11)	0.15641 (5)	0.0482 (3)
C7	0.6979 (4)	0.63901 (13)	0.15754 (6)	0.0619 (4)
C8	0.5996 (5)	0.55956 (15)	0.19670 (7)	0.0739 (5)
C9	0.4053 (5)	0.59340 (17)	0.23446 (7)	0.0761 (5)
C10	0.3007 (5)	0.70634 (19)	0.23316 (7)	0.0789 (5)
C11	0.3980 (4)	0.78668 (15)	0.19443 (6)	0.0630 (4)
C12	0.8116 (3)	0.91222 (11)	−0.01947 (6)	0.0512 (3)
O13	0.5259 (2)	0.89721 (9)	−0.02506 (5)	0.0592 (3)
C14	0.8498 (3)	1.12880 (9)	0.09044 (5)	0.0409 (3)
C15	0.7732 (3)	1.23437 (11)	0.06599 (6)	0.0543 (3)
C16	0.9014 (4)	1.33881 (12)	0.08107 (7)	0.0681 (4)
C17	1.1019 (4)	1.33838 (13)	0.12064 (7)	0.0663 (4)
C18	1.1794 (4)	1.23448 (15)	0.14528 (7)	0.0656 (4)
C19	1.0548 (3)	1.12933 (12)	0.13020 (6)	0.0541 (3)
H4A	1.092 (4)	0.9450 (13)	0.0443 (6)	0.053 (4)*
H5A	0.559 (3)	1.0366 (13)	0.0502 (6)	0.046 (4)*
H7A	0.843 (5)	0.6148 (17)	0.1319 (8)	0.083 (6)*
H8A	0.679 (5)	0.476 (2)	0.1952 (9)	0.099 (7)*
H9A	0.341 (5)	0.5391 (18)	0.2623 (9)	0.087 (6)*
H10A	0.166 (5)	0.730 (2)	0.2613 (9)	0.105 (7)*
H11A	0.313 (5)	0.8696 (19)	0.1932 (8)	0.088 (6)*
H12A	0.869 (4)	0.9860 (16)	−0.0401 (7)	0.065 (4)*
H12B	0.921 (4)	0.8417 (15)	−0.0357 (7)	0.064 (5)*
H13A	0.492 (5)	0.826 (2)	−0.0419 (8)	0.092 (7)*
H15A	0.630 (4)	1.2322 (15)	0.0377 (7)	0.073 (5)*
H16A	0.844 (4)	1.4148 (17)	0.0645 (8)	0.076 (5)*
H17A	1.193 (5)	1.4129 (18)	0.1314 (8)	0.088 (6)*
H18A	1.317 (5)	1.2351 (17)	0.1740 (8)	0.081 (5)*
H19A	1.099 (4)	1.0573 (17)	0.1490 (7)	0.069 (5)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0609 (6)	0.0336 (4)	0.0735 (6)	−0.0047 (4)	0.0270 (5)	−0.0076 (4)
C2	0.0460 (7)	0.0348 (5)	0.0529 (6)	−0.0034 (5)	0.0014 (5)	−0.0072 (5)
N3	0.0509 (6)	0.0346 (5)	0.0508 (5)	0.0060 (4)	0.0020 (5)	−0.0022 (4)
C4	0.0403 (7)	0.0311 (5)	0.0572 (7)	−0.0014 (4)	0.0065 (5)	−0.0049 (4)
C5	0.0396 (6)	0.0322 (5)	0.0565 (6)	−0.0015 (4)	0.0058 (5)	−0.0054 (5)
C6	0.0529 (7)	0.0438 (6)	0.0480 (6)	−0.0089 (5)	−0.0032 (5)	−0.0035 (5)
C7	0.0792 (11)	0.0470 (7)	0.0594 (7)	0.0003 (7)	0.0041 (8)	0.0032 (6)
C8	0.1008 (14)	0.0525 (8)	0.0684 (9)	−0.0056 (9)	−0.0036 (9)	0.0118 (7)
