(1'S,2R,3R)-3-(1'-tert-Butyl­di­methyl­silyl­oxy-1'-phenyl­methyl)-2-(4''-methyl­phenyl­thio)-2-nitro­oxirane

The title compound, C₂₂H₂₉NO₄SSi, displays an anomeric effect in the marked shortening of one C-O bond relative to the other in the oxirane ring, concomitantly weakening the C-S bond to the aryl­thio substituent. This correlates with the selective reactivity of nucleophiles at the C atom having the longer C-O bond. The absolute configuration has been determined from anomalous scattering effects.

Key indicators

• Single-crystal X-ray study
• T = 160 K
• Mean [sigma](C-C) = 0.003 Å
• R factor = 0.036
• wR factor = 0.085
• Data-to-parameter ratio = 19.5

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry

General Notes



REFLT_03
         From the CIF: _diffrn_reflns_theta_max           28.91
         From the CIF: _reflns_number_total               5239
         Count of symmetry unique reflns         3305
         Completeness (_total/calc)            158.52%
         TEST3: Check Friedels for noncentro structure
         Estimate of Friedel pairs measured      1934
         Fraction of Friedel pairs measured     0.585
         Are heavy atom types Z>Si present          yes
          Please check that the estimate of the number of Friedel pairs is
          correct. If it is not, please give the correct count in the
          _publ_section_exptl_refinement section of the submitted CIF.

---

S1. Comment

The title compound, (I), was prepared as one of a series of (arylthio)nitrooxiranes during the development of stereoselective syntheses of protected β-hydroxy-α-amino acids (Adams et al., 1999). The original purpose of the crystal structure determination was to establish the relative stereochemistry of the epoxide ring and the adjacent C atom bearing the phenyl and protected hydroxyl groups, in order to demonstrate the stereoselectivity of the synthetic procedures. In fact, the Si and S atoms in the molecule provide sufficient anomalous scattering to enable the absolute configuration to be determined unambiguously, and it is shown in Fig. 1. It is as expected from the starting material used in the synthesis.

Further interest in the structure arises from the electronic effects of the nitro and arylthio substituents on the bond lengths of the epoxide ring. We have recently shown that a marked asymmetry in the C—O bond lengths of such rings in a number of substituted oxiranes can be ascribed to a generalized anomeric effect, in which a lone pair of electrons on the ring oxygen atom interacts with the antibonding orbital associated with the bond to the heteroatom substituent (here the arylthio group), thus weaking this bond and strengthening the corresponding ring C—O bond (Jackson et al., 2003). This effect is particularly marked with (arylthio)nitrooxiranes, and is believed to be responsible for the selective reaction of these oxiranes with nucleophiles at the carbon atom giving the longer C—O bond.

A search of the Cambridge Structural Database (Version 5.24 plus two updates, June 2003; Allen, 2002) provides known structure for five oxiranes with a nitro substituent (Bowman et al., 1991; Hartshorn et al., 1983; Jackson et al., 1995; Szarek et al., 1988) and five oxiranes with an alkylthio or arylthio substituent (Hewkin et al., 1991; Jackson et al., 1995; Krishnakumar et al., 2002; Valle et al., 1988), two of these structures having both types of substituent. The title compound is thus the third structurally characterized example of an (arylthio)nitrooxirane. In all of these structures, the C—O bond adjacent to the nitro and/or thio substituent is shortened relative to the other C—O bond, though the difference is much more marked in some cases than in others.

Of the three (arylthio)nitroxiranes, the shorter C—O bond of the title compound, adjacent to the nitro and arylthio substituents, has essentially the same length as those in the other two structures [C1—O1 = 1.391 (2) Å, compared with 1.398 (7) and 1.394 (2) Å], but the longer C—O bond is somewhat shorter than the corresponding bond in the other two structures [C2—O1 = 1.448 (2) Å, compared with 1.463 (6) and 1.466 (2) Å]. This fact correlates well with the fact that the title compound is by far the least reactive towards nucleophiles; for example, it requires treatment at 353 K for 6 h with aqueous ammonia, whereas the other compounds react completely within 2 h at room temperature (Jackson, 2003). This is further evidence that the ground-state molecular geometry, resulting from the anomeric effect, influences reactivity, although the larger steric bulk of the substituents in the title compound may also contribute.

