R,R-(+)-Bis­[(3-benzyl­oxazolan-4-yl)­methyl] di­sulfide

R,R-Bis­[(3-benzyl­oxazolan-4-yl)-methyl] di­sulfide, C₂₂H₂₈N₂O₂S₂, is a chiral di­sulfide which is a highly effective catalyst for the enantioselective addition of diethyl­zinc to aldehydes, including aliphatic ones. The mol­ecule has crystallographic twofold rotation symmetry.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.005 Å
• R factor = 0.034
• wR factor = 0.087
• Data-to-parameter ratio = 9.4

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


 Alert Level C:



ABSMU_01  Alert C The ratio of given/expected absorption coefficient lies
          outside the range 0.99 <> 1.01
          Calculated value of mu =     0.263
          Value of mu given      =     0.260

General Notes



REFLT_03
         From the CIF: _diffrn_reflns_theta_max           27.00
         From the CIF: _reflns_number_total               1272
         Count of symmetry unique reflns         1275
         Completeness (_total/calc)             99.76%
         TEST3: Check Friedels for noncentro structure
         Estimate of Friedel pairs measured         0
         Fraction of Friedel pairs measured     0.000
         Are heavy atom types Z>Si present          yes
          WARNING: Large fraction of Friedel related reflns may
                   be needed to determine absolute structure


 0 Alert Level A = Potentially serious problem

 0 Alert Level B = Potential problem

 1 Alert Level C = Please check

---

S1. Comment

The title compound [alternatively called 3,3'-dibenzyl-4,4'-dithiodi(oxazolane)], (I), a chiral disulfide, was prepared from L-cysteine in a short synthetic sequence and applied successfully as a highly efficient catalyst (Braga et al., 1999).

The asymmetric unit contains a half molecule of the disulfide. The complete molecule is generated by a twofold axis parallel to b, bisecting the S—S bond.

All bond distances and angles are normal. The torsion angle C1—-S1–S1ⁱ—C1ⁱ [symmetry code: (i) 1 - x, y, 1 - z] of 90.4 (2)° is close to the average found for similar compounds in the Cambridge Structural Database (Allen & Kennard, 1983) (86.29°). No close intermolecular contacts are seen, though the S—S bonds are almost aligned along the z axis and the intermolecular S···S distance is 4.0177 (17) Å.

The Cremer & Pople (1975) puckering parameters for the five-membered ring C2—N3—C4—O5—C6 were calculated by PLATON (Spek, 1995) to be Q₂ = 0.373 Å and ϕ₂ = 14.92°, corresponding to a twist conformation with the axis through C2.

S2. Experimental

In a 50 ml round-bottomed flask fitted with a Dean–Stark apparatus, benzene (30 ml), N,N'-dibenzyl-(R)-cystinol (392 mg, 1 mmol), paraformaldehyde (90 mg, 3 mmol) and p-toluenesulfonic acid (10 mg) were added. The mixture was heated at reflux for 5 h and cooled to room temperature. The benzene was removed under vacuum and the residue dissolved in CH₂Cl₂ (30 ml), washed with 0.5 N NaOH aqueous solution, dried with MgSO₄, filtered, and the solvent removed under vacuum to afford 353 mg (yield 87%) of the title compound. A crystal suitable for X-ray analysis was grown by slow evaporation of a dichloromethane solution (m.p. 320–321 K). Elemental analysis for C₂₂H₂₈N₂O₂S₂, calculated: C 63.43, H 6.77, N 6.72%; found C 63.20, H 7.26, N 7.10%. [α]_D²⁰ = +14.8 (c 1.96, CHCl₃). ¹H NMR (200 MHz, CDCl₃, Bruker): δ 2.47 (dd, 2H, J = 8.4 Hz, J = 13.2 Hz), 2.76 (dd, 2H, J = 5.8 Hz, J = 13.2 Hz), 3.21–3.36 (m, 2H), 3.48 (dd, 2H, J = 5.0 Hz, J = 8.4 Hz), 3.70–3.76 (m, 4H), 4.04 (dd, 2H, J = 7.0 Hz, J = 8.4 Hz), 4.29 (s, 4H), 7.19–7.34 (m, 10H). ¹³C NMR (50 MHz, CDCl₃): δ 41.08, 58.92, 62.06, 69.06, 85.98, 127.97, 128.24, 128.60.