C9	0.0919 (13)	0.0748 (11)	0.0616 (9)	−0.0196 (10)	0.0004 (8)	0.0186 (8)
C10	0.0837 (13)	0.0876 (12)	0.0654 (9)	−0.0072 (11)	0.0170 (9)	0.0119 (8)
C11	0.0668 (10)	0.0610 (8)	0.0613 (8)	−0.0027 (7)	0.0093 (7)	0.0026 (6)
C12	0.0595 (8)	0.0411 (6)	0.0531 (7)	0.0008 (6)	0.0102 (6)	−0.0003 (5)
O13	0.0625 (6)	0.0420 (5)	0.0731 (6)	0.0008 (4)	−0.0130 (5)	−0.0125 (4)
C14	0.0420 (6)	0.0319 (5)	0.0488 (5)	−0.0015 (5)	0.0070 (5)	−0.0049 (4)
C15	0.0572 (8)	0.0389 (6)	0.0667 (8)	−0.0016 (5)	−0.0018 (7)	0.0042 (5)
C16	0.0789 (11)	0.0341 (6)	0.0912 (11)	−0.0052 (7)	0.0067 (9)	0.0042 (6)
C17	0.0693 (10)	0.0472 (7)	0.0825 (9)	−0.0198 (7)	0.0136 (8)	−0.0158 (7)
C18	0.0586 (9)	0.0698 (9)	0.0684 (8)	−0.0146 (8)	−0.0029 (8)	−0.0152 (7)
C19	0.0526 (8)	0.0470 (7)	0.0627 (7)	−0.0004 (6)	−0.0041 (6)	−0.0006 (6)

Geometric parameters (Å, º)

O1—C2	1.3563 (14)	C10—C11	1.381 (2)
O1—C5	1.4568 (16)	C10—H10A	0.98 (2)
C2—N3	1.2677 (16)	C11—H11A	1.03 (2)
C2—C6	1.4723 (17)	C12—O13	1.4163 (19)
N3—C4	1.4660 (15)	C12—H12A	1.010 (18)
C4—C12	1.5090 (19)	C12—H12B	1.037 (18)
C4—C5	1.5479 (16)	O13—H13A	0.92 (2)
C4—H4A	1.011 (17)	C14—C19	1.3806 (19)
C5—C14	1.4999 (16)	C14—C15	1.3822 (17)
C5—H5A	0.949 (16)	C15—C16	1.387 (2)
C6—C11	1.383 (2)	C15—H15A	0.974 (18)
C6—C7	1.389 (2)	C16—C17	1.361 (3)
C7—C8	1.383 (2)	C16—H16A	0.99 (2)
C7—H7A	0.98 (2)	C17—C18	1.369 (3)
C8—C9	1.365 (3)	C17—H17A	0.99 (2)
C8—H8A	1.02 (2)	C18—C19	1.386 (2)
C9—C10	1.379 (3)	C18—H18A	0.96 (2)
C9—H9A	0.96 (2)	C19—H19A	0.955 (19)
C2—O1—C5	106.52 (9)	C9—C10—H10A	119.6 (14)
N3—C2—O1	117.81 (10)	C11—C10—H10A	120.4 (14)
N3—C2—C6	126.79 (11)	C10—C11—C6	120.14 (16)
O1—C2—C6	115.40 (10)	C10—C11—H11A	118.9 (12)
C2—N3—C4	107.69 (9)	C6—C11—H11A	120.9 (11)
N3—C4—C12	111.46 (10)	O13—C12—C4	110.98 (11)
N3—C4—C5	104.34 (10)	O13—C12—H12A	109.3 (11)
C12—C4—C5	112.35 (11)	C4—C12—H12A	108.3 (9)
N3—C4—H4A	106.8 (8)	O13—C12—H12B	112.5 (10)
C12—C4—H4A	109.9 (8)	C4—C12—H12B	107.5 (9)
C5—C4—H4A	111.8 (9)	H12A—C12—H12B	108.1 (13)
O1—C5—C14	110.61 (10)	C12—O13—H13A	108.9 (15)