S2. Experimental

The synthesis and spectroscopic characterization of the title compound have been fully described by Adams et al. (1999).

S3. Refinement

H atoms were placed geometrically and refined with a riding model (including free rotation about C—C bonds), and with U_iso constrained to be 1.2 (1.5 for methyl groups) times U_eq of the carrier atom.

Computing details

Data collection: SMART (Bruker, 2001); cell refinement: local programs; data reduction: SAINT (Bruker, 2001); program(s) used to solve structure: SHELXTL (Sheldrick, 2001); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and local programs.

Figures

Fig. 1. The molecular structure of (I), with atom labels and 50% probability ellipsoids for non-H atoms.

(1'S,2R,3R)-3-(1'-tert-Butyldimethylsilyloxy-1'-phenylmethyl)- 2-(4''-methylphenylthio)-2-nitrooxirane

Crystal data

C22H29NO4SSi	F(000) = 460
Mr = 431.61	Dx = 1.214 Mg m^−3
Monoclinic, P21	Mo Kα radiation, λ = 0.71073 Å
a = 10.0904 (12) Å	Cell parameters from 5503 reflections
b = 8.9428 (11) Å	θ = 2.4–28.6°
c = 13.1503 (16) Å	µ = 0.21 mm^−1
β = 95.531 (3)°	T = 160 K
V = 1181.1 (2) Å^3	Block, colourless
Z = 2	0.51 × 0.38 × 0.35 mm

Data collection

Bruker SMART 1K CCD diffractometer	5239 independent reflections
Radiation source: sealed tube	4405 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.020
Detector resolution: 8.192 pixels mm^-1	θmax = 28.9°, θmin = 2.4°
ω rotation with narrow frames scans	h = −9→13
Absorption correction: multi-scan (SADABS; Sheldrick, 2002)	k = −11→12
Tmin = 0.90, Tmax = 0.93	l = −14→17
7705 measured reflections

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)] = 0.036	H-atom parameters constrained
wR(F^2) = 0.085	w = 1/[σ^2(Fo^2) + (0.0461P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 0.98	(Δ/σ)max = 0.001
5239 reflections	Δρmax = 0.24 e Å^−3
268 parameters	Δρmin = −0.22 e Å^−3
1 restraint	Absolute structure: Flack (1983), 2251 Friedel pairs
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.05 (6)