Computing details

Data collection: CAD-4 EXPRESS (Enraf-Nonius, 1992); cell refinement: CAD-4 EXPRESS; data reduction: HELENA (Spek, 1995); 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) with 50% probability ellipsoids. H atoms have been omitted for clarity. The C atoms of the phenyl ring are numbered consecutively.

R,R-(+)-Bis[(3-benzyloxazolan-4-yl)methyl] disulfide

Crystal data

C11H14NOS	F(000) = 444
Mr = 208.29	Dx = 1.265 Mg m^−3
Monoclinic, C2	Mo Kα radiation, λ = 0.71073 Å
a = 20.281 (3) Å	Cell parameters from 25 reflections
b = 8.925 (2) Å	θ = 10.5–14.3°
c = 6.053 (1) Å	µ = 0.26 mm^−1
β = 93.112 (12)°	T = 293 K
V = 1094.1 (3) Å^3	Plate, yellow
Z = 4	0.2 × 0.2 × 0.1 mm

Data collection

CAD-4 diffractometer	996 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.025
Graphite monochromator	θmax = 27.0°, θmin = 2.5°
ω/2θ scans	h = 0→25
Absorption correction: ψ scan (North et al., 1968)	k = −11→0
Tmin = 0.949, Tmax = 0.974	l = −7→7
1307 measured reflections	3 standard reflections every 200 reflections
1272 independent reflections	intensity decay: 4.3%

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.034	H-atom parameters not refined
wR(F^2) = 0.087	w = 1/[σ^2(Fo^2) + (0.0379P)^2 + 0.1198P] where P = (Fo^2 + 2Fc^2)/3
S = 1.10	(Δ/σ)max = 0.001
1272 reflections	Δρmax = 0.18 e Å^−3
136 parameters	Δρmin = −0.20 e Å^−3
1 restraint	Absolute structure: Flack (1983), no Friedel pairs
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.1 (3)

Special details

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

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

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

	x	y	z	Uiso*/Ueq
S1	0.50087 (3)	0.53766 (15)	0.66834 (13)	0.0510 (2)
C1	0.56305 (13)	0.3979 (4)	0.7434 (5)	0.0435 (7)
H1A	0.5598	0.3714	0.8979	0.052*
H1B	0.5543	0.3083	0.6559	0.052*
C2	0.63272 (14)	0.4520 (4)	0.7074 (5)	0.0452 (7)
H2	0.6365	0.4809	0.5524	0.054*
N3	0.68072 (11)	0.3317 (3)	0.7682 (4)	0.0461 (6)
C4	0.73203 (16)	0.4033 (5)	0.9075 (6)	0.0608 (9)
H4A	0.7529	0.3316	1.0095	0.073*
H4B	0.7655	0.4466	0.8184	0.073*
O5	0.69972 (12)	0.5151 (4)	1.0224 (4)	0.0733 (8)
C6	0.6552 (2)	0.5801 (4)	0.8590 (7)	0.0746 (13)
H6A	0.6772	0.6569	0.7766	0.090*
H6B	0.6177	0.6249	0.9274	0.090*
C7	0.70738 (16)	0.2514 (5)	0.5825 (6)	0.0550 (9)
H7A	0.7464 (18)	0.184 (5)	0.648 (5)	0.068 (11)*
H7B	0.7223 (15)	0.318 (4)	0.472 (6)	0.058 (10)*
C11	0.65849 (14)	0.1447 (4)	0.4731 (5)	0.0468 (7)
C12	0.63029 (16)	0.1704 (5)	0.2645 (5)	0.0546 (9)
H12	0.6413	0.2570	0.1892	0.066*
C13	0.58643 (19)	0.0713 (5)	0.1657 (6)	0.0676 (12)
H13	0.5680	0.0913	0.0247	0.081*
C14	0.5694 (2)	−0.0573 (5)	0.2731 (8)	0.0760 (12)
H14	0.5403	−0.1257	0.2048	0.091*
C15	0.5962 (2)	−0.0836 (5)	0.4837 (7)	0.0765 (12)
H15	0.5839	−0.1687	0.5602	0.092*
C16	0.64076 (17)	0.0152 (5)	0.5811 (6)	0.0626 (10)
H16	0.6593	−0.0051	0.7217	0.075*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
S1	0.0418 (4)	0.0495 (4)	0.0606 (5)	0.0064 (5)	−0.0073 (3)	−0.0063 (5)
C1	0.0350 (13)	0.0422 (16)	0.0525 (17)	0.0012 (13)	−0.0032 (12)	0.0057 (14)
C2	0.0366 (15)	0.0467 (17)	0.0510 (17)	−0.0041 (14)	−0.0080 (13)	0.0115 (15)
N3	0.0354 (12)	0.0534 (16)	0.0481 (14)	0.0002 (12)	−0.0086 (11)	0.0109 (13)
C4	0.0440 (17)	0.077 (3)	0.0595 (19)	−0.0090 (19)	−0.0152 (14)	0.005 (2)
O5	0.0687 (14)	0.073 (2)	0.0745 (15)	−0.0062 (17)	−0.0276 (12)	−0.0053 (16)
C6	0.063 (2)	0.057 (3)	0.100 (3)	−0.0080 (18)	−0.033 (2)	−0.001 (2)
C7	0.0410 (17)	0.068 (2)	0.056 (2)	0.0025 (18)	0.0040 (15)	0.0097 (19)
C11	0.0399 (15)	0.0497 (19)	0.0514 (17)	0.0082 (15)	0.0073 (13)	0.0081 (16)
C12	0.0539 (18)	0.058 (2)	0.0522 (18)	0.0004 (17)	0.0032 (15)	0.0156 (18)
C13	0.067 (2)	0.070 (3)	0.065 (2)	0.0010 (19)	−0.0102 (18)	0.0026 (19)
C14	0.075 (3)	0.059 (3)	0.093 (3)	−0.014 (2)	−0.007 (2)	0.001 (2)
C15	0.083 (3)	0.053 (3)	0.093 (3)	−0.010 (2)	0.002 (2)	0.025 (2)
C16	0.0609 (19)	0.065 (3)	0.0612 (19)	0.006 (2)	−0.0027 (16)	0.025 (2)