O1—C5—C4	103.13 (9)	C19—C14—C15	118.86 (12)
C14—C5—C4	116.55 (10)	C19—C14—C5	121.68 (11)
O1—C5—H5A	108.2 (9)	C15—C14—C5	119.45 (12)
C14—C5—H5A	108.3 (9)	C14—C15—C16	120.42 (14)
C4—C5—H5A	109.8 (9)	C14—C15—H15A	117.7 (11)
C11—C6—C7	119.43 (13)	C16—C15—H15A	121.9 (11)
C11—C6—C2	120.46 (12)	C17—C16—C15	120.19 (14)
C7—C6—C2	120.10 (12)	C17—C16—H16A	119.1 (12)
C8—C7—C6	119.86 (16)	C15—C16—H16A	120.7 (12)
C8—C7—H7A	119.5 (11)	C16—C17—C18	120.01 (13)
C6—C7—H7A	120.6 (11)	C16—C17—H17A	120.2 (13)
C9—C8—C7	120.31 (17)	C18—C17—H17A	119.8 (13)
C9—C8—H8A	123.2 (14)	C17—C18—C19	120.37 (16)
C7—C8—H8A	116.5 (14)	C17—C18—H18A	119.6 (12)
C8—C9—C10	120.33 (16)	C19—C18—H18A	120.0 (12)
C8—C9—H9A	120.4 (12)	C14—C19—C18	120.14 (14)
C10—C9—H9A	119.2 (13)	C14—C19—H19A	118.8 (12)
C9—C10—C11	119.91 (18)	C18—C19—H19A	120.9 (12)
C5—O1—C2—N3	5.53 (16)	C7—C8—C9—C10	1.4 (3)
C5—O1—C2—C6	−174.27 (11)	C8—C9—C10—C11	−1.7 (3)
O1—C2—N3—C4	−1.09 (16)	C9—C10—C11—C6	1.0 (3)
C6—C2—N3—C4	178.69 (12)	C7—C6—C11—C10	0.1 (2)
C2—N3—C4—C12	−125.02 (12)	C2—C6—C11—C10	178.62 (15)
C2—N3—C4—C5	−3.54 (14)	N3—C4—C12—O13	68.15 (14)
C2—O1—C5—C14	−132.27 (11)	C5—C4—C12—O13	−48.55 (14)
C2—O1—C5—C4	−6.95 (13)	O1—C5—C14—C19	51.81 (15)
N3—C4—C5—O1	6.35 (13)	C4—C5—C14—C19	−65.53 (16)
C12—C4—C5—O1	127.24 (11)	O1—C5—C14—C15	−129.16 (13)
N3—C4—C5—C14	127.72 (11)	C4—C5—C14—C15	113.50 (14)
C12—C4—C5—C14	−111.39 (13)	C19—C14—C15—C16	0.3 (2)
N3—C2—C6—C11	−169.62 (14)	C5—C14—C15—C16	−178.78 (13)
O1—C2—C6—C11	10.16 (19)	C14—C15—C16—C17	−0.8 (3)
N3—C2—C6—C7	8.9 (2)	C15—C16—C17—C18	0.6 (3)
O1—C2—C6—C7	−171.30 (13)	C16—C17—C18—C19	0.0 (3)
C11—C6—C7—C8	−0.4 (2)	C15—C14—C19—C18	0.4 (2)
C2—C6—C7—C8	−178.91 (15)	C5—C14—C19—C18	179.39 (13)
C6—C7—C8—C9	−0.4 (3)	C17—C18—C19—C14	−0.5 (2)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O13—H13A···N3^i	0.92 (2)	1.89 (2)	2.7948 (14)	169 (2)
C16—H16A···O13^ii	0.99 (2)	2.49 (2)	3.3314 (18)	142.3 (16)
C5—H5A···O13	0.949 (16)	2.394 (14)	2.8419 (16)	108.5 (11)

Symmetry codes: (i) x−1/2, −y+3/2, −z; (ii) x+1/2, −y+5/2, −z.