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

	x	y	z	Uiso*/Ueq
O1	0.33416 (13)	0.41659 (15)	0.35992 (10)	0.0359 (3)
C1	0.21246 (18)	0.4483 (2)	0.30530 (14)	0.0326 (4)
C2	0.28023 (18)	0.3071 (2)	0.28598 (13)	0.0319 (4)
H2	0.2415	0.2155	0.3151	0.038*
N1	0.09616 (18)	0.4315 (2)	0.37214 (14)	0.0439 (4)
O2	−0.00947 (16)	0.4871 (2)	0.34073 (16)	0.0679 (5)
O3	0.11668 (17)	0.3605 (2)	0.45007 (13)	0.0711 (6)
C3	0.35306 (18)	0.2825 (2)	0.19186 (14)	0.0325 (4)
H3	0.3772	0.3812	0.1631	0.039*
C4	0.26396 (17)	0.1982 (2)	0.11369 (14)	0.0318 (4)
C5	0.24227 (19)	0.0459 (2)	0.12654 (16)	0.0381 (4)
H5	0.2863	−0.0049	0.1836	0.046*
C6	0.1573 (2)	−0.0317 (2)	0.05692 (16)	0.0430 (5)
H6	0.1427	−0.1354	0.0667	0.052*
C7	0.0935 (2)	0.0399 (3)	−0.02632 (17)	0.0421 (5)
H7	0.0349	−0.0143	−0.0738	0.051*
C8	0.1146 (2)	0.1905 (3)	−0.04091 (16)	0.0418 (5)
H8	0.0716	0.2402	−0.0988	0.050*
C9	0.19913 (19)	0.2689 (2)	0.02950 (15)	0.0373 (5)
H9	0.2127	0.3728	0.0198	0.045*
O4	0.47070 (12)	0.20244 (15)	0.22525 (10)	0.0372 (3)
Si1	0.61268 (5)	0.23361 (6)	0.17355 (4)	0.03532 (13)
C10	0.5900 (3)	0.1795 (3)	0.03609 (17)	0.0582 (6)
H10A	0.5637	0.0742	0.0302	0.087*
H10B	0.6738	0.1941	0.0055	0.087*
H10C	0.5205	0.2419	0.0003	0.087*
C11	0.6533 (2)	0.4356 (3)	0.18729 (18)	0.0501 (5)
H11A	0.6170	0.4891	0.1258	0.075*
H11B	0.7502	0.4484	0.1965	0.075*
H11C	0.6141	0.4759	0.2469	0.075*
C12	0.7392 (2)	0.1124 (3)	0.24831 (15)	0.0428 (5)
C13	0.8753 (2)	0.1316 (3)	0.2051 (2)	0.0647 (7)
H13A	0.9416	0.0677	0.2433	0.097*
H13B	0.9035	0.2363	0.2117	0.097*
H13C	0.8672	0.1029	0.1328	0.097*
C14	0.7521 (2)	0.1612 (3)	0.36047 (18)	0.0607 (7)
H14A	0.6645	0.1573	0.3867	0.091*
H14B	0.7866	0.2636	0.3659	0.091*
H14C	0.8134	0.0938	0.4005	0.091*
C15	0.6982 (2)	−0.0524 (3)	0.2397 (2)	0.0601 (7)
H15A	0.7666	−0.1142	0.2772	0.090*
H15B	0.6885	−0.0822	0.1677	0.090*
H15C	0.6132	−0.0663	0.2688	0.090*
S1	0.19777 (5)	0.60295 (6)	0.22149 (4)	0.04069 (13)
C16	0.23489 (19)	0.7470 (2)	0.31291 (14)	0.0332 (4)
C17	0.3673 (2)	0.7821 (2)	0.34352 (17)	0.0416 (5)
H17	0.4370	0.7293	0.3157	0.050*
C18	0.3967 (2)	0.8932 (2)	0.41392 (17)	0.0447 (5)
H18	0.4873	0.9159	0.4345	0.054*
C19	0.2976 (2)	0.9733 (2)	0.45583 (15)	0.0416 (5)
C20	0.1654 (2)	0.9388 (2)	0.42300 (16)	0.0421 (5)
H20	0.0959	0.9937	0.4496	0.051*
C21	0.1336 (2)	0.8264 (2)	0.35245 (15)	0.0383 (5)
H21	0.0432	0.8038	0.3313	0.046*