Geometric parameters (Å, º)

S1—C1	1.814 (3)	O5—C6	1.427 (4)
S1—S1^i	2.0363 (16)	C7—C11	1.502 (5)
C1—C2	1.520 (4)	C11—C12	1.377 (4)
C2—N3	1.482 (4)	C11—C16	1.385 (5)
C2—C6	1.520 (5)	C12—C13	1.369 (5)
N3—C4	1.452 (4)	C13—C14	1.373 (6)
N3—C7	1.462 (4)	C14—C15	1.378 (6)
C4—O5	1.399 (5)	C15—C16	1.373 (5)
C1—S1—S1^i	102.98 (11)	O5—C6—C2	105.7 (3)
C2—C1—S1	112.6 (2)	N3—C7—C11	112.8 (3)
N3—C2—C6	103.0 (2)	C12—C11—C16	117.8 (3)
N3—C2—C1	109.7 (2)	C12—C11—C7	122.0 (3)
C6—C2—C1	113.8 (3)	C16—C11—C7	120.2 (3)
C4—N3—C7	112.3 (2)	C13—C12—C11	121.4 (3)
C4—N3—C2	105.4 (3)	C12—C13—C14	120.5 (4)
C7—N3—C2	115.5 (2)	C13—C14—C15	119.0 (4)
O5—C4—N3	105.2 (3)	C16—C15—C14	120.3 (4)
C4—O5—C6	104.0 (3)	C15—C16—C11	121.0 (3)
S1^i—S1—C1—C2	72.9 (2)	C4—N3—C7—C11	164.8 (3)
S1—C1—C2—N3	−179.02 (19)	C2—N3—C7—C11	−74.3 (4)
S1—C1—C2—C6	66.3 (3)	N3—C7—C11—C12	109.9 (3)
C6—C2—N3—C4	−10.8 (3)	N3—C7—C11—C16	−70.6 (4)
C1—C2—N3—C4	−132.2 (3)	C16—C11—C12—C13	−0.4 (5)
C6—C2—N3—C7	−135.3 (3)	C7—C11—C12—C13	179.2 (3)
C1—C2—N3—C7	103.3 (3)	C11—C12—C13—C14	−0.1 (6)
C7—N3—C4—O5	159.3 (3)	C12—C13—C14—C15	1.3 (6)
C2—N3—C4—O5	32.8 (3)	C13—C14—C15—C16	−2.1 (7)
N3—C4—O5—C6	−42.1 (3)	C14—C15—C16—C11	1.7 (6)
C4—O5—C6—C2	34.7 (4)	C12—C11—C16—C15	−0.4 (5)
N3—C2—C6—O5	−14.1 (4)	C7—C11—C16—C15	180.0 (3)
C1—C2—C6—O5	104.5 (3)	C1—S1—S1^i—C1^i	90.2 (2)

Symmetry code: (i) −x+1, y, −z+1.