C22	0.3320 (3)	1.0933 (3)	0.53381 (18)	0.0614 (6)
H22A	0.4105	1.0629	0.5787	0.092*
H22B	0.2568	1.1086	0.5746	0.092*
H22C	0.3510	1.1867	0.4991	0.092*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0356 (7)	0.0379 (8)	0.0328 (7)	−0.0006 (6)	−0.0035 (6)	0.0036 (6)
C1	0.0301 (10)	0.0345 (10)	0.0323 (10)	−0.0027 (8)	−0.0016 (8)	0.0022 (8)
C2	0.0311 (10)	0.0313 (10)	0.0333 (10)	−0.0021 (8)	0.0028 (8)	0.0056 (8)
N1	0.0447 (11)	0.0392 (10)	0.0489 (11)	0.0000 (8)	0.0107 (9)	−0.0060 (9)
O2	0.0337 (9)	0.0737 (12)	0.0970 (14)	0.0026 (8)	0.0109 (8)	0.0128 (11)
O3	0.0731 (12)	0.0923 (15)	0.0524 (10)	0.0186 (11)	0.0292 (9)	0.0183 (10)
C3	0.0295 (10)	0.0339 (10)	0.0343 (10)	−0.0001 (8)	0.0039 (7)	0.0081 (8)
C4	0.0259 (9)	0.0365 (11)	0.0344 (10)	0.0032 (8)	0.0091 (7)	0.0047 (8)
C5	0.0354 (11)	0.0389 (11)	0.0396 (11)	0.0010 (9)	0.0018 (8)	0.0097 (9)
C6	0.0412 (12)	0.0364 (11)	0.0521 (13)	−0.0026 (9)	0.0076 (10)	0.0001 (10)
C7	0.0336 (11)	0.0505 (13)	0.0423 (12)	0.0021 (10)	0.0041 (9)	−0.0074 (10)
C8	0.0370 (11)	0.0522 (14)	0.0354 (11)	0.0105 (10)	0.0001 (9)	0.0065 (10)
C9	0.0384 (11)	0.0365 (11)	0.0375 (10)	0.0079 (9)	0.0065 (8)	0.0080 (9)
O4	0.0284 (7)	0.0455 (8)	0.0378 (7)	0.0024 (6)	0.0033 (5)	0.0083 (6)
Si1	0.0318 (3)	0.0439 (3)	0.0310 (3)	−0.0024 (2)	0.0065 (2)	−0.0034 (2)
C10	0.0607 (15)	0.0773 (17)	0.0371 (12)	−0.0078 (13)	0.0082 (10)	−0.0090 (11)
C11	0.0434 (12)	0.0530 (14)	0.0551 (13)	−0.0070 (11)	0.0116 (10)	−0.0008 (11)
C12	0.0339 (11)	0.0537 (12)	0.0420 (11)	0.0055 (10)	0.0094 (8)	−0.0015 (11)
C13	0.0355 (13)	0.086 (2)	0.0746 (17)	0.0088 (13)	0.0140 (11)	0.0026 (16)
C14	0.0559 (16)	0.0828 (19)	0.0413 (13)	0.0073 (13)	−0.0066 (11)	0.0022 (12)
C15	0.0580 (16)	0.0550 (15)	0.0694 (16)	0.0091 (12)	0.0161 (12)	0.0033 (13)
S1	0.0514 (3)	0.0353 (3)	0.0332 (2)	0.0029 (2)	−0.0069 (2)	0.0039 (2)
C16	0.0372 (10)	0.0293 (9)	0.0322 (9)	−0.0002 (8)	−0.0016 (8)	0.0082 (8)
C17	0.0350 (11)	0.0384 (12)	0.0503 (12)	−0.0001 (9)	−0.0009 (9)	0.0108 (10)
C18	0.0369 (11)	0.0391 (12)	0.0548 (13)	−0.0072 (9)	−0.0122 (10)	0.0109 (10)
C19	0.0549 (14)	0.0333 (10)	0.0346 (10)	−0.0080 (10)	−0.0062 (9)	0.0116 (9)
C20	0.0468 (12)	0.0371 (11)	0.0431 (12)	−0.0005 (10)	0.0081 (9)	0.0063 (9)
C21	0.0321 (11)	0.0377 (11)	0.0439 (11)	−0.0040 (9)	−0.0021 (9)	0.0074 (9)
C22	0.0884 (18)	0.0447 (13)	0.0466 (13)	−0.0111 (14)	−0.0164 (11)	0.0023 (12)

Geometric parameters (Å, º)

O1—C1	1.391 (2)	C11—H11A	0.980
O1—C2	1.448 (2)	C11—H11B	0.980
C1—C2	1.470 (3)	C11—H11C	0.980
C1—N1	1.540 (2)	C12—C13	1.546 (3)
C1—S1	1.7656 (19)	C12—C14	1.531 (3)
C2—H2	1.000	C12—C15	1.532 (3)
C2—C3	1.515 (3)	C13—H13A	0.980
N1—O2	1.212 (2)	C13—H13B	0.980
N1—O3	1.207 (2)	C13—H13C	0.980
C3—H3	1.000	C14—H14A	0.980
C3—C4	1.502 (3)	C14—H14B	0.980
C3—O4	1.419 (2)	C14—H14C	0.980
C4—C5	1.392 (3)	C15—H15A	0.980
C4—C9	1.383 (3)	C15—H15B	0.980
C5—H5	0.950	C15—H15C	0.980
C5—C6	1.380 (3)	S1—C16	1.777 (2)
C6—H6	0.950	C16—C17	1.394 (3)
C6—C7	1.373 (3)	C16—C21	1.386 (3)
C7—H7	0.950	C17—H17	0.950
C7—C8	1.380 (3)	C17—C18	1.370 (3)
C8—H8	0.950	C18—H18	0.950
C8—C9	1.387 (3)	C18—C19	1.386 (3)
C9—H9	0.950	C19—C20	1.397 (3)
O4—Si1	1.6673 (13)	C19—C22	1.502 (3)
Si1—C10	1.864 (2)	C20—H20	0.950
Si1—C11	1.858 (2)	C20—C21	1.385 (3)
Si1—C12	1.878 (2)	C21—H21	0.950
C10—H10A	0.980	C22—H22A	0.980
C10—H10B	0.980	C22—H22B	0.980
C10—H10C	0.980	C22—H22C	0.980
C1—O1—C2	62.31 (12)	Si1—C11—H11B	109.5
O1—C1—C2	60.76 (12)	Si1—C11—H11C	109.5
O1—C1—N1	111.64 (15)	H11A—C11—H11B	109.5
O1—C1—S1	119.93 (13)	H11A—C11—H11C	109.5
C2—C1—N1	114.05 (15)	H11B—C11—H11C	109.5
C2—C1—S1	125.27 (14)	Si1—C12—C13	109.07 (16)
N1—C1—S1	114.21 (13)	Si1—C12—C14	109.29 (16)
O1—C2—C1	56.93 (11)	Si1—C12—C15	110.58 (16)
O1—C2—H2	115.6	C13—C12—C14	109.06 (19)
O1—C2—C3	117.80 (15)	C13—C12—C15	108.81 (19)
C1—C2—H2	115.6	C14—C12—C15	110.0 (2)
C1—C2—C3	122.46 (16)	C12—C13—H13A	109.5
H2—C2—C3	115.6	C12—C13—H13B	109.5
C1—N1—O2	117.32 (18)	C12—C13—H13C	109.5
C1—N1—O3	117.29 (17)	H13A—C13—H13B	109.5
O2—N1—O3	125.35 (19)	H13A—C13—H13C	109.5
C2—C3—H3	109.6	H13B—C13—H13C	109.5
C2—C3—C4	109.08 (15)	C12—C14—H14A	109.5
C2—C3—O4	106.13 (14)	C12—C14—H14B	109.5
H3—C3—C4	109.6	C12—C14—H14C	109.5
H3—C3—O4	109.6	H14A—C14—H14B	109.5
C4—C3—O4	112.74 (15)	H14A—C14—H14C	109.5
C3—C4—C5	119.90 (18)	H14B—C14—H14C	109.5
C3—C4—C9	121.62 (17)	C12—C15—H15A	109.5
C5—C4—C9	118.5 (2)	C12—C15—H15B	109.5
C4—C5—H5	119.8	C12—C15—H15C	109.5
C4—C5—C6	120.4 (2)	H15A—C15—H15B	109.5
H5—C5—C6	119.8	H15A—C15—H15C	109.5
C5—C6—H6	119.7	H15B—C15—H15C	109.5
C5—C6—C7	120.6 (2)	C1—S1—C16	98.39 (8)
H6—C6—C7	119.7	S1—C16—C17	119.50 (15)
C6—C7—H7	120.1	S1—C16—C21	120.67 (15)
C6—C7—C8	119.9 (2)	C17—C16—C21	119.83 (19)
H7—C7—C8	120.1	C16—C17—H17	120.1
C7—C8—H8	120.2	C16—C17—C18	119.8 (2)
C7—C8—C9	119.6 (2)	H17—C17—C18	120.1
H8—C8—C9	120.2	C17—C18—H18	119.1
C4—C9—C8	121.07 (19)	C17—C18—C19	121.73 (19)
C4—C9—H9	119.5	H18—C18—C19	119.1
C8—C9—H9	119.5	C18—C19—C20	117.84 (19)
C3—O4—Si1	121.04 (11)	C18—C19—C22	120.9 (2)
O4—Si1—C10	108.77 (10)	C20—C19—C22	121.3 (2)
O4—Si1—C11	108.25 (9)	C19—C20—H20	119.3
O4—Si1—C12	104.91 (8)	C19—C20—C21	121.3 (2)
C10—Si1—C11	110.61 (12)	H20—C20—C21	119.3
C10—Si1—C12	111.83 (11)	C16—C21—C20	119.46 (19)
C11—Si1—C12	112.20 (11)	C16—C21—H21	120.3
Si1—C10—H10A	109.5	C20—C21—H21	120.3
Si1—C10—H10B	109.5	C19—C22—H22A	109.5
Si1—C10—H10C	109.5	C19—C22—H22B	109.5
H10A—C10—H10B	109.5	C19—C22—H22C	109.5
H10A—C10—H10C	109.5	H22A—C22—H22B	109.5
H10B—C10—H10C	109.5	H22A—C22—H22C	109.5
Si1—C11—H11A	109.5	H22B—C22—H22C	109.5
C2—O1—C1—N1	106.29 (16)	C2—C3—O4—Si1	−144.35 (12)
C2—O1—C1—S1	−116.18 (16)	C4—C3—O4—Si1	96.30 (16)
C1—O1—C2—C3	112.38 (18)	C3—O4—Si1—C10	−63.96 (16)
O1—C1—C2—C3	−104.20 (19)	C3—O4—Si1—C11	56.28 (16)
N1—C1—C2—O1	−102.30 (17)	C3—O4—Si1—C12	176.25 (13)
N1—C1—C2—C3	153.50 (17)	O4—Si1—C12—C13	179.23 (16)
S1—C1—C2—O1	107.73 (17)	O4—Si1—C12—C14	−61.63 (18)
S1—C1—C2—C3	3.5 (3)	O4—Si1—C12—C15	59.61 (16)
O1—C1—N1—O2	164.08 (18)	C10—Si1—C12—C13	61.5 (2)
O1—C1—N1—O3	−17.9 (2)	C10—Si1—C12—C14	−179.36 (17)
C2—C1—N1—O2	−129.39 (19)	C10—Si1—C12—C15	−58.13 (18)
C2—C1—N1—O3	48.6 (2)	C11—Si1—C12—C13	−63.47 (19)
S1—C1—N1—O2	24.0 (2)	C11—Si1—C12—C14	55.67 (19)
S1—C1—N1—O3	−158.04 (17)	C11—Si1—C12—C15	176.91 (15)
O1—C2—C3—C4	−165.07 (15)	O1—C1—S1—C16	−62.77 (16)
O1—C2—C3—O4	73.21 (18)	C2—C1—S1—C16	−136.33 (17)
C1—C2—C3—C4	−98.4 (2)	N1—C1—S1—C16	73.74 (14)
C1—C2—C3—O4	139.90 (17)	C1—S1—C16—C17	83.59 (16)
C2—C3—C4—C5	−74.9 (2)	C1—S1—C16—C21	−97.63 (16)
C2—C3—C4—C9	103.40 (19)	S1—C16—C17—C18	179.95 (15)
O4—C3—C4—C5	42.8 (2)	C21—C16—C17—C18	1.2 (3)
O4—C3—C4—C9	−138.97 (17)	C16—C17—C18—C19	−0.3 (3)
C3—C4—C5—C6	177.91 (17)	C17—C18—C19—C20	−0.9 (3)
C9—C4—C5—C6	−0.4 (3)	C17—C18—C19—C22	179.26 (19)
C4—C5—C6—C7	0.4 (3)	C18—C19—C20—C21	1.3 (3)
C5—C6—C7—C8	0.2 (3)	C22—C19—C20—C21	−178.82 (19)
C6—C7—C8—C9	−0.8 (3)	C19—C20—C21—C16	−0.5 (3)
C3—C4—C9—C8	−178.46 (17)	S1—C16—C21—C20	−179.50 (15)
C5—C4—C9—C8	−0.2 (3)	C17—C16—C21—C20	−0.7 (3)
C7—C8—C9—C4	0.8 (